I have a 10" GunTec MLok handguard.  It covers a Vltor low profile, clamp on style gas block.  The problem is that while the handguard does clear the gas block, it does so just barely, especially the gas block's screws.  As seen in this picture:



I'm pretty sure the gas block's screws will come into contact with the handguard when the barrel flexes under firing.  This, of course, defeats the entire purpose of free floating a barrel, so I have to do something about this.

The handguard, when the screws are not cinched down, has some vertical up and down play.  Two of the screws pull the handguard into its highest position when tightened.  One thing I'm considering is using some shim stock to keep the handguard in a lower position after cinching down the mounting screws, which would give the gas block screws more clearance.

The second thing I'm considering is a bit more extreme.  This handguard is an MLok handguard.  Notice the little ridge that is nearly contacting the screws.  This is part of the mlok system.   I could take that ridge down with a file, at the cost of losing my most forward slot on the bottom for any mlok accessories.  That and completely trashing the finish in that particular area.

The third thing I'm considering is a lower profile gas block.  My barrel isn't dimpled for set screws, so I'm kind of locked into clamp ons.  I don't know which clamp on blocks would be smaller than the Vltor though...it's pretty darn small as it is.

I really don't want to buy a new handguard if I can help it.  The things are expensive.  Looking back I do kind of wish I'd just bought the 9 inch Clark Custom carbon fiber clamp on handguard and used a clamp on FSB instead, but water under the bridge at this point.  Then again, I've been thinking about doing a 9mm at some point...I could go ahead and do my 9mm upper and use this handguard on it, since the 9mm won't have a gas block at all.

What should I do here?  Would the shims be a reasonable solution?  My big concern there is my iron sights holding zero.  I have a magpul front sight on the top rail of the handguard.

Buy a new smaller LPGB.  That thing looks freaking huge on the bottom end.  IIRC, the Guntec handguards are the same profile as the Noveske NSR, and I know for a fact I had way more clearance with an NSR and a DD LPGB.  

Also, just because you don't have dimples doesn't mean you can't use a set screw gas block.  Dimples only help in aligning the gas block and do nothing to help keep it secure.  If it really bothers you that much, I have hand dimpled a few barrels using a small punch (to give myself something to keep the drill bit centered) and a handheld drill.  It's not that hard.  Either way, the thought that you're stuck with clamp on blocks is incorrect.  

The DD looks like a quality unit.  Do you know where I might find measurements on it, just to ensure it will clear?

It would depend on which specific DD gas block you're looking at.  Being honest, just about any quality set screw style LPGB will fit under there without issue based off your pictures.  The bottom of any one of those gas blocks is going to be quite a bit smaller than the clamp on block that's on there right now.

My current block is Vltor. Been doing some searching and, sadly, it doesn't look like any clamp on types are going to fit properly.

how well do those dumpling jigs work for dimpling a barrel for a set screw block?

No idea, never used one.  Like I said before, dimples are not necessary what so ever for a set screw gas block.  Dimples, for the most part, only help to align the gas block.  Anybody with even a little bit of mechanical skill can get one aligned and installed perfectly fine.

If you just have to have the dimples, I've dimpled a few barrels with nothing but a handheld drill (not bubba style, either, I have a process that works).  It's not hard.

What is your method? With a hand drill, I mean?

I align the gas block and then tighten/loosen the set screws a few times so they'll leave little circular cut marks in the barrel surface indicating where the dimples need to be.  I then take a small automatic center punch, carefully position it smack dab in the middle of those circles and give it a few clicks.  This will leave a small divot in the barrel surface which helps keep the drill bit properly aligned.  

I then start off with the handheld drill and a relatively small drill bit (I'd have to look at the exact size when I get home).  I position the drill bit in the divot made by the punch and start drilling.  To start off, I use high speed and extremely light pressure.  This helps to prevent the drill bit from jumping around/slipping off the barrel.  Once I get a nice small dimple started, I switch to a larger drill bit (once again I'd have to check on size).  I continue with high speed and light pressure until I get the dimples to the size I want them.  

Typically, you want the dimples slightly larger than the circular cut marks made by the set screws, seeing as you want the screws clamping down inside the dimple.  It's really not very complicated or labor intensive, usually only takes me 10-15 minutes.

I really want to reiterate though, none of this is necessary for a set screw gas block.  You can install one without dimples and if properly done (screws properly torqued using some form of threadlocker or staking), it isn't going to move, especially since yours is relatively protected underneath a handguard.

Maybe it's the angle of the camera, but the screw for the rail mount looks pretty close, too. I might see about shortening that screw a little.

MAS Defense uses this gas block on their upper builds with GunTec handguards....

http://www.shop.masdefense.com/750-LOW-PROFILE-GAS-BLOCK-STEEL-MELONITE-NITRIDE-750SLPGB.htm

Gas block dimples are the way to go on this one.

Jeff's method and mine sound identical and they'll work just fine.

Dimples aren't required and don't do anything other than help locate the gas block.   Any force that's strong enough to remove a properly installed gas block from a non-dimpled barrel will simply shear the tip of the set screw off on a dimpled barrel.  

I know you're using a name brand (a well respected one too) clamp on gas block, but damn that thing looks big...are you sure it's a low profile?
I'm also a Daniel Defense LoPro Clamp-on gas lock user and never had any clearance issues.

It is fairly close, though the angle makes it look closer than it is.  I probably will cut that screw down some though.

It's this model: https://www.vltor.com/shop/gas-blocks/gb-clamp-on-set-screw/

If my measurements are correct, the DD block is actually a little larger from the center of the bore to the bottom of the block.

According to Vltor, the distance from the center of the bore to the bottom of their .625 clamp on is 0.6".  According to a diagram DD sent me of their clamp on low pro, that same distance is 0.67".  The diagram DD sent me doesn't have that dimension, but it's derived easily enough.



1.455 total height - 0.785 from center of bore to top, leaves you the center of bore to bottom dimension (0.67 as mentioned).

Vltor doesn't list total heigh but I measure one with a ruler at slightly less than 1.375".  This makes sense since the GunTec handguard has an ID of 1.34".  The actual height of the Vltor is probably around 1.33 or so.  Don't have calipers on hand to measure it.

The GunTec handguard I'm using has an ID of 1.34" according to their website.  This is why I haven't bought the DD and tried it yet, all indications are its too big and that the Vltor is smaller.  I could always be wrong.

Overall height on any gas block is always going to be larger than 1.34"  When measuring the ID of their handguards companies leave out the gas tube channel on the top if there is one.

I think the critical dimension is the center of bore to bottom of block.  DD measures 0.67" there and Vltor is at 0.6".  Since at 0.6" the Vltor is way to cozy with the handguard, that makes me think the DD is too big.

I'm probably just going to get the set screw block, probably from Vltor, and the dimple jig from BRD Engineering and do it that way.  Shouldn't be that hard, even for me