Primers backing out

[xcalibor67]

Just built a new 222mag and my primers are backing out about 8/10k.
Using new R&P brass CCI SR primers. Head Clearance was checked with both GO, and NO_GO gauges, and in spec. Since its new brass, and I neck sized only, the setting of a size die is out of the scenario. I think the new brass is just under-sized from the factory, and I will have to seat bullets long and try to fire form cases? One thing I am confused about is: I read that a low pressure charge can cause primers to back out.. Well, im no rocket scientist,but i don't see how this is even physically possible. If the case fits snug between the shoulder and the bolt face, there is no room for the primer to back out, even with a low charge...A high pressure load will cause primers to flatten....What im getting at is, I think that head clearance is the ONLY factor that can cause primers to back out...

 

[45_auto]

Since you reload, you know how hard it is to de-prime a case.

Not very hard, right?

Normal cartridge pressure will expand the brass (move the case back and expand the shoulder forward) to fill the chamber. There's no where for the primer to go.

I'm not sure how far 8/10k is, but low pressure will cause the primer to act like a piston. The primer will move backwards forcing the case forwards till the shoulder of the brass contacts the shoulder of the chamber. There's not enough pressure to expand the brass at the shoulder and force the case backwards so you have a backed-out primer.

You're right in that the headspace of the rifle controls the distance that the primer can move. If you fire-form some brass to the chamber and reload it without resizing, you might have to hammer the bolt closed but the primers won't be able to move.

 

[BBBBill]

Stick a primed case (no bullet, no powder) in any gun and fire it. That's about as low pressure as you can get. The primer will often be backed out. It will tie up a revolver.

 

[beag_nut]

Stick a primed case (no bullet, no powder) in any gun and fire it. That's about as low pressure as you can get. The primer will often be backed out. It will tie up a revolver.

And, almost every time! That's why I hate to demonstrate to non-gun people with a primed-only case (but anything hotter is way too loud in my workshop).

 

[243winxb]

I think the new brass is just under-sized from the factory, and I will have to seat bullets long and try to fire form cases?

Yes, correct. No need to seat long, normal is ok. The firing pin strike can set the shoulder back .006" in my Savage Axis 223 rem when measuring head to datum. If pressure is low from a starting load, the primer may back out a litte. Funny what one can learn from a defective primer. The 2nd strike sets the shoulder back even more, if the round does not fire. The type/fit of extractor has something to do with it.

 

[xcalibor67]

Most of my rifles I neck size only, using a FL die only when chambering problems arise..
I just loaded 2 rounds with IMR4198, middle of the road and seat some 55gr
Horn. SP long into the lands..And primers still backed out...Think i'll chamber a new empty case and use shims to check clearance..may end up putting a false shoulder on the brass, as I really don't want to pull the action and reset the head clearance, as its in specs with gauges. Thanks.

 

[243winxb]

Fire the same neck sized case 3 times or till the bolt closes hard with a near maximum load to get a good measurement of the brass head to datum. Then compare to the new unfired brass.

 

[moxie]

What is 8/10k?

Do you mean 8-10 thousandths of an inch, as in .008"-.010"?

 

[243winxb]

K meaning 1000 . So i took it as .008" to .010" Not a lot for factory new brass.

 

[fguffey]

K meaning 1000 . So i took it as .008" to .010" Not a lot for factory new brass.

.008" to .010" primer protrusion is the equivalent to firing a minimum length/full length sized case in a no go-gage length chamber.

If the case fits snug between the shoulder and the bolt face, there is no room for the primer to back out, even with a low charge.

The case length is measured from the datum/shoulder to the case head. the chamber length is measured from the datum/shoulder of the chamber to the bolt face. The clearance between the chamber and case is the difference in length between the minimum length/full length sized case and the chamber. that leaves enough room (.005" +/- a few) for the primer to back out?

Then there is that narrow window between minimum and maximum load, the primer should be seated when firing normal loads. It has to do with one of two things happening.

Then there is the seating a primer with the bolt, start a primer into the primer pocket but do not seat it, leave it protruding .010". After seating the primer chamber the case and slowly close the bolt, the bolt will seat the primer but not completely. After closing the bolt remove the case and then measure the primer protrusion. If there is no room between the shoulder of the case and the shoulder of the chamber and there is no room between the case head and bolt face the primer will be seated flush.

