Must Gas Block Be Pinned on SD AR? Flip or Fixed FSB? [Archive] - Glock Talk

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duncan
01-17-2010, 23:15
I'm trying to set up my CHTF/zombie AR-15. 16" A3 flattop with a standard FSB and a fixed rear sight for the maximum durability and reliability. If the EoTech fails, irons always on.

Thinking about installing a carbine-length free float tube for accessories and that theoretical accuracy.

Question One: Must serious rifles have pinned on gas blocks?

I'm hearing that if my gas block is going to be outside of my forearm, that it is best to pin it. Just have not seen any pinned gas blocks (in person).

Being told that the supplied set screws still are subject to impact and movement. For example, would this YHM flip up front sight really come loose to the point I shouldn't mount on a SD rifle?

http://www.pkfirearms.com/product_images/0000/6157/DD_M-4_YHM_Rail_Flip_sight_2.jpg

Or this Stag gas block? Anyone rockin this on their zombie rifle?

http://dynamicarmament.com/images/stagarms2007/STAG%20ARMS%20gasblock.jpg

Question Two: Are people mounting YHM flip up front sights or other flip sights on their free float rails on their home defense rifles?

Rifle could be used for SD but most likely more range time.

What does the tribe say?

blaster_54738
01-17-2010, 23:26
i've never heard that. i have a daniel defense clamp on gas block that is outside of my lite rail and it aint going anywhere.

as for front sight, i use YHM QDS front and rear mounted on my forend. haven't let me down yet

crazymoose
01-18-2010, 01:17
The only clamp-on I'd trust is VLTOR's gas block/folding front sight combo; they have a video of it taking well over 100 ft.-lbs of torque and not moving. Then again, that particular piece of kit costs more than separately buying almost any railed gas block, having it pinned, and installing almost any fixed or folding sight. However, it's been my experience that with VLTOR, you get what you pay for.

I'm not crazy about folding front sights. I'll usually use a fixed front and a fixed or folding rear. I do mount front sights on railed forearms all the time. With a good rail, there is no shifting of your zero whatsoever.

If you are going to use a clamp-on gas block, I recommend using Rocksett threadlocker on the screws after de-greasing them and the holes in the block. The gas block can get hot enough to melt most common threadlockers, but Rocksett is good to something like 2,000 degrees Fahrenheit. It also is strong enough for the job, but weak enough that you'll actually be able to get the screws out if you want to do so.

faawrenchbndr
01-18-2010, 05:15
I do not care for the railed gas blocks.
I prefer a pinned FSB or a low profile gas block with set screws at the
6 o'-clock position. Barrel is dimpled for the set screws, set screws are
secured with LockTite then staked. They will not back out.

The other option is to "shave" the FSB for use with a free float tube/rail

furioso2112
01-18-2010, 09:12
I like folding front sight bases - changed out my Bushy ORC pinned gas block to a YHM flip-up (like the one pictured). As Bushmaster does not treat the entire barrel, I had to figure out which product to use to blue it (didn't want to remove the barrel and send it out for a complete refinish). After some questions and research, I chose Oxpho-blu (Brownell's). I used the no-drip, and it worked very well. The YHM did not cover the same space as the pinned FSB, so without bluing, little silver circles were noticeable where the barrel was not covered by the contact area of the YHM sight. The bluing took care of that, not to mention the improved durability from treating the metal with Oxpho.

I like flip sights because I like the lower/more-streamlined profile when the sights are flipped down - just seems to make sense to me. Also, it allows me to comfortably squeeze two guns into my Pelican case. With standard FSB, two guns would have to be positioned in a way that would cause parts of the guns to impact the outer ege of the case if the case gets tossed around.

It hasn't been mentioned, so I will: I recently bought a BCM upper with a 12" DD free-float handguard - this is my favorite setup of all. I put a flip-up sight on the rail, so even less worries about barrel/block/sight contact. It extends the sight radius by a couple of inches on a carbine, too, increasing the potential 'accuracy of the sights.' If you are going to change your block/sight and add a rail anyway, I highly recommend considering this option. I really like the look of it, too, alhtough that doesn't mean much - the only real consideration is performance for application.

A final note - especially if it is not already, the idea of drilling into (for pinning) or dimpling (for staking) gas blocks/FSBs seems like a bad idea to me. I know its been done more often than not, but it just seems like bad idea to screw with a barrel like that. I want my barrels as they come from the factory - a solid piece of steel that I have not hammered or drilled.