Doing a run of 44-40 for a SASS shoot this weekend...ran out of CCI 300 Standard Large Pistol Primer and grabbed a carton of CCI 350 Magnum Primers to finish with.....my real question is this...

Is there a dimensional difference between the two? The Magnum primers are NOT fitting the primer pockets very well at all...like they are very slightly larger in diameter....

My caliper shows them the same however....

Just thought some of you would have a good answer.

Randy

PS. Better caliper shows 1 thousandths of an inch larger in magnum....standard is .209 and .210 for the magnum

Both are LP primers and should have identical dimensions and tolerances.

I have found that in some brands of primers, that the thickness of magnum primers is about .002 or .003 inch more. It made absolutely no difference in the seating depth of my ammo. But in the tube holding the primers, I could only get 106 magnum in the same space 109 or 110 standard primers would fit.

The sizes of primers and primer pockets have been standardized since well before WW I. If you found a sizable amount of difference with different "BETTER" micrometer, you should either change how you hold your micrometer, or return it for you money back. I have a friend with a digital micrometer to 1/10,000 (.0001) inch. Measuring one sample of shim material ten times, I got 8 different readings, most people got 10! Technique is everything!

Ivan

Both are identical in size but the cup on the magnum primer is slightly thicker. My guess is they don't flex as easily so they seem to be tighter when seating in the case. I have never felt a difference but I prime handgun brass on press so I might not feel a slight difference noticeable when hand priming.

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SWCA #3437

Thanks guys! I finished the run (500) with some Winchester Large Pistol primers...went without incident.

Randy

There can be very small diff in primer size. When I have rifle brass with tight primer pockets, I use RP primers, they fit with much less pressure. Conversely, if I have primer pockets that are slightly oversize, then the RP don't work as well so they get something else, often CCI. You really can't measure the diff properly with calipers.

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The OP was not asking about different brands of primers. Both were made by CCI.

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SWCA #3437

Over the years with rifle and revolvers I have learned that there
can be a different POA or accuracy with a load with the use of std and mag primers.

Even changes with different std primers with the same bullet and powder amount.

I just treat the mag primer as a little hotter and made for Ball type powders that might be harder to ignite...... and have yet to have any problem of the "Mag" sitting too high in a case in
my rifle or pistol loads.

Have fun.

This I think is the correct answer.

As a side note - the CCI-350 is the hottest American made primer on the market. It can raise your peak chamber pressure by a bunch and then some, so one could find it more difficult in finding a real accurate load with it - the meaning "real accurate" varies according to the shooter.

This primer is highly recommended using H110/WW296 in very cold weather, if you absolutely need that bullet to exit your barrel at expected velocity.

A little off topic, but I have used SR primers exclusively in 9mm, .38 Special, .38 Super, and .357 for many years (over 40). Way back when, I did some extensive testing of both with .38 Special wadcutter Bullseye loads. I could see no meaningful difference in POI, MV, or grouping performance between SR and SP primers. I have never used a single LP Magnum primer that I can remember, so I can't say anything about that. .