I agree, you are correct. I guess what I'm asking is, is that normal? I was always under the assumption that really nice groups are usually from really tight ES's (providing of course the shooter is consistent in their fundamentals on the gun) If you would have told me a really tight group can be had with a 121 es I would have called bs.
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6.5 Grendel
- Thread starter padom
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Basic,
Yes, you can have a 120fps spread and still group well. Accuracy is more about all the velocities, not just the extremes. Standard deviation (SD) is a better metric to describe a string of shots than extreme spread. This is because it describes all the shots, not just two.
If you still have a record of every shot in the string what is its SD?
Yes, you can have a 120fps spread and still group well. Accuracy is more about all the velocities, not just the extremes. Standard deviation (SD) is a better metric to describe a string of shots than extreme spread. This is because it describes all the shots, not just two.
If you still have a record of every shot in the string what is its SD?
At 100 yards you can have big extreme spreads but good groups, because the velocity variation doesn't affect the trajectory very much. As you increase the distance though, you need smaller velocity variations to maintain the same accuracy, because those velocity differences start to show up as vertical stringing on the target.
And yes, at 100 it's "normal" at least in the sense that it can and does happen. Group size is not really linked to velocity consistency at that distance. And, conversely, consistent velocity is no guarantee of accuracy, at any distance.
My buddy helped me work up a load ladder (only 3 rounds of each as we're short components right now) and the SD was 53.51 between the three.
Not that you need a co-sign…
But
26.8 ARComp
Starline or Barnes Brass
129 Hornady SST
(Didn’t work with 129 ABLR- ejector swipes)
2.260
BCA 18 inch barrel
Submoa on 11 shots.
Attachments
Except that when you get big numbers with just 3 shots, it is meaningful - it tells you right away something isn't working as desired, and you don't need to waste any more rounds to get a "statistically meaningful" number.
Same if we're talking about group sizes - 3 shot groups are relevant when they are spread out a lot and tell you it's a bad group; more rounds won't make it smaller.
People like to chime in about statistical relevance on most gun forums these days, but it seems common to forget that while you can't prove a great group or low SD etc with just a few shots, if things are going bad instead of great there's usually no reason to continue.
Sooooooo, you can tighten a SD with more shots. Let’s say you have 2 velocity measurements that are close together, and one wildly outside of that. If that one outlier is truly an outlier, continued measurements can shrink the standard deviation- if they are all close to the other 2 measurements. But, you’ll never shrink a large ES with more shots.
Basic,
As a relevant part of the conversation, what powder(s) are you using and how are you measuring / dispensing it ?
As a relevant part of the conversation, what powder(s) are you using and how are you measuring / dispensing it ?
This is not true and the last paragraph is rubbish. When things go bad this is no reason to quit.
Shooting involves statistics and we need decent sample sizes to reveal meaningful metrics. One group of three shots tells you where the gun is zeroed, but that's about it.
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SD's are tightened with careful loading of ammunition, not by firing more shots. SD's are a single number/metric used to describe the distribution of a sample. The more shots, the more accurate the SD will be, and the more confident you can be the SD describes accurately the statistical distribution.
As for your second claim, this is true. however with more shots it might end up even greater.
My point is that 3 shots is not statistically significant to make a claim about the standard deviation of a population. Lets hypothesize that we have 10 rounds in a box. We shoot each and calculate the standard deviation and extreme spread for the growing group of measurements after each shot. It is entirely possible that we could come up with a series of measurement that look like the following...
We have one wild outlier on the 3rd shot, and the rest of the shots fall much more in line with the first two. The standard deviation after all 10 have been fired is much more representative of the population than after 3. And, it may be showing us that shot 3 is a true outlier. Maybe the charge was heavy. Maybe the chrono hiccuped.
Yes, careful loading tightens the SD, but the measured SD is only reliable if it is valid. The SD after 3 shots is not.
It's absolutely true, but maybe you'll need to stop and think about what I said. His 53 fps SD isn't going to turn into single digit SD by shooting 10 or 30 or even 50 rounds. Same if you're shooting a 4" group with those first 3 shots, there's no reason to keep going hoping it'll turn into a 1/2" group. These are examples when just a few shots tells you all you need to know to move on to something else; it doesn't matter whether the SD or whatever is statistically significant at that point.
Some people nerd out on the numbers way too much without stopping to consider how/when they're meaningful. Typical internet armchair quarterbacking.
Here's an example of how your SD can shrink by firing more rounds. It highlights the random nature of shots in a string. If we delete all but the first three rounds and look at the SD it is now larger at, '20'. My point is, firing three rounds does not tell us the real picture, and certainly no reason to quit.It's absolutely true, but maybe you'll need to stop and think about what I said. His 53 fps SD isn't going to turn into single digit SD by shooting 10 or 30 or even 50 rounds. Same if you're shooting a 4" group with those first 3 shots, there's no reason to keep going hoping it'll turn into a 1/2" group. These are examples when just a few shots tells you all you need to know to move on to something else; it doesn't matter whether the SD or whatever is statistically significant at that point.
