Primer initiated premature bullet jump

358156 hp

Well-Known Member
Below is a copy of an Army testing board report on primer initiated bullet jump in 5.56 & 7.62 military ammo. I think we've all known of the potential for this, but could/would the effects of the primer firing be mitigated or at least modulated by the type of powder used? Could this be having an effect on the old "extruded powders tend to be more accurate" theories?


Well-Known Member
Ok, mind blown. Ric and Brad aren't members of AR.

Great find there, filed under "suspicions confirmed".

Primer pop is why I use Federal LP in the .44 Magnum with 2400. Not so bad with faster powders. Also why the small-primer .45 ACP brass is such a good idea.


High Steppes of Eastern Washington
Ian, I have too many interest to belong to another board. You guys are it for me. HP, second link worked.

I don't know if I am reading something else into this, but I suspected something like this. 100% load density gives good chronograph data, but do not equal good accuracy. Figures 11 and 12 seem to suggest that having compressible empty space in the case allows for smoother acceleration and maybe better accuracy?


Well-Known Member
Interesting along with the new Fed. primer compound (and explanation). Also a squib can produce 300 fps velocity? Seems like they could compute engraving force as a 180gr 40SW cast sticks in bore for a squib. Also good reasoning behind throat erosion. I didn't see an explanation of the 2 pressure spikes from the primer. Also somewhat infers the reason for powder position sensitivity as hot metal from the primer ignites the powder.


Well-Known Member
It is not unusual for a third, lower peak also to be recorded. Our analyses of these data indicate that any peak after the first is understood to be due to reflection from compression of the propellant bed.

this from page 5.
I wonder how much that third [and other] lower peak is influenced by something like case shape???
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Redlands, Kalifornistan
OK--THAT was a fascinating read. Many thanks for posting this info!

My own far-less-sophisticated observations over the years have been that primer brisance/strength/heat propagation is a lot more critical element than we give it credit for being. I didn't give it much thought until about 10-12 years ago when rassling with flyers in my 25/20 WCF and 32/20 WCF rifles. My Nevada Cast Of Cast Bullet Characters were having a not-too-deeply-irrigated discussion about the Slings And Arrows Of Outrageous Fortune regarding flyers that spoiled groups.....those not related to the Nut Supporting The Stock, more specifically. Urny stated that he had seen immediate group shrinkage with his 22 Hornet/Ruger #3 through the use of Remington #6-1/2 primers. He explained that Remington makes two small rifle primers--the #6-1/2 for cases sizes like 22 Hornet, 218 Bee, 25/20 WCF, 30 Carbine, and 32/20 WCF--and the #7-1/2, for the 222/223-sized cases. The #6-1/2 uses a rifle-pressure cup but a smaller primer fuel element tailored to smaller case capacities and powder weights.

Such things are called CLUES where I once worked. I suspect (but am not certain) that this meet-up was during one of the Big Reno Gun Shows I showed up for. Folks, I'll visit the United States any time I can get away to do so. I do recall picking off a sleeve of Rem #6-1/2 primers right after this discussion, and I still have about 1500 of that 5K acquisition on hand. Remington primers are largely unobtainium hereabouts, so another visit to the Miwall table at the reconstituted BRGS is called for. Aw, shucks.

The results were immediate and conclusive. Jacketed or cast, flyers were largely eliminated and group sized shrank SIGNIFICANTLY. Velocity ES and sd were significantly reduced--across the board--22 Hornet, 25/20, 30 Carbine, 32/20--rifles and handguns. This correction was one of the most significant improvements I have seen in my reloading outcomes in all the time I have been involved in this madness of ours. Primer selection definitely matters--A LOT.


Redlands, Kalifornistan
I'm sure that SP primers would have the same effect as the Rem #6-1/2s. I just don't trust the cup strength of the SP primers in a 30k PSI+ environment. CCI #500s would likely be all right--those little monsters are harder than woodpecker lips. Federal 100s, though? Dunno. Kinda soft IME.


Well-Known Member
I use magnum SR primers in those cases.
I guess doing the full on opposite looking for the same results.


Most of my .22 Hornets, my .17 Ackley Hornet and my .218 Mashburn Bee all get Rem 6.5 primers. My only .22 Hornet that doesn't is my Ruger #1B, it shoots way better with the Rem 7.5's.

Roger Allen

Active Member
I think the small pistol primers will handle the 35k pressure a 9mm needs to handle. I always thought about using them in my 300 blackout boltaction subsonic but developed the load to it with Eastern European small rifle primers bc I have tons of them


Well-Known Member
even in cast bullet rifle loads I use a lot of pistol primers.
my cut-off for them is around 40-K