Can't Get 'em To Go Slow Enough!

[ridingfar]

Team Cast Boolits,

First - Thanks for all the great info I've gotten here! Most helpful folks!

Second - I'm working up some subsonic 308 loads and have been surprised at how slowly speed has dropped off with increasingly reduced charges. Using a Ruger GSR w/ 16.5" barrel, 193 grn/.310 to .311 hard cast lead molly coated bollits over Trail Boss and maginum rifle primers in R-P unmodified cases.

Started at 11.0 grn hitting just over 1200 fps and have been between 1100 to 1020 fps from 9.5 grn working down to 7.8 grn. I will go from 7.5 down to 7.0 grn of Trail Boss in the next flight but, wow, that's way less a charge than I expected to get into the 950 to 1000 fps range I'm looking for. It's also down to ~half full, or less, in a 308 case even with this "fluffy" powder. Each charge level I've shot so far show pretty good speed consistancy so that's a good sign, but they do not drop much fps with .2 to .3 grn reduction steps.

So now my question: Is this load range (low 7.X grn of Trail Boss) what others have found to get just under 1000 fps in a 308 with ~200 grn boolits?

Just wonderin'...

Thanks in advance for your consideration and assistance!
Courtney

[Harter66]

I don't have any expirence w/TB , but I've read it often that TB and air space is no good . Your describing a half case or less that's a lot of airspace.

Red Dot and Unique worked well for me going up w/Red Dot topping out in an 06' and x39 w/200 boolit about 1100fps .IIRC. Charges were tiny also , like 8.0 and 5.0 .

[Larry Gibson]

Switch to Unique....no wad or filler.

Larry Gibson

[Jim]

69578

[GaryN]

I would also try Bullseye. It would probably only need 4 grains to go that fast. It's kinda funny when you see 4 grains. I swear I could pick up that much powder between my thumb and forefinger.

[runfiverun]

bet your pressure ain't coming down either.

[cbrick]

Jim, come up a couple of clicks and one to the left. :mrgreen:

Rick

[Artful]

I discovered that trailboss is position sensitive when you get to low volume loads - IE tilting up or down the bore will impact speeds delivered. Are you getting these speeds with or without a suppressor?

[Jim]

Jim, come up a couple of clicks and one to the left. :mrgreen:

Rick

:bigsmyl2:

[ridingfar]

I discovered that trailboss is position sensitive when you get to low volume loads - IE tilting up or down the bore will impact speeds delivered. Are you getting these speeds with or without a suppressor?

Unsuppressed as I am working up (or, more correctly, down) to find a subsonic load I and use going forward and do not want to get an unstable boolit causing a baffle strike. I'll keep working down and may try some filler to keep the load back by the primer.

Thanks for the feedback.

[Driver man]

5.4 grains of unique will give you 1040fps. 5grains 975fps. Sako Finwolf 308 1983

[Artful]

with the shorter 16.5 in barrel, I'm thinking you will need to move to a faster powder - Have you tried clays or titegroup?

This might help you
http://www.quarterbore.net/forums/showthread.php?t=280