The tale of two 308 reload batches

[skyfire1201]

Hi folks,

I'm working on developing my 308 handloads for a 16" AR10, and came across the following observation. I'm a bit perplexed as to the root case, and am hoping the community can shed some light.

I made two batches of handloads: same bullet, same powder load, two different brass, and tested on two different days using the same gun. Here's the results I got:

2019/9/22, 73F, 56% humidity
SMK 175gr
41.4gr of VV N140
Lapua factory new case
WLR primer
Avg vel: 2442 fps
Group: 0.400" @ 100yrds

2019/12/28, 42F, 87% humidity
SMK 175gr
41.4gr of VV N140
Lapua once fired brass
WLR primer
Avg vel: 2280 fps
Group: 1.180" @ 100yrds

2019/12/28, 42F, 87% humidity
SMK 175gr
41.4gr of VV N140
Winchester once fired brass
WLR primer
Avg vel: 2307 fps
Group: 1.081" @ 100yrds

As you can see, the grouping I've got on the second test is sub-optimal compare to my original load. The groups opened up by 2X+, and I'm perplexed as to what may be the contributing factor. During load development with SMK 175gr and VV N140 combo, I noticed as velocity lowers, my groups also opened up. The following numbers were obtained on 2019/9/22 in 73F temperature:
41.4 2400fps 0.400"
41.0 2388fps 0.728"
40.6 2344fps 1.384"
40.2 2312fps 1.161"
39.7 2261fps 1.320"

The groups I got on 12/28 in 42F temperature appears to match pretty well with the groups obtained with different powder load at the similar velocities.

So my question is, what is the most probable contributing factor to the decline in precision? Is it barrel harmonics due to a drop in velocity? If so, should a difference of 30F make as much as 150fps difference?

Or does the problem lie with the once fired brass I used in the second trial? They were resized to 308 chamber spec by a brass processing service. I also chamfered the case a bit aggressively with a Lyman case prep tool to aid with bullet seating, how big of a factor does that contribute to precision?

I highly appreciate any advice, thanks in advance!

 

[nn8734]

I treat new brass and once fired brass as separate; in other words, if I make two batches of loads, identical in every way except the “newness” of the brass, I consider them two different load recipes.

That said, there may have been
material differences in the brass prep between the first batch and two subsequent batches, driving the variance

id start by comparing your records for that first batch to the records for the other batches, including base-shoulder length (cartridge-chamber headspace) , neck tension, bullet jump, etc.

I would also duplicate and re-test your first load recipe in similar conditions using new lapua brass to see if you can get similar results, unless you are out of the new lapua brass.

Temp differences will impact velocities thus it could also be as simple as that. Seems like 2400 FPS is what the rifle needs to perform...

 

[straightshooter1]

Most likely it's that the Lapua Factory New brass had smaller dimensions than your "Lapua Once Fired Brass". Typically, it take 2 firings to fully fire form a case (making it actually conform to your gun's chamber), where most of that fire forming was done for the once fired brass. That once fired brass, though you did a full sizing of it to SAAMI specs, very likely had more volume that the factory new cases. It's just like your Winchester brass, where Winchester is well known for having much thinner case walls resulting in more case volume. More case volume with the same amount of powder = less pressure = less velocity and often = change in barrel harmonics effecting precision.

 

[Deleted member 113831]

Basically, once fired brass has less velocity than virgin brass because it has been expanded and has more volume. Therefore, you need more powder on the second firing to keep it in a certain velocity window.

The Winchester brass already has greater volume than the thicker and tougher Lapua brass, so you start out at a lower pressure, and therefore velocity.

Work both loads back up to 2440 fps and I bet you see groups improve.

 

[ShtrRdy]

Regarding the first two tests, were the loads build from the same lot number on all the components? Were the cartridges assembled on the same date? Was the once fired Lapua brass fired from the same rifle?

Something I've noticed from my own experiences is that new brass velocity will be less than once fired brass velocity. My explanation is that new brass is looser in the chamber. So when you fire the new brass some of the energy is used up moving the brass outward to contact the chamber walls. I see this goes against what Straightshooter1 and Skookum wrote

I dont know the temperature sensitivity of VV N-140. But the lower velocity coincides with the lower temperature. I had a .308 load group open up for me because of air temperature difference. I was using IMR-4064 powder then.

 

[AIAW]

Regarding the first two tests, were the loads build from the same lot number on all the components? Were the cartridges assembled on the same date? Was the once fired Lapua brass fired from the same rifle?

