Depends on the powder. The AR Match primer is great. It boosted on of our H322 or XBR loads 40 fps if I remember right. With TAC It behaved much milder.
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Good article on .223 loads involving the RMR 69
https://loaddata.com/Article/LoadDev...-Handloads/733
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I'm seeing a strange issue with the 69RMR.
Twice this has happened where I shoot a couple of sub MOA 5 shot groups with 77 SMKs. I will then switch to the 69 RMR and the first five have a ton of vertical, between 2-4", then the next five settle down to around 1 MOA. Same case, powder, and primer.
The jacket looks like a different color and I'm wondering if the metal is different,
creating the difference.
I'm not sure I follow what you're trying to say. You shoot a couple groups with 77 grain SMKs, and they're sub MOA. You then shoot a group with 69 grain RMRs and there's 2-4" of vertical deviation, then you shoot a second 5 shot group with 69 grain RMRs that's MOA?
I've read multiple times that some barrels take a few shots to deliver best accuracy after changing what bullets are used. As you mentioned, different manufacturers use different alloys of copper, and it's clear to me that RMR's allow isn't exactly the same as any other bullet I've ever used.
The other possibility I was notionalizing was that the barrel gets happier as it heats up a little.