Brass prep tasks- case volume, primer pockets et al

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Tim L
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Brass prep tasks- case volume, primer pockets et al

#1 Postby Tim L » Mon Dec 10, 2018 10:31 am

I thoight I'd pull this topic from the Alpha munitions thread due to some interesting comments.
Case volume.
As i understand it, case volume (or rather the effect of case volume) relates not so much to the gross case volume, but rather to the net volume after loading ie the gap. I know pressure traces show a variation that correlates with this but I'm left wondering if a compressed load shows the same variation. i.e. does a compressed load eliminate any case volume concerns?
Primer pocket and hole size.
My own rationale behind using palmer brass was to reduce the uncontrolled variation that primers may cause. Small primer = less energy meaning the variation primer to primer should also be less than that of LR primers. I found large to small primer equates to approximately 1gn of powder (2208-2209) (although that doesn't account for differences in behavior between lr and palmer cases, if there is any). I note that, generally, using a large primer hole with a small primer is not seen as a good idea so a question on this topic is what is the effect of chamfering the primer hole. They theory is a chamered hole will mimic a rocket nozzel providing a 'jet' of burning gas into the powder rather than a 'flare'. This should produce a more constant ignition and put consistancy in the hands of the powder as the flame/burn propogates through the case. A 'flared' ignition may be less consistant igniting more or less powder in the ignition phase causing variations in the burn propogation. This is all theory of course what are the views, or evidence, out there to confirm or deny this.
Neck tension.
I carried out a little experiment on this and did not get the results i expected. To use the current terminology of "thous" of neck tension i set necks to 2 thou 3 thou and 4 thou of tension, then inserted and pulled a projectile. Its easy to feel the difference when inserting the projectile but not so much when pulling out. On measuring i found that after extraction, all the cases were sitting with 1.5 though of tension. These were all newly annealed cases (AMP on 95) so i repeated on new brass with 3 cases that showed 3 thou of tension. The results were the same. Does this indicate that regardless of neck tension set in the die that inserting the projectile will exceed the point of plastic deformation and every round ends up relying on the elasticity of the brass, which appears to be 1.5 thou on a 308 neck?

Edided to add, if the last question proves to be true, what is the effect of turning necks? I don't turn 308 neck so they are all in the region of 15thou. If turned to 13 thoug does one actually get less tension?

bruce moulds
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Re: Brass prep tasks- case volume, primer pockets et al

#2 Postby bruce moulds » Tue Dec 11, 2018 6:28 am

good questions tim.
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880
http://youtu.be/YRaRCCZjdTM

Tim L
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Location: Townsville

Re: Brass prep tasks- case volume, primer pockets et al

#3 Postby Tim L » Tue Dec 11, 2018 3:45 pm

Looking into high speed cameras to investigate that second one. Damned expensive little buggers!

bruce moulds
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Re: Brass prep tasks- case volume, primer pockets et al

#4 Postby bruce moulds » Wed Dec 12, 2018 6:51 pm

tim,
loading black powder cartridges, a starting load is a full case to the base of the bullet.
test that load, and then increasing charge wts compressed to the same column height.
somewhere there will be an optimum compression wt for best grouping.
these loads often exhibit e.s. (nots.d) of things like for to 6 fps for 10 shots.
ammunition is often loaded with no neck tension at all.
of course black powder does not have the energy of smokeless, and tends to explode more than burn progressively.
different primers can have a huge difference in grouping, and due to lower pressures you can include large pistol with large rifle in testing.
different powders seem to prefer more or less compression.
i often wonder if this relates in any way to smokeless.
in some cartridges i have compressed smokeless so heavily that bullets will be pushed out unless you leave the round in the seating die while you load the next round.
in all cases s.d. have been very low, and accuracy as good as i can shoot.
probably should try it in an fclass rifle with slow burning powder.
ar2217 was found by some to work very well in the 6.5/284, and some have found the next slower adi powder to work well it the 7mm saum, compressed.
there is also the potential that compressing powder, black or smokeless, might midify ignition, which then ties into small/large primer/flashhole talk.
you have to ask the questions to get the answers.
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880