Something I've noticed from my own experiences is that new brass velocity will be less than once fired brass velocity. I see this goes against what Skookum wrote. My explanation is that new brass is looser in the chamber. So when you fire the new brass some of the energy is used up moving the brass outward to contact the chamber walls.

I dont know the temperature sensitivity of VV N-140. But the lower velocity coincides with the lower temperature. I had a .308 load group open up for me because of air temperature difference. I was using IMR-4064 powder then.

It’s similar to Varget, but just a tad less stable. My records show .7 FPS/degree F (40F baseline, up to 101F).

I use .5 FPS/degree F for Varget.

 

[straightshooter1]

Hi folks,

I'm working on developing my 308 handloads for a 16" AR10, and came across the following observation. I'm a bit perplexed as to the root case, and am hoping the community can shed some light.

I made two batches of handloads: same bullet, same powder load, two different brass, and tested on two different days using the same gun. Here's the results I got:

2019/9/22, 73F, 56% humidity
SMK 175gr
41.4gr of VV N140
Lapua factory new case
WLR primer
Avg vel: 2442 fps
Group: 0.400" @ 100yrds

2019/12/28, 42F, 87% humidity
SMK 175gr
41.4gr of VV N140
Lapua once fired brass
WLR primer
Avg vel: 2280 fps
Group: 1.180" @ 100yrds

2019/12/28, 42F, 87% humidity
SMK 175gr
41.4gr of VV N140
Winchester once fired brass
WLR primer
Avg vel: 2307 fps
Group: 1.081" @ 100yrds

As you can see, the grouping I've got on the second test is sub-optimal compare to my original load. The groups opened up by 2X+, and I'm perplexed as to what may be the contributing factor. During load development with SMK 175gr and VV N140 combo, I noticed as velocity lowers, my groups also opened up. The following numbers were obtained on 2019/9/22 in 73F temperature:
41.4 2400fps 0.400"
41.0 2388fps 0.728"
40.6 2344fps 1.384"
40.2 2312fps 1.161"
39.7 2261fps 1.320"

The groups I got on 12/28 in 42F temperature appears to match pretty well with the groups obtained with different powder load at the similar velocities.

So my question is, what is the most probable contributing factor to the decline in precision? Is it barrel harmonics due to a drop in velocity? If so, should a difference of 30F make as much as 150fps difference?

Or does the problem lie with the once fired brass I used in the second trial? They were resized to 308 chamber spec by a brass processing service. I also chamfered the case a bit aggressively with a Lyman case prep tool to aid with bullet seating, how big of a factor does that contribute to precision?

I highly appreciate any advice, thanks in advance!

Going to my trusty QuickLoad app and entering the data you've shown here with variations in case capacities, this is what I'm looking at:

Lapua factory new case volume: 54.5 gr H2O = 2280 fps @ 70°F
Lapua factory new case volume: 54.5 gr H2O = 2246 fps @ 41°F
Lapua fired brass volume: 55.8 gr H2O = 2216 fps @ 41°F
Winchester fired brass volume: 57.4 gr H2O = 2182 fps @ 41°F

I ran the numbers for factory new case volume at the lower temperature to give you some idea of the effect of cartridge temperature. So, you see case volume is a key factor and I think there may be other contributing factors . . . like neck tension and crimping that the new Lapua brass put on the bullet vs the others. Anyway, hope that give you some ideas.

 

[918v]

You’re not going to lose 160 FPS from new to 1x. Your chrono sux.

 

[straightshooter1]

You’re not going to lose 160 FPS from new to 1x. Your chrono sux.

Yup, the chrono could indeed be part, even a big part, of the issue.

And, we're assuming the powder charges were measured very accurately. ?

 

[nn8734]

I think there may be other contributing factors . . . like neck tension and crimping that the new Lapua brass put on the bullet vs the others. Anyway, hope that give you some ideas.

This is what I was thinking also, esp since he didn’t size/prep the brass for those other batches...Perhaps he will respond with some measurement data asked for in my first post as that might help understand what went on during development between the two recent batches and the first one...

plus I’d like to know why he went away from using the new lapua brass in the first place, given the data provided...need SD/ES info to validate it was a good load; group sizes at 100 only tell part of the story (I would advise him to test at 300 if possible).

 

[Snuby642]

You lost controll when someone else worked your brass.
Do you have new brass and worked first fired to compare.

