I have a very early model Colt CAR-15, SP1 with a thin 16" barrel (circa 1976). I would like to get a three or four rail gas block for it, so I can mount a folding front sight. Can anyone tell me what the barrel diameter is and which gas block will fit?

I also have a Colt H-BAR upper that I would like to do the same thing to. What is the barrel diameter for this barrel and what gas block rail system would work?

Any help would be gretly appreciated.....

THX,

Mic

I'm thinking it is 0.625, but I don't know of any manufacturers who make a railed gas block with that diameter.  PRI makes a folding sight/gas block with the 0.625 diameter.

Thanks for the info. It looks like I will go with the YHM gas block and folding sights for the HBAR. As for the CAR-15, I am still looking. I may go with a solid, low profile gas block (if I can find one that fits the .625 barrel) and put a folding front sight on a railed hand guard. Failing that, I just may end up going with an M-4 or "Patrol" style barrel that is .750 under the gas block area and then go with the YHM gas block.

Thanks again for the info,

Mic

J & T Enterprises has 0.625  forged FSB available for around $30.00.
I just ordered one.

Is that J & T Distributing? I checked their site and did not find it. Do you have a model or part number? Does the one you bought have rails or is plain?

THX,

Mic

It is a FORGED FRONT SIGHT BASE just like a regular FSB but in 0.625 instead of 0.75 ...

I am looking for a .625 gas block without the front sight and preferably with rails on it. Failing that, I would like to find a .625 gas block with a folding front sight. I checked the J & T Distributing web site and can't seem to locate the one you mentioned. If you had a part number that would be helpful.

THX,

Mic

Quoted: Thanks for the info. It looks like I will go with the YHM gas block and folding sights for the HBAR. As for the CAR-15, I am still looking. I may go with a solid, low profile gas block (if I can find one that fits the .625 barrel) and put a folding front sight on a railed hand guard. Failing that, I just may end up going with an M-4 or "Patrol" style barrel that is .750 under the gas block area and then go with the YHM gas block. Thanks again for the info, Mic

That's the front sight/gas block that I'm  getting  on my new build. Once I'm sure that the sight is lined up ok and the gas port is large enough to work right(building a .300FB) I'm going to take out one set screw at a time and drill a slight indent for the set screw to screw into, that'll hold on the sight base better and stop it from twisting if it's bumped hard.  I should have my kit tomorrow, I'll let ya' know how it looks. Talk to ya' later.

TNFrank,

I would like to see a pic of your set up when you are done. I like the idea of drilling a set screw indent in the barrel. What type of drill bit would you need for that? I would imagine that barrels would be pretty difficult to drill into even a little bit.


Mic

Quoted: TNFrank, I would like to see a pic of your set up when you are done. I like the idea of drilling a set screw indent in the barrel. What type of drill bit would you need for that? I would imagine that barrels would be pretty difficult to drill into even a little bit. Mic

Actually the guy at Model 1 Sales said that the barrel is soft enough for the screws to cut into it and not allow the sight to move, still, just to be safe I'd like the indents for the screws to recess into. I'll try to post a pic tomorrow of the sight on the barrel, I'll remove the handguards to it'll show up better. Just hope that Hunt 101 isn't down so I can post the pic.  I kind of had second thoughts about getting the folding sight after I placed the order but they had my order out in less then 2 hrs. so by the time I called to change my mind it  was already on the UPS truck.  I'd like to put a low power scope on this set-up at a later date for hunting so it'll be nice not to have a front sight blocking my view thru the scope.  My main optics will be a Trijicon Reflex II with the 12.9MOA Triangle, I should have a nice view of the Triangle without the sight in the way as well. Talk to ya' later.

That sounds like you have the right way to go with your project. I put a Tasco Rubber Armored 3x9 (Delta style) on my HBAR flat top upper and I got a "Ghost image" of the front sight when I looked through the scope (very annoying). I ended up buying an A.R.M.S. mount for the carry handle and set up my scope that way. The lower receiver I have is an old SP-1, CAR-15, with the collapsible stock, so I also had to add a cheek piece to get my head up high enough to use the scope. It works pretty good now, but I would prefer to mount the scope lower on the gun.

As for my SP-1 Upper with the .625 diameter barrel, I  have a Rock River Arms flat top receiver coming and my idea is to put the .625 barrel on it with some sort of gas block that does not have the front sight. I plan on adding an EOTech sight to this upper and I did not want the front sight getting in the way. If all else fails on the gas block issue, I will end up getting an M-4 barrel for this project as they are .750 under the front sight and then the YHM railed gas block will fit.