http://youtu.be/YRaRCCZjdTM

GSells
Posts: 417
Joined: Sun Aug 13, 2017 11:04 pm

Re: Brass prep tasks- case volume, primer pockets et al

#5 Postby GSells » Wed Dec 12, 2018 8:45 pm

bruce moulds wrote:tim,
loading black powder cartridges, a starting load is a full case to the base of the bullet.
test that load, and then increasing charge wts compressed to the same column height.
somewhere there will be an optimum compression wt for best grouping.
these loads often exhibit e.s. (nots.d) of things like for to 6 fps for 10 shots.
ammunition is often loaded with no neck tension at all.
of course black powder does not have the energy of smokeless, and tends to explode more than burn progressively.
different primers can have a huge difference in grouping, and due to lower pressures you can include large pistol with large rifle in testing.
different powders seem to prefer more or less compression.
i often wonder if this relates in any way to smokeless.
in some cartridges i have compressed smokeless so heavily that bullets will be pushed out unless you leave the round in the seating die while you load the next round.
in all cases s.d. have been very low, and accuracy as good as i can shoot.
probably should try it in an fclass rifle with slow burning powder.
ar2217 was found by some to work very well in the 6.5/284, and some have found the next slower adi powder to work well it the 7mm saum, compressed.
there is also the potential that compressing powder, black or smokeless, might midify ignition, which then ties into small/large primer/flashhole talk.
you have to ask the questions to get the answers.
bruce.


Hmmm, like 2225 in 280 ai ?? The extreme spreads seems to shrink the more the powder is compressed, I imagine to a point .

I was getting sd of 2 FPS with my edge at 2860 FPS with I can’t even remember the load but was 92.5?? 2225 and fed mag primers 300 smk . Only the cases were stuffed after 2 Nd firing. Accuracy at 1.7 km was a lot of vertical and not overly accurate at 600 yds . So OBT was out but OCW was great !!

So I backed off and retuned the load harmonically whispered the Lilja barrel with orings and retuned ocw again. From memory without looking at my notes load was 89.0 gr 2225 sd of 8-9 FPS over 10 shots at 2760 FPS but accuracy went through the roof. I would love to shoot it at 1000 yds at Belmont and see how it would fair ?? But we will never know !!
Point is, backed of pressure sd went up . More pressure sd went down ! But more importantly obt rules the day !! Eg postive compensation .
Ps , don’t bother with orings !!! Waste of time !!

GSells
Posts: 417
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Re: Brass prep tasks- case volume, primer pockets et al

#6 Postby GSells » Wed Dec 12, 2018 8:52 pm

Hang on , I’ll say that is not always the case with pressure. But there seems in my experience with slower powders at 100% or slightly compressed loads , a reduction in SD’s

GSells
Posts: 417
Joined: Sun Aug 13, 2017 11:04 pm

Re: Brass prep tasks- case volume, primer pockets et al

#7 Postby GSells » Wed Dec 12, 2018 10:49 pm

Tim L wrote:I thoight I'd pull this topic from the Alpha munitions thread due to some interesting comments.
Case volume.
As i understand it, case volume (or rather the effect of case volume) relates not so much to the gross case volume, but rather to the net volume after loading ie the gap. I know pressure traces show a variation that correlates with this but I'm left wondering if a compressed load shows the same variation. i.e. does a compressed load eliminate any case volume concerns?
Primer pocket and hole size.
My own rationale behind using palmer brass was to reduce the uncontrolled variation that primers may cause. Small primer = less energy meaning the variation primer to primer should also be less than that of LR primers. I found large to small primer equates to approximately 1gn of powder (2208-2209) (although that doesn't account for differences in behavior between lr and palmer cases, if there is any). I note that, generally, using a large primer hole with a small primer is not seen as a good idea so a question on this topic is what is the effect of chamfering the primer hole. They theory is a chamered hole will mimic a rocket nozzel providing a 'jet' of burning gas into the powder rather than a 'flare'. This should produce a more constant ignition and put consistancy in the hands of the powder as the flame/burn propogates through the case. A 'flared' ignition may be less consistant igniting more or less powder in the ignition phase causing variations in the burn propogation. This is all theory of course what are the views, or evidence, out there to confirm or deny this.
Neck tension.
I carried out a little experiment on this and did not get the results i expected. To use the current terminology of "thous" of neck tension i set necks to 2 thou 3 thou and 4 thou of tension, then inserted and pulled a projectile. Its easy to feel the difference when inserting the projectile but not so much when pulling out. On measuring i found that after extraction, all the cases were sitting with 1.5 though of tension. These were all newly annealed cases (AMP on 95) so i repeated on new brass with 3 cases that showed 3 thou of tension. The results were the same. Does this indicate that regardless of neck tension set in the die that inserting the projectile will exceed the point of plastic deformation and every round ends up relying on the elasticity of the brass, which appears to be 1.5 thou on a 308 neck?

