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I'm aready using LRM primers. The problem biggest was accuracy. once I got to 12 gr (TB) I seemed to max out in vel with an average of 980ish. The range went anywhere from 860-1040. This created a pie plate group, generally vertical in nature. It filled up the cases with the 240s so I wouldn't think there would be an issue of powder placement at ignition.
I tried 15 gr of Greendot and pierced a primer. 10.5 gr in a 16" krieger got me 1050 behind a 220 RNSP, but the powder had to seated against the primer. This did create excellent accuracy, but I missed 3 deer last year because the rifle was generally pointed down (treestand) and the powder was against the bullet.
Also, I've been getting the first shot to dump on every string. Consequently, as I was shooting those loads Friday, I would wait 15-20 min between shots. Shooting 200 Speer Spitzers, 12.0 TB, WIN LRM primers, Rem Cases, 10" Encore, 1/8; I averaged 960fps with a range of 946-974. By allowing the bore to return to ambient temp (33deg) I had a better representation of actual velocities that I would find in the field and lowered the range of velocities.
I'd like to try another powder. Based on the posts I've found AA#9 or IMR SC4957 (I think that's the right powder, I'll have to check my notes). I looked up the IMR powder and it was specifically formulated for reduced velocity loads. I also came across some Accurate 2215 (?) at Gander MT which said it was also formulated for low volume loads and a hig tolerance to powder position at ignition.
Any idea what length barrel it would take to get TB to push a 240 at 1050? I don't have another 1/8 twist barrel to test with, just the 10". With a little extrapolation, I was figuring each inch would gain 7fps, but I'm not certain.
If I don't get it worked out in the next month, I'll order a 16" whisper upper. I would assume someone has found an accurate 240 load for that.
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