Shoulder bump inconsistent infrequently

[eod_tek]

I'm trying to track down what is going on with some irregularity in my resizing process.
I have a bullet central sizing die for my 300 Norma, I'm using a redding t7, I set my die up to the headspace I'm looking for, locked it down, use Hornady case lube, and size 100 pieces of brass. 90 of those pieces are within a half thousandth to a thou of each other, but 10 pieces were three thousandths shorter than the shortest of the rest of them. Is there anything obvious that I should be looking for? I generally like to test the first few pieces and then just keep moving with my process, but this is giving me trust issues lol.

 

[Rio Precision Gunworks]

Could be too much lube on some cases. Or dwell time (meaning you take longer to size those 10 cases). And then there's annealing and spring back variations.

But, as long as you're not already pushing it, you won't have any case head separations....well, you shouldn't that is. Saami allows for something like .007 variance in brass and .010 variance in chamber.

So, if a piece of brass was the shortest allowed and a chamber was the longest allowed, there would be around 0.014 difference and still inside saami.

 

[Marine52]

Need more info. Are you getting solid contact between shellholder and bottom of die? Is there camover? With a case in the shellholder and ram all the way up, can you see a space between shellholder and bottom of die? does your press have a lot of play in it? Can you see any movement in the turret when case is being sized? Most of these questions/isssues go away with a bit of camover that provides a firm contact between shellholder and bottom of die.

also: has the brass been annealed? Is it mixed brass or from the same manufacturer? Is the brass new, once shot, twice shot or mixed?

 

[Raufoss]

I’d say those 10 pieces have not shot the same powder charge in the past ( lower charges). They behave differently Thant the other ones because of that.

 

[eod_tek]

Need more info. Are you getting solid contact between shellholder and bottom of die? Is there camover? With a case in the shellholder and ram all the way up, can you see a space between shellholder and bottom of die? does your press have a lot of play in it? Can you see any movement in the turret when case is being sized? Most of these questions/isssues go away with a bit of camover that provides a firm contact between shellholder and bottom of die.

also: has the brass been annealed? Is it mixed brass or from the same manufacturer? Is the brass new, once shot, twice shot or mixed?

Good point, I definitely left out some needed details!

I do have solid contact and camover at the end of the stroke.
I can see a small amount of movement in the turret head, and maybe that is the cause? I've been looking at Creedmoor sports upgrade kit with the nylon bushings.

The brass is lapua, flame annealed every firing, on its 5th firing, and all from the same lot.

 

[BuildingConceptsllc]

Good point, I definitely left out some needed details!

I do have solid contact and camover at the end of the stroke.
I can see a small amount of movement in the turret head, and maybe that is the cause? I've been looking at Creedmoor sports upgrade kit with the nylon bushings.

The brass is lapua, flame annealed every firing, on its 5th firing, and all from the same lot.

I have a Lyman 8 (which is either a copy of the redding or the redding is a copy but they are very similar presses). The center bushing is what controls how tight the turret is allowed to synch down so what I did is get some 1500 grit paper and slowly, in circular pattern, honed down that bushing just a tiny bit until there was absolutely zero movement in my turret. Be careful, if you go too far you're screwed and will have to add a washer at the bottom or get a new bushing. It's super easy and makes the press super tight while still being able to turn it when you want to.

 

[Marine52]

Good point, I definitely left out some needed details!

I do have solid contact and camover at the end of the stroke.
I can see a small amount of movement in the turret head, and maybe that is the cause? I've been looking at Creedmoor sports upgrade kit with the nylon bushings.

The brass is lapua, flame annealed every firing, on its 5th firing, and all from the same lot.

The Bullet Central Micron die you have is an excellent precision die and matching that with annealed Lapua brass from the same lot is all very good. Since you have solid contact and camover with the shellholder and die, it may be that the movement you are seeing in the turret head is causing the inconsistent bump. Do you have a reliable single-stage non-turret press like a Rockchucker you can set up and compare shoulder bump?

 

[axarob44]

I've seen it posted before that that movement in the T-7 press is accounted for in the design of the press.

 

[eod_tek]

The Bullet Central Micron die you have is an excellent precision die and matching that with annealed Lapua brass from the same lot is all very good. Since you have solid contact and camover with the shellholder and die, it may be that the movement you are seeing in the turret head is causing the inconsistent bump. Do you have a reliable single-stage non-turret press like a Rockchucker you can set up and compare shoulder bump?