Edided to add, if the last question proves to be true, what is the effect of turning necks? I don't turn 308 neck so they are all in the region of 15thou. If turned to 13 thoug does one actually get less tension?

Hi Timmy ! In Bryan Litz’s book modern advancement in long range shooting . He tested many cases and cals . His final conclusion was that with drilled primer flash holes like Lapua, it was better to leave em alone. But if your flashholes are punched eg Winchester yes it was beneficial to use a Sinclair type chamfer and deburr primer tool.

My personal experience with lap Palmer cases is I’ve chamfered all of them with the Sinclair tool and to a LR size flash hole . It worked for me ! . But have only doe it on .308 only not .708 ai . For 7/08 I leave the lap lr primer flash holes as factory.

In regards to neck tension , there I believe is a tipping point. Basically, again litz says to have enough tension to to hold the projectile still until the primer ignites the powder . My opinion is , a little more
neck tension around 2-3 thou is better than pulling out a case full of powder and a stuck projectile. But also delays release and a more uniform ignition curve .

With the last question of turning necks . If u turned down to 13 thoug , I believe u would loose 2 thou tension.
Regards G Man lol! 8)

Tim L
Posts: 391
Joined: Mon May 19, 2014 7:11 pm
Location: Townsville

Re: Brass prep tasks- case volume, primer pockets et al

#8 Postby Tim L » Fri Dec 14, 2018 1:42 pm

Thanks for the replies guys, food for thought for sure. I switched to 2209 in the 308 because i had been trialing vhit 550 and found it reduced recoil. When we lost the supply of vhit i went to 2209 and it just ended up compressed. Like you Bruce, when seating 215s it tries to push the bullet out and needs a pause on the press,,,, or a double seating procedure. Good results though.
G, i don't read Bryans boiks myself (same reason i don't read sponsored articles in the paper) but I'd be interested in how he drew the conclusions on flash holes?
I discovered there is a high speed camera at work so I've asked Peter Bevan to see if he can put together a test rig that mimics firing pin strike. Yes, i know i can just hit it with a nail).
If i can get it all together I'll be able to film what is actually going on.
Should be fun if not educational

williada
Posts: 788
Joined: Wed Jul 22, 2009 12:37 am

Re: Brass prep tasks- case volume, primer pockets et al

#9 Postby williada » Fri Dec 14, 2018 8:45 pm

Tim, its easy to get numbered drills to test primer efficiency. You might surprise yourself with 3mm flash hole in the large primer .308 using 46.3 thereabouts of 2208 and Berger 155's using Federal Gold. This is the base light theory being an efficient burn. Could explain the essential difference in burn characteristics between large and small primer. If you run with the jet nozzle then champher the inside hole with an angle that will direct spark to the shoulder of the case. May have to grind a tool. Get an appropriate mill bit and make a holder. Drill out a bit of rod to take it. Used a pressure trace years ago but ended up in the draw because the only real judge is the paper. Have fun.

With regard case necks. The answer probably lies after the fact and not during the event of release because different neck tensions do create different group shapes. Cases may be re heat treated on firing and so give similar figures. Worthy of further investigation, great find. I should mention that when myself and Peter P were reviewing ammo prep at a commercial factory they used sealant. Sample push and pull forces were significantly different. I can't supply the figure as it was commercial-in-confidence, but what I will say that in the underground 100 yard test range projectiles without sealant and low extraction force would not group as well in their test barrels. The quality assurance of the ammunition was measured by the sampling process of the push and pull forces in a tension test jig.

Hope no idiot Superglues projectiles in place after reading this stuff as the compound was water based and not the old bituminous stuff and allowed controlled release. Good lesson in firm neck tension though without sealant. Boyer also shot with firm neck tension.

Bruce, always enjoy your incisive comments, keep punching.


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