Some people nerd out on the numbers way too much without stopping to consider how/when they're meaningful. Typical internet armchair quarterbacking.
Again:
You’re not looking at what I said, or the specific context of this thread. The guy had an SD of 53, not 20. Nobody except you was talking about your made-up scenario; we all know the numbers can change like that but you’re arguing against something nobody said. This is exactly what I meant about people nerding out on the numbers. Don’t be so stuck in your own head that you can’t see what other people are saying, i.e. a nerd.
When groups or spreads are bad enough, any rationally thinking person can see there’s no need to waste additional rounds on it. That doesn’t mean a marginal SD of 20. It means “BAD”, like I said a bunch of times. An ES of 150 is another good example.
Lol, all good points. Well at least I know at 100 yards, a crap es of 121 can still print a decent group lol. Past that, I'm not sure. I have more reloading equipment coming and will find out here soon.
Yondering,Again:
You’re not looking at what I said, or the specific context of this thread. The guy had an SD of 53, not 20. Nobody except you was talking about your made-up scenario; we all know the numbers can change like that but you’re arguing against something nobody said. This is exactly what I meant about people nerding out on the numbers. Don’t be so stuck in your own head that you can’t see what other people are saying, i.e. a nerd.
When groups or spreads are bad enough, any rationally thinking person can see there’s no need to waste additional rounds on it. That doesn’t mean a marginal SD of 20. It means “BAD”, like I said a bunch of times. An ES of 150 is another good example.
Ironically, while you deride shooters who rely on statistics too much as being 'nerdy', at the same time you advise Basic to stop because of a statistic. You believe his SD of 53 to be valid and meaningful. My argument is that both of you should ignore it because it is meaningless. Again, ironically, I am the one advising not to rely on statistics in this context.
BTW, my example above was not manufactured for this thread. Every muzzle velocity is real and in the order they were shot. And it was the first column I saw when opening my records. The idea an SD drops the more shots are fired can also validated by doing the same to your own records. Use the first string you see and do a SD calculation for the first three rounds, and then all the rounds.
Here's the same string above with the first shot altered to increase the SD of first three shots to be the same as Basic's 53. You are saying that 53 is so extreme as to be meaningful in some way. But when we keep shooting the SD drops to 29. In this case, one unusual shot can blow out the SD when there are only two other shots, but more shots reveals the truer picture.
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If one absolutely trusts every step along the reloading and data generation process, a 3 shot group with an unacceptable ES is probably sufficient to move on. As Yonderling says, it’s not getting better. But, if there is fault to be found in any step along the way, grounds may be found- through further testing- to ignore a questionable reading. Using the example I posted above, 9 of 10 measurements fall within 25 fps, with a single outlier over 100 fps outside of that range. Yes, it is hypothetical data. But, it is an entirely possible dataset as well- especially with a human in the reloading process. Maybe I bumped the scale and dumped more powder in that one and didn’t notice. The dataset would arguably be even more plausible if I had made the outlier wildly low.
That said, a 3 shot string with really great ES and SD- even with impeccable reloading- only signals that more testing is warranted. As JustinAmateur is want to say over in the rimfire forum “random acts of accuracy (or precision)” are a thing.
I think the biggest thing that all shooters should take from any discussion about shooting and statistics is that it is rare that any dataset created by s shooter would pass muster with a statistician. We are all mostly drawing dubious conclusions from incomplete data.
That said, a 3 shot string with really great ES and SD- even with impeccable reloading- only signals that more testing is warranted. As JustinAmateur is want to say over in the rimfire forum “random acts of accuracy (or precision)” are a thing.
I think the biggest thing that all shooters should take from any discussion about shooting and statistics is that it is rare that any dataset created by s shooter would pass muster with a statistician. We are all mostly drawing dubious conclusions from incomplete data.
hlee,
Well said, I couldn't agree more.
Talking about sample sizes, I find amazing the number of people who swear by the Satterlee 10-shot optimum load method. The idea you can graph a ladder of 10 shots and determine with any confidence what the best load is beggars belief. Yet there are shooters who swear by it like a religion.
Well said, I couldn't agree more.
Talking about sample sizes, I find amazing the number of people who swear by the Satterlee 10-shot optimum load method. The idea you can graph a ladder of 10 shots and determine with any confidence what the best load is beggars belief. Yet there are shooters who swear by it like a religion.
Genius, we're not talking about your shot string though. We were talking specifically about Basic User's numbers. Not your made up stuff that has no relevance to the conversation.
.
Like I said, don't be so wrapped up in your own head that you can't tune in to what other people are saying. I never said a 20 SD couldn't turn into 15, never even implied anything of the sort. I DID say a 53 SD isn't going to turn into single digits, and neither is a 100+ fps ES. It doesn't take a mathematician to figure out those numbers are high enough that it's not worth expecting miracles from that load.
