Greetings, sorry for the delay in reporting back on IMR 8208 XBR powder in the 30X47 HBR chambering. I had a bit of an accident at work and crushed my left hand, almost completely severed my left index finger. A few surgeries, a ton of PT and a little better than a year later you can hardly tell… well pretty much anyway. I built a new HBR rig as “therapy” so this post relates to that rig and not the 30X47 Lapua rig I inquired about.
The rig - Reworked Remington 700 action; McMillan Edge stock; Shilen SM 15 Twist barrel with my take on the 30X47 HBR chamber, .330 neck and a finished length of 23 inches. I put on a 36X scope in place of a 6X for testing
The cartridge – Parent brass, Winchester .308; .328 loaded neck dimension; resized after turning with a .325 bushing; empty case weight 150 grains plus or minus .5 grains; bullet 125 TNT (don’t want to waste the good stuff fire forming and checking for pressure signs) seated .015 jam.
The weather – 35 Deg. F. with four inches of snow on the range, the wind was calm and the light was very flat with a high overcast.
Results – Five shot groups shot at 100 yards. I did not chronograph. I broke in the barrel and sighted in with 40 grain loads and I fired two 40 grain loads as fouling shots after cleaning between strings four and five. These shots at 40 grains were not included in the data.
40 - grains just barely came up to the base of the neck, filled out the brass nicely on firing but the shoulder was not quite sharp. The carbon swirl was about half way down the neck. The group was nice and round just at a ¼ inch.
40.3 - grains was about the same, group was round just a little bigger,
40.6 - grains again about the same group had a little vertical and was a touch bigger.
40.9 - grains again, about the same as 40.6 grains but a little more vertical.
41.2 - grains starts to fill up the neck, shoulders starting to sharpen up, group was starting to get round but larger than 40 grains
41.5 - grains shoulder nice and sharp, neck clean and the group was a little rounder but still a touch bigger than 40 grains.
41.8 - grains shoulders look great, neck clean, group round and smaller than 40 grains.
42.1 - grains the case looked great, easy bolt lift, primer was slightly flat with round edges, group was round and well under ¼ inch. Things started to come alive at this charge weight but I was out of loaded ammo, the light was going away and the wind was coming up. I think that somewhere around 42 grains and 42.5 grains I find a good load. I don’t think that you can get much more than 43 grains of this stuff in the case even after it is fire formed, I’ll let you know. I’m sure that when I go back to the range with fire formed cases the 42.1 grain load will have a different pressure curve because the case is stretched out already. I think I’ll start at 41.8 and shoot two or three five shot groups for each load as I work my way up.
Individual results may vary,
Nic.