View Full Version : Oversized gas port, but how much is an issue?
I just received a new barrel for my carbine to replace the DD LW I had before. The barrel is a PSA CHF 14.7" - carbine gas. I measured the gas port in our machine shop @ work and was disappointed to find that it is .070. The Colt spec for a 14.5" carbine gas barrel is .063. So now that we know it's going to be over-gassed, the question is, how much. I'll be running it with a DD FA BCG and an H2 buffer. Should that make it ok? I'm a little more concerned that I would normally be because I have paperwork pending on an M4-2000 and if this gun is already going to be way over-gassed, the silencer will only make things worse.
Thoughts on "how" overgassed the gun will be? Likely to be an issue or not?
Thanks!
patrick sweeney
03-06-13, 12:00
Build it and find out. Short of that, it is at best guesswork predicting what will happen.
Build it and find out. Short of that, it is at best guesswork predicting what will happen.
Yeah, I know, but I guess my real question, is, "Is the 0.070 gas port large enough that the gun is going to be so overgassed that it's worth returning the barrel and waiting to find a Colt/BCM?" I have been looking/waiting for a couple weeks and jumped on the PSA when I found it. Most of what I've found talking about overgassed "commercial-grade" AR's from the likes of Bushmaster, RRA, ETC puts the gas port in the .083 range. I'm not that bad off. Just wondering how much of a difference .007 makes in reality.
Magic_Salad0892
03-06-13, 12:15
Yeah, I know, but I guess my real question, is, "Is the 0.070 gas port large enough that the gun is going to be so overgassed that it's worth returning the barrel and waiting to find a Colt/BCM?" I have been looking/waiting for a couple weeks and jumped on the PSA when I found it. Most of what I've found talking about overgassed "commercial-grade" AR's from the likes of Bushmaster, RRA, ETC puts the gas port in the .083 range. I'm not that bad off. Just wondering how much of a difference .007 makes in reality.
As long as you're not shooting suppressed, you can probably throw in a Sprinco Blue, and an H2 and be good.
But I'd still prefer an .063'' port.
My 14.5 runs good at .063 with no can. It's functional with the can but it's flinging the brass forward.
In all actuality, I ran that turd for years before I put an insertable port into the FSB and choked it down to .063.... and it worked ok with an H3 buffer.
With a silencer, there's no question it's going to have TOO MUCH gas. But possibly not so much that an H3 buffer can't help.
If you plan to run the can most of the time... I'd look at restricting that gas flow a bit. Properly gassed guns just run SO MUCH smoother.
patrick sweeney
03-06-13, 12:25
.070" is 23% larger an orifice than .063" but that doesn't mean 23% more gas.
Run it and try it. If it proves to be too much, even with an H3, you can always throttle it down. Or put on a switchable gas block.
Or put on a switchable gas block.
The problem with a switchable is you give up the FSB and then most likely have to reconfig the handguard.
It's a good option if you're wanting a lo pro gas block anyway.
Yeah, the gas block will be under a 12.5" DD RIS II rail, so no switchable. I guess I'll throw it together and hope it works. Good thing I have an SBR lower to run it on so I don' have the FH pinned only to find out I have gas issues.
Yeah, the gas block will be under a 12.5" DD RIS II rail, so no switchable. I guess I'll throw it together and hope it works. Good thing I have an SBR lower to run it on so I don' have the FH pinned only to find out I have gas issues.
Oh for Christ's Sake. Get the SYRAC. It has long wrenches that can adjust from the front like 5 or 6 inches under the rail. I have one on my shelf that I haven't got to install yet... But i've played with the adjustment system. It's solid.
Slam Dunk. I thought you were keeping the FSB.
Magic_Salad0892
03-06-13, 12:59
Yeah, the gas block will be under a 12.5" DD RIS II rail, so no switchable. I guess I'll throw it together and hope it works. Good thing I have an SBR lower to run it on so I don' have the FH pinned only to find out I have gas issues.
SYRAC will fit under a rail.
SYRAC will fit under a rail.
No kidding. This guy, ASH... he's killing me. :p
If you have any questions, contact PSA
If you have any questions, contact PSA
...right, because that's easy to do; and they're going to tell me, what exactly?
"Well sir, we size our gas ports where we believe they should be.":suicide2:
I just received a new barrel for my carbine to replace the DD LW I had before. The barrel is a PSA CHF 14.7" - carbine gas. I measured the gas port in our machine shop @ work and was disappointed to find that it is .070. The Colt spec for a 14.5" carbine gas barrel is .063. So now that we know it's going to be over-gassed, the question is, how much. I'll be running it with a DD FA BCG and an H2 buffer. Should that make it ok? I'm a little more concerned that I would normally be because I have paperwork pending on an M4-2000 and if this gun is already going to be way over-gassed, the silencer will only make things worse.
Thoughts on "how" overgassed the gun will be? Likely to be an issue or not?
Thanks!