And I didn't "deride shooters who rely on statistics", not even close; I use statistics all the time. That's a foolish thing to say, and just illustrates further that you haven't bothered to consider what was actually being said. Take a breath and look around you a little bit instead of focusing on yourself so much.
Arguing against things nobody said, that aren't relevant to the conversation, is what singles you out as acting like a nerd. Not the use of statistics, but your general cluelessness of how it fits in to the conversation. If you think I'm being rudely dismissive of your commentary, it's because you earned it; I don't have much respect for someone who repeatedly twists my words to argue that I said something different.
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Yondering,
I hope you don't mind, I've condensed your spray to the above...You are assuming the high SD means something specific - a dud load. But, Basic's high SD could also be as a result of a single outlier, caused perhaps by something like the chronograph or a dud primer. Without shooting more rounds we won't know if it is an anomalous round, or a true reflection of a bad load. It may indeed be a 'miracle' load, but without firing more than 3 rounds none of us will ever know for sure.
A thought provoking discussion about internal and external ballistics, no doubt, and worthy of its own thread. However, seems like Basic could give us a bit more info about the actual load details of the loads generating these widely disparate numbers, if we’re to be of any value to his original query.
-Brass mfg and were cases weighed? Have seen some wide case weight variance in Hornady brass, as much as 8-10gr difference depending on lots. Lapua brass very consistent weights, but new brass requires fire forming as it’s at least .010 short of chambers in 8 different Grendel barrels I have owned-7 still currently in play.
-Cases annealed, neck tension and shoulder setback for gun used in testing?
-Bullet used, distance from lands and same for all loads?
-Primer mfg, and same for all loads?
-Powder mfg, charge weights and measuring devices used?
-Chrono mfg used to gather data?
-Ambient weather conditions same for all testing?
Lots more variables possible that could generate ES/SD in ranges discussed, but more info definitely reqd to help Basic User.
And now, back to regularly scheduled programming….
-Brass mfg and were cases weighed? Have seen some wide case weight variance in Hornady brass, as much as 8-10gr difference depending on lots. Lapua brass very consistent weights, but new brass requires fire forming as it’s at least .010 short of chambers in 8 different Grendel barrels I have owned-7 still currently in play.
-Cases annealed, neck tension and shoulder setback for gun used in testing?
-Bullet used, distance from lands and same for all loads?
-Primer mfg, and same for all loads?
-Powder mfg, charge weights and measuring devices used?
-Chrono mfg used to gather data?
-Ambient weather conditions same for all testing?
Lots more variables possible that could generate ES/SD in ranges discussed, but more info definitely reqd to help Basic User.
And now, back to regularly scheduled programming….
Cases were annealed with an amp.
Gun wasn't present when my buddy loaded these; don't have distance to lands. (those tools are en route)
130gr Berger. Loaded to 2.278 oal (he didn't have a mag there)
Winchester primers for all. Weight batched Nosler cases.
29.2 grains of varget. measured on an autotrickler
I chronoed with a magnetospeed
73 degrees, low humidity, 5mph headwind. Sunny.
Shot with a Rainier ultra match 16" pipe that I glued in to a lapped aero upper. direct thread Q suppressor on the end.
Good info, and what appears to be good process. Couple of things that come to mind-That’s a pretty stout load of Varget-2 gr over a max per Nosler data for 130gr bullets, but we all know most factory can be somewhat conservative, and if cases or primer pockets are showing pressure, may be an indication of an unbalanced charge weight, but Varget is generally considered slow for a 6.5 Grendel. 4895 and the double based CFE/Lever are often recommended for heavy bullets in Grendel, with temp sensitivity a variable. WW41’s or other WW primers?
Three barrels I’ve measured 130AR Hybrids for are in the 2.38-2.4 OAL to lands, so don’t think you’re challenging the lands.
Any chance a baffle strike could have impacted data? Odd chance with pretty good groups.
The collected wisdom here will likely offer their council, as well. Keep at it-Grendel has been very forgiving to load for in my experience.
Three barrels I’ve measured 130AR Hybrids for are in the 2.38-2.4 OAL to lands, so don’t think you’re challenging the lands.
Any chance a baffle strike could have impacted data? Odd chance with pretty good groups.
The collected wisdom here will likely offer their council, as well. Keep at it-Grendel has been very forgiving to load for in my experience.
So 2569's kind fast for that bullet? I didn't know lol. I'll watch out for that. There were no pressure signs on the brass thus far. We also shot some cfe under some 120's and these berger 130's but there were fliers. We're definitely going to retry the 30.9 of cfe w/ 120gr lapua scenars, 27.3gr of varget under the 130 bergers and 28.9 gr of varget under the 130 grainers again. They showed that they wanted to group good. I had a solid shooting platform (1.5lbs trigger tech with a super tight harris and solid benchrest type rear bag) but the 15 power max vortex pst gen 2 kinda limited my precision as my eyes arent what they used to be. I will find out what those primers were.
