My first AR was a Windham SRC with flat top and picatinny rail front gas block.  The stock handguard always annoyed me so I ordered an Aero ATLAS R-One 15" handguard and went to order an Aero low pro gas block and thought I better take a look at what's on the SRC first, so I removed the flash hider, handguard, and gas block.  The gas block has two pins through the barrel and barrel is standard .750 diameter (actually measures .748 on my caliper).  All the vids and posts I'm seeing for my rifle seem to just put another two piece handguard on there.  Now I've got a few things I'm wondering about such as:

What if the set screws on a new gas block hit the pin holes on the barrel?  Seems like that would wreck the holes and not be secure.

If I want or need to pin a new gas block how would I do it and match the holes up to the barrel holes?

Is this the ideal setup for a clamp-on gas block instead of set screws?

As a side note, the barrel doesn't have a dimple for a set screw, just the pin holes.  Also where the factory gas block wrapped around the barrel it's bare metal and inside the pin holes it's bare metal.  Should I hit that with paint or some protectant?

Do you have a pic of the GB and barrel so we can see where the pins were?  I don't know if a clamp on GB will fit under the new rail.

If you can measure how far away from the gas block shoulder the pin cut is, someone can measure a LPGB for you and tell you how the spacing will match up.  Looking at a pic of the gun, a LPGB will be much shorter than what you have on there, so you really only need to be worried about the one pin cut, the forward one will not be covered by a new gas block (unless you get one specifically made to do that).

Also, you won’t be able to “match” a new pinned GB to the holes that are already there, it’ll require a new gas block drilled to your barrel, with potentially oversized pins if the pin hole will overlap your already existing holes.

As for a clamp-on LPGB, it may or may not fit.  I have no experience with that handguard, so I can’t say one way or the other.

You may want to look at having your existing gas block re-profiled and parkerized since it is already pinned to your barrel.

Thanks, I read about how the original pinned gas blocks are pretty much a one-shot deal, that's why I was looking at the set screw or clamp style.  From what I read on this forum it sounds like the clamp style is the second most secure, behind the pinned style because there's more surface area or something.  Also I like that you don't have to worry about dimpling in the correct spot.  After reading the replies here and watching some more videos I'm thinking I'll just grind the rail off mine until it fits under the Aero rail.  That way I don't have the factory pin holes exposed and I'll have a pinned gas block again, and I won't have a gas block sitting around for the rest of my life that I'm never going to use again.

Looks like it's between 3/16" and 1/4" from the shoulder where the gas block would butt up to.  I updated the OP with pics of the barrel.  Here's what it looked like with the handguard and gas block installed factory:

Windham Weaponry

I remembered when I bought the rifle there was something different with the front rail gas block and I had to get a special front sight.  Now I remember most ARs supposedly have a front gas block rail lower than the upper rail but the SRC has the same height.  Thank God, because I spent a crapload on Troy irons.  Looks like that should work fine if I can get the Aero rail installed.

Yeah, I hate to do that, but I did see a couple vids doing that.  I'll have to take a closer look at it tomorrow, but basically you'd just be grinding down the rail.  On the other hand, my gas tube is currently stuck in the gas block, so may not be a bad idea just to grind it and use it.  I saw one guy chuck it in a drill and it came right out and all the comments said it worked for them too.  Seems like a quick way to bend up the gas tube, but looks like it works.  I put a little oil around it to soak in for a couple days.

It's certainly doable with hand tools if you have the skills.

I was thinking more along the lines of having a machinist or gunsmith put it in a vise and mill the top and sides around the gas tube.  Regular end mill for the top, ball nose end mill for the sides, and touch up the top around the gas tube with an OD radius cutter. Should be easy to do for anyone competent.  You could reach out to John Thomas at retroarmsworks and see if he would do it for you.

Another option here: https://shop.windhamweaponry.com/product/gb-lopro-2u/

The front set screw on that gas block shouldn't interfere with with your existing taper pin holes.

Oh cool, I didn't even think to look on Windham's site.  I found a couple clamp style adjustable gas blocks on gunbroker for around $26-35, but when I asked one of the sellers where it was made and what kind of finish it has he replied "Earth.  Dark."  Guess that means it's made in China with poor tolerances and painted with Krylon or something.  Now I'm thinking you have the right idea with making my GB fit.  I want to do it myself because I'm trying to learn and I like doing these things myself.  I've done a couple AR builds but never dealt with this gas block problem.  I'm thinking I'll just grind the rail down on my bench grinder until it fits under the Aero rail, keeping it cool as I go, then grind off the sling part, and hit it with some high temp black paint.  I don't think you'll be able to see the top very much anyway under the rail.

I would recommend using a hacksaw with a sharp blade to remove as much material as possible.  Do one side first so you can measure off the uncut side to keep everything straight.

If you have them, use some bastard files to finish the roughing then some finer files for finishing.

If all you have is a grinder then stop and cool the part when it starts turning color.

I've got all the tools.  I figured there wasn't too much to take off, but maybe there is.  What about the paint/blue?  I've used engine paint a few times on dirt bike heat shields on the exhaust and they're still holding up fine after several years and all I did was sand down the metal and painted, no priming.  I have a couple containers of Birchwood Casey bluing also.

Sealing the surface with temp resistant paint would be better than bluing IMO.  If the engine paint works for you then do that.

Well that was a chore, but I got er done.  First thing I had to do was remove the stuck gas tube from the gas block.  I had put gun oil on it for a couple days to soak in and that worked great, came right out.  The Aero handguard is pretty slim and required grinding pretty close to the gas tube hole to fit the gas block under it.  Took about 2 hours of hacksawing off the top rail and sling mount and grinding and sanding with a dremel, bench grinder, and sandpaper and test fitting.  I filled the holes with aluminum foil and only got a little overspray inside the barrel rings.  I painted it with two coats of Duplo engine paint.  Looked great, then I did a test fit and it got stuck on the barrel because of the little bit of overspray.  I tried tapping it off with a mallet and chipped some paint off around the gas tube hole.  That sucked.  I ended up putting a piece of wood across the muzzle and a flat file wrapped in a shop towel behind the gas block and used two ratcheting quick clamps on each side of the file/wood to break it loose and ended up putting up a couple scrapes on the barrel near the gas block.  Sanded inside the rings and it went on without a hitch.  Other than that it all worked.  Looks a lot better if I do say so myself.  Now I can finally add some stuff, and have my sights anywhere.

Here's what it looked like before (random google image of same rifle):
https://cdn.imgchest.com/files/dmyd5cmv64b.jpg

Here's what the gas block looked like (random google image):
https://cdn.imgchest.com/files/o3yrgc9ll4z.jpg

After I modified and painted (sorry for the crappy phone pics):
https://cdn.imgchest.com/files/dmyd5cmvg4b.jpg
https://cdn.imgchest.com/files/o3yrgc9lj4z.jpg
https://cdn.imgchest.com/files/xl7lxcxmq7o.jpg
https://cdn.imgchest.com/files/w84jdc6do4k.jpg

Finished with ATLAS handguard:
https://cdn.imgchest.com/files/6pyq9cvrj42.jpg

You done good, Grasshopper!