6.5 Creedmoor - Small vs. Large Primers

Rathmatik · Jul 1, 2020

Howdy,

So I currently have all brass with large primer pockets and use CCI 200 (Large Rifle Primer) primers. I'm interested in trying out some different brass (Starline, Lapua, etc.), potentially with small primer pockets.

For small primer pocketed brass, is there a consensus on whether Small Rifle Primer vs. Small Rifle Primer Magnum primers should be used? I haven't found anything that really explains why to use one or the other, but have seen a few videos on YT where magnum primers are used. It'd be great if there was some actual documentation on this.

robertc1024 · Jul 1, 2020

I've read a million conflicting articles on primers. For what it's worth (which isn't much), my conclusions were that magnum primers have a little more oomph and have slightly thicker metal in them. I generally just go with whatever my reloading manuals say.

One thing to be aware of though, is the flash hole is smaller on small primer brass. You need to make sure your de-capping pin is the right size, otherwise, you'll wind up with bigger flash holes on your small primer brass. That means more pressure on the primer!

deemus · Jul 1, 2020

robertc1024 said:
I generally just go with whatever my reloading manuals say.

!

This is what i do too. Not sure what a person would hope to gain by using small primers on this round. It would seem that its possible not all the powder would burn. I know I have had that issue on a couple rounds in the past.

Vaquero · Jul 1, 2020

Regular small rifle primers work fine.
The only real advantage over large primers is the brass thickness at the base. Supposed to keep the primer pocket from stretching.
I'm using small primers in 6cm.
Alpha brass, it has the larger flash hole already. I've not seen any evidence of unburnt powder or pressure variations.

ETA
I have not used any magnum primers.

Younggun · Jul 1, 2020

Yep, it’s more about case life for me. Probably not an issue if you run mild loads or don’t anneal for case life.

If you use Hornady brass it won’t matter anyways. The primer pockets will stretch if the weather changes.

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Rathmatik · Jul 1, 2020

Good stuff to know, thanks all. Yeah, I had read/heard that the large primer pockets can get too loose after multiple reloads, so we'll see if that's the case. I'll probably just stick with large for now, as I know they work and haven't had any issues. My rounds burn pretty clean overall.

dee · Jul 2, 2020

Smaller handles pressure better due to thickness of the case head. Be sure your rifle is capable of using sr brass or you'll end up needing to get your fp bushed or run really soft loads.

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Deavis · Jul 3, 2020

robertc1024 said:
You need to make sure your de-capping pin is the right size, otherwise, you'll wind up with bigger flash holes on your small primer brass. That means more pressure on the primer!

Larger flashole equates to lower pressure, not more. It is a volume calculation, adding more volume cannot make the pressure go up in the system at any point where it is not constrained in a non-normal way.

Most decapping pins are under 72 thou and for normal brass, small or large primers, the flash hole is larger than thatn usually around 80 thou. Exceptions exist, I've seen 60 thou holes on certain casings but that isnt the norm outside BR specific "silliness" for the sake of being BR or real load specific needs on an edge case.

Txhillbilly · Jul 3, 2020

I prefer to use small primer brass. I push the pressure limits with both my custom 6.5 CM's. I can't get the velocities out of large primer brass that I do with small primer brass.
All brass is different though,I get the best results with Lapua. Peterson brass is too thick,and will pressure up too fast. Nosler (Norma) brass is pretty good large primer brass. Hornady brass has always sucked,I'm lucky to get 3 firings out of it before I start popping primers out when fired.
Starline makes some good brass,I neck down Starline small primer 6mm CM for my custom 22 CM.
I've been shooting the 6.5 CM since 2009,so I've tried just about every brand & type of brass out there. If you don't push the limits,any brand will work just fine. If you seek shooting full house loads for 1000+ yards,just buy some Lapua brass and be done with it.

Deavis · Jul 3, 2020

Txhillbilly said:
buy some Lapua brass and be done with it.

Isn't that the answer to all brass problems?

6.5 Creedmoor - Small vs. Large Primers

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