Building my first rifle and want a low-pro gas block.  Found out from BCM that their barrels are already dimpled for a set-screw gas block so I will go with that instead of a clamp on since it is cheaper.  Question is:  Is one set-screw gas block any better than another?  For example, the Vltor is ~$65 and the Troy is $35, is there any difference between them or is a low-pro gas block a low-pro gas block?  Thanks for the help

The BCM barrels have one dimple at the rear near the shoulder ... you have to drill the other one that is specific to the length and location of the second set screw for the GB you purchase ... just figured I would let you know in case you weren't aware of that.

With the Troy your getting a basic looking quality GB ... the Vltor has cool ribs running down the side and the Vltor logo on it ... they both make quality parts take your pick.

No, I did not know that.  Thank you for the info, might be going back to a clamp on now.  Im not sure if I am comfortable drilling into my new barrel

Is it difficult to drill out a dimple for the screw?  I guess there is a first time for everything and if its not too difficult I might give it a shot

No ... it's pretty easy ... you put the GB on the barrel and insert the rear screw to index it then take a drill bit that is a couple of sizes smaller then then the screw hole in the GB to start the dimple hole ... then remove the GB and go to the correct size of the screw and take to the depth of the other dimple and your done.

You don't need to dimple the barrel anyway.  That dimple is there to make it easier to get your gas block located correctly.  If the set screw goes in the dimple, then the gas port in the gas block MUST be centered over the gas port in the barrel and there is no need to measure distances and shim the gas block while tightening it down.  There is also no need to eyeball the GB to TDC.  That is all the dimples do.  If you really think the dimples will make the gas block less likely to rotate, you are kidding yourself.  I have set screw gas blocks on all kinds of ARs in all kinds of calibers and only recently were any of them dimpled.  I will put you dollars to doughnuts, you tighten down the set screw like you have a pair but not to the point of stripping and it is not going anywhere, dimple or not.  But dimpling is great if for no other reason than for alignment and removal ease.
When you do tighten down the set screw types, if there is no dimple or the dimple is too small, it throws up a burr on the barrel and that can make removal later on a twist and cuss ordeal.  I really do think the dimpling helps prevent that burr from making the gas block hard to take off later and that is another plus for dimpling, and would be the only reason to dimple the second set screw.
Personally, I prefer the clamp on like the VLTOR, YHM, or Lo-Pro DD.  DD now makes a clamp on similar to the VLTOR and YHM and all three of them are great.  They are very snug on the barrel so you must spread it a bit to get it on but that is a no-brainer.  Put the clamp screw in from the other side, put a penny in there to butt the screw up against and tighten it down slightly to spread the clamp apart, then it slides right on.  Loosen the screw, rotate to align, and tighten down.  The DD and VLTRO clamp on you can use the hole in the bottom of the gas block to align with the dimple, if your barrel has one, and that will help you align it if you don't want to use calipers and feeler gauges and eye-balls to get it all aligned down to the .001 of an inch, which is NOT necessary.

thanks for the informative response- I have been thouroughly educated.   So sounds like dimpling is purely optional and I can go ahead and get the set-screw with no worries about reliability (this is my first build and will be my SHTF rifle)   thanks guys

After doing further research (on some other websites) it seems that some disapprove of both the clamp on and set screw and that pinned is better all the way.   any merit???

Sure .. the standard FSB with the two taper pins is the most durable solid FSB (my SHTF rifle has the standard FSB for that reason) I know of especially if the rifle is a full auto rig. IMHO  

Me and you not having that glorious "fun switch" for our rifles and not beating down doors with it will probably never have a problem with the clamp on or set screw type GB (I have two older Daniel Defense clamp on versions and never had an issue and the newer versions are even better made IMHO) you can also have the set screw Vltor's pinned by ADCO they do nice work indexing and pinning the low pro GB's.

Would anyone recommend using the "shaving off the standard FSB into a low-pro block" mod?  Does that affect reliability at all?  If not, it sounds like that may be the best of both worlds, low-pro, pinned and cheaper to boot

Done it .. works fine.

Just coat the bare metal with something to protect it from rusting after you cut it like aluma hyde II or something along those lines and you should be GTG.

Alright, and besides, if I screw it up I can just order a low-pro block.  Thanks for all of the help.

No problem ... good luck with your project.

Just saw this and wanted to throw out that dimpling the barrel is easy , just go slow. Also I have used the Vltor on my fist build and then got a Larue for my 2nd build. The Larue does cost a little more but they are worth it. Good luck.

Only if you plan on beating on your gas block with a hammer.  And since you are going with a low-pro, will it not be under the forend?  If it is, it is going to take such a blow that it would have to wreck your forend and your gas block that having your gas block rotated is the least of your worries.  Too many people live in the 'what if' world and not the real one.  A huge A2 or M4 type front sight tower, yes, pin that sucker on if it is on a life and death rifle.  It sticks up like a sore thumb and is very likely to get bumped if dropped or fallen on, but a low profile gas block?  Get bumped and rotated?  Yah, sure it will, if you take a 10 pound sledge hammer and beat the snot out of it.