Basic,
I agree with bobke, that is a hot load, definitely over SAAMI's 52K lbs recommended limit. The trouble with Grendel is that by the time you see pressure signs in cases it will already be too hot for an AR. The first thing that shooters report on the Grendel forum is one of the bolt lugs breaks off. It may take a few hammer blows for this to happen but AR's are the canary in the coal mine for over-pressure. This, given they are relatively fragile compared to bolt guns.
A 130 Berger (either Hybrid or VLD) at that OAL, and 29.2gn of Varget is about 113% full (Ref: Quickload). That's some serious crunching of stick powder as the bullet is seated. Compressed loads steepen the fill/pressure curve so a difference of even 0.1 of a grain will have big changes in pressure/velocity.
I agree with bobke on choice of powder for heavy bullets in Grendel. The slightly faster H4895 would be a better choice for that 130Berger. That said, 130 is a heavy bullet for efficiency in a small case. Again, from the Grendel forum, the consensus is about 123gn gets the longest ranges at safe pressures. I save my 130Hybrids for the larger 6.5x47.
I agree with bobke, that is a hot load, definitely over SAAMI's 52K lbs recommended limit. The trouble with Grendel is that by the time you see pressure signs in cases it will already be too hot for an AR. The first thing that shooters report on the Grendel forum is one of the bolt lugs breaks off. It may take a few hammer blows for this to happen but AR's are the canary in the coal mine for over-pressure. This, given they are relatively fragile compared to bolt guns.
A 130 Berger (either Hybrid or VLD) at that OAL, and 29.2gn of Varget is about 113% full (Ref: Quickload). That's some serious crunching of stick powder as the bullet is seated. Compressed loads steepen the fill/pressure curve so a difference of even 0.1 of a grain will have big changes in pressure/velocity.
I agree with bobke on choice of powder for heavy bullets in Grendel. The slightly faster H4895 would be a better choice for that 130Berger. That said, 130 is a heavy bullet for efficiency in a small case. Again, from the Grendel forum, the consensus is about 123gn gets the longest ranges at safe pressures. I save my 130Hybrids for the larger 6.5x47.
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Understood. We will reexamine that load then. Thanks for that intel. I chose 130's as an option for bullet choices (not to mention you buy what you can buy, and learn to make it work in this biden world) because that's what the federal GMM load was; 130 bergers. I've always had excellent results with GMM so I trust them blindly. I know in the world of reloading you shouldn't do that but, it was all I knew at the time I purchased them (about 6 mos ago) I'm about to dive into this 'gordons reloading tool' thing to get a deeper understanding of reloading. As for now all I have is a hornady book and it's SUUPER basic. About all it says is 'gunpowder is explosive' so I quit reading it; the questions about reloading I have are far too complex for that book.
Edit: Just looked up federals gmm stats for the 130s and they claim 2400fps; is that from I'm presuming a 20" barrel may be? Because a lot of my loads are around 2300. 2494 was the average for this super tight group-94 fps faster than the GMM. If federals average is from a 20 incher, 94 fps faster on a four inch shorter barrel IS moving out pretty stoutly lol.
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Basic,
There are some interesting points in your comment.
When finding a reasonable load I use as many sources as possible. Manufacturer tables (conservative), 6.5 Grendel forum (on average hot loads), and Quickload (conservative). Adding to that you can look at spent cases for an idea of pressure but it's like reading tea leaves. By the time primers are cratering and flattening it's too late. Ejector swipes are common and can occur with mild loads. The first thing to break is the weakest link in the pressure containment system, the bolt lug. Grendel is a wider diameter bolt face than 5.56 so there is more pressure on the lugs. No doubt part reason why the SAAMI recommended max pressure is only 52K. The issue I think from being on the 6.5 Forum is Grendelers are always pushing the limits of what is by design a slow calibre and reports of bolts breaking are common enough to be comfortable that's what breaks first.
That said, if you want to consider the bolt as a consumable part (and always carry a spare like I do in the butt) then you can push hot loads through it until the bolt prematurely breaks - then replace it and carry on. It is highly unlikely to blow up in your face and you may not even know a lug has broken off until you get home. We replace barrels when they wear out, so we can also replace bolts every now and then. Just a thought, but requires acceptance of the risks that go with loading hot.
From the opposite perspective you can ask whether that extra velocity is critical to achieving your shooting goals. If shooting paper or steel at known distances; so what if the bullet arrives at the target 100fps less. A slower bullet will be affected slightly more by the wind, but that's about it. If hunting, the animal is not going to know the bullet is 100fps less than it could be - Dead is dead. So from this perspective, why wear out the gun faster if you don't need to?