One reason I reload is to get my brass to closely fit my chambers not speck stuff.

I have a theory that virgin brass is just new range pickup brass with good annealing and less dents.

If your brass service is good you can get loads consistant but they will not fit your chamber unless custom loaded.

Some guns shoot speck ammo well.
My son has a 308 that loves fc gmm 168's . Some won't shoot factory rounds well.

 

[x_789]

I can't imagine 150fps drop over 30 degress. Thats 5fps per degree. I thought the general rule was 1fps per 1 degree F. Were theses 5 shot groups? Was the Lapua brass built strait from the box? No prep or sizing? Honeslty I think you have multiple factors are play here. Big part being the diffrences in brass prep.

 

[skyfire1201]

I treat new brass and once fired brass as separate; in other words, if I make two batches of loads, identical in every way except the “newness” of the brass, I consider them two different load recipes.

That said, there may have been
material differences in the brass prep between the first batch and two subsequent batches, driving the variance

id start by comparing your records for that first batch to the records for the other batches, including base-shoulder length (cartridge-chamber headspace) , neck tension, bullet jump, etc.

I would also duplicate and re-test your first load recipe in similar conditions using new lapua brass to see if you can get similar results, unless you are out of the new lapua brass.

Temp differences will impact velocities thus it could also be as simple as that. Seems like 2400 FPS is what the rifle needs to perform...

@nn8734, I ran out of factory Lapua brass so I couldn't really make a comparison between the first and second. Using my Hornady headspace gauge, I got the average base-shoulder length of the once fired Lapua (processed and loaded) at 1.622". The average for once fired Winchester is 1.617".

I loaded the rounds to mag length, with Case Base To Ogive of 2.207" for all three batches. Haven't got a chance to measure the jump yet, since I wasn't sure it'll be super relevant as I'm mag length restricted.

I too suspect 2400fps is the sweet spot for this rifle with SMK 175gr. 41.4gr is the max recommended load from VV for SMK 175gr, and I don't want to risk blowing up the gun by exceeding the max load just to get velocity back to 2400 with once fired brass.

How do I check neck tension? This may or may not be related, but I got one split neck on the Winchester brass. That round didn't sound any different and the rifle continue to function. I guess I lucked out?

 

[skyfire1201]

Most likely it's that the Lapua Factory New brass had smaller dimensions than your "Lapua Once Fired Brass". Typically, it take 2 firings to fully fire form a case (making it actually conform to your gun's chamber), where most of that fire forming was done for the once fired brass. That once fired brass, though you did a full sizing of it to SAAMI specs, very likely had more volume that the factory new cases. It's just like your Winchester brass, where Winchester is well known for having much thinner case walls resulting in more case volume. More case volume with the same amount of powder = less pressure = less velocity and often = change in barrel harmonics effecting precision.

@straightshooter1, thank you for your insights. I didn't know case volume between new vs once fired would make this much difference. I know brass expands once fired, but I thought the full length sizing die would return it to SAAMI specs. When the round fires, wouldn't the internal pressure expand the brass the fill the chamber anyway? So why does case volume, especially for the same amount of brass, make such a big difference?

Since I'm shooting out of a semi-auto, would a small base die help to reduce volume further and help me gain velocity without increasing the powder charge?

 

[nn8734]

@skyfire1201 I never use “bookmax to determine where I should stop...You can find if your load is at pressure by measuring the base of the unfired case just above the extractor groove then take the measurement again after you fire it. Then subtract the unfired measurement from the fired value to derive your net case expansion. My standard, which hasn’t failed me yet, is <=.0015” expansion.

Once I see expansion of .0015” I know I am at my max safe charge weight...Sometimes this is above book max, sometimes below it. Besides, pick up any two reloading manuals/references and chances are they will have different max charge weights for the same bullet/powder combo- which one is “right”? (Neither).

here is a good article covering neck tension. Superficially, it’s the difference between OD of the case neck before after seating but neck thickness also factors...

You are being redirected...

Edit: split neck is ugly - I never use Winchester brass in any of my semis...it’s too thin for my tastes... I like Federal and Lake City for my SR25.

 

[skyfire1201]

You’re not going to lose 160 FPS from new to 1x. Your chrono sux.

That's a possibility. I'm using a Shooting Chrony Beta. Though certainly not the latest and best on the market, it has worked reliably for the last decade. I would think if the problem lies with the chrono, the numbers would vary between shooting strings on the same day, but that's not the case. All shooting strings on the colder day are consistently lower than the warmer day.

