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Posted: 9/24/2011 8:57:47 PM EST
Hey everyone,

I'm in the process of gathering parts for my next AR upper. My question is, how tightly should a gas block fit on a barrel? I have a Denny's Guns/GTS Recon II barrel and a GTS gas block. The gas block barely fits onto the barrel. There are two steps at the muzzle-end of the barrel - I am assuming they're for use of the Ops-Inc 15th model muzzle break. However I'm just using an A2 flash suppressor. But the gas block won't fit over the 2nd step. I'm guessing I'll need to apply some grease either to the barrel or to the inside diameter of the gas block to get it to slide down into position...does that sound normal? I'm afraid of marring the barrel during installation. Even though it will be hidden by my rail, I'd rather not cause any exterior damage to the barrel. What says the hive?

Thanks in advance for your help....
Link Posted: 9/24/2011 9:42:43 PM EST
Use a caliper and measure the barrel and block to determine how close they are.

Is it really tight? Can it go on with some tapping from a plastic mallet or a piece of wood?

Look inside barrel hole of the gas block.
Is it rough from finish (parked inside)?
You may need to rub a green scrubbie or piece of emery cloth around the inside of the gas block (always modify the cheapest part) to smooth it out a bit.
Be VERY judicious.

You can also put the barrel in the freezer for an hour and heat the gas block with a heat gun for a few minutes before you slip it on the cold barrel.
Link Posted: 9/25/2011 4:13:40 AM EST
^^^This...I've had a few tight one's. I use a rubber mallet with a piece of wood, or a piece of emery cloth and smooth the inside of the GB.
Link Posted: 9/29/2011 9:59:56 AM EST
Thanks guys. I'll try the freezer trick first and if that doesn't work, I'll get some emery cloth. The inside of the gas block is already very smooth though. We'll see how it goes.
Link Posted: 9/29/2011 11:20:10 AM EST
To get my YHM lo pro gas block onto my WOA 16" SDM barrel, I had to use a mallet to whack it on.

I also used some 40 grit sand paper followed by 600 grit (polish). Go slow, and take only a little bit off at a time. If it doesn't fit still, you can always sand off some more; but once you've sanded off too much, you're out of luck.
Link Posted: 9/29/2011 11:59:18 AM EST
What is barrel dimensions, & are u sure u have appropriate gas block?
Link Posted: 9/29/2011 12:15:31 PM EST
I have sanded the inside a YHM block to fit on a barrel. IIRC I used 600 grit paper and went slow.
Link Posted: 9/29/2011 1:33:01 PM EST
[Last Edit: 9/29/2011 1:37:06 PM EST by Direct-Drive]
Originally Posted By wayne1one:
What is barrel dimensions, & are u sure u have appropriate gas block?

Yep, get a caliper and see where you're at. Digital calipers are cheap now and very handy on the gun bench.
I have heard of folks using a brake cylinder hone to open up a gas block.
They're cheap....using a light cutting oil (or similar) and go S-L-O-W....checking for fitment frequently.
One quick, light pass may do it if you dimensionally close to begin with and your cut will be more concentric than by hand.

I have used these on brake cylinders and come to think of it they would be ideal for the above task as well.
Link Posted: 9/30/2011 7:49:35 AM EST
[Last Edit: 9/30/2011 7:50:35 AM EST by Spitfire75]
Well, it's this gas block (without the front piece):
http://global-tactical.com/modblockgasblocksystem.aspx

And I'm trying to mate it to this barrel:
http://global-tactical.com/16inchmidlengthreconbarrel556mminstock.aspx

The barrel is .750 at the gas port and the block is a .750 gas block, so they "should" fit. I'm going to try to freeze the barrel first. If it comes down to me having to relieve the inside of the
gas block a tiny amount...man, I hope I don't screw it up! Fortunately the gas block was only $25, so if I accidentally remove too much material I can always just pick up another one. Thanks for the advice everyone...I might also need to find a wood block to use as a hammering device. I just don't want to mar the finish on the barrel.

Would it be ok to use oil or grease to help the block slide down the barrel?

ETA: Oh yeah, I think my buddy whose tools I'll be using has a set of calipers. I'll be taking a lot of measurements to check my progress.
Link Posted: 9/30/2011 8:14:56 AM EST
I don't have the exact components that you have but mine is a Denny's Operator midlength 16" barrel with a standard F marked FSB, the FSB slips into the proper location easily without using any tool, I also applied lots of oil on the parkerized finish of my barrel before the installation.

Since your components are from Denny it should fit unless one of them is out of spec and you could first check it with a caliper/ micrometer.

If the barrel is exactly 0.750" OD, the hole of your gas block ID should be at least 1 thousand of an inch bigger (or slightly more) in order for it to slip fit into place.

Generally if your OD and ID are the same it won't be a slip fit, you need to force fit it, but don't do this to your barrel because it is better to take some off the gas block to have it slip in.


Link Posted: 9/30/2011 12:39:09 PM EST
I wouldn't use grease, its going to make it a tigher fit. Use light oil or better yet a lube for press fitting (dry moly). Hone the GB if you can. Heat the BG with a LP or mapp torch, even a light bulb could be used to heat the GB.
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