I’ve been working on reloading .308 subsonic rounds with Red Dot and Clays powder. I’m looking to get around 975fps-1000fps with 170gr-190gr projectiles. When shooting a string of 5 rounds (same powder charge, primer, seating depth, etc.) I am seeing the velocity drop on every round using a MagnetoSpeed V3. I read on another forum that when using TrailBoss the same thing occurs due to the lack of trace lube in the powder. I’ve looked all over and can’t find anything about that happening with a shotgun powder. Any help on to why this is happening? Also sometimes my first shot is 100fps or so lower than the next 4 shots and sometimes all 5 shots hold steady and I can get an SD below 10 Specs: .308 22” 1-10 twist Alpha brass Fed GM215M primers Hornady MATCH 168gr BTHP Sierra ProHunter 170gr FN (flat base) Sierra ProHunter 180gr RN (flat base) Hornady SUB-X 190gr (boat tail)
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Thanks. Good to know.
Do you find a filler necessary with Trail Boss?
I have loaded a lot of subs for my .308s with Trail Boss and had great success with velocity. I am with the others that the issue is powder position in the case. Either use a filler or change powder.
Google “The Load by C. E. Harris.” Lot of information. I agree that low powder charges might be position sensitive.
Like gkeiths says... I'm also guessing it's position sensitivity, which would explain the difference between the first round and the next rounds (which are subject to recoil, so the powder is shaken up). Those cases really aren't filled very full. Can you try a test with single-loading the cartridges and intentionally tipping them back before loading them in the rifle? If that evens things out, then case filler might help like gkeiths said.
It’s possible with such a light load that the powder is position sensitive and a filler may be needed to take up space in the case.
This a good question. Back about 10 years ago when I was Fudd’ing and said the 300 blk was a fad, I had my first can (30 cal) and a threaded 308 bolt gun. I used the tight group load from hodgons website, believe it was a 168. Even opened up flash holes. Couldn’t ever find trail boss at the time. Had the same issues and walked away from the project as stability issues with the projos cost me a chrono. Interested to see what someone else says about this. Sorry I couldn’t help.