 

[skyfire1201]

Yup, the chrono could indeed be part, even a big part, of the issue.

And, we're assuming the powder charges were measured very accurately. ?

Powder charges were measured on an RCBS Chargemaster 1500. The machine was warmed up, calibrated before dispensation, and each charge weigh was stable before I filled the case.

 

[skyfire1201]

I can't imagine 150fps drop over 30 degress. Thats 5fps per degree. I thought the general rule was 1fps per 1 degree F. Were theses 5 shot groups? Was the Lapua brass built strait from the box? No prep or sizing? Honeslty I think you have multiple factors are play here. Big part being the diffrences in brass prep.

Yes, the Lapua brass from the first batch was straight from the box, without any prep or sizing.

 

[skyfire1201]

Regarding the first two tests, were the loads build from the same lot number on all the components? Were the cartridges assembled on the same date? Was the once fired Lapua brass fired from the same rifle?

Something I've noticed from my own experiences is that new brass velocity will be less than once fired brass velocity. My explanation is that new brass is looser in the chamber. So when you fire the new brass some of the energy is used up moving the brass outward to contact the chamber walls. I see this goes against what Straightshooter1 and Skookum wrote

All components were the same, same loads build, fired out of the same rifle, though the rounds were assembled on different dates with exactly the same equipment. The only difference was the brass, and ambient temperature.

I dont know the temperature sensitivity of VV N-140. But the lower velocity coincides with the lower temperature. I had a .308 load group open up for me because of air temperature difference. I was using IMR-4064 powder then.

Interesting. Did you measure the velocity from the opened up group? My theory is my rifle barrel harmonics likes SMK 175gr at around 2400fps with VV N140 powder, and anything lower than that the groups open up. Though I probably need to wait another 6 months before I can verify that theory.

What's a good 308 powder that isn't very temperature sensitive?

 

[nn8734]

@nn8734, I ran out of factory Lapua brass so I couldn't really make a comparison between the first and second. Using my Hornady headspace gauge, I got the average base-shoulder length of the once fired Lapua (processed and loaded) at 1.622". The average for once fired Winchester is 1.617".

I wonder if the lapua brass out of the box had a shorter base-shoulder measurement by ~.005” or so which may account for some of the differences in chamber pressure between the fresh out of box vs once-fired velocities

Also, what is the base-shoulder measurement for the now-2x-fired Lapua brass?

Measure five cases and take an average... Curious to see how much the case is expanding in the chamber...for semis, I like .003-.004 headspace clearance.

Either way, looks like that once fired Winchester brass was expanding at least .004” into the chamber, probably more...you don’t want too much expansion on brass with multiple firings as that could lead to case head separation (catastrophic failure), esp using thin ass brass like Winchester.

Great thread thus far - lots of insight shared.

 

[skyfire1201]

This is what I was thinking also, esp since he didn’t size/prep the brass for those other batches...Perhaps he will respond with some measurement data asked for in my first post as that might help understand what went on during development between the two recent batches and the first one...

plus I’d like to know why he went away from using the new lapua brass in the first place, given the data provided...need SD/ES info to validate it was a good load; group sizes at 100 only tell part of the story (I would advise him to test at 300 if possible).

Simply put: I ran out of factory new Lapua brass. I bought once fired Winchester brass based on recommendation from this article on AccurateShooter.com. Data from 9/20 on the new Lapua brass load is as follows:
Low: 2406 High: 2489 Avg: 2442 ES: 83 SD: 43 Group: 0.400 @ 100yds

Data from the 12/28 once fired Lapua load is:
Low: 2269 High: 2297 Avg: 2280 ES: 28 SD: 15 Group: 0.855 @ 100yds

Interestingly, although ES and SD went down on the second set, precision degraded.

I also tested once fired Winchester load on 12/28, with this result:
Low: 2275 High: 2345 Avg: 2307 ES: 70 SD: 32 Group: 1.081 @ 100yds

Two days later on 12/30, I shot the same Winchester lot at 200yds (unfortunately I didn't have time to chrono), and got a 2.139" group. So MOA stayed fairly constant between these two days.

Given the limitations of my local range (anything >200yds is 1hr away), I followed the OCW load development method described here, with the exception I never exceeded the maximum charge weight recommended by VV. According to this method, I should be looking for three groups with the same relative offset from POI, which is how I arrived at 41.4gr on my first batch.