F. Guffey

 

[MEHavey]

If the case fits snug between the shoulder and the bolt face, there is no room for the primer
to back out, even with a low charge

Just because chamber headspace dimension is within spec (passes the GO/NoGO test), that doesn't
mean that any particular case (even if it's in spec) doesn't have some slop when the bolt closes.
In fact most commercial brass is sized to SAAMI minimums to ensure bolt closure in a SAAMI min chamber.
That means a SAAMI Max chamber gives it 6-8 thou slop right off the bat (depending on spec).

Further, Bart B. makes a pretty good case that even if the case/chamber is a perfect (no clearance) fit,
the firing pin strike will drive the case intothe chamber shoulder enough to set it back ~0.005" or so before
ignition. If the charge is low enough that the case doesn't then stretch far enough back to meet the bolt
face, the primer will instead be the only thing protrude back to the bolt.

See
http://thefiringline.com/forums/showpost.php?p=6051047&postcount=21
http://thefiringline.com/forums/showpost.php?p=6051131&postcount=25

 

[fguffey]

pin strike will drive the case intothe chamber shoulder enough to set it back ~0.005" or so before
ignition

A shooter purchased a new rifle and new ammo. He went to the range to test his new rifle and new ammo. He had 5 rounds that failed to fire out of the first box of 20 rounds. Two other shooters had a go at the failed to fire rounds, in all the failed to fire rounds were struck 5 times +. I got a call, someone wanted to know what was wrong with R-P ammo, I instructed the caller to call Remington, the phone number is on the box.

That afternoon the 5 fail to fire rounds and 15 fired cases show up, I want to know where the box is and contact information for the shooter. NOTHING!

I dug out gages, store bought and home made. The failed to fire ammo did not have shoulder set back, according to the story the case should have had massive shoulder set back, the cases length from the shoulder to the head of the case was minimum length/full length sized.

We measured the fired cases, magnificent cases, the fired cases would fit my chamber gages with slight thumb pressure. We checked the fired cases in take off barrels, nothing suspect. We then pulled the failed to fire cases for dimensions and components. My friend only trust 10-10 Ohaus scales so I put my electronic scales away. Everything was within 1/10 grain. we removed the primers, we reinstalled the same primers back into the 5 cases without bullet and or powder.

AND THEN? I dug out one of my M1917s with killer firing pins, I chambered the primed cases, pulled the trigger and fired all 5 primers one after the other.
We measured the case length of the 5 cases, nothing changed, the case length from the shoulder to the case head did not shorten. I would have bet the case would have shortened but not for the same reason everyone else claims.

F. Guffey

 

[MEHavey]

Did you read the cite in Post 11 above?

 

[fguffey]

AND THEN? I dug out one of my M1917s with killer firing pins, I chambered the primed cases, pulled the trigger and fired all 5 primers one after the other.
We measured the case length of the 5 cases, nothing changed, the case length from the shoulder to the case head did not shorten. I would have bet the case would have shortened but not for the same reason everyone else claims.

Did you read the cite in Post 11 above?

Is there something about the quote above your quote you did not understand?

F. Guffey

 

[MEHavey]

Did you read the cite ?





...and now to [a] data point:

I took an HXP-68 case which [as it was fired in my Garand] would not re-chamber in my `03A1;
- Sized it until it would just re-chamber (with feel);
- Hand-primed it w/ a CCI large rifle primer (so the primer cup would be "hard");
- And fired it.

Headspace Comparator Reading < firing: 2.0505"
Headspace Comparator Reading > firing: 2.0505" (de-primed w/ 45-120 die)

Hmmmmm.....
The answer to primer backout w/ a low charge due to headspace is a very definite no/maybe/probable -- and likely totally dependent on shoulder annealing condition

 

[243winxb]

is there something about the quote above your quote you did not understand?

lol

 

[MEHavey]

is there something about the quote above your quote you did not understand?

Yes.

You did not answer the question (in case no one else noticed.)

Incidentally, did you read data point result below the quote about the quote about the quote ?

 

[fguffey]

You did not answer the question (in case no one else noticed.)

If there is a very remote chance someone did notice I avoided the question there is a more remote chance they understood I was trying to avoid one of those mindless internet exchanges.

F. Guffey

 

[MEHavey]

If there is a very remote chance someone did notice I avoided the question there is
a more remote chance they understood I was trying to avoid one of those mindless
internet exchanges

Not a prayer....