Magnum primers

[M4bushy]

Yeah, right! It takes a LOT of pressure to gain 100 fps. Good call.
Both cartridges mentioned do best with standard SP primers---yes even the ACP.

Ok, so your an expert. Just relaying what my chronograph detected.
During the last primer shortage all i could get my hands on was mag primers so i did some experimenting. No the primer alone probably doesn't make the
Velocity increase, it's the rate that the powder is ignited that can cause the spike.

[44man]

Ok, so your an expert. Just relaying what my chronograph detected.
During the last primer shortage all i could get my hands on was mag primers so i did some experimenting. No the primer alone probably doesn't make the
Velocity increase, it's the rate that the powder is ignited that can cause the spike.

Exactly, you are correct. It is the very small cases that the mag primer is the worst choice in.
But ignore the spike for a second, primer pressure alone can move a boolit before ignition and that causes other problems. It will increase air space a different amount between rounds shot.
Even a standard LP primer can be too much in the ACP, my tests have shown a standard SP primer works better.
I refuse to use a mag primer in my .44 mag or .45 Colt even with 296. They instantly triple groups.

[44man]

Ok, so your an expert. Just relaying what my chronograph detected.
During the last primer shortage all i could get my hands on was mag primers so i did some experimenting. No the primer alone probably doesn't make the
Velocity increase, it's the rate that the powder is ignited that can cause the spike.

Exactly, you are correct.
But ignore the spike for a second. Primer pressure alone can move out a boolit before good ignition. That changes air space from shot to shot.
Tests have shown the tiny cases can not absorb the pressure from the primer. The ACP works better with a standard SP primer.
I refuse to use a mag primer in the .44 mag and .45 Colt even with 296.
With a rifle, LP mag primers can work fine depending on case size and powders. Large cases need LR and larger yet need LR mag primers. Primers of all kinds can take a lot of pressure, I have taken LP mags to over 50,000 psi without making them flat. That is not the reason, it is flame front, the amount of heat, primer pressure, powder choice and the size of the case.
Primer thickness can be an issue with very strong mainsprings or wrong shaped pins that can puncture them. Primers for an AK must be very tough or the gun will slam fire. Floating pins need very hard primers.
Beside the point anyway. Too much primer pressure in tiny brass is wrong just like not enough in large cases. Primer balance must be determined by what you are shooting, NEVER by what you can buy. If they are not right, don't buy the things.

[M4bushy]

Exactly, you are correct.
But ignore the spike for a second. Primer pressure alone can move out a boolit before good ignition. That changes air space from shot to shot.
Tests have shown the tiny cases can not absorb the pressure from the primer. The ACP works better with a standard SP primer.
I refuse to use a mag primer in the .44 mag and .45 Colt even with 296.
With a rifle, LP mag primers can work fine depending on case size and powders. Large cases need LR and larger yet need LR mag primers. Primers of all kinds can take a lot of pressure, I have taken LP mags to over 50,000 psi without making them flat. That is not the reason, it is flame front, the amount of heat, primer pressure, powder choice and the size of the case.
Primer thickness can be an issue with very strong mainsprings or wrong shaped pins that can puncture them. Primers for an AK must be very tough or the gun will slam fire. Floating pins need very hard primers.
Beside the point anyway. Too much primer pressure in tiny brass is wrong just like not enough in large cases. Primer balance must be determined by what you are shooting, NEVER by what you can buy. If they are not right, don't buy the things.

I agree this is an issue with the slower powders ie 2400 but i haven't seen any data of that happening with faster pistol powders. Except for the sse claims with powders such as Tightgroup with tiny charges in karge cases.

[44man]

I agree this is an issue with the slower powders ie 2400 but i haven't seen any data of that happening with faster pistol powders. Except for the sse claims with powders such as Tightgroup with tiny charges in karge cases.

Yes, boolit punch out from the primer does happen with fast powders too but it is masked by quick pressure rise.
It is crazy. Think of a few gr. of Bullseye in a huge case. It is all over the place with no gr. close together. Now you need FIRE. Just keep primer pressure down.
What happens in a powder column with a primer? I don't profess to know. What is the difference in squirting flame and pressure through the column versus lighting it at the start and getting a progressive burn?
Most of my accuracy comes from a progressive burn, light the powder at the flash hole and let it go. Don't blast all the way through the powder charge. Do not reach the boolit base with pressure before the powder lights off.
Do I make any sense?