Optimal gassing is critical to the reliable operation of the weapon.
There's no need to "build it to find out".
You measured the port and it is 25% too large for normal unsuppressed operation.
A good starting gas port size for dedicated suppressed use is around 25% smaller than normal.
These days, there is no good reason to "live with" a large gas port.
Get a CustomTune Gas Port and go shoot 556 and steel case without issue.
Magic_Salad0892
03-06-13, 13:56
No kidding. This guy, ASH... he's killing me. :p
Lol. Not everybody is gas port Nazis like me, and you now I guess. :p
There's no need to "build it to find out".
Yep. Unless there's something funky with the bore diameter that alters the normal pressure curve. It's overgassed.
And I'm guessing this barrel came off of FN's hammer forge.. so the bore diameter should be fine.
Yep. Unless there's something funky with the bore diameter that alters the normal pressure curve. It's overgassed.
And I'm guessing this barrel came off of FN's hammer forge.. so the bore diameter should be fine.
Didn't you have one of those insertable gas ports "disappear" from inside your gun?
Didn't you have one of those insertable gas ports "disappear" from inside your gun?
Yeah. I lost the A2 kit piece. I don't know if it fell out when I took it apart or what happened.
The standard kit is in two of my guns now. My 14.5 .063", and my 11.5 .060" dedicated suppressed.
Yes, it is large, but it's also not the end of the world. I have seen some middy barrels with ports as large as .076.
I am still rather perplexed as to why they seem to have some inconsistent port sized when it's generally know what the standard is for most of the barrels being used.
In your case if you want to run it suppressed alot and you know you are going to be using xxx ammo use an H2/3 and a Springco spring.
...right, because that's easy to do; and they're going to tell me, what exactly?
"Well sir, we size our gas ports where we believe they should be.":suicide2:
It's like the rifle itself- you won't know how it shoots until you shoot it and you won't know what they'll say until they say it. Isn't contacting the vendor the rule?
Heavy Metal
03-06-13, 17:16
Might be a good candidate for an LMT Enhanced Carrier.
Yes, but this isn't a defect (as they seem to do this alot) it's how they make the ports.
It's like the rifle itself- you won't know how it shoots until you shoot it and you won't know what they'll say until they say it. Isn't contacting the vendor the rule?
It's more than likely that size to avoid people calling in about problems with cheaper underpowered ammo.
My 16" PSA Carbine Gas Barrel has some pretty stout recoil with both a standard H2 setup and a VLTOR A5H3.
You probably shouldn't use that barrel on a suppressed setup or get an adjustable gas block.
I've been meaning to try one of these kits out. Black River Tactical - Insertable Gas Block Kit (http://www.blackrivertactical.com/store.html#!/~/product/category=2710008&id=18000700)
You should take a look at markm's thread on his Sabre Defence 11.5" barrel.
Over-gassed 11.5.. cut to 10.5 help at all?? (http://m4carbine.net/showthread.php?t=118010&page=9)
Correct.
It's more than likely that size to avoid people calling in about problems with cheaper underpowered ammo.
Optimal gassing is critical to the reliable operation of the weapon.
There's no need to "build it to find out".
You measured the port and it is 25% too large for normal unsuppressed operation.
A good starting gas port size for dedicated suppressed use is around 25% smaller than normal.
These days, there is no good reason to "live with" a large gas port.
Get an insertable gas port and go shoot 556 and steel case without issue.
Clint, I just sent you payment for a .063 insertable gas port.
Thanks!
Clint, I just sent you payment for a .063 insertable gas port.
Thanks!
Just saw that.
Was just shipping orders, should be able to get yours out today.
Thanks!
Alrighty I'm ready to go now. My weapons of gas destruction have arrived. I'll bring the barrel with me to work tomorrow and see how much damage me and a drill press can do. Thanks for the super-quick shipping, Clint!
http://i854.photobucket.com/albums/ab104/ASH556/20130311_140415.jpg
Let us know how that jig works out for pinning the gas block? Where did you get that one? Looks like the one Rainier is selling.
Let us know how that jig works out for pinning the gas block? Where did you get that one? Looks like the one Rainier is selling.
I've got the same one purchased from Rainier. Use it with a drill press but honestly you could use a hand drill because the jig guides the drill bit.
Works like a charm when pinning the BCM gas block (Vltor and rainier GB as well). I use a taper reamer also to allow me to use 2/0 BCM taper pins for the gas block.
These plus loctite set screws are pretty secure. I also use their dimpler jig to add a second set screw dimple. Again, couldn't be much easier.
Let us know how that jig works out for pinning the gas block? Where did you get that one? Looks like the one Rainier is selling.
Rainier and BCM (and I think Brownells too) all sell it. I got it @ BCM because I needed the LPGB since I'm putting it on a stripped barrel. I have everything with me here at work and am trying to get enough actual work done to justify slipping back to the machine shop (either that, or I'm procrastinating because I'm scared :fie:)
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