Fire forming and primer pockets

[skiutah02]

Learned a lesson today, and maybe this was common knowledge, but I put this out here for your thoughts.

In a 223 throated for 90vlds.

Brand new Lapua brass, fully prepped and neck turned.

Thought I'd try fire-forming with full power load known to work well in the rifle but is unquestionably hot. Chamber (headspace) is a bit long as fire formed brass is about 0.006-0.007 longer than virgin and I suspect this is the reason I blew out all primer pockets in one shot using a load that is hot (but not insane) for this rifle. If I fire form with a lesser load, then use this load I can get 5-6 firings on Lapua brass before the pockets are toast.

I only tried a few, just in case, but it still brought a tear to my eye.

So am I correct in thinking that the cartridge head has too much clearance to the boltface and that is why it primer pockets all blew out. I was thinking that some of the energy of the load would be transferring into reshaping the brass, but clearly not.

Drew

 

[fguffey]

Chamber (headspace) is a bit long as fire formed brass is about 0.006-0.007 longer than virgin

Will never convenes anyone here but the .006" to .007" difference dropped the pressure. The difference in length is not the reason you 'blew the primer pockets'. And, when the case forms with a difference in length between the chamber from the shoulder to the bolt face and case length from the shoulder of the case to the case head the case suffers. Meaning the case stretches. A few years ago there was a thread about greasing the case. Bench resters were fire forming and lubing the case to prevent the case from locking onto the chamber. Anyhow I believe that thread went for 60 pages.

F. Guffey

 

[bigedp51]

What type and brand primer were you using, primer cup thickness could have something to do with it. With new factory loaded Federal M193 cartridges I have .006 head clearance in my AR15 carbine and I have never blown a primer. And my Lee full length .223 dies "IF" setup per the instructions with the press reaching cam over will bump the shoulder back .009 shorter than the GO gauge with approximately .012 head clearance. And I have fired .303 British cases with .026 head clearance without any ill effects other than .007 to .009 thinning in the base web area.

What do the primers look like and can you take a close up macro photo of them?

 

[carlsbad]

What do you mean by "blew out the pockets". I assume you mean they are now too loose to hold new primers?

Did the primers puncture?

What type of primers?

--Jerry

 

[dkhunt14]

>.006 to .007 is not really a great amount of movement to cause this. I would say the loads are too hot and maybe the chamber is too large of diameter. When the brass is new, it is soft and I prefer not to hammer them real hard. They get harder with each firing and loading. Matt

 

[skiutah02]

OK, interesting replies.

The primers were BR4s

OK, then why can I get 5-6 firings on the brass with exactly the same load if I fireform with a lesser charge first?

I like dkhunt's thought that new brass is soft and needs to work harden, but what other explanation is there?

I did not keep the primers, but they did not pierce the primer pocket itself opened up dramatically.

Some detail for those still interested.

Measured at case head just above groove on body side.

New: 0.X74
FF low pressure: 0.X75
1st "hot" load 0.X76
grows to 0.X775 over next 3-4 firings.
over 0.X775 primer can be almost fully seated with thumb
at 0.X79 primer falls out of case when turned upsidedown

Measured FF cases at same location after "hot" FF attempt

smallest was 0.X80 largest was 0.X83

Drew

 

[kyreloader]

The virgin cases will have less internal volume than the fire formed cases. That should/would cause a higher pressure in those cases versus the fire formed ones.

I would think that would be a large piece of this problem puzzle.

 

[Jdne5b]

How hot is hot, what is your velocity?

 

[Shynloco]

....When the brass is new, it is soft and I prefer not to hammer them real hard. They get harder with each firing and loading. ....

+1. What's the point of hammering new brass from the git go??? Seems to me that is not a wise thing to do.

Alex

 

[skiutah02]

90vld ~2900 in 223

I did it to see if I could get away with it, mostly. "Wasting" barrel life, brass life and components fireforming brass seems wasteful if I could get away with finding a load that works well in virgin brass. Been able to do it with almost all of my calibers/bullets in the past (often different loads in virgin brass vs. 1X+ fired, but I do not normally load hot, just accurate. It is just that this combo is stupid accurate and has low ES, etc but is hard on the brass so I was trying to see if I could get another firing out of it by shooting at a match while fireforming.

Clearly this will not work, but now I am interested in why.

 

[Geno C]

I don't know the answer to your why it happen. I would never try running my full power ai loads in the standard case though. I never run over book mad when fire forming actually. I usually find an accurate load at or near max in the parent round for fireforming.

 

[fguffey]

The virgin cases will have less internal volume than the fire formed cases. That should/would cause a higher pressure in those cases versus the fire formed ones.

I would think that would be a large piece of this problem puzzle.

