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Interesting Research - Primer Pushing Bullet

uashooter

I stumbled across a string of Army Research Laboratory (ARL) Technical Reports. While they are written for cartridges of maximum interest there (5.56 and 7.62), there may be wider applicability. It started with their development of experimental hardware to measure force on primer bases, in order to examine blown primers (ARL-TR-5862).

However - the measurement of force on the base of the primers, when combined with bullet position measurements - has lead them to determine that when the primer actuates - it pushes by compression on/thru the main charge upon the base of the bullet, and ejects the bullet towards/into the start of the engraving process - PRIOR to the primary pressure buildup from the burning of the powder charge. Further - they are seeing variation in bullet 'pitch' during the process.

The implication is that this research MAY give us insight into why jump/jam distances yield different results, and why fill ratios(including compressed loads) may yield different results - and if we are REALLY lucky - why short bearing surface bullets like the SMK 2231 are difficult to achieve consistency with.

The attached is one of the recent papers - but the sequence mostly starts at ARL-TR-5862.
 

Attachments

you can forget powder one time and fire a primer off and see that the primer will move the bullet- quite a bit. most shooters have done this. it is also a way to prove how different primers create their own pressures and why different primers yield different results with the same powder charge.
 
The inline muzzleloader world has been working on this for quite awhile. It's one of the reasons for a move away from 209 primers.
 
This is something I've wondered idly about for some time. Now, if we do this with different types of powders, would the potential for premature bullet jump increase with certain powders? Specifically, would extruded powders compress a bit more (or less), and ease or at least modulate any bullet jump differently than a ball powder could/would?
 
Does this prior knowledge----primer energy moving bullet----suggest any
changes in how we seat bullets to compensate for this movement ?

Do we just ignore this and listen to the target ?

The report refers to "off axis" motion. Does this throw out a challenge to us ?

How about chamber changes such as decreased freebore diameter and
increased freebore length ?

We go to quite a bit of effort to produce carefully assembled rounds. Are these efforts
rewarded as we previously thought ?


Sorry for so many dumb questions but sometimes I feel like I have a terminal case
of the DA's. This report certainly made me think outside my box.

A. Weldy
 
Well as far as i'm concerned, it sure shed some light on what goes on in that first few milliseconds after the pin hit the primer. The bullet is driven out of the neck, before there is any neck expansion, by a piston-like column of propellant, with the bullet possibly going slightly sideways as it moves toward the lands. Possibly a shower of not yet ignited powder going past the bullet and into the lands to lubricate the bullet, and then ignited, or not.

Helps to explain why some bullets like to be seated IN the lands, and some out.

I met a guy at the range who was shooting a 308 with 125 grain bullets and H414. He was seating the bullet at a jump of .180 and getting screaming fast velocities. I suspected that at that jump, he was getting a lot of ball powder, some possibly burning and between the bullet and the barrel and driving the bullet on a cushion of hot gas. Wouldn't that be a hoot if such a theory were proved true.
 
You dont think the pressure differences in the differing case capacities of bullets taking up more/less space is what changes the tune of the load? Or is it the different time that the bullet is in the barrel, exiting at different times, changes the point at which the bullet exits finding a sweet spot is what does the tuning?
 
Find something else. You can't change anything that you found out that is happening after the firing pin strike. You still have to tune the load to the gun.
 
Check out the photos of simulated propellant being ejected from the short barrel as the bullet exits following the primer ignition. Pretty cool!

I can imagine a very short barrel, one that ended at the shoulder/neck junction leaving the neck and bullet visible to a camera and then perform the primer with propellant simulant test.
 
Last edited:
The findings of this report may help explain the general observation that loads which fill the case are more consistent than loads which partially fill the case. Partially filled loads, when fired, would in most instances be laying horizontally in the chamber with a space between the powder and the case wall. In this scenario, the primer impulse would take the path of least resistance and pressurize this space, compressing the powder charge against the bottom of the case and subsequently pushing the bullet out of the case month with an asymmetric force on the “top” portion (as it’s oriented in the chamber) of the base of the bullet – possibly canting it off axis to the bore. It is unclear how the powder charge would burn if compressed against one side of the case but it seems it would be different than if the powder charge were compressed against the base of the bullet.



Interesting to think about. Thanks to the OP for posting this report.
 
First time on here, good post, this is a noticeable issue in smaller cartridges with thinner cases (light neck tension), like the .22 Hornet. Crimping proved to be valuable for added consistency.
As for full cases vs less, with a full case the ignition area of the powder column is consistent. In a partially filled case the powder might be level, sloped to the front or sloped to the back. Either way, the surface area of the powder varies in regards to ignition.
I was in Field Artillery for years and way back in the day they learned that ignition was seldom consistent and caused considerable variations in performance. The solution was to add a pad (round pouch of black powder) to the base of the charge. This provided consistent and uniform column ignition, end of problem. Anyhow, maybe it helps, maybe not ( I think it does) but I make sure I handle and load each case the same when on the range developing loads.
 
Dusty Stevens said:
you can forget powder one time and fire a primer off and see that the primer will move the bullet- quite a bit. most shooters have done this. it is also a way to prove how different primers create their own pressures and why different primers yield different results with the same powder charge.
Click to expand...
Dusty, the only time I forgot powder in a load, a 210 Berger in a .308 Winchester with CCR BR2 primers, the bullet barely got into the throat. Admittedly, it was a competition chamber & a .3085" throat & a .300/308 barrel, but I was surprised how anemic the push was.
 
JohnKielly said:
Dusty, the only time I forgot powder in a load, a 210 Berger in a .308 Winchester with CCR BR2 primers, the bullet barely got into the throat. Admittedly, it was a competition chamber & a .3085" throat & a .300/308 barrel, but I was surprised how anemic the push was.
Click to expand...

Ive seen them do that and ive seen a ppc get stuck so bad i tore up a dewey rod getting it out
 
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