I do have a rockchucker hiding somewhere I could setup, and next batch I definitely will, see if the turret head is the issue.

 

[eod_tek]

I've seen it posted before that that movement in the T-7 press is accounted for in the design of the press.

I would imagine to some degree it would have to be. There has to be some flexibility to allow it to move, I just wonder if maybe this one is worn enough to allow a few thousandths more of movement. I bought it used and have no idea how many rounds are on it.
Although, you'd think that it would be closed to 50/50 if it were turret head movement. Or at least all over the place, vs 90 super consistent then 10 also consistent just bumped more

 

[MarshallDodge]

What length was the brass before it was sized?

It does not sound like a press issue so consider these causes-

-Difference in hardness of brass
-Lube on shoulder (I only lube the case body and neck)
-Dirty die

 

[Marine52]

I do have a rockchucker hiding somewhere I could setup, and next batch I definitely will, see if the turret head is the issue.

It may be worth it. I guess it depends on your goals. If you’re loading for hunting or just banging steel with friends then, as Rio Precision said above, a .003 variation in bump is still with SAAMI spec and will not hurt anything. Just make sure it’s not getting to the point where you may get a case head separation. However, if you are loading for competition or serious precision, I would want to chase the inconsistency down.

 

[axarob44]

Million round T7

 

[eod_tek]

What length was the brass before it was sized?

It does not sound like a press issue so consider these causes-

-Difference in hardness of brass
-Lube on shoulder (I only lube the case body and neck)
-Dirty die

It measured 2.0460 with my whidden .450 comparator. After sizing, the good ones were 2.0425-35 and the 10 shorter ones were 2.0400.
Case lube could definitely be it, I line them up, spray one shot, and go to town.
I cleaned my die very recently, but, still definitely a possibility too.
Brass differences could be as well. I used this brass for load development and a few of them have experienced pressure signs in their life as I experimented with charge weight.

 

[eod_tek]

It may be worth it. I guess it depends on your goals. If you’re loading for hunting or just banging steel with friends then, as Rio Precision said above, a .003 variation in bump is still with SAAMI spec and will not hurt anything. Just make sure it’s not getting to the point where you may get a case head separation. However, if you are loading for competition or serious precision, I would want to chase the inconsistency down.

99% of this rifles purpose is hunting and long range steel shooting, but I do plan to shoot the NF ELR match every year with it, so I definitely want to track it down too. If for no other reason, then for my own gratification lol.

My 20 round ES isn't what I feel like it should be, so maybe it's been doing it a while and that could play a small faction velocity variance.

 

[BuildingConceptsllc]

OP- do you know when the longer ones were done ? Were they just randomly in the 100 or were the 10 longer ones all at the end or what?

 

[Rio Precision Gunworks]

99% of this rifles purpose is hunting and long range steel shooting, but I do plan to shoot the NF ELR match every year with it, so I definitely want to track it down too. If for no other reason, then for my own gratification lol.

My 20 round ES isn't what I feel like it should be, so maybe it's been doing it a while and that could play a small faction velocity variance.

What is your 20 round ES?

 

[eod_tek]

OP- do you know when the longer ones were done ? Were they just randomly in the 100 or were the 10 longer ones all at the end or what?

I don't, it wasn't in the first 4, I can tell you that. I checked the first 4, then I checked mid way through the 100 and I got a shorter measurement. I checked the next few and they were normal length, so once they were all done I checked them all.

 

[eod_tek]

What is your 20 round ES?

37 fps and an SD of 9.8

 

[Marine52]

99% of this rifles purpose is hunting and long range steel shooting, but I do plan to shoot the NF ELR match every year with it, so I definitely want to track it down too. If for no other reason, then for my own gratification lol.

My 20 round ES isn't what I feel like it should be, so maybe it's been doing it a while and that could play a small faction velocity variance.

yes, if you’re doing ELR competition, I would want a consistent bump. My guess is it’s the turret flex. Good luck and let us know what you find.

 

[Rio Precision Gunworks]

37 fps and an SD of 9.8

That's actually low for a 9.8sd. You'll have an ES of around 60 for 99.7% of your shots if your SD is actually 9.8fps. Keep in mind, with an actual real to life SD of 5fps, your ES is 30fps. Just to make sure you're keeping realistic expectations.

