The Down Range Forum
Member Section => Tactical Rifle & Carbine => Topic started by: Badgersmilk on January 24, 2010, 01:18:05 PM
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When you start hanging all kinds of toys on the gas block like:
(http://www.leapers.com/production/images/370X235/MNT_GBQR04A_APP_2.jpg)
What keeps the gas block from spinning on the barrel if, say, the flashlight got bumped hard from the side? I know there are a few (2, or 3) little set screws that hold this type of gas block on. But do AR barrels have a slot cut in them to keep the gas block from turning (similar to the press pins used on the front sights of AK's, and SKS's)?
I've heard quoted from a very respectable source. "The way you know a rookie AR guy in combat is he doesn't use a pinned gas block.". So I'm wondering if the barrels are grooved for the pins, or is it just that the pins aren't as likely to back out / become loose.
Without something more than the grip of the set screws keeping the gas block from turning on the barrel, it seems shockingly stupid to use the gas block as a sling mount, or to hang other crap on it that would add leverage leading to it getting turned by accident, and rendering the gun a single shot.
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It's pinned in place
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You make a valid point BM, standard front sight bases use 2 tapered pins, that engage grooves on the bottom of the barrel, it is a very solid set up. When using set screw type gas blocks, the user should, file or mill a flat on the bottom of the barrel for the set screws to seat against, and if you want to go better, after mounting and tightening the set screws, remove the gas block and drill detents at the screw marks, for the set screws to go into. Definitely use loctite on the screws.
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Yeah, I agree what your saying m25.
It's hard to believe without detents drilled and matching profiles on the set screws the clamp type gas blocks are going to hold up in any real world heavy use.
I found this picture. I don't know if all AR barrels are like this. But I sure hope so!
(http://ar15barrels.com/tech/mrp-gas-port.jpg)
In pictures of most aftermarket gas blocks all I can see holding them would be the screws. :(
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It's applications like this I'm worried about.
(http://www.varminthunters.com/ar15tech/freefloat/clampgasblock.gif)
I'm scoping my AR, and will probably need to ditch the A2 style gas block currently pinned in place (won't know for sure till the scope and rings get here). I was thinking it'd be nice to have a single rail like that pictured to mount a folding back up iron sight on, but I just don't see anything on the "clamp on" gas blocks that'd prevent the sight, or anything else mounted on the rail from acting as a lever to spin the gas block around on the barrel. Not only bumping your sights out of line, but making your fancy AR into a not so fancy single shot PITA.
Shoot, looking around at today's AR's I RARELY see a pinned gas block... :-\
I guess it's not a huge concern for mall ninja's. :P ;D
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According to the article I got some pictures from Bushmaster just does this.
http://www.varminthunters.com/ar15tech/freefloat/ar15freefloat.html
(http://www.varminthunters.com/ar15tech/freefloat/milledgasblock3.jpg)
Solid, and reliable? Yes.
Looks like total s#it? Yes.
I guess a little effort with a dremel would make it look nicer. But still no back up sight. :( It'd still be a lot less work than putting detents in the barrel and finding the right screws (more reliable to I'd guess).
Thoughts?
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Can't remember which one, but one of the major AR manufacturers stated in their catalog that they do not sell the traditional front sight tower because of the difficulty drilling the taper pin grooves in the barrel. I think some manufacturers use dowel pins for the front sight towers. I think Rock River does. I imagine that getting the sight holes and barrel grooves aligned properly and milled or drilled for either type would be difficult for the home shop do it yourseler for either type. I'm not a machinist or know much about machining, and have know I idea how it would be done properly.
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All mine are pinned except for the gas block on my bull barrel but nothing can go on it (no rail, no sling mount).
If you are mounting a scope there is no reason to change the front sight. You will not see it when looking through the scope.
What are YOU doing with an AR? ??? ;D
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Hopefully your right about not seeing the front sight post in the scope. I ordered tall rings, but I don't think their as high as the factory iron sights. This is the gas block on the DPMS .308 I've had for years. I've finally decided to drop the Eotech off it in favor of a scope with adjustable magnification. With the .308's potential range of service I think the rifle's potential was limited using a 1x sight.
(http://i703.photobucket.com/albums/ww40/BigCheeseStick/P1010491.jpg?t=1264387904)
CLEARLY the pins are going through the barrel, not just under it. So if the front sight is a problem cutting down the factory gas block may actually be the best option. A little ugly even with good trimming. But certainly solid and reliable. Set screws reeeeaaaly seem like a poor option for any weapon you may actually have to rely on one day (an AR is a crap choice for that anyway! ;D)
IMO the whole gas block set screw subject is something for all AR boys to strongly consider if they're ever thinking of having to rely on one for anything more important than killing paper.
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BM,
I've been reading your question, concerns and on going debate with yourself. I normally don't jump in on something like this, because even though I play a gunsmith in my dreams I am not really one. However, being a true American male of pasty pale Nordic decent I need to ask you one question ...
Have you ever heard of that modern invention ... DUCT TAPE ???
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I didn't want the front sight sticking up in front of my scope so I lopped off the top with a hacksaw. After I filed and sanded it I used some cold bluing on it. Now it looks like it was made that way.
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I'll be the very first to admit I'm no expert of the minute details that make AR's work. Or as is more often the case, not work.
For as many people that will sing the praises of AR's I was just looking for more insight like "the right way to do it is...". Looks like what Jumbo has done is the best answer. Bushmaster even does it as a manufacturing practice.