I note on Hogdgon's website they don't list anything heavier than 123gn. Like I said, 130gn is less efficient for a small calibre like Grendel. This is because heavier bullets are longer, and in an AR the magazine length limits the OAL. When loading rounds to fit in an AR mag the longer bullets are pushed further into the case. This displaces precious space and there is less left over for powder. Heavier bullets also require slower powder and that has a compounding effect on the smaller volume available for bulkier powder.
Here's your 29.2gn 4895 load predicted in Quickload out of a 16" barrel...2435fps. Computer predictions never match reality exactly for all sorts of reasons, but they are close.
There are some interesting points in your comment.
When finding a reasonable load I use as many sources as possible. Manufacturer tables (conservative), 6.5 Grendel forum (on average hot loads), and Quickload (conservative). Adding to that you can look at spent cases for an idea of pressure but it's like reading tea leaves. By the time primers are cratering and flattening it's too late. Ejector swipes are common and can occur with mild loads. The first thing to break is the weakest link in the pressure containment system, the bolt lug. Grendel is a wider diameter bolt face than 5.56 so there is more pressure on the lugs. No doubt part reason why the SAAMI recommended max pressure is only 52K. The issue I think from being on the 6.5 Forum is Grendelers are always pushing the limits of what is by design a slow calibre and reports of bolts breaking are common enough to be comfortable that's what breaks first.
That said, if you want to consider the bolt as a consumable part (and always carry a spare like I do in the butt) then you can push hot loads through it until the bolt prematurely breaks - then replace it and carry on. It is highly unlikely to blow up in your face and you may not even know a lug has broken off until you get home. We replace barrels when they wear out, so we can also replace bolts every now and then. Just a thought, but requires acceptance of the risks that go with loading hot.
From the opposite perspective you can ask whether that extra velocity is critical to achieving your shooting goals. If shooting paper or steel at known distances; so what if the bullet arrives at the target 100fps less. A slower bullet will be affected slightly more by the wind, but that's about it. If hunting, the animal is not going to know the bullet is 100fps less than it could be - Dead is dead. So from this perspective, why wear out the gun faster if you don't need to?
I note on Hogdgon's website they don't list anything heavier than 123gn. Like I said, 130gn is less efficient for a small calibre like Grendel. This is because heavier bullets are longer, and in an AR the magazine length limits the OAL. When loading rounds to fit in an AR mag the longer bullets are pushed further into the case. This displaces precious space and there is less left over for powder. Heavier bullets also require slower powder and that has a compounding effect on the smaller volume available for bulkier powder.
Here's your 29.2gn 4895 load predicted in Quickload out of a 16" barrel...2435fps. Computer predictions never match reality exactly for all sorts of reasons, but they are close.
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Random question, wasnt the 130 AR hybrid designed with the AR platform in mind? I picked the 130AR (2458fps using CFE223) as it performs better than the 123ELDM in regards to wind deflection.(2590fps with XBR8208 when i had it) at the speeds I able to obtain.
Works in a Grendel-know another shooter who shoots them very successfully at 1K, though its real sweet spot is in the 6.5CM.
The only issue I have had with this load has been the CFE223 powders temp instabilities, I live in Eastern NC so I seen some fun temp swings . I have been looking a replacement but sadly no luck.
I dont mean to derail this thread topic.
Warnera-you’re not hijacking a thread, we’re all here to learn and shoot smarter. Once you’re at the perimeter of bullets weights outside of the original cartridge designers intent, some compromises are sure to surface. Think the Grendel’s sweet spot is in the 107/108-120/123 range. Want more velocity from 129/130 class bullets, you work with double base powders like CFE223/Lever, and accept that you might have two loads to accommodate their temp sensitivity, or go single base like 4895 that might not yield the velocity, but may offer year round stability/consistency for your particular circumstances. And those are not the only options, but do perform well in their pocket.
I’m in the Tx Hill Country, and temps in the next week will hit 105-107 with plenty of humidity. Or the winter can be easily in the teens/20’s. I’ve settled with 120 Scenars and AR Comp for 90% of my needs for its temp stability and lower burn temp, as well as accuracy and velocity. For hunting, likely 129 ABLR’s or 115gr Barnes, and specific loads for either. Good to have options, and a cartridge platform that can deliver to your needs.
I’m in the Tx Hill Country, and temps in the next week will hit 105-107 with plenty of humidity. Or the winter can be easily in the teens/20’s. I’ve settled with 120 Scenars and AR Comp for 90% of my needs for its temp stability and lower burn temp, as well as accuracy and velocity. For hunting, likely 129 ABLR’s or 115gr Barnes, and specific loads for either. Good to have options, and a cartridge platform that can deliver to your needs.
Too fast for 130’s. Best with lighter weight bullets in Grendel. See attached burn rate reference. You might look at 2520, VV powders, 748, Power Pro Varmint, even old school BLC2. Best to be on the slower side of 335 for sure. You should also check out the 65Grendel site ‘preferred loads’ section for another reference point.
