Question for the guy's who've built AR's

[Badgersmilk]

When you start hanging all kinds of toys on the gas block like:

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. 

[tombogan03884]

It's pinned in place

[m25operator]

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.

[Badgersmilk]

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!



In pictures of most aftermarket gas blocks all I can see holding them would be the screws.   

[Badgersmilk]

It's applications like this I'm worried about.



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.    

[Sponsor]

[Badgersmilk]

According to the article I got some pictures from Bushmaster just does this.


http://www.varminthunters.com/ar15tech/freefloat/ar15freefloat.html


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?

[blackwolfe]

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.

[1911 Junkie]

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?   

[Badgersmilk]

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.   



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!  )

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.

[MikeBjerum]

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