DPMS barrel/gas block specs

[gnatshooter]

Friends,

 

I have a DPMS LR 308 T and would like to add an extra gas block at the muzzle so that I can mount the front sight further forward and get a longer sight radius.

 

When I put a calipers on the barrel, I get 0.730". When I shop for a gas block, they're offered with a 0.750" inside diameter.

 

Is the DPMS barrel an odd size, or is the 0.750" block supposed to clamp down onto a 0.730" barrel?

 

Any other advice you could give on this would be welcome. I'm an iron sights shooter and really want that extra sight radius.

[EasyEJL]

I'm pretty sure the answer is that your barrel is .750 under its gas block, but it profiled down slightly narrower after it.

[Robocop1051]

It's perfectly normal for a barrel to be between .74" and .73" between the gas block and the muzzle.

 

If you want to mount a faux-gasblock to the barrel, it can be done with a little ingenuity. The simplest way is to build a shim for the missing .02"

 

I did exactly this for my 300Blk build.

 

The best shim I was able to make seemed little hokey, but it worked out great. I cut strips from an aluminum can and wrapped the barrel with several layers. After I achieved the desired thickness, I just clamped the gas block on. You can't even see the aluminum unless you disassemble the rifle.

[gnatshooter]

Thanks Robocop! I got aluminum cans around here once in a while. What I did was order the "PRI Gas Block Single Picatinny Rail AR-15, LR-308 Standard Barrel .750" Inside Diameter Aluminum Matte" at http://bit.ly/11FO7Bw

 

I might not need the shim stock, though, depending on how much room for adjustment is there between the "ears" of the mounting clamps.

 

You'll notice from the design that the mounting rail will be able to 'hang forward' of the muzzle mounting point to give me just a smidgen bit more of sight radius. It may actually also look extra tacticool once it's mounted.

 

Speaking of mounting, I sure would like to have a better idea than 'eyeballing' for getting this bad boy 'clocked' at high noon on the muzzle. I'm not a big fan of canted sights.

[EasyEJL]

does your handguard have a top rail? if it does, you can just take your longest scope with its rings set straight, attach one ring to the handguard and then use the other ring to get the gas block centered :)

[Robocop1051]

Thanks Robocop! I got aluminum cans around here once in a while. What I did was order the "PRI Gas Block Single Picatinny Rail AR-15, LR-308 Standard Barrel .750" Inside Diameter Aluminum Matte" at http://bit.ly/11FO7Bw

 

I might not need the shim stock, though, depending on how much room for adjustment is there between the "ears" of the mounting clamps.

 

I actually used the same gas block. I had the front clamp milled off, and then re-parkerized the whole thing. This is a 14.5" barrel with a rifle length faux-gasblock.

 

As for the "room for adjustment is there between the "ears" of the mounting clamps"... There isn't any.

I used a small file to take out a considerable amount of material from between the "ears" to get them to close tighter. If you take off too much you will cause a football shape to the clamp closing.

 

The other idea I had planned was some foil tape my brother-in-law had laying around. It had very little adhesive (similar to painters masking tape) and was very thin. I planned on wrapping several layers of the foil around the barrel, and then trimming the excess after the install. 

 

If you have one in stock, you can use a rifle length gas tube to line up the gas block... EasyEJL's way is easier.

Edited June 25, 2013 by Robocop1051

[survivalshop]

Does DPMS make a Gas block with a rail for that barrel ?

[edgecrusher]

I second the beer can shim, uh, I mean aluminum can shim.

[Rsquared]

I second the beer can shim, uh, I mean aluminum can shim.

No....he meant beer can. Don't let him fool ya.

[Magwa]

yes they do make a gas block with a rail for that barrel I have one