6.5 Grendel Preferred Loads - 6.5 Grendel Forum : : For the 6.5 Grendel Aficionado
I think the 6.5 Grendel is a fantastic cartridge, mild but yet effective over a wide range of conditions, and of course the fact it fits into the AR platform is just icing on the cake. One of the things that seems to elude us, is a bullet and a powder that just works in everyones gun. Since I...
www.65grendel.com
BFT's Lengthy List of Loads - 6.5 Grendel Forum : : For the 6.5 Grendel Aficionado
Whenever I run across a 6.5 Grendel load — here or on other forums — that seems reasonable and from a responsible reloader who carefully inspects brass and primers for over-pressure signs, I copy it down. Thought I'd share. Bear in mind that almost all of these loads — unless you see a work-up...
www.65grendel.com
If you achieve even bolt lug contact with the barrel extension lugs, the bolt can handle higher pressure than the Grendel standard for quite a long time. This can be done through truing of some sort (lapping, lathe truing, etc) or using a thermofit upper with a good quality barrel extension and bolt. Easy enough to check with some dye or even sharpie marker on the bolt lugs; most AR15 upper assemblies do not have even bolt lug contact because of the loose barrel extension to receiver fit and uneven receiver face. (And no, the "floating" bolt design of the AR doesn't compensate for for that; the bolt doesn't float in angular dimensions, just radially which doesn't help this problem.)
Of course even bolt lug contact can help bolt life but doesn't help the extractor - that comes down to proper gas tuning for the load being used. The higher pressure the load, the more careful tuning is required to maintain extractor life.
The other limiting factor with higher pressure Grendel loads is the dimensional matchup between the brass and the "feed ramp" bevel or radius on the rear of the barrel itself. If that bevel is deep, reaching beyond the shallow Grendel case web, you'll start to see bulged cases that look like belted magnums long before bolt life is an issue. Some barrels are beveled much deeper than others, and some brass is more prone to this than others. As an example, in my barrels Lapua brass (despite being excellent quality, it has a pretty shallow case web) is much more likely to bulge than Starline, simply due to thickness of the brass in that narrow unsupported part of the case above the extractor groove.
While I generally like to see my good brass last 10 loads or more, sometimes I do run fairly hot loads in my Grendel and Grendel-based wildcat barrels, but I do this knowing that each one of them has even bolt lug contact so that no one or two bolt lugs are taking more than their even share of the load. And while I emphatically do NOT recommend considering case bulges as a determination of a specific pressure range in general practice (like when looking at someone else's bulged cases online), it is a good indication that the pressure, whatever it may be, is too high for that specific brass/barrel/load combination. As you get to know your barrel and brass for a specific powder type, you'll be able to spot the earliest signs of case bulges and use that as one method of indicating excessive pressure for your setup.
Of course even bolt lug contact can help bolt life but doesn't help the extractor - that comes down to proper gas tuning for the load being used. The higher pressure the load, the more careful tuning is required to maintain extractor life.
The other limiting factor with higher pressure Grendel loads is the dimensional matchup between the brass and the "feed ramp" bevel or radius on the rear of the barrel itself. If that bevel is deep, reaching beyond the shallow Grendel case web, you'll start to see bulged cases that look like belted magnums long before bolt life is an issue. Some barrels are beveled much deeper than others, and some brass is more prone to this than others. As an example, in my barrels Lapua brass (despite being excellent quality, it has a pretty shallow case web) is much more likely to bulge than Starline, simply due to thickness of the brass in that narrow unsupported part of the case above the extractor groove.
While I generally like to see my good brass last 10 loads or more, sometimes I do run fairly hot loads in my Grendel and Grendel-based wildcat barrels, but I do this knowing that each one of them has even bolt lug contact so that no one or two bolt lugs are taking more than their even share of the load. And while I emphatically do NOT recommend considering case bulges as a determination of a specific pressure range in general practice (like when looking at someone else's bulged cases online), it is a good indication that the pressure, whatever it may be, is too high for that specific brass/barrel/load combination. As you get to know your barrel and brass for a specific powder type, you'll be able to spot the earliest signs of case bulges and use that as one method of indicating excessive pressure for your setup.
An example of the barrel feed ramp chamfer where the brass bulges:
A view of bolt lug and barrel extension lug lockup (the shiny piece is a barrel extension by itself without a barrel):
An example of uneven bolt lug contact. Notice the large contact areas where the purple dye is worn away on the bottom lugs, a little less on the top lugs, and very little contact on the right lugs. (The untouched lug on the left is where the extractor goes; no lug on the bolt for that position.) In this example, the upper receiver face was proud at what would be the 7:00 region in the pic (the extension is rotated a bit so top of the receiver wouldn't be at the top of the pic if it were installed). Truing the receiver fixed this one, but sometimes gentle lapping of the bolt lugs can be necessary too.
