Velocities are as follows
CCI 350- 1307 fps
Fed 155-1206
Fed 150-1219
Kind of interesting that the Fed 155 was slower than the Fed 150. We assume that a mag primer will give more velocity but not always.
The CCI is certainly the king of velocity here.
First, this is a target load not a mastodon load. You aren't (or shouldn't be) looking for which is fastest. Fastest is meaningless here. Use the chrono to determine which has the most uniform burn. You didn't post the important chrono numbers, standard deviation and extreme spread but my guess would be the CCI was more consistent.
I still think the load is too hot at 21.5 gr H-110, try 1/2 grain less as the next test. Yes a slower powder could help as could a stronger alloy but even there the load is too hot. Your CCI primer load of 1307 fps is nearly the same velocity as the most accurate and winningest 44m 240 gr jacketed load in silhouette at 1320 fps even though your bullet is considerably heavier.
I used the 357m in silhouette far more than the 44m. for a long time I used 16.0 gr H-110 with a 188 gr bullet and the Fed 205. When I tested the CCi 550 velocity was up about 80 fps, S.D., E.S. AND 200 meter groups were all cut in half.
I did test 1680 in the 357m and it actually shot fairly well but in the 357 case I simply ran out of room before the velocity goal was met. About one more grain could have worked, at the time I planned on having a mold cut of the RCBS 180 silhouette bullet with the crimp groove move closer to the bullet base to allow less bullet in the case and more powder room. Just never did get around to that. Never tried 1680 in the 44m.
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