I was surprised by the 170 grain cases. Were the new Winchester Palma cases not yet available at the time you were doing the testing?
I had a similar issue with 2520. I tried using it in my M1A in '94 IIRC. I had a decent barrel that would shoot Brigadier 3032 under 168 grain SMK's into 0.7 moa at 100 yards, but the 2520 would never do better than 1.25 moa with those bullets. At the time I was using LC and sometimes Remington brass and Federal 210M primers. Then one day, on a whim, I took my flash hole deburring tool and went over all my Remington cases. I didn't really expect anything, but the tool was a new one I'd got that I could chuck in my drill press, so I just wanted to try using it. Next time out, though, the 2520 groups shrank to 0.75 moa. About where the stick powders shot without the special treatment. The 3032 loads stayed the same and didn't notice the deburring, so I may have been at that barrel's limits.
On reflection I expect that 2520 needed magnum primers. I improved the ignition with what I did, but Alan Jones says CCI altered their magnum primer formulation in 1989 specifically to optimize it for spherical propellant ignition requirements, so that might be something to try. If I ever have some time an money to waste, I may replicate the 2520 experiment. I've never bought any more of that powder after I used up the jug I purchased to try it out in '94, so this won't been a high priority with me.
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