308 Subsonic RedDot/Clays

[Galen_Lee]

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 thread 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)

 

[Dmr400]

Did you ever find a solution for this? My dad has been working on a 308 subsonic load with a 175 sub x bullet and trailboss for a subsonic coyote hunting rifle, and has been having fits with the first round of the day only being supersonic, with every other round being subsonic.

 

[redbullitt]

Consistency in sub 308 wih red dot etc 308 is difficult... simple as that. EVERYTHING matters there and any inconsistency in components, trigger pulling, and loading practice shows up. Case capacity vs charge is less than ideal, so you are working up hill for sure there.

For me, good cast bullets with proper low speed lube do this job better than jacketed and have pretty much always been more consistent overall.

Velocity matters too. Ive seen better consistency and noise level with trail boss at 900 to 1000 fps in multiple 30 cal rifles. 308, 300 whisper with very light bullets, 303brit, 762x54, 3040 krag etc.

If you only have jacketed available, lubing them can help consistency. Ive had significantly fewer outlier shots in 300blk and 308win with 220 smks doing this. Lee liquid alox has done well for me, but ymmv of course. You can also try running a lubed patch down the bore before shooting that first shot, see if it changes your issue. Ive ised a little bore butter or similar bullet lubes make a difference here. keep in mind this can increase pressure if youre running hot already.