Effects of Primer Change in 6.5 CM

[OzzyO20]

After reading some of the debate regarding SRP vs LRP, I learned a few things. While I believe Lapua did their homework, and don’t fully agree with Hornady’s position on the dangers of using SRP in a 6.5 CM. There have just been too many people shooting it for too long with little documentation of issues.

What I did find most interesting was the CEO of Alpha brass advising against using match primers in SRP 6.5 CM brass. That lead me to the PRB Blog where I found his suggestion of CCI 450 small rifle magnum primers were far and away the choice among a lot of top shooters. I was under the impression Federal GMM 205M’s were the best option, really just from ignorance.

I picked up a brick of 1,000 450’s, but wanted to ask a few questions. Will this dramatically change how my handloads shoot? Will I have to start over with a new ladder test? Can I just try my current load with the new primers? I mainly don’t want to create an unsafe situation by changing primers. I know it’s going to have some kind of impact, which sucks becaus I have a excellent load worked up. I’m not at max pressure, but I’m getting ever so slightly flattened primers where I am currently.

Thanks in advance.

 

[XLR308]

The safe and best answer would be to back off .5 to .8 grains and work back up.
If all you are changing is the primer you may actually find a better spot in your charge weight with a minimal work up.
My guess though is you will see very little or no change in the end at your current charge weight, if you are switching brass then definitely work up a new load.

 

[XLR308]

When I switched from Nosler LRP to Lapua SRP in 308 win I had read the reports of possible issues with cold weather ignition problems but I have run CCI 450's from the start.
I tried to see if I would experience any of the aforementioned issues but haven't been able to duplicate, even after picking days to go shoot that were inn the low teens and leaving the ammo in the vehicle overnight. That is with using both AR-COMP and Varget max book charges with 178amax, other powders may be more sensitive to this situation but I try and only use the most temp stable powders i can find.
Since then I have pretty much standardized the use of CCI 450 in everything I can use it in to simplify what components I have on hand, 556/223, 68spc, 308, 65 creedmoor.

 

[OzzyO20]

The safe and best answer would be to back off .5 to .8 grains and work back up.
If all you are changing is the primer you may actually find a better spot in your charge weight with a minimal work up.
My guess though is you will see very little or no change in the end at your current charge weight, if you are switching brass then definitely work up a new load.

Thanks man, that’s what I’ll do then. Brass is the same, and annealed after every shot. I’m hoping you’re right about minimal change. It’s shooting just over 1/4 MOA over multiple 5 shot groups, right at the edge of pressure, and single digit SD. I want to stay there haha.

 

[XLR308]

Let us know what you come up with, a guess would be you will be in the ballpark of 10-15 fps difference going from a standard to magnum srp with the same charge in a case the size of the 65 creedmoor.

My loads running 40.7 gr of AR-COMP with the 178 AMAX are pretty spot on to listed book velocities even with using a different case and primer.

 

[OzzyO20]

Let us know what you come up with, a guess would be you will be in the ballpark of 10-15 fps difference going from a standard to magnum srp with the same charge in a case the size of the 65 creedmoor.

My loads running 40.7 gr of AR-COMP with the 178 AMAX are pretty spot on to listed book velocities even with using a different case and primer.

Pretty good guess. I found at the same 42.4 grains of H4350 my speed picked up 16’ish FPS and my SD shrunk in half.

 

[OzzyO20]

*26’ish not 16’ish.

 

[XLR308]

Good to see you had a favorable outcome but not really very surprised, cutting your SD while picking up a little velocity while saving yourself some coin by switching to the lowly non match SRP primer Win/win.

That was my experience as well and the reason I've tried to standardize the use of the CCI 450 and if you have trouble in the future locating them don't hesitate to use the milspec version CCI #41.