Jamming bullets and case head/bolt face contact during firing..some facts.

A

Al Nyhus

"It'll never work!"
There's some controversy on whether a bullet that's jammed hard into the lands can actually keep the case head in contact with the bolt face during firing. Lots of shooters, myself included, use this process when fireforming and/or blowing shoulders forward on various wildcats. Whether or not this happens is pretty easy to demonstrate. After reading one particular thread, I decided it was time to post some pics of the deal. The test mule is my RFD 30BR.

-First, I removed the priming compound from a new Fed 205 primer. The priming compound is the yellow-ish stuff. The anvil was left in the primer so as to replicate things as best I could.

p1.jpg


-Next, I f.l. sized a case normally with the same bushing that I always use in this gun (.003 neck tension). Shoulder 'bump back' is .0015. 'Dud' primer is seated.

p2.jpg


-Firing pin is removed from the bolt. Bullet is seated with .020 'jam', as per usual with this gun.

p3.jpg


-Case head-to-ogive measures 1.698 on the seated bullet. Again, this seating depth is a .020 'jam'.

p4.jpg


-Dummy round is chambered, then extracted. The rifling marks from the bullet being 'jammed' .020 are very pronounced, as you can see in this pic.

p8.jpg


-The case head-to-ogive is again checked to see if it's changed after being extracted. It's still 1.698. Again, the rifling marks are visible.

p6.jpg


-Firing pin assy. reinstalled, trigger pulled and round extracted. Case head-to-ogive measures 1.695.

p7.jpg


So, at most, the bullet pushed back into the neck .003 (1.698-1.695). Given that the shoulder was back .0015 from the sizing process and the case can move forward in the chamber that much when the pin hits the primer cup, what we're really seeing is a .0015 bullet 'push back' into the case neck.

Connect dots accordingly..............

Good shootin'. :) -Al
 
The question is about SHOULDERS :)

It pushed in until it hit the shoulder of the case.

Now do the same thing but with the shoulder out of the way.

al
 
alinwa said:
The question is about SHOULDERS :)

It pushed in until it hit the shoulder of the case.

Now do the same thing but with the shoulder out of the way.

al
Click to expand...

Yes... maybe use a different case that the shoulder doesn't come close to touching and see how far the bullet gets driven into the neck. That would be a better test...
 
The Wolf Pup cases are f-formed this way....bullets hard into the lands with plenty of neck tension and the shoulder goes forward .240. Checking these the same way before f-forming showed about the same amount of bullet 'set back' into the case neck neck as I got with the 30BR. So, why no head seperations or other evils? ;)

unfiredpup.jpg


Hint: the answer is right in the photo.

Good shootin'. -Al
 
Fresh new brass will take tremendous abuse,

remember it was formed from a small disc, the 'button.'

The shoulder DOES blow forward it just doesn't do so consistently.

It's quite rare to get a casehead separation from one firing on new brass.

As long as you're happy with your method, all pertinent parties are happy.:)

al
 
By The Way Al....... you've got the perfect test venue here!

Use a Wolfpup case set up exactly as you've fireformed hunnerds of 'em....BUT.... you must not only do the before and after measures on the bullet, you must also measure headspace by shimming with extractor removed.

Another way to do this is to loosen your barrel and use it like a micrometer to close on the cases setting on shims on the boltface. (the case/bullet should still be stuck in the lands) and perhaps the easiest way is to stick a home 'ade shim (pop can) for the test, then release the shim and check with feeler gages. In other words do the test with 10 thou exter headspace, then remove the 10 thou shim.

Also, check 10-15 ff'd cases with gizzie after manually removing the primer. Spin them in the caliper to quick-n-dirty check for casehead squareness.

hoping to hear........ EVEN IF YOUR BULLETS DON'T MOVE!! :) :)

al
 
I think this is making a mountain out of a mole hill. Fireforming brass by either a hard jamb or by creating a false shoulder or neck both work. I've done it both ways, with the BR case with the shoulder .075" forward. I do the false neck more if I'm making up a bunch of cases, neck up over chamber diameter, then size down where the case neck wedges, and use about 12 grains of bullseye. Or, I load them long and use them as fouler shots at the beginning of a relay. Are they perfect first time? Maybe not, but it is certainly ready for a normal load and fire from there.

People get all worked up over the Ackley chamber if you don't set the barrel back so the headspace is .004" under. No difference in this than fireforming most any "wildcat".
 
Exactly, Wayne. The extractor limits the cases forward movement in the chamber...the positive stop, so to speak. The most a jammed bullet can be 'set back' in the case neck is roughly the amount of clearance between the extractor lip and the back of the extractor groove in the case and the shoulder set back amount.

Case head-to-datum on these 50 are identical after the first firing (shoulder blown forward .240). The shoulders will finish sharpening up when fired the next time.

cases.jpg
 
Al Nyhus said:
Exactly, Wayne. The extractor limits the cases forward movement in the chamber...the positive stop, so to speak. The most a jammed bullet can be 'set back' in the case neck is roughly the amount of clearance between the extractor lip and the back of the extractor groove in the case and the shoulder set back amount.

Case head-to-datum on these 50 are identical after the first firing (shoulder blown forward .240). The shoulders will finish sharpening up when fired the next time.
Click to expand...

Question- looks like you are turning the neck past the new shoulder before fireforming. Guess this does away with the donut problem??
 
Alinwa
The other Al is probaly using Fed 205 primers.If he switched to CCI 450's and chambered his rounds with an actual 0.020 worth of jam 85% of them wouldn't even fire.
If your using CCI 450's and the false shoulder method common to the Dasher type cases and you chamber a round then re-chamber the round it won't fire either most of the time.
Soft primers like the Fed 205's get used for all of my fireforming because they allow you to use either method.
Lynn
 
JerrySharrett said:
Question- looks like you are turning the neck past the new shoulder before fireforming. Guess this does away with the donut problem??
Click to expand...

Hi Jerry. Yes, turning the necks down into the shoulders makes for a nice 'blend' at the neck/shoulder junction and does wonders for the donut problem. The turned length is .150 on the 'Pup cases. Even on 'normal cases (30BR, etc.), I push the shoulders back .020-.025 using a faced off shell holder, then neck turn to the 'set back' neck/shoulder junction and blow the shoulders forward when f-forming. I started doing this back when making our 30 Ware Wolf (30X47-ish) for the HBR guns (308 Lapua shortened .165). It virtually eliminated any donut issues on those cases, as well. This wasn't an original thought by me as HBR shooters have been doing their cases like this for a long time.

Hope all is well in the Tri Cities. :) -Al
 
Al
I just ran the same test with a 6 Dasher and got 0.011 movement.The only thing that was different was on the CCI 450 Magnum primer.I had to remove the anvil in order to get rid of the primer compound.I tried using a very skinny needle and some pliers but the anvil on the 450 covers up much of the primer cup requiring its removal.
I will repeat the test with a Fed 205 and see what I get.
Lynn
 
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