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Posted: 1/29/2016 10:32:15 PM EDT
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Today I loaded 20 rounds of 300 BLK, it was my first time loading this cartridge. I ended up seating the bullets to an overall length of 2.10 to get the .250 mark on the bullet to sit on the ridge in a G.I. mag. The Nosler loading data showed a length of 2.260. Their minimum load started at 11.0 grains, so I started at 10.9. My upper is a 10.5" barrel with a 1/8 twist rate, with adjustable gas block. The rounds all functioned well, and the bolt locked back. The primers were slightly flattened, but no other signs of overpressure, but I did notice that at least 6 of the rounds were not completely stable at 25 yds. I used a lee bullet seating die, and lee factory crimp die, the brass was done already. Is this a common issue with short barrels, or is my twist rate not sufficient. or is it something I am doing. I have fired Sig, Remington, and Gemtech 220 grain ammo and never noticed any stability issues at that distance. Thanks for any input.
Recipe I used : Converted LC brass CCI SRP 10.9 GR. AA1680 Nosler Competition 220 GR HPBT Length 2.10 +/- .02 due to differences in the bullet tips |
| Never mind Just saw it. I am running 1/7 and have not had that happen yet. I have not seen that barrel length is a factor. Your load is reasonable. nothing out of the ordinary. What barrel maker? Did run across a post in the 300 BO only thread and seems like he had same problem with 1/8 twist. Said 1/7 fixed it. |
| Load them at 2.260 like nosler says. Experiment by reducing lenght in increments to see which lenght your barrel likes. Bullet seating depth makes a huge difference in accuracy and pressure. I thought 300 blk would act like a rifle bottleneck round in which shortening decreases pressure, but it sometimes acts like a pistol round where pressure builds up when you shorten a round. I think that's why you had pressure signs with such a low charge. |
| With the tiny case capacity of the 300BLK, a big COAL difference (going from 2.1 to 2.26) is going to take a very different powder charge. I'm surprised that at 10.9gr at COAL 2.1 you're not supersonic. Seems to me that at your short COAL that's too much powder to be subsonic. |
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