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Small rifle magnum primers

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Duck dogn

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Please don't bash me but I have a question. I've been reloading for several years, I'd say I know alittle about it but I always follow the books precisely because I load for my daughters rifle and make sure all is safe. My 5.56/223 call for winchester small rifle primers and my grendel calls for small rifle primers. How ever Alexander calls for magnum primers in the 6.5 . I found small rifle magnum primers in stock locally and bought some, I've been reading online about using magnum primers causes the bullet to move outward prior to full powder ignition. I'm loading ten thousandths from the lands and mid range on what the book calls for in powder, in both rifles because that's what groups well. I use varget powder do you all have experience with the magnum primers in smaller calibers and varget? Thanks in advance.
 
In the case of the .223/5.56 I would consider crimping the bullet in the case, not only for keeping the bullet from sliding back into the case during firing, but would also help keep the bullet stationary during ignition as well. Just my thinking.
 
I bought some magnum primers but have not run any yet. I plan to do some testing when it cools down. From what I read, it is suggested to back off the load just a little and work up. Also read that cci41 military primers are basically magnum primers with a harder cup for making slam fires unlikely in ar's I had not seen anything to say there would be a premature bullet jump from a magnum primer ignition.

I have been running Remington small rifle 6 1/2 for small pistol 9mm with no issues.
 
As MUP said, crimp will help the bullet from moving. I haven't noticed any difference between the CCI41 military primers (which are technically SRMP) and small rifle primers. My suggestion is to load a few up a little lighter than normal, maybe a half grain lighter and test it. Check the velocity compared to SRP and look for any pressure signs and then work the load back up if needed.
 
There is a reason that the Grendel calls for SRMPs with AA brass.

Bill Alexander designed the cartridge to use magnum primers (since they have a harder cup and help reduce the risk of slam fires, and to give a better ignition rate to the increased case capacity of the round originally designed for AR15s), so he insisted that AA headstamp brass use a smaller flash hole. AA brass has a smaller flash hole than other brands, and that's the reason that I don't use it. I truly don't like the logic applied to it, but I'm not an engineer either.

Starline and Hornady brass uses a larger (standard sized) flash hole and you could get by with standard SRPs for it (I do for some of my loads), but you still may get better performance out of the magnums, and the CCI41s and magnums will have less chance of a slam fire in an AR15 (I've never had one, and I don't shoot my rifle hot or dirty, so I'm not too terribly worried about it… but maybe I should be).

As with anything, if you change components then you should work back up. The Grendel can be particularly tricky with pressure on top end loads, so be very mindful of pressure signs.
 
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