Group Siz Issue - Neck Tension?

[Logan1080]

300 WSM
175gr LRX
63.9gr H4350

I neck turned this brass before first loading to 0.0145” thickness. I have not neck turned it again and it’s on its fourth firing. I’m starting to see variance in neck tension and today I used a .334 bushing but I found after loading 12 rounds that my inconsistent neck thickness could be felt in the press as some rounds seated easier than others so I went and shot them to see what results I’d find. I estimate these rounds to have roughly .005” tension.

I have shot quite a few rounds with this rifle and it’s fairly consistently a MOA or better at 100 yards, 275 yards and 375 yards. Today I shot the 3 shot groups at each of those ranges. 7/8”, 2.25” and 3 7/8” respectively. Then at 475 the group opened up to 10”. My velocity has always been fairly steady around 3030 fps. And I verified that today as well.

I feel like I need to internally neck turn the brass as the outside should be fairly even as it’s been turned and fire formed multiple times. Or, should I attempt to neck turn them again on the outside to get some consistency back. Would neck tension affect my groups as seen in the picture?

I used a very solid shooting rest so the shooter error would not be anything significant.

Update: my brass still has fairly consistent thickness around .014” however with a .334 bushing my diameter is measure .331”. I have no idea why it squeezed them so much. I’m going to run the expander ball through them see where to go from there.

 

[Billogna]

That's definitely a large variation. Maybe something came loose? Did you check torque specs on action screws, and scope bases and rings?

 

[Logan1080]

That's definitely a large variation. Maybe something came loose? Did you check torque specs on action screws, and scope bases and rings?

Torque has been checked and was good.

 

[Billogna]

Torque has been checked and was good.

what were the specs? (if you don't mind me asking)

 

[Muleface]

Would neck tension affect my groups as seen in the picture?

Can't say how much of change is caused by variable neck tension, but neck tension sure can cause accuracy issues. That's why lots of money is spent on force packs and stuff.

How do you get a 0.005" tension estimate? Do you use pin gauges? Those are handy.

Have you put an identical or at least similar batch of brass through this 4x cycle, and did groups not open up for that cycle?

Do you anneal your brass (is 0.331" the result of reduced springback due to hardening)?

 

[Harvey_NW]

It usually shoots MOA for how many shots? If you're judging by 3 shot groups, that could easily be within the cone that rifle produces. If you're talking 10 shots within 1 MOA at 100 yards (which is a pretty good number to use for baseline precision measurement), yeah that 475 yard group is outside of what I would expect, disregarding environmental conditions and shooter ability.

In my experience, I haven't seen neck tension effect precision in my rifles. I now purposely set my neck tension around .003-4" by polishing my expander down .002-3" under bullet diameter. All the examples I've seen of those doing ladder or similar tests are small enough sample size that you can't extrapolate any valid data from the results. If you have the ability to anneal, that might help.

 

[Logan1080]

what were the specs? (if you don't mind me asking)

20 inch pounds on rings, 35 on base and 67 on action screws

 

[Logan1080]

Can't say how much of change is caused by variable neck tension, but neck tension sure can cause accuracy issues. That's why lots of money is spent on force packs and stuff.

How do you get a 0.005" tension estimate? Do you use pin gauges? Those are handy.

Have you put an identical or at least similar batch of brass through this 4x cycle, and did groups not open up for that cycle?

Do you anneal your brass (is 0.331" the result of reduced springback due to hardening)?

Neck tension is determined by wall thickness, calibre size, and diameter of sized neck.

 

[Lawnboi]

This is what happens when you don’t anneal. By 4-5 firings you get some inconsistency. This is why most standard dies squeeze the piss out of the case.

Annealing will fix the inconsistencies your feeling in the press. It will also fix the difference you’re seeing with your bushing. As brass hardens it has more spring back, by 4-5 firings it can be hard enough that the old bushing dosnt even do it. Seen it, and been down that road.

I anneal so it does the same exact every time.

Whether that matters on target is another story. Your rifle is still shooting well, and I can’t see a 7/8” load open to 10” at 400. Something else is happening.

Good luck.

