These tend to have a long, oversize throat. Here is some data posted by a member:
Results from 7/15/06 Testing
San Fracisquito Canyon Range
Temp Starting: 82F Ending: 109F
Wnds Lgt and Vrbl
Guns cleaned between strings.
Gun #2 Win BB94 .375 Win
Again, barrel cleaned between strings.
1) Load… 261 grn. RCBS FP GC .3785 LBT Blue, 30 grns. RL 7, Win cases, Win Lrg Rifle primer
Group tightly centered 9:00 from 10 ring. All shots in 2”
Very accurate but groups began to vertically string as barrel heated. Very lgt leading.
2) Load… Same bullet XMP5744 24.5 grains
Moderate Recoil, all shots under 2” 3 in X ring
3) Load… Same bullet, IMR 4198 24.5 grains
Very Heavy felt recoil, 4” group 2 flyers
4) Lyman PB 251 Grain, .379 24 grains 2400 LBT Blue
Excellent accuracy, 4 shot under 2” Mod recoil. Load came from Lyman #38 for 38-55
5) Lyman 251 PB, .3785 LBT Blue
18.0 grains XMP 5744
All shot 6:00 low in 9 ring, 2” group. One flyer 7:00 in 7 ring
This load had light recoil, kind of smoky, very easy to shoot. Mild leading. This cleaned with two patches.
The next three loads are all duplexed BP loads. I used a compression die to compress the powder .103” in the case. Over powder wads were cut from cardboard and were .016” thick
6) Lyman BP 251 gn. .379 White Lightning lube.
5.0 gns. RL7, 33 grns (by weight) GOEX 3F
1303,1293,1302,1336,1309 @ 50 yrds, this group went into 1.5”
7) Same Load @100 yrds
1298,1313,1302,1295,1297 all shots when into 2” but were low at 6:30 in the 9 ring
8) RCBS 261 GC .379 WL lube same powder charge as in #6 and #7
1257,1273,1252, error, 1244, 1264
This was the most accurate load at 100 yrds. All shots went into 1.5” at 6:00 on the 8 ring
So, from all of this two things stand out. First, I need to investigate 2400. This powder seems to really shoot well in my gun. I’d like to try it with the RCBS bullet and see what happens. There were no signs of high pressure but surely it must have been up there to get those velocities. This was a full 3 grains under the old Lyman specs for the old pre-Alliant 2400 powder.
Second, this gun loves BP. Those loads all shot well and did not lead excessively. The shot to shot variation was almost nil. Clean up was easy and they were not all that hard to make.
I suspect that some of the weird velocities registered were due to the guy with the Barrett 50 cal four benches down. Sometimes, his shock waves would register on my screens. Ditto the guy with the ported 44 mag to my left.
Any way, it was a good day for shooting. I hope some of these loads get a few more guys to experimenting with this caliber. I’d love to see some other recipes. I have some H4895 that looks promising too.