 

[eod_tek]

This was 14 rounds, I compiled this with another 6 round group fired the same day in excel to come up with those numbers.

 

[BuildingConceptsllc]

I don't, it wasn't in the first 4, I can tell you that. I checked the first 4, then I checked mid way through the 100 and I got a shorter measurement. I checked the next few and they were normal length, so once they were all done I checked them all.

That's odd. I would recommend doing the honing of the bushing anyway but it would be more than just 10 of them if the turret movement was the issue. Maybe you have a lot of cam over and just didn't push as hard on most but did on these 10 or something? Probably the lube if not.

 

[eod_tek]

That's actually low for a 9.8sd. You'll have an ES of around 60 for 99.7% of your shots if your SD is actually 9.8fps. Keep in mind, with an actual real to life SD of 5fps, your ES is 30fps. Just to make sure you're keeping realistic expectations.

Absolutely, and I'm guessing that a higher SD with only a 37fps es means I have a lot of shot to shot variance vs one or two outliers?
And completely understand on the expectations, my goal for this rifle (10.5 lb 300 Norma) is to consistently shoot sub moa (3/4 moa ideal), and to keep an ES under 30 and single digit SD. I think that using the components I'm using, it's achievable, I just need to solidify my processes maybe?

 

[918v]

I’d say those 10 pieces have not shot the same powder charge in the past ( lower charges). They behave differently Thant the other ones because of that.

I think those 10 annealed differently and are softer. I would mark them and watch out for that next time they are resized.

 

[Stephen Bachiler]

OP - I am in the same boat. I will resize 100 Starline .223 brass and a handful of those will come out roughly 2 thou more bumped than my average set bump. I bump about 1 or 1.5 thou. Using RCBS Rebel Press, RCBS dies and either Hornady spray lube or Imperial Sizing Wax. Kinda annoying

 

[Rio Precision Gunworks]

Absolutely, and I'm guessing that a higher SD with only a 37fps es means I have a lot of shot to shot variance vs one or two outliers?
And completely understand on the expectations, my goal for this rifle (10.5 lb 300 Norma) is to consistently shoot sub moa (3/4 moa ideal), and to keep an ES under 30 and single digit SD. I think that using the components I'm using, it's achievable, I just need to solidify my processes maybe?

No, that's not what it means. What it means is you likely haven't shot enough rounds to get your actual ES.

And the only way it's possible to get an ES under 30 is to have a true to life SD of 5 or less. Everyone posts these low SD numbers online, but the fact is that a real life 5sd is world class ammo and not something most people are capable of.


But, as mentioned above, you won't get there with inconsistent brass. Mark those pieces and see if they consistently size different. As well as seeing if they are noticeably different velocities than the rest. That's the only way you will know if they are actually hurting your velocity numbers.

 

[Rio Precision Gunworks]

TLDR version: don't use ES.

SD is the number you want to pay attention to and extrapolate.

 

[Jack's Dad]

I just think it's crazy to measure 100 pieces of brass. Set it and forget it! Maybe I'm just dangerous

 

[918v]

I just think it's crazy to measure 100 pieces of brass. Set it and forget it! Maybe I'm just dangerous

Maybe you should pay attention to detail.

 

[eod_tek]

OP - I am in the same boat. I will resize 100 Starline .223 brass and a handful of those will come out roughly 2 thou more bumped than my average set bump. I bump about 1 or 1.5 thou. Using RCBS Rebel Press, RCBS dies and either Hornady spray lube or Imperial Sizing Wax. Kinda annoying

Definitely annoying! I'm such a perfectionist at heart that it drives me nuts.

 

[Stephen Bachiler]

I just think it's crazy to measure 100 pieces of brass. Set it and forget it! Maybe I'm just dangerous

I will have one of my kids do some of the measuring (12 year old boy and 15 yr old girl - my 17yr old just wants to shoot ). It is good for them to learn. If they get one that is "off" the tell me and I remeasure it.

 

[eod_tek]

TLDR version: don't use ES.

SD is the number you want to pay attention to and extrapolate.

