Clamp on vs Set screw gas blocks...

[acebanana]

So I planned on using a 15" PXT FFSSR handguard but it doesn't appear my YHM clamp on gas block is going to fit underneath it using my awesome picture measurement skills. So, my real question is there really a measurable accuracy difference between a clamp on and a set screw style gas block? My barrel has one dimple for a set screw gb so I can't decide if I want to just switch to the set screw style or use a shorter (11.5") handguard. I'll be shooting off a bipod if that makes a difference, personally I think the 15" will look a lot better on a 18" rifle length barrel.

 

[biggin69]

I use VLTOR low profile gas blocks on all my AR's. I have not found a free floating tube they wont fit under and they seem to manufacture them with a larger gas port area on the barrel side. To my understanding, clamp on is a better system as it distributes the clamp stress uniformly around the barrel where as the set screw style seems to concentrate on the bottom of the barrel. Some say these concentrated stresses will cause accuracy issues down range (I guess). Also, the clamp on system seems to fit better so the gas loss between the barrel and the block is minimized. These observations are based on the AR's I built. I'm sure those smarter than me shall chime in ;o)

 

[BigJohn141]

Honestly I doubt most of us can shoot good enough to notice the difference between a clamp on or set screw style. I do agree with the VLTOR block, I have one under a Wilson 13.5" TRIM and it seems to be tighter than most hand guards. With that said, I did just buy a Wilson gas block (set screw style) because I wanted an adjustable and its just as small as the VLTOR.

 

[acebanana]

Yea I had read a while back about the stress points and such with set screw gb's but I didn't know if that actually degraded accuracy enough to actually measure, so I just stuck with a clamp on. I was looking at the GB-2CS from Vltor, does anyone have the height measurements for one of their clamp on .750 gbs? The rail I want is 1.35" diameter (excluding the top notch), so I guess 0.675" at the bottom half.

 

[rideHPD]

Ideally, someone gets two similar blocks, one set screw, one clamp one (or more of each), and fires many 5 round groups and looks for a consistent change in group size, not just in average, but in maxima and minima as well. If there is a clear winner, it will probably be less than .1 MOA.

 

[tipper]

that handguard is not round is it, the shape is more like a plus sign

 

[acebanana]

Nah it's round, well at least from this picture it appears to be. Only the top has the notch. After looking at the measurements the VLTOR is .600 from the center bore to the bottom and the guard is .675 so that'd be .075 of clearance...

 

[2guard]

since you have a pxt rail, check out there low profile adjustable gas block. It is not listed on their website, but you can contact them and they probably still have some. They are the set screw variety, lightweight and it fit under a very slim handguard on a build I just finished. The reason I went with it, besides being able to fit under slim handguards, was the adjustment screw is in the front of the block and easily accessible (I run a folding front sight on the free float rail). bought mine off ebay actually, was the only place that had them in stock at the time, but here is a picture on the aim surplus site (sold out also):

Parallax Tactical PXT Super Light Low Profile .750 Lightweight Adjustable F

 

[Larry Morrison]

I just ordered one of these gas blocks too. Can you you tell me how yours is working out? Thanks

 

[Scaevola]

Neither.

Low profile block and have it pinned, unless it's a true precision build. IIRC, pinning can lead to vertical stringing when the barrel gets warmer.

But if it's not a precision rig, pin that bitch and be done with it. JMO.

 

[1slow01z71]

Id concetrate more on a quality barrel and trigger before I worried about types of gas blocks. My precision rig will put 10 shots inside of an inch like clockwork with a vltor set screw gas block. If its hurting me I cant see it. Thats with a WOA barrel and geissele national match trigger which have a lot more effect on accuracy than the type of gas block. Its not like youre putting 100ftlbs of tq on the set screws. If the barrel is dimpled for the gb it doesnt take much tq at all on the screws. Snug them up using some red loctite and roll with it IMO.