teddy_d wrote:Fired 5 rounds of the barnes 200 grain hollow point, 40 grains of lil gun, OAL 2.210, taper crimp 0.476", 2300 fps, ssub 2" group at 75 yards using a soft case as a rest on a plastic table, 3x32 nikon bdc compact. Inspected each round to note if crimp help after previous shot fired, no movement noted.
Time to load another 5 rounds with 41 grains of lil gun, might adjust the crimp to 0.475/4" if possible. It will be interesting to get this to a higer fps and test trajectory out at 250 yards...?
Hoping these will be the hunting rounds for deer this year.
If I'm not too late, I'd advise sticking with the 40gr and taper crimp down into the groove a little further, to yield a diameter measured as close to the mouth as possible, of .474 inch. It'll still headspace with diameter to spare. If your chronographed velocity goes up, without the group size suffering, you might be able to stop there. Measure each round's casehead diameter right at the web before and immediately after each shot as soon as it cools, to watch for pressure signs. You can incur some excessive pressure without the primers showing much flattening at all. If the post shot casehead has increased .001, your knocking on the door of excessive pressure. At a growth of .0015, you're in the door. Beyond that, you're heading for a firearm failure, not to mention some really short case life. Keep your barrel from getting too hot and don't let the loaded rounds sit in the chamber too long, where they soak up heat and increase the volatility of the powder. At least try to keep all of them in there the same amount of time. Ball powers are sensitive to heat. Doing some pre and post shot casehead measurements, helps the time pass while the barrel has some time to cool. Its been ferociously hot lately. Keeping the action open and the mag out helps the barrel cool quicker if its hot where you are shooting.
Hoot