View Full Version : Clamp on GB on hard use SBR?
dlraymond30
10-20-17, 16:28
Just like the title says, im wondering what the possibilities of running a clamp on GB (bleed off, sentry or seekins/odin) on my upcoming 11.5 im building as well as putting one on my 18" rifle gassed "SPR"?
im posting this in the tech section because ive heard that the uniformity of the clamping pressure from this kind of GB helps minimize the accuracy degredation that the non uniform tension of a screw on GB, is this correct?
Also, would the shorter barreled rifle, being much more violent and harsh in recoil and general use, be too much for a clamp on?
Eager to hear your replies and opinions everyone.
Regards,
Darrin
titsonritz
10-20-17, 17:12
No thank you, I'm not into clamp on gas blocks at all. If the gas block in concealed by the handguard I am ok with a properly dimpled barrel and set screw, if the gas block or FSP is exposed I want it pinned.
SomeOtherGuy
10-20-17, 20:14
im posting this in the tech section because ive heard that the uniformity of the clamping pressure from this kind of GB helps minimize the accuracy degredation that the non uniform tension of a screw on GB, is this correct?
About 1-3 years ago someone posted a computer model (FEA) showing strain from the set screw of a gas block on the barrel. It did indicate some strain, but whether that results in any real-world effect on accuracy I don't know.
Clamping gas blocks hold very, very tight as long as the screws are tight. Another site (I think it is Military Morons http://www.militarymorons.com/map.html ) tested the VLTOR clamping gas block and found that it held tightly enough that you could unscrew the barrel before it came loose.
But the screws have to hold tight. Many of the more range-oriented makers sell guns with clamping gas blocks that seem to hold for years, but it could come loose at a bad time. To get more security you could either stake the screws or lock them with a high temperature threadlocker, either Rocksett or red Loctite. Rocksett is easier to remove if you ever need to and should be adequate.
TL;DR properly installed a clamping gas block should be fine, but installing it securely is about as much work as dimpling for a set screw, and not far off from drilling and pinning. I would go the clamping route only if (1) you are willing to do threadlocker and measured torque, but not the alternatives, or (2) you believe there will be some accuracy benefit by avoiding a dimple or a pin-hole.
I have been using on two SBRs the clamp on style gas blocks for a combined total of approximately 11,000 rounds. I have never experienced any problems with them what so ever. All said and done I would not chose that style to ho to war with.
The unanswered question is who's clamp-on? If you purchased a known quality GB, then you won't have a single problem. Handguard clearance may be something to consider.
Here is the set screw FEA thread
https://www.m4carbine.net/showthread.php?172573-Set-Screw-Gas-Block-Internal-Deflection
Mr. Goodtimes
10-21-17, 11:50
I would not use anything other than a set screwed or pinned gas block. The KAC Mod 2 design is very secure as well but that’s obviously proprietary.
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dlraymond30
10-21-17, 13:35
Nim actually very interested in trying out the POF dictator as it resembles a shaved FSB and can be taper pinned in rather easily. Any knowlege of this BG? I know it uses a straight gas tube and when i got a chance to try out a POF (cant remember exsct model, 415? It has slect fire function i remember) and it was easier to use than even the noveske switchblock after shooting a whole bunch both suppressed and not. I think it will make a very nice little informative post after the fact, no?
Hey i just read that informative post about the bore deformity that occurst from a set screwed BG and that a taper pin prob doesnt have the same amount of deformation and that clamp on GBs give uniform pressure thus decreasing deformation sooooo... Would taper pinning a clamp on be a viable option that would give both the added benefits of both?
Oh and righttobear.com has superlative bleed offs for $79.99 for clamp ons as well as set screws for .625 GB joirnals. I may go for this option because it looks like a damn good option for a short barrel.
BufordTJustice
10-21-17, 15:32
Clamp on gas blocks also place an unpredictable amount of torsional stress on the screws. They are prone to failure after heat cycling.
And, IIRC, the FEA didn't model a cup tipped set screw, but pointed one. With a knurled-cup-tip set screw and appropriate thread locker, one doesn't need very much torque to keep everything right even for prolonged full auto use.
Clamp on gas blocks are not for serious use. Range use? Sure, no prob.
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I run the old Daniel Defense clamp on gas blocks (1st gen I believe) and TIG welded about 1/3rd of the screw heads to the gas block. Been about 10k rounds on my main 16” middy, 2 classes, and still runs 100%. As long as the screws don’t literally pull apart I can’t see the setup going anywhere. But this is coming from a welder, not an engineer.
Quality unit, but not a lot of fine adjustment if you prefer not to bleed-off gas when using a suppressor. SLR Rifleworks or ODINworks are GTG for a restrictive system. Just FYI.
Oh and righttobear.com has superlative bleed offs for $79.99 for clamp ons as well as set screws for .625 GB joirnals. I may go for this option because it looks like a damn good option for a short barrel.
Another site (I think it is Military Morons http://www.militarymorons.com/map.html ) tested the VLTOR clamping gas block and found that it held tightly enough that you could unscrew the barrel before it came loose.
And what types of barrels screw into the receiver?
Fixed it for ya.
And what types of barrels screw into the barrel extension?
Answer: I think all of them.
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