Primer impulse and bullet movement
- Thread starter SeabeeKen
- Start date
If u could go back in Precision Shooting, German Salazar did some extensive testing of the popular brands of primers we use. His observations were focused on primer intensity based on the flash that they produced from a stub rifle bbl. that was constructed specifically for the tests. He then ranked the primers based on their intensity.
it was interesting to see that primers that were popular in competition shooting all had a milder flash intensity. His testing results might be correlated with the information from the Army research to infer that the milder primers have less disruptive effect on the bullet/ power combination. Starting the bullet down the bbl. in a less violent manner must have a benefit to more consistently centering the bullet in the throat and beginning the rifling engraving process.
One of these factors is contributing to these milder primers being associated with increased accuracy/consistency!
it was interesting to see that primers that were popular in competition shooting all had a milder flash intensity. His testing results might be correlated with the information from the Army research to infer that the milder primers have less disruptive effect on the bullet/ power combination. Starting the bullet down the bbl. in a less violent manner must have a benefit to more consistently centering the bullet in the throat and beginning the rifling engraving process.
One of these factors is contributing to these milder primers being associated with increased accuracy/consistency!
A chronograph suggests that off the land(OTL) bullets do not reach land contact before powder has ignited.
For instance, if you seat a bullet 10thou OTL, and another touching lands, the bullet touching causes higher muzzle velocity/pressure. If primers pushed bullets to this same touching land relationship -before powder ignited, there would be no difference in muzzle velocities.
It is reasonable to suspect, and I believe, that primers alone provide enough pressure to push bullets through neck friction(eventually)(in small cases). But it's another thing all together to suggest that this ever happens with loaded ammo.
I'll suggest it does not. That instead, powder ignites well before a primer has risen pressure enough to affect a seated bullet, and then that ignited powder liberates enough gas/pressure to expand necks for normal bullet release. Basically, it all happens way faster than the study assumed.
And THIS passes all tests (that I've ever seen).
For instance, if you seat a bullet 10thou OTL, and another touching lands, the bullet touching causes higher muzzle velocity/pressure. If primers pushed bullets to this same touching land relationship -before powder ignited, there would be no difference in muzzle velocities.
It is reasonable to suspect, and I believe, that primers alone provide enough pressure to push bullets through neck friction(eventually)(in small cases). But it's another thing all together to suggest that this ever happens with loaded ammo.
I'll suggest it does not. That instead, powder ignites well before a primer has risen pressure enough to affect a seated bullet, and then that ignited powder liberates enough gas/pressure to expand necks for normal bullet release. Basically, it all happens way faster than the study assumed.
And THIS passes all tests (that I've ever seen).
I've found this to be true with the WOLF SRM primer. It's VERY mild and yields great SDs and Accuracy. I tried to leverage this excellence in Palma brass, but the mild WOLF primer didn't have enough energy to ignite a 308 powder charge reliably.
Lucky Shooter
Gold $$ Contributor
I don't know how to make anything useful out of this.
I made two dummy rounds----222,BR4, SMK 52.
One round was seated to barely touch the lands and the other
round was seated .010 off the lands.
After firing the two dummies:
The bullet that was seated barely into the lands advanced
slightly more than .001".
The bullet that was seated .010" off the lands advanced
slightly less than .003".
If there is anything useful here, I've failed to see it and hope
others can produce something useful to us.
A. Weldy
I made two dummy rounds----222,BR4, SMK 52.
One round was seated to barely touch the lands and the other
round was seated .010 off the lands.
After firing the two dummies:
The bullet that was seated barely into the lands advanced
slightly more than .001".
The bullet that was seated .010" off the lands advanced
slightly less than .003".
If there is anything useful here, I've failed to see it and hope
others can produce something useful to us.
A. Weldy
It may be case size dependent , but I have observed 223 cartridges loaded without powder , drive a bullet into the lands with sufficient force that it could not be dislodged with a cleaning rod . That was just a SR primer’s force lodging a bullet beyond just engraving the bullet.
I believe that SR 308 brass is known for misfires in temps on the 40 degree range. Warmer temps have not been an issue for me.
If a case is not loaded to max density, do u think the primer ignition effects powder distribution in the case? ie. moving/ disrupting the powder charge in the case ( like a rim fire)?
I believe that SR 308 brass is known for misfires in temps on the 40 degree range. Warmer temps have not been an issue for me.
If a case is not loaded to max density, do u think the primer ignition effects powder distribution in the case? ie. moving/ disrupting the powder charge in the case ( like a rim fire)?
divingin
Gold $$ Contributor
The bullets didn't make it out of the necks? And the one loaded short never made it to the rifling?
Any idea what kind of neck tension you were running?
Lucky Shooter
Gold $$ Contributor
divingin,
"The bullets didn't make it out of the necks? And the one loaded short never made it to the rifling?" This statement is correct.
Neck Tension----my understanding.
.248" chamber neck diameter
.0105 case neck thickness
.003" loaded neck clearance
Necks were sized with collet die and .221" gage pin.
.221" gage pin had a snug fit in case neck.
.2215 gage pin wouldn't go into case neck
My understanding is that results in neck tension from
.0025" to .003".
Another note: This chamber has a slightly short headspace.
Possibly eliminating any forward movement of the case from
firing pin impact.
I didn't see what I expected and hope someone can shed more
light on the subject.
A. Weldy
"The bullets didn't make it out of the necks? And the one loaded short never made it to the rifling?" This statement is correct.
Neck Tension----my understanding.
.248" chamber neck diameter
.0105 case neck thickness
.003" loaded neck clearance
Necks were sized with collet die and .221" gage pin.
.221" gage pin had a snug fit in case neck.
.2215 gage pin wouldn't go into case neck
My understanding is that results in neck tension from
.0025" to .003".
Another note: This chamber has a slightly short headspace.
Possibly eliminating any forward movement of the case from
firing pin impact.
I didn't see what I expected and hope someone can shed more
light on the subject.
A. Weldy
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