Question for GunPlumber

[Venom6]

We've got a DSA OSW with the 11" barrel. Runs fine as issued. However, when we put the STW suppressor on it, it literally almost tears the heads off the cases even with the gas port fully exposed to maximum exhaust. Clearly the back pressure from the can is causing it, but what's the cure? Ideally we'd like it to be able to work with or without the can, and are prepared to adjust the gas system accordingly, but at this point I'm not comfortable taking it into a fight with the can on (one of these days it IS gonna tear a case head off). Should we have the gas port drilled out oversize? Is so, how much? Many thanks for any help you can provide.

NOTE to all: this is NOT a gunplumber gun, it's a factory OSW; we're asking gunplumber because we have a lot of respect for his expertise. The gun is registered to the department where I head the SWAT team.

[vmtz]

adjust the gas.

Fr. Vince

[lew]

Originally posted by vmtz
adjust the gas.

Fr. Vince

Did you read his post at all? He said he adjusted the gas for maximum venting, i.e. wide open.

[ggiilliiee]

GP ...???..got body armour and beneficiarys ???.hehe ..drop the piston size ...di a meter ......thought you guys was supposed ta know this stuff ...hehe ..:)

[vmtz]

Ok, ok, I bet to make the OSW, with matching sunglass, run they had to open the gas port to larger than standard size, which should be at most .120. With the can added the the pressure increases. Suggest you either run it with or without the can.

Fr. Vince

P.S. opening the port more will only make it worse, assuming you know how to adjust the gas.

[Bolt2Bounce]

I find it strange the question was directed at Gunplumber and he failed to answer?? He has answered many other posts..on this board... I'd say if your running a SS and the head of the case is almost coming off; you'd need to slow down the bolt unlocking so chamber pressure can drop before the weapon begins to unlock... I saw this problem before with the early AR10's tight chamber, short throats, large, heavy, thick, soft, Cavim Brass problematic... but one hole groups were normal..... so are you shooting Federal 168gr BTHP match ammo in 308 or are you running LC 762mm ball ammo. Ammo may make some difference... Is the gun a para or does it have a full butt stock... try a stronger main spring. Chamber may need to be polished...the vent hole may need to be opened up...is the head of the case bulged or is the cartridge rim torn backwards check out what a G3/ HK-91 does to the brass sometime... other option is to ASK DSA What's their opinion on their gun ... B2B

[phillip]

"I find it strange the question was directed at Gunplumber and he failed to answer?? "



DONT TAZE HIM BRO!

[Venom6]

Bolt2bounce: thanks for your well-reasoned reply. I think vmtz is right, DSA has to open the port to get the short gas system to work. Therefore what we probably need is a smaller port, but that's outside our range of options.

Federal 168 match brass is notoriously soft. We run it in our sniper rifles, then reload it for practice; get about three low-pressure reloads before the primer pockets are loose. However, even military ammo (Lake City) gets badly deformed coming out of the OSW. You can see where the extractor nearly pulls through the rim where the extractor contacts it. Again, this is with the gas port wide open to maximum exhaust (and with the can on). Gun runs fine without the can, but if you've ever fired a short-barreled .308 (or even a .223 for that matter) inside a house it's an experience you'll never forget.

[gunplumber]

Originally posted by Bolt2Bounce
I find it strange the question was directed at Gunplumber and he failed to answer??

I find it strange that you think I read every day every post on the Fal Files. Most intelligent people, when wishing to contact me, will do just that - contact me. Not post on some obscure sub-forum on the internet and expect I will instantly flaggelate before you.

As it is, you're already on the right track. The backpressure is too much. Perhaps a second gas piston adjusted to bleed off more gas will help. I believe POF made a reversible piston - one side for suppressors and the other for without.

[dscottch]

Venom6, if I may inquire, what possible need does a SWAT team have a STW suppressor for? Does that need justify the cost of one? I just can't seem to solve this riddle in my own head. Thanks in advance.

