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Saturday, 13 August 2016

PRIMERS .. Small Rifle & 'Small Pistol Magnum' - What's the Diff?

I know that large primers are bigger (.210") than the small (.175") ones eh.. but -

I am anticipating my 327 Ruger's landing down here by getting some hand loaded ammunition ready and the question has arisen as to which are the right small primers to use for this rounds HOT top-end loads.

For 'ordinary' or lesser power ranges - normal small pistol primers should suffice - but it seems that the factory Federal 327 cartridges are loaded using small rifle primers - and I have seen various suggestions that these small rifle primers are the rule - but others say that small pistol magnum primers are the go.
Small Pistol primers have cup thickness of 0.017".

 Large Pistol Primers measure 0.020" thick

Small Rifle Primers vary in cup thickness from 0.019" up to 0.025"

Large Rifle Primers generally measure 0.027" thick.

Note: Considering the different thicknesses and hardness of the brass used to make primers - trying to 'read' pressures by looking at the flatness after firing must be a very approximate art.

The issue I'm addressing here is that the 327 FM is a *HOT* cartridge with an internal pressure ceiling of 45,000 psi. - and there might be a problem at these high pressures with the thinner standard pistol primers suffering 'flow-back' and even pierced primers that may leak hot gasses to the rear.

However - on the forums - I am reading that - for some makers anyway - their Magnum Small Pistol primers are exactly the same spec. item as their 'Small Rifle Primers' - except for the packaging.. Not confirmed.

Rifle primers use tougher/thicker cups than pistol primers to withstand the higher pressures - and the firing pin blow of rifles is usually harder than the firing pin blow of pistols. Rifle primers are said to contain more priming compound than pistol primers.

Problem is that the hotter Magnum (and Rifle?) primers will produce higher velocities and internal pressures than the standard Pistol item so.. Warning: - Do not develop your load using standard primers then change to magnumsKaboom? - something to do with "Brisance".

- So that may resolve this issue at least for the small primers.

I read that the 327 cases are both longer than the other .32"s and have beefed-up thicker inner walls at the base and may also have different heat treatment in their manufacture to handle the higher pressures.

The 327 Federal Magnum is a powerful .32 - up there with the 32-20 Winchester, the .30 Carbine and the 357 Magnum. - writer 'Chuckhawks' says they should be known as .303 calibre (same bullet diameter) - and Jeff Quinn at Gunblast has a good opinion of these too..

- An interesting review and comparative testing of the Ruger SP101 in 327 Federal Magnum here:

So I now need to buy some small rifle primers ..

Marty K.