Suppressor back pressure and hand loads

brmfan · November 25, 2012, 02:25 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, 03:19 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, 03:49 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.

brmfan · November 25, 2012, 07:19 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, 07:33 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.

November 25, 2012, 02:25 PM	#1
brmfan Senior Member Join Date: October 21, 2008 Posts: 521	Suppressor back pressure and hand loads 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.

November 25, 2012, 03:19 PM	#2
Brian Pfleuger Staff Join Date: June 25, 2008 Location: Central, Southern NY, USA Posts: 14,662	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. __________________ Still happily answering to the call-sign Peetza. --- You do not HAVE a soul. You ARE a soul. You HAVE a body. ----- He is no fool who gives what he can not keep to gain what he can not lose. -Jim Eliott, paraphrasing Philip Henry.

November 25, 2012, 03:49 PM	#3
Deja vu Senior Member Join Date: March 14, 2010 Location: Border of Idaho & Montana Posts: 1,755	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. __________________ Shot placement is everything! I would rather take a round of 50BMG to the foot than a 22short to the base of the skull. all 21 of my guns are 45/70 govt 357 mag, 22 or 12 ga... I believe in keeping it simple

November 25, 2012, 07:33 PM	#5
Brian Pfleuger Staff Join Date: June 25, 2008 Location: Central, Southern NY, USA Posts: 14,662	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. __________________ Still happily answering to the call-sign Peetza. --- You do not HAVE a soul. You ARE a soul. You HAVE a body. ----- He is no fool who gives what he can not keep to gain what he can not lose. -Jim Eliott, paraphrasing Philip Henry.

November 25, 2012, 07:19 PM	#4
brmfan Senior Member Join Date: October 21, 2008 Posts: 521	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.