[Venom6]

Mark: many thanks for the response. Makes sense. We'll look for a POF piston.

dscottch: we use suppressors when possible primarily to reduce or eliminate hearing loss in our operators. Most centerfire bottleneck rounds generate north of 165 decibels; having the sound waves bounce back off the walls really aggravates things. You can suffer permanent and irreversible hearing loss with even one round going off indoors if your ears aren't protected. We tried sonic ear muffs, but the guys don't like them because even if they're stereo they still don't offer as much sound direction as the uncovered ear; also, they won't fit under a lot of ballistic helmets. We don't like ear plugs because there's lots of stuff going on during a warrant service that you need to hear. We'd like to go to the in-ear amplified plugs, but they cost as much as a suppressor and have to be refitted once a year, according to the folks we've talked to; they are also not as directional as the ear by itself. The suppressors have additional benefits; for example, "command and control" (it's a lot easier to hear your radio and/or the team leader yelling) if the guns are suppressed. This stuff is not just theory. We did an entry a year and a half ago. Two of our guys fired four rounds of unsuppressed .223 at a rifle-armed suspect in a utility room. He died but our two guys now have measurable permanent hearing loss.

[gunplumber]

Originally posted by gunplumber
I believe POF made a reversible piston - one side for suppressors and the other for without.

For their .223 Piston driven AR-15

[Para Driver]

okay, I didn't stay at a Holiday Inn last night...

sounds like the increased backpressure on the supressor drives the BC too hard? run the rifle with two different pistons? maybe cut a very thin grove in one piston along it's axis, that will bleed some of the gas off the face? repeat until the gun behaves 'normal', same as turning the piston down slightly in diameter, allows more gas to blow by??

[gunplumber]

Originally posted by Para Driver
okay, I didn't stay at a Holiday Inn last night...

sounds like the increased backpressure on the supressor drives the BC too hard? run the rifle with two different pistons? maybe cut a very thin grove in one piston along it's axis, that will bleed some of the gas off the face? repeat until the gun behaves 'normal', same as turning the piston down slightly in diameter, allows more gas to blow by??

Thats what I was thinking - but will keep the piston centered, as turning the diameter down won't - that would just let it flop. Also, cut a groove too deep and it can be fixed, not so with the OD.

[dscottch]

Thank you Venom6 for the reply. I wish you well on the search to protect your guys and their hearing. And thanks for trying to keep every one safe. I salute you.

[bykerhd]

Is the gas piston in that OSW anything more than just a cut-down version of the full size rifle's gas piston ?

If not, original military gas pistons can be had pretty inexpensively.
Cut a couple of those to the proper length and then try Dremeling a bleed groove. Too bad if you screw up, or it just plain doesn't help or work.
That's why you experiment on the inexpensive ex-military ones.
They're just as good, or better quality, than about any of the U.S. versions anyway. I wouldn't worry about damaging the chrome on them.

[Para Driver]

pistons is cheap.. buy 5 and experiment?
I'd try a thin cut off wheel and have a go at it with a dremel??
small cuts and work your way 'into the zone'..

[gunplumber]

Originally posted by bykerhd
Is the gas piston in that OSW anything more than just a cut-down version of the full size rifle's gas piston ?

If not, original military gas pistons can be had pretty inexpensively.
Cut a couple of those to the proper length and then try Dremeling a bleed groove. Too bad if you screw up, or it just plain doesn't help or work.
That's why you experiment on the inexpensive ex-military ones.
They're just as good, or better quality, than about any of the U.S. versions anyway. I wouldn't worry about damaging the chrome on them.

Doesn't work that way - they will bend. They are heat treated both ends, softer in the middle.

[Venom6]

Good stuff, guys! many thanks for everybody's help and ideas.

[Bolt2Bounce]

No offense intended GP, strange as in weird not strange as is bad,, some times typing can not convey intent very well... I just saw many other replies and didn't see your input..yet. I also respect your expertise, I've read you posts for years and your usually right on the mark....

Ven6 I've shot a 44 mag super black hawk from inside my house out the front door (door was open) and it hurts a lot with out ear plugs, living in the country has it's perks ... I've never (yet) had to shoot a rifle indoors, but I have shot 3 shots from a 300 H&H mag rifle with a ported barrel at a running deer, wow did that ever hurt probably did perm damage as well.. I couldn't hear right out of one ear for days, but the worst part was I missed that huge buck... B2B

[Matt(formerly@)EntrepriseArms]

Originally posted by gunplumber


Doesn't work that way - they will bend. They are heat treated both ends, softer in the middle.

Yes, we found that out the hard way when we tried to make our own SBRs and simply cut the pistons down.