If there were not so many members that are so wildly indignant about everything I would disagree.

F. Guffey

 

[Patch700]

The virgin cases will have less internal volume than the fire formed cases. That should/would cause a higher pressure in those cases versus the fire formed ones.

I would think that would be a large piece of this problem puzzle.

If there were not so many members that are so wildly indignant about everything I would disagree.

F. Guffey

Last time I did some fire forming (2 days ago) my fire formed cases measured slightly larger after firing at a few locations.... The chronograpgh noticed that once fire formed and carefully resized then shot again (same charge) the velocities were different (25-28fps to be exact in a case that holds around 42 grains) as compared to the virgin cases... I suppose that doesn't make sense to some but I sure get it.

Incidentally I should add that I never fire form without stuffing the bullets , and in this case they were also jammed after fire forming.

 

[Patch700]

New: 0.X74
FF low pressure: 0.X75
1st "hot" load 0.X76
grows to 0.X775 over next 3-4 firings.
over 0.X775 primer can be almost fully seated with thumb
at 0.X79 primer falls out of case when turned upsidedown

Measured FF cases at same location after "hot" FF attempt

smallest was 0.X80 largest was 0.X83

Drew

So from virgin brass to your load that you say shoots well you are seeing .009" expansion in some cases in one firing??? That is a lot of brass movement in the basement.

 

[skiutah02]

New: 0.X74
FF low pressure: 0.X75
1st "hot" load 0.X76
grows to 0.X775 over next 3-4 firings.
over 0.X775 primer can be almost fully seated with thumb
at 0.X79 primer falls out of case when turned upsidedown

Measured FF cases at same location after "hot" FF attempt

smallest was 0.X80 largest was 0.X83

Drew

So from virgin brass to your load that you say shoots well you are seeing .009" expansion in some cases in one firing??? That is a lot of brass movement in the basement.

No, that's not what I am saying. Grows in case head diameter only about 0.002 if ff first, but up to 0.009 if full power load on virgin brass. Not sure why.

 

[Patch700]

And this is a bolt gun?

 

[skiutah02]

Yep.

 

[jsthntn247]

Neck tension is greater on new brass if your doing something to open them up.

 

[skiutah02]

I turned the necks on these, so expanded with mandrel then turned, annealed, wire brushed then neck sized with bushing to give 0.002-0.003 "neck tension". My barrel likes more neck tension than is common, and this is the same neck tension I use for the load. So, as best I can do, all the elements of the case/case preparation/powder/primer/annealing/seating/etc/etc for the round is identical to a known good load for this barrel except it is virgin lapua (and no neck carbon).

How about this for a hypothesis then. Virgin brass (as mentioned above) is very soft and needs at least one firing of a normal pressure to work harden the case head plus the case itself is expanding to fill the chamber and gains too much "inertial energy" (for lack of a better work) for when it comes to an abrupt stop at the chamber dimensions it transfers it to the head and expands the web/PP.

Once fired, the combination of harder head and less room to expand is gentler on the primer pockets.

Simplistically I have been thinking that while the virgin brass has less capacity before fireforming, the potential excess pressure is offset by the expenditure of energy involved with expanding the case itself, but the primer pocket expansion is a problem.

 

[fguffey]

No, that's not what I am saying. Grows in case head diameter only about 0.002 if ff first, but up to 0.009 if full power load on virgin brass. Not sure why.

If there were not so many members that are so wildly indignant about everything I would disagree.

F. Guffey

Before the Internet it was possible reloaders had an answer. There is no way a case head can expand .009" with the first firing. In the old days reloader did not use new brass as a standard, the used factory ammo. I have tested receivers that were sold as suspect. I wrecked a few cases when determining the receivers were not suspect, the cases were fired once, the plash holes increased in diameter, the primer pockets would no longer hold a primer and the case head was shortened from the top of the cup to the case head because the case heads were crushed.

Then there was stretch, the case body was locked to the chamber, when fired and the case head crushed the case head moved away from the case body causing the case to start case head (insipient) separation. .009"? You did not measure the case head thickness, no one does, so you will never know how much the case stretched between the case head and case body.

If you lubed the case to prevent the case body from locking onto the chamber you made a big mistake when you went straight for heavy loads. You need a better plan. A heavy load with a greased case can cause crushed case heads.

Fire forming: Chamber a round, pull the trigger, instantly, the shooter becomes a fire former. I have never has aspirations of becoming a fire former. I choose to form first then fire.

The .002" case head increase was 8 times the recommended allowable before the Internet. .00025" was acceptable. I know, that was before reloaders got their hands on hardness testers and decided there is nothing a reloader can do is say "Whoa is me".

G. Guffey