I have a 6.5 saum that I have been shooting a few years, 5 to 600 round count, 1/4 minute gun. Last November I loaded 100 rounds with proven load that I have recorded velocities at 3130 over 10 plus rounds. Put it away with a clean barrel. I got it out a couple weeks ago and noticed I was almost a full minute high at 800yrd, so I ran 5 down it with the mag speed. All 5 were between 3160 and 3170. Asked around a bit with neck tension increasing over time being the only answer I could wrap my head around. Wondering If anyone has a better explanation for the 30 to 40 fps increase. FYI all same Lots powder, primer, bullets etc.. Since the 5 I have ran 5 more with the same result. Still shoots 1/4 minute, just curious. H1000 powder and similar temperature.
Increase in velocity with stored ammo question?
- Thread starter Rflamm250
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Your bullet has cold welded to the case thus causing more pressure and more velocity,
I will bet if you put them in your seater die and bump then a couple of thousands you will hear and feel them break free.
I will bet if you put them in your seater die and bump then a couple of thousands you will hear and feel them break free.
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Agreed. Sedancowboy has the problem identified and given you a fix. How do you clean your brass? Perhaps if too clean, it adds to the problem. Do a search on cold welding. There was a good thread a few months back. Perhaps leaving a little carbon in the necks, moly coating bullets, or graphite may help with long term storage in the future.
kiwikid
Well-Known Member
Another possibility is a reduction in the ralitive humidity that your ammo has been stored at. Norma did tests on the effects of RH on velocity with 30-06 ammo and they found that a reduction of RH of 10% will increase the velocity by up to 1% over a 12 month period. At 3130fps a 1% increase would add 31 odd fps to 3160 fps. Is your ammo stored in a place where there is a dehumidifier or air conditioning operating?
Mikecr
Well-Known Member
Tension does increase over time. Were these necks FL sized?
lancetkenyon
Well-Known Member
Do/did you anneal the necks also?
Yes. Cases annealed every firing with amp annealer. Sized in whidden FL size die non bushing. Mandreled with Sinclair carbide expander. Primers seated to.004 below case head. Powder measured to the.02g with FX 120i. Etc.
I was running .015 under loaded round on neck tension, so pretty light.
Mikecr
Well-Known Member
15thou under loaded is extreme. I'm sure you meant .0015" interference.
1.5thou interference is plenty & good.
Things in play here:
#1 FL sizing of necks is nothing but bad. You should stop doing that. Especially when sizing length exceeds seated bullet bearing.
#2 Even with annealed, grain structure is broken with sizing down & again with sizing up. I don't think I could prove it now, but I suspect that early hardening is more dramatic than later, and that this condition is actually LESS stable to manage.
#3 Sizing adds energy that puts brass at a new balance. Then a new lowest energy state(counter to last action) is not recovered immediately.
I believe you're right. That your neck tension is likely rising with time.
In fact, every part of your reloaded cases react over time to counter last energies added. Body, shoulders, necks, and primers/pockets.
You can account for this with a little bit of testing (over time) and reloading adjustments. An extra 1/2thou bump, extra 2thou primer crush, couple less kernels of powder, etc. Date the box.
If I load ammo today, for shooting today, it's stable.
If I'm delayed a week with shooting, it will not shoot the same.
It will be stable but different again several months from now.
So to hold stable hunting ammo where I cannot load for each day of shooting, I purposely load it several months in advance. With this, I've got ammo ready for groundhog hunting -before it peaks out for a shadow.
1.5thou interference is plenty & good.
Things in play here:
#1 FL sizing of necks is nothing but bad. You should stop doing that. Especially when sizing length exceeds seated bullet bearing.
#2 Even with annealed, grain structure is broken with sizing down & again with sizing up. I don't think I could prove it now, but I suspect that early hardening is more dramatic than later, and that this condition is actually LESS stable to manage.
#3 Sizing adds energy that puts brass at a new balance. Then a new lowest energy state(counter to last action) is not recovered immediately.
I believe you're right. That your neck tension is likely rising with time.
In fact, every part of your reloaded cases react over time to counter last energies added. Body, shoulders, necks, and primers/pockets.
You can account for this with a little bit of testing (over time) and reloading adjustments. An extra 1/2thou bump, extra 2thou primer crush, couple less kernels of powder, etc. Date the box.
If I load ammo today, for shooting today, it's stable.
If I'm delayed a week with shooting, it will not shoot the same.
It will be stable but different again several months from now.
So to hold stable hunting ammo where I cannot load for each day of shooting, I purposely load it several months in advance. With this, I've got ammo ready for groundhog hunting -before it peaks out for a shadow.
Yes. Lost a zero in the .0015 under statement. I'm well away from neck shoulder junction with bearing surface so not worried about FL sizing. I actually started out with redding bushing die but moved away from it. That's another subject though. So I guess we are back to brass hardening increasing NT this pressure thus velocity?
Mikecr
Well-Known Member
When you size donut area you bring it and shoulder into neck tension.
And while sized beyond seated bearing length, you cause the donut & shoulder tension to grip bullet base-bearing junction, binding it. Then as this continues to contract with time, that binding goes up.
Pretty much the worst thing you could do for neck sizing..
And while sized beyond seated bearing length, you cause the donut & shoulder tension to grip bullet base-bearing junction, binding it. Then as this continues to contract with time, that binding goes up.
Pretty much the worst thing you could do for neck sizing..
Had some time to experiment today. So when I prepped brass in the rounds we are talking about I did 200. This was last november. So I have 100 ready to load. So I loaded 6 with same components same spec. Shot over chrono and all 6 were between 3155 and 3167. So I believe that takes the cold welding idea out. I am sure that the original 100 were sized and loaded within a day or two of annealing. I wonder if it would be a good practice to anneal and then let the brass settle a month or so. I could anneal a handful prep and load immediately then shoot and see if velocity returned to the 3130?