Just shocked nobody here (Jumbo, & M25 aside) has looked into this simple modification more. :-\
Nobody ever said the internet lacked posers.
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Suggest that you mount your scope first and see if the front sight is a hinderance first. On my ACOG (mounted on flat top)equipped M4 this is what you see.
(http://www.hunt101.com/data/500/Mule_deer_NM_Dec_07.jpg)
(sorry for the lousy photo, taken with my cell phone, and holding the rifle on a ceder fence post on a mule deer)
If you have a fixed carrying handle and mount the scope on top of that you will clear the front sight.
CD
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That's actually an excellent photo! Thanks. Reflects the "ghost image" of the front sight really well. I've got a flat top, and ordered "tall" rings, so yeah, I agree that's an effect I could deal with to. Just a waiting game now to see how everything "fits up".
Why I started the thread is that nearly all aftermarket gas blocks I see that are just "clamp on", and more and more firearm manufactures are using them. Then people hang ALL KINDS of stuff off them. It left me thinking. "What am I not seeing that keeps these things from being a serious liability?". Looks like the answer is "nothing". They are a liability. And the source that said "only an amateur would use one" sure seems to know whats up! ;)
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Pinning a front sight / gas block isn't difficult, it just requires good, solid fixturing, and care when doing it. This is the reason you see so many Century, Romanian WASR 10 AK-47 builds with canted front sights. It was done "quick and dirty". The fixtures they use are most likely not the best either. Put all of it in the hands of a relatively unskilled, low paid worker, and you would be amazed at how badly they can screw things up! This is yet another result of a manufacturer operating on the principal that, "You can train anyone to do anything!" Bill T.
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Well... I caved. Actually I got in the rings I want to use, and the scope, and the cross hairs of the scope were below the front iron sight. I don't want to give up using a pinned block. And with the barrel already having been drilled through for this block...
This is the result.
(http://i703.photobucket.com/albums/ww40/BigCheeseStick/P1010541.jpg)
It took about half an hour with a hack saw, grinder, and belt sander. Unlike the pins used on Russian rifles, those used by DPMS tap right out! Quite easily in fact! I've bent punches on AK and SKS pins! These took about three taps each to pop out. It was such an easy process I'm actually gonna take it of and do some fine tuning on it with a file, remove the sling hoops on the bottom, and maybe even the bayonet lug. :-\
If anybody's thinking about doing this, just do it! It's WAY, WAY easy. Part come right apart. Nothing like surplus guns! :)
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I'd keep the Bayonet lug for 3 reasons, it's subtle "up Your's" to the Anti's and , Hey, you never know, you MIGHT actually need to bayonet some thing with it.
It would also make a workable skewer for cooking what you just killed ;D
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I wish I was better at the picture thing, I have a WOA aluminum forend that I milled flat for the last 3" and put a 3" piece of picattiny for a folding front sight, looks like you could do the same BM. The WOA forend go's well forward of the gas manifold.
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You would have to bang the hell out of the thing to get it to spin I would think. even if it did it wouldn't turn far because the gas tube would keep it roughly in place. If it turned hard enough to shear the gas tube then you have a single shot gun like you said. Never seen or heard of this happening before.. been armoring the AR type rifle for some time. my two cents.
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I always go with a quad rail gas block because I put a Burris fast fire sight on the inside rail. I have one on the side of my ps90, my ar15 in 223 and I will put one on my 6.5 Grendel AR when I complete it. Scope on top and back up iron sights. Make sure those gas blocks are locked down tight.
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(http://i703.photobucket.com/albums/ww40/BigCheeseStick/P10105952.jpg)
This is where it's at right now (minus a new sling setup I'm really happy with). But I like M25's idea of going with a rifle length, quad rail, free floating forearm that completely covers the gas block. I like this idea because I'm thinking of mounting a laser on the forearm for anything that might be considered "close quarters shooting". And completely removes the gas block as an issue.
I'll have to cut off the bayonet lug for the longer forearm to clear. But that's only about a 10 minute job. And the DPMS flashhider is EASILY sharp enough to serve as a bayonet if things every got that ugly. ;)
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(http://i703.photobucket.com/albums/ww40/BigCheeseStick/P10105952.jpg)
This is where it's at right now (minus a new sling setup I'm really happy with). But I like M25's idea of going with a rifle length, quad rail, free floating forearm that completely covers the gas block. I like this idea because I'm thinking of mounting a laser on the forearm for anything that might be considered "close quarters shooting". And completely removes the gas block as an issue.
I'll have to cut off the bayonet lug for the longer forearm to clear. But that's only about a 10 minute job. And the DPMS flashhider is EASILY sharp enough to serve as a bayonet if things every got that ugly. ;)
Were you trying to co-ordinate your floor and your avatar or was that just a pleasant accident?
I would go with who ever posted earlier with, "What are you planning on doing with your AR?"
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(http://i703.photobucket.com/albums/ww40/BigCheeseStick/P10105952.jpg)
This is where it's at right now (minus a new sling setup I'm really happy with). But I like M25's idea of going with a rifle length, quad rail, free floating forearm that completely covers the gas block. I like this idea because I'm thinking of mounting a laser on the forearm for anything that might be considered "close quarters shooting". And completely removes the gas block as an issue.
I'll have to cut off the bayonet lug for the longer forearm to clear. But that's only about a 10 minute job. And the DPMS flashhider is EASILY sharp enough to serve as a bayonet if things every got that ugly. ;)
Looks good as it is.
But if you go with the other fore end please post pics , that sounds interesting too.