 

[Snuby642]

The virgin brass I have used, 3 brands none of it lapua have all been minimum spec in different calibers.

All needed necks straightened in general and trimmed. I just decided to run all virgin brass through my entire process of tumble (to get wax on them) run through sizing die to straiten necks and set neck tension, trim debur and retumble.
Consistancy.

The sizing die normally doesn't move the shoulder as it is minimum anyway.

 

[nn8734]

Interestingly, although ES and SD went down on the second set, precision degraded.

That sometimes happens but over larger samples and further testing/data collection, on-paper precision and SD/ES will typically correlate.

 

[skyfire1201]

I wonder if the lapua brass out of the box had a shorter base-shoulder measurement by ~.005” or so which may account for some of the differences in chamber pressure between the fresh out of box vs once-fired velocities

Also, what is the base-shoulder measurement for the now-2x-fired Lapua brass?

Measure five cases and take an average... Curious to see how much the case is expanding in the chamber...for semis, I like .003-.004 headspace clearance.

You mean fired and unprocessed? They are 1.625, 1.624, 1.625, 1.626, 1.624, avg = 1.625"

Either way, looks like that once fired Winchester brass was expanding at least .004” into the chamber, probably more...you don’t want too much expansion on brass with multiple firings as that could lead to case head separation (catastrophic failure), esp using thin ass brass like Winchester.

Great thread thus far - lots of insight shared.

For comparison, here's the data on the Winchester brass:
Processed: 1.616, 1.617, 1.614, 1.618, 1.618, avg = 1.617"
Fired and unprocessed: 1.627, 1.624, 1.624, 1.624, 1.624, avg = 1.625"

The Winchester expanded quite a bit, 0.008" or so. Is this to much headspace clearance? What I don't get is, since both the Winchester and Lapua were processed together by the same shop (albeit not by me), how did they end up with different case-shoulder lengths?

 

[nn8734]

You mean fired and unprocessed? They are 1.625, 1.624, 1.625, 1.626, 1.624, avg = 1.625"



For comparison, here's the data on the Winchester brass:
Processed: 1.616, 1.617, 1.614, 1.618, 1.618, avg = 1.617"
Fired and unprocessed: 1.627, 1.624, 1.624, 1.624, 1.624, avg = 1.625"

The Winchester expanded quite a bit, 0.008" or so. Is this to much headspace clearance? What I don't get is, since both the Winchester and Lapua were processed together by the same shop (albeit not by me), how did they end up with different case-shoulder lengths?

.008 is way too much for my tastes...esp on thin walled previously fired brass in a semi.

lapua brass looks like it’s expanding .003ish which is fine for a few firings. Lapua brass is a Ferrari compared to Winchester...keep with the lapua and forget the Winchester brass exists.

You other question speaks to why I would never outsource brass prep (or any part of the load production process, other than maybe annealing).

When you give up control of the process, you give up directly controlling the applicable risks. Here the risk in this case is that the brass could potentially be under or oversized relative to your requirement...the requirement being your desired headspace clearance/max case expansion...that risk was realized with the Winchester brass.

Sounds like the brass company just ran your stuff through the die not bothering to ensure they were all headspaced the same between the two brands of brass.

did they ever ask you for a headspace spec?

 

[skyfire1201]

.008 is way too much for my tastes...esp on thin walled previously fired brass in a semi.

lapua brass looks like it’s expanding .003ish which is fine for a few firings. Lapua brass is a Ferrari compared to Winchester...keep with the lapua and forget the Winchester brass exists.

You other question speaks to why I would never outsource brass prep (or any part of the load production process, other than maybe annealing).

When you give up control of the process, you give up directly controlling the applicable risks. Here the risk in this case is that the brass could potentially be under or oversized relative to your requirement...the requirement being your desired headspace clearance/max case expansion...that risk was realized with the Winchester brass.

Sounds like the brass company just ran your stuff through the die not bothering to ensure they were all headspaced the same between the two brands of brass.

did they ever ask you for a headspace spec?

No, they did not ask for a headspace spec. Lesson learned.

Lapua is a bit expensive for my budget, my application (<1MOA for training with a semi) mostly likely doesn't require Ferrari level brass. What are some good, less expensive alternatives?

Thank you very much for the good info and advice! I learned a lot.

 

[nn8734]

No, they did not ask for a headspace spec. Lesson learned.