 

[Logan1080]

It usually shoots MOA for how many shots? If you're judging by 3 shot groups, that could easily be within the cone that rifle produces. If you're talking 10 shots within 1 MOA at 100 yards (which is a pretty good number to use for baseline precision measurement), yeah that 475 yard group is outside of what I would expect, disregarding environmental conditions and shooter ability.

In my experience, I haven't seen neck tension effect precision in my rifles. I now purposely set my neck tension around .003-4" by polishing my expander down .002-3" under bullet diameter. All the examples I've seen of those doing ladder or similar tests are small enough sample size that you can't extrapolate any valid data from the results. If you have the ability to anneal, that might help.

5 shot group minimum, have shot 10 shot groups before as well. Bullet impacts haven’t really shown any surprises over the 50 rounds or so that I’ve had this exact recipe, it has shot much tighter at 500 yards prior to today and the only thing I can finger point is neck tension. I went and ran the elliptical expander through the rest of my brass and now I should be at .003” neck tension. I’ll have to get to the range to check results. I have no idea why a .334 bushing resulted in a neck OD of .331.

 

[Logan1080]

This is what happens when you don’t anneal. By 4-5 firings you get some inconsistency. This is why most standard dies squeeze the piss out of the case.

Annealing will fix the inconsistencies your feeling in the press. It will also fix the difference you’re seeing with your bushing. As brass hardens it has more spring back, by 4-5 firings it can be hard enough that the old bushing dosnt even do it. Seen it, and been down that road.

I anneal so it does the same exact every time.

Whether that matters on target is another story. Your rifle is still shooting well, and I can’t see a 7/8” load open to 10” at 400. Something else is happening.

Good luck.

I anneal after every firing.

 

[Lawnboi]

I anneal after every firing.

Then forget that, maybe a doughnut at the bottom of your neck. I’d check that and I’d be taking a peek with a bore scope at my chamber and throat.

 

[Logan1080]

Then forget that, maybe a doughnut at the bottom of your neck. I’d check that and I’d be taking a peek with a bore scope at my chamber and throat.

Good call, should probably dive into that. Seen it on my 6.5 PRC

 

[Harvey_NW]

5 shot group minimum, have shot 10 shot groups before as well. Bullet impacts haven’t really shown any surprises over the 50 rounds or so that I’ve had this exact recipe, it has shot much tighter at 500 yards prior to today and the only thing I can finger point is neck tension. I went and ran the elliptical expander through the rest of my brass and now I should be at .003” neck tension. I’ll have to get to the range to check results. I have no idea why a .334 bushing resulted in a neck OD of .331.

I know there is some springback that's hard to account for but I also don't think the bushing numbers are exact. I had a similar experience with a SAC bushing where I measured loaded round neck OD's and subtracted .004" for the bushing size, and I could pull the bullets out of that sized brass by hand.

I personally don't think it would be neck tension causing that big of an issue. What brand of optic? It didn't open up the worst until you dialed the most, may potentially be a tracking/erector issue.

 

[Logan1080]

Then forget that, maybe a doughnut at the bottom of your neck. I’d check that and I’d be taking a peek with a bore scope at my chamber and throat.

Good call, should probably dive into that. Seen it on my 6.5 PR

I know there is some springback that's hard to account for but I also don't think the bushing numbers are exact. I had a similar experience with a SAC bushing where I measured loaded round neck OD's and subtracted .004" for the bushing size, and I could pull the bullets out of that sized brass by hand.

I personally don't think it would be neck tension causing that big of an issue. What brand of optic? It didn't open up the worst until you dialed the most, may potentially be a tracking/erector issue.

Yeah I measured the bushing the best I could and it is within half a thou. The optic is a Burris Signature Series HD, brand new. From what I can tell, it isn’t tracking properly and it will be going back to Burris shortly to get looked at. But I do think it holds accuracy fine but who knows could be something else going on with it.

 

[Wrench]

Sometimes they will weld into the case....but I'd be more inclined to think you had parallax or just a bad fundamentals day. You're not too far off your baseline.

 

[Wrench]

....and unless you have a tight neck and are trying to get clearance or you're necks are just gross....I'd stop turning them. You're applying the .002" techniques to the 1.00 gun.