View Full Version : Suppressor back pressure and hand loads

November 25, 2012, 01:25 PM
Anyone load their own .308 subsonics for suppressed use? I fired 3 rounds (10.0 Trail Boss, new Lapua Brass, CCI 200, 180 Hornady sp flat base) from a clean 21.75" 5R barrel with no problems without the can (YHM Phantom) but #4 stuck in the barrel once I put the can on. I assume it was due to the back pressure.

Has anyone else experienced this?? I'm I missing something??
No chrono data to report, sorry.

Brian Pfleuger
November 25, 2012, 02:19 PM
QuickLoad thinks that load would only generate 870fps if standard default barrel friction is included and that's without considering any potential back-pressure from the can.

With default case capacity and OAL, it thinks that load is just 68% case fill, which would be below IMRs starting load calculations.

Real guns almost always have more case capacity than SAAMI standard so it's almost certainly even less than 68% and even lower velocity.

It's hard to say where the line would be and you'll only be guessing without a chrony, but 1,200fps should be somewhere between 11.5 and 14.5gr

10.0gr is just too low.

Deja vu
November 25, 2012, 02:49 PM
if I had to get Id say 12 grains is a better starting point. So long as you are not compressing the powder you should be fine with trailboss.

November 25, 2012, 06:19 PM
Brian: I was thinking of bumping up to 11.5 but I'll also take Deja's advice & start high and work down. I have a chrony but was just seeing if they were stable first. I'll do both next go around.

Brian Pfleuger
November 25, 2012, 06:33 PM
That's probably what I'd do.

Start at 100% fill and work backwards 0.5gr at a time until subsonic then back up 0.1gr to find max subsonic load.

There's a fair chance you'll find that 100% max load is still subsonic.