Lapua is a bit expensive for my budget, my application (<1MOA for training with a semi) mostly likely doesn't require Ferrari level brass. What are some good, less expensive alternatives?

Thank you very much for the good info and advice! I learned a lot.

You’re quite welcome. Good discussion all around.

I use Lake City and Federal brass for 308 and never had any issues...Lake City has thicker walls then commercial brass thus less case capacity so start with lower charge weights if working with it....Federal is softer then others...Remington is ok, Nosler better.

 

[ShtrRdy]

What's a good 308 powder that isn't very temperature sensitive?

I keep ending up with Varget for .308 Win loads. The other powders I've tried are IMR-4064 and RE-15

Just checking, ...... are you assembling the cartridges with brass you had someone else process?

I'll look at my notes to see how much velocity change I had due to temperature change and IMR-4064.

 

[skyfire1201]

You’re quite welcome. Good discussion all around.

I use Lake City and Federal brass for 308 and never had any issues...Lake City has thicker walls then commercial brass thus less case capacity so start with lower charge weights if working with it....Federal is softer then others...Remington is ok, Nosler better.

Is this generic LC or the rarer LRP variety? I've heard of FC being softer, is the primary problem with that being primer pocket getting loose after a few reloads?

 

[nn8734]

Is this generic LC or the rarer LRP variety? I've heard of FC being softer, is the primary problem with that being primer pocket getting loose after a few reloads?

I use all LR stamped LC brass with IMR4064 currently for my M40A5 but have standard (ie machine gun fired) LC brass that I occasionally load with RE15 for my SR25. I use SB dies when working that stuff.

Commercially sold Federal brass is softer and you will tend to find loose primer pockets after a couple firings so expect some minor supply shrinkage as a result. That said, Fed brass has given me favorable MV/SD/ES with both IMR4064 and RE15 plus it’s readily available and cheap.

 

[skyfire1201]

I keep ending up with Varget for .308 Win loads. The other powders I've tried are IMR-4064 and RE-15

Just checking, ...... are you assembling the cartridges with brass you had someone else process?

I'll look at my notes to see how much velocity change I had due to temperature change and IMR-4064.

Yes, it was once fired Winchester brass I paid someone else to process, since I lack the full set of tools to polish and trim the brass.

 

[skyfire1201]

I use all LR stamped LC brass with IMR4064 currently for my M40A5 but have standard (ie machine gun fired) LC brass that I occasionally load with RE15 for my SR25. I use SB dies when working that stuff.

Commercially sold Federal brass is softer and you will tend to find loose primer pockets after a couple firings so expect some minor supply shrinkage as a result. That said, Fed brass has given me favorable MV/SD/ES with both IMR4064 and RE15 plus it’s readily available and cheap.

What's the primary difference between the LR vs standard LC brass? Have you noticed any accuracy differences between the two, while keeping other variables constant?

 

[nn8734]

The LR brass was fired in bolt guns (m40a3,5,6, etc) while the other stuff used in machine guns typically...no real difference in consistency/precision for me but haven’t done extensive comparison testing. With most brass, as long as it’s serviceable and prepped/sized correctly you can usually develop a workable load for any given rifle.

 

[straightshooter1]

Commercially sold Federal brass is softer and you will tend to find loose primer pockets after a couple firings so expect some minor supply shrinkage as a result. That said, Fed brass has given me favorable MV/SD/ES with both IMR4064 and RE15 plus it’s readily available and cheap.

Of 10 firings of my Federal brass (220 cases), I've had 2 with loose primer pockets, one at around 5 firings and the other at 7. The loads I use with this brass has been moderate. The pockets are NOT "tight", but they're not loose either. I do feel if I used hot loads, the primer pockets would probably not have lasted this long.

 

[Slab74]

All components were the same, same loads build, fired out of the same rifle, though the rounds were assembled on different dates with exactly the same equipment. The only difference was the brass, and ambient temperature.



Interesting. Did you measure the velocity from the opened up group? My theory is my rifle barrel harmonics likes SMK 175gr at around 2400fps with VV N140 powder, and anything lower than that the groups open up. Though I probably need to wait another 6 months before I can verify that theory.

What's a good 308 powder that isn't very temperature sensitive?

Varget!

 

[skyfire1201]

Varget!

So I heard, wish I had bought pounds of them back then instead of the N140. Unfortunately these days they are like unobtainium...