And finally, an example of a trued receiver (by lapping in this case) to fix that uneven contact. Note the untouched dark area indicating the low spot on the right; I took this one down a little further after the pic, but as shown here is all that's really needed for truing. With about 90% of the receiver face trued up, it has enough support to hold the barrel extension true to the receiver bore..
A little further just because I prefer to do it that way:
Hope that helps.
A view of bolt lug and barrel extension lug lockup (the shiny piece is a barrel extension by itself without a barrel):
An example of uneven bolt lug contact. Notice the large contact areas where the purple dye is worn away on the bottom lugs, a little less on the top lugs, and very little contact on the right lugs. (The untouched lug on the left is where the extractor goes; no lug on the bolt for that position.) In this example, the upper receiver face was proud at what would be the 7:00 region in the pic (the extension is rotated a bit so top of the receiver wouldn't be at the top of the pic if it were installed). Truing the receiver fixed this one, but sometimes gentle lapping of the bolt lugs can be necessary too.
And finally, an example of a trued receiver (by lapping in this case) to fix that uneven contact. Note the untouched dark area indicating the low spot on the right; I took this one down a little further after the pic, but as shown here is all that's really needed for truing. With about 90% of the receiver face trued up, it has enough support to hold the barrel extension true to the receiver bore..
A little further just because I prefer to do it that way:
Hope that helps.
I haven't noticed enough of a trend to matter. IMO though, when it comes to even lug contact, it's one of those things where if you miss by an inch, you've missed by a mile; it's either square and true or it's not. Keep in mind an unevenness of only .001" at the receiver face can result in in a gap under the opposite bolt lug of about 3/4 that much, if the receiver/barrel fit has enough tolerance which most do.
What I have seen is that pretty much every receiver I've used that's not a thermo-fit can benefit from truing; they're all off by at least a little bit, it's rare to find one off by more than .004-.005" (which I'd consider a lot, in perspective). That doesn't mean that the completed assembly will shoot more accurately, which is a common "refute" some people try, and in a 5.56 you can get really long bolt life without truing, but in most larger cases like the Grendel, or even the 5.56 if you're pushing higher pressure, this can/does improve bolt life IF the rifle is also tuned well and not badly overgassed.
Excellent info from all of your recent posts; thank you! Although I am aware of everything you said, putting it all to pictures helps cement it in, and re-affirms that I'm not as crazy as my friends try to make me out to be by being anal on my "precision if you will" AR builds. (which this one was) Your bolt lug contact points really give me something to start paying closer attention to. Although this is a JP bolt, I am definitely going to be checking all of this now.
Not to get off the subject too much, but I did lap this upper and glue (sleeve retainer) this barrel in but my question on lapping remains, which is this - if I use a standard issue lapper that you see out there in the wild (mines wheeler), and I insert it in and begin lapping, if the upper's bore was bored unevenly to begin with, or the threads were cut cock-eyed where the barrel nut threads on to, aren't I just taking down material on the same uneven plane and not squaring anything up? To TRULY square a receiver, shouldn't it be chucked up in some sort of device that is truly centered, and it be brought up against a cutting bit much like truing up a bolt gun's receiver face? Or am I way off.
Uneven with what though? It’s important to understand the receiver bore IS the thing the receiver face needs to be trued too; it’s what houses both the BCG and the barrel extension, and the point is to hold those two things perfectly inline.
The barrel nut threads would have to be WAY off to cause any sort of issue; all it does is press the flat barrel extension shoulder against your newly flattened/trued receiver face. Generally there is enough tolerance in the thread fit to accommodate a few thousandths tilt, which is all we’re talking about here.
I will add that the receiver face needs to be square with itself. Specifically two things: the face needs to be square with the top rail, and the internal BCG race.
Squaring the face with the top rail - this is for cranking the scope/elevation. When cranking the scope's elevation no horizontal bias is introduced, and when cranking windage no vertical bias is introduced. For squaring the face with the race - when the bolt enters and goes into battery those lugs (as Yondering has been talking about) need to share the load evenly, and therefore need to mate evenly.
Squaring the face with the top rail - this is for cranking the scope/elevation. When cranking the scope's elevation no horizontal bias is introduced, and when cranking windage no vertical bias is introduced. For squaring the face with the race - when the bolt enters and goes into battery those lugs (as Yondering has been talking about) need to share the load evenly, and therefore need to mate evenly.
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You can't have a flat surface be "square with itself". The receiver face is just a flat plane. No idea what you're trying to say there, but the rest of that post is wrong anyway.
The receiver face needs to be perfectlyt square with the receiver bore to achieve even lug contact. It does NOT need to be perfectly square with the rail. That's what scope setup and adjustments take care of. Any advice to square the receiver face with the rail is very misguided and fundamentally flawed. Have you never used (or understood?) a 20 moa scope base? That intentionally makes the scope mounting out of parallel with the bore, and for good reason.