Statistics was never my game . I'll have to refresh myself on SDs soon.
I only used ES to determine a "max range" based on my target size and maximum spread of my recorded velocities, if that makes sense.
I hunt in Wyoming and Idaho and want to keep my ammo as consistent as possible because longer shots are often a reality. Obviously I practice frequently at ranges much further than I'd ever shoot an animal, with generally good success, but missing an animal is just so much more consequential than missing steel and I obsess over making my system as consistent as I can

 

[Rio Precision Gunworks]

Statistics was never my game . I'll have to refresh myself on SDs soon.
I only used ES to determine a "max range" based on my target size and maximum spread of my recorded velocities, if that makes sense.
I hunt in Wyoming and Idaho and want to keep my ammo as consistent as possible because longer shots are often a reality. Obviously I practice frequently at ranges much further than I'd ever shoot an animal, with generally good success, but missing an animal is just so much more consequential than missing steel and I obsess over making my system as consistent as I can

Oh it makes sense on its face. All of us used to think the same thing.

The issue is that we will almost never know what our actual SD/ES is as there are too many changing factors as well as barrel degradation. So we can only predict as best we can. SD is the number that allows us to predict where our real SD/ES is. So it's also the number we want to pay attention to when attempting to make the best ammo we possibly can.

I'll post this pic for now. If you're still unsure what it's showing in relation to SD and ES, let me know and I'll send over a longer reply.

Each @ = 1 standard deviation. 1@ is one SD, 2@ is two SD, etc. Meaning 68% of your shots will be +/- 1x your SD. 95% will be +/- 2x your SD, etc etc.

Your actual ES will be the tail ends of the curve. Technically speaking, your ES will continually get larger over time. But realistically, it will stay in that 99.7% area unless you're "lucky" enough to find those pesky 6 shots out of 2000 rounds.

 

[eod_tek]

Oh it makes sense on its face. All of us used to think the same thing.

The issue is that we will almost never know what our actual SD/ES is as there are too many changing factors as well as barrel degradation. So we can only predict as best we can. SD is the number that allows us to predict where our real SD/ES is. So it's also the number we want to pay attention to when attempting to make the best ammo we possibly can.

I'll post this pic for now. If you're still unsure what it's showing in relation to SD and ES, let me know and I'll send over a longer reply.

Each @ = 1 standard deviation. 1@ is one SD, 2@ is two SD, etc. Meaning 68% of your shots will be +/- 1x your SD. 95% will be +/- 2x your SD, etc etc.

Your actual ES will be the tail ends of the curve. Technically speaking, your ES will continually get larger over time. But realistically, it will stay in that 99.7% area unless you're "lucky" enough to find those pesky 6 shots out of 2000 rounds.

View attachment 8249738

I think that makes sense!
So, looking at that 14 shot string, the sd was 9.06, so if I used that number as an example (I know 30 is a more significant total than 14, but, as an example it works), 95% of my shots should be +/- 2sd either direction of my median velocity, so within 36.24 fps total variation (+/- 18.12 fps from my median velocity).

 

[Rio Precision Gunworks]

I think that makes sense!
So, looking at that 14 shot string, the sd was 9.06, so if I used that number as an example (I know 30 is a more significant total than 14, but, as an example it works), 95% of my shots should be +/- 2sd either direction of my median velocity, so within 36.24 fps total variation (+/- 18.12 fps from my median velocity).

Exactly. The easy way to remember:

68% of shots are 2x your SD
95% of shots are 4x your SD
99.7% of shots are 6x your SD


The tricky part is that 9sd. That's a "sample" SD. You actually need to extrapolate that out using a confidence interval. You can find calculators for this online.

Based on your 9sd and 14 shots, you true SD 95% of the time will be between:

7fps and 14fps

Now we can say that your ES will be:

68% of shots: 14fps - 28fps
95% of shots: 28fps - 56fps
99.7% of shots: 42fps - 84fps

This is how to use your chrono data properly.


The takeaway is that if you shoot 14 shots if load A and 14 shots of load B:

If they both have a 9fps, but A has a 60es and B has a 40es.......you do NOT have enough data to say that load B is better than load A. Even though 99% of shooters would think load B is clearly better.

You can pick load B in an attempt to give yourself a better chance at a load being better but you can not say that it actually is based on your chrono.

 

[Rio Precision Gunworks]

Since you want a 30es.....what that breaks down is this:

To be 95% sure that our ES is 30 or less for 99.7% of our shots, if we shoot 20 round strings.....our SD can NOT be over 3.5fps.



That's not an entirely realistic goal. But that is the only way we will have 95% confidence in a 30es for almost all the shots we take.