Large Pistol Magnum Primers vs. Large Pistol Primers

[That Guy]

I've tried to google this, but the discussions I've found elsewhere have been so devoid of actual information that it's driving me crazy. Perhaps you guys could help me out here?

In my country, the shipping regulations make it basically impossible to have primers shipped to you. Even picking them up yourself, there is a hard limit on how many they can sell you at a given time. I am all out of large pistol primers, but I have a box of magnum primers that I bought by mistake some time ago. Because of the current situation I'd like to use these instead of making a road trip for the express purpose of a single box of primers. But can I?

The gun I am loading for is a Smith & Wesson Mountain Gun in .45 Colt. I have previously worked up a load that launches plated 250gr bullets at 900fps using Magtech large pistol primers, and VV N-340 powder. I'd like to more or less duplicate this load, but using the aforementioned magnum primers.

Some people on the Greater Internets claim magnum primers are interchangeable with regular ones, others that one should drop the powder charge by one grain (strangely enough it matters not how much and what kind of powder the previous load was, the answer is always "lower one grain"...), and yet others claim that any deviation from published load data (no matter how reliable the publisher, or whether the publisher themselves have later deviated from the previous data...) is unpossible. I find myself somewhat sceptical of all these opinions, especially since nobody ever says why they think they are right.

[mtnbkr]

It varies by primer, but by and large there's not a huge difference. The reason for dropping the charge 1 grain is to compensate for any sort of pressure differences that my result, but you are free to work the load back up to the previous levels after dropping it. Sometimes using a mag primer *might* increase your groups, but sometimes might improve them. Some powders work better with standard primers (anecdotally, Alliant 2400 in mag loads).

I've seen a couple tests that show (via high speed camera) that some mag primers are a little hotter (longer, thicker...er flame). However, when I've used mag instead of standard, I've noticed no difference in firing or performance on paper.

FWIW, Winchester Large Pistol Primers are listed for "Standard and Magnum Loads" and they don't offer mag primers in that size.

Use a tighter crimp, I have heard reports that using a mag primer *might* cause the bullet to start moving before the powder is fully lit, but I don't know how scientific that statement is.

Chris

[That Guy]

Oh, right, it might help if I actually mentioned the specific primers too?

Old primers were, like I said, Magtech large pistols. New ones are CCI 350's.

[Lester Polfus]

I mistakenly purchased a bunch of magnum large pistol primers back when I was reloading 10mm. I just worked my load up from scratch (200 grain bullet over Longshot) with no issues. I wound up at the same exact max powder charge. I do think I had a higher standard deviation, but it didn't matter for accuracy.

[okie john]

I just worked my load up from scratch (200 grain bullet over Longshot) with no issues. I wound up at the same exact max powder charge.

I’d do this. You’re near the top end for VV-340 with a 250. Some powders get spiky and weird when pressures are high. Best to play it safe.


Okie John

[nwhpfan]

Wow, 250g at 950 fps

So I've loaded a couple thousand CCI 350 in place of CCI 300. I noticed zero difference on the chrono, performance, brass markings, etc.

I had a guy that gave me a box and a half, or maybe 2 or more boxes, I don't remember. I recall wondering the same thing as you; was it OK. I searched and found everything from no difference to drop a tenth to you shoot your eye out. I was shooting 3.8 Clays and 230g coated RN at that time.

I hope this helps.

[45dotACP]

I've used magnum primers in some standard calibers as well. I noticed no difference in pressure signs, but have no access to a chronograph.

Sent from my moto g(6) using Tapatalk

[fatdog]

I have loaded both Federal magnum and standard large pistol primers in .45ACP and .45LC and I cannot detect any difference with smokeless powders, Bullseye, Titegroup, N350, N320, Trailboss. I have seen measurable differences between different lots of powder however.

With black powder in .45LC I get a bit more consistency with the magnum primers, especially my 3F loads.

[Mirolynmonbro]

I loaded small pistol magnum primers and the FPS increased by 10-15. But, never loaded large magnum before

[mikld]

As mentioned above, and for safety sake, just do another load work up. Early on in my reloading I experimented with using "different" primers than what was "common" (1970-1980). I used many magnum primers in standard primer applications, but I rarely got close to max loads. In a situation where components are hard to find and one doesn't want to "waste" any, just drop your present powder charge and test (one to two grains depending on hop close to max it is)...