No. That's not how that works at all. You get cross bias in the scope adjusments if the scope is not level, whether you mounted it crooked or just held the rifle that way. It doesn't matter whether the rail was true to any part on the rifle or not; if the scope is level when you make your corrections, you won't get any cross bias (other than due to flaws in the scope itself, but that's a completely different topic).
Yondering,
Here we go again. Check your ad hom at the door please and concentrate on the merits of our arguments.
I never said the receiver face needs to be square with itself, and on that I agree with you - It makes no sense.
I said the face needs to be square with two things: the rail and the race. The logic being the bore to the reticle is an interface of connected parts. It helps if they are square with themselves, so when they come together the bore axis is square with the aiming point of the erector mechanism in the scope. And the barrel extension is square with the bolt lugs. By square with themselves I am referring to square at either end of the part.
You can connect the receiver to its scope mount for example and call that one whole part. Then as one part you still need to consider what are the two faces that connect at either end to make this a square interface between the bore axis and the scope's erector mechanism. For a mount it is the axis of the rings. Given how difficult a mount is to square we hope the manufacturer has machined this carefully, or source a scope rod. Wheeler makes a kit for this too. Those kits square the rings to each other, but not necessarily to the interface between the bore axis and scope erector mechanism.
As for the scope - you can have a scope that is out of alignment with the bore axis, regardless that the bore is pointing up at a 20MOA angle. And Yes, we can correct this misalignment at different ranges by dialing the windage and elevation. Consider a situation however where the bore is clamped in a vise pointing directly ahead, or in the case of a 20MOA angled mount the bore axis is clamped so the ballistic arc of the bullet is perfectly vertical. You can still have a scope pointing say at 10 O'clock which has been mounted so its erector mechanism tracks perfectly vertical and horizontal (checked using a Tall Target Test). But as you crank the elevation horizontal bias is introduced which the shooter will assume is wind downrange. As for the vertical bias of a 10 O'Clock pointing scope it will manifest in the Scope Correctional Factor. What you crank on the turret is not what the bullet moves on the target. For example, I have a March on a 0-cant mount/rail where the Correction Factor is 0.981. Sure, that could be from sloppy machining in the factory, but in this hypothetical it can also be from the scope mounted pointing at 10 OClock. And this odd angle is due to a lack of square at both ends of the interface.
Here we go again. Check your ad hom at the door please and concentrate on the merits of our arguments.
I never said the receiver face needs to be square with itself, and on that I agree with you - It makes no sense.
I said the face needs to be square with two things: the rail and the race. The logic being the bore to the reticle is an interface of connected parts. It helps if they are square with themselves, so when they come together the bore axis is square with the aiming point of the erector mechanism in the scope. And the barrel extension is square with the bolt lugs. By square with themselves I am referring to square at either end of the part.
You can connect the receiver to its scope mount for example and call that one whole part. Then as one part you still need to consider what are the two faces that connect at either end to make this a square interface between the bore axis and the scope's erector mechanism. For a mount it is the axis of the rings. Given how difficult a mount is to square we hope the manufacturer has machined this carefully, or source a scope rod. Wheeler makes a kit for this too. Those kits square the rings to each other, but not necessarily to the interface between the bore axis and scope erector mechanism.
As for the scope - you can have a scope that is out of alignment with the bore axis, regardless that the bore is pointing up at a 20MOA angle. And Yes, we can correct this misalignment at different ranges by dialing the windage and elevation. Consider a situation however where the bore is clamped in a vise pointing directly ahead, or in the case of a 20MOA angled mount the bore axis is clamped so the ballistic arc of the bullet is perfectly vertical. You can still have a scope pointing say at 10 O'clock which has been mounted so its erector mechanism tracks perfectly vertical and horizontal (checked using a Tall Target Test). But as you crank the elevation horizontal bias is introduced which the shooter will assume is wind downrange. As for the vertical bias of a 10 O'Clock pointing scope it will manifest in the Scope Correctional Factor. What you crank on the turret is not what the bullet moves on the target. For example, I have a March on a 0-cant mount/rail where the Correction Factor is 0.981. Sure, that could be from sloppy machining in the factory, but in this hypothetical it can also be from the scope mounted pointing at 10 OClock. And this odd angle is due to a lack of square at both ends of the interface.
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Interesting.
And then you did it again. LOL
Geez kid. You really have no idea what the words mean that you're trying to use, or what the correct terminology is, much less actually have any logic to present here. Your theories are not reality, and all your lengthy commentary on scope and rail alignment are flat out wrong. SMH, you've gone full on loony tunes with this.
I'd be happy to consider the merits of your comments, if they had any. They don't; it's all complete and utter nonsense. This is the problem with making up your own theories of how things work, while knowing nothing about anything, and not bothering to verify if they make any sense.
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