A2 front sight installation

tavares86

tavares86

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Alright, so I just learned with my first AR build that I can't just take any A2 sight and mount it on any barrel.
Norinco barrel and Norinco sight, bought both off two different people. I guess my only option if I want to use this barrel with an A2 sight is to use a bolt on type?
Anyone know of any Canadian suppliers that have these, or is Brownells my only choice?
Thanks.
 
When you say "A2 sight" I'm assuming you are referring to an actual standard original AR gas block sight?
The Norinco carbine barrels have a 0.75" gas block mounting area diameter.
Any gas block/font sight base with a 0.75" diameter mounting brackets will fit the Norc barrel (depending on the type of barrel I'm assuming it's not a Norinco old school rifle with a a pencil barrel)
 
Yes, that's right, I am referring to the original gas block triangular looking sight. I had the sight as far back as it could possibly go against the barrel, right tight against the hand guard cap.
And looking at the holes on the sight for the taper pins, they were way off from the grooves on the bottom of the barrel. Not possible to put in the pins.
This barrel isn't a pencil barrel.
I read that each FSB is drilled while it's on it's original barrel, and that's hard to match one up on another barrel.
 
tavares86 said:
Yes, that's right, I am referring to the original gas block triangular looking sight. I had the sight as far back as it could possibly go against the barrel, right tight against the hand guard cap.
And looking at the holes on the sight for the taper pins, they were way off from the grooves on the bottom of the barrel. Not possible to put in the pins.
This barrel isn't a pencil barrel.
I read that each FSB is drilled while it's on it's original barrel, and that's hard to match one up on another barrel.
Click to expand...

Yeah thats true. normally FSB are drilled while on that barrel. I know friend gave me an upper to rebarrel, the barrel that was shot out the FSB for that wouldnt lined up with the new barrel.

If the slots are crooked aint much you can do to straighten the FSB w/o going with a clamp on gas block route.
 
Hmm.
Well then you are pretty much stumped for now.
There's a few options though. The easiest would definitely get a clamp on set screw gas block in 0.75" diameter.
I see them all over google, however they all seem to be in the US. You would have to find one willing to ship to Canada.
The other issue you may run into (I know this from a friend who used a Norc barrel and put a low profile North American gas block on it) is that the gas hole did not line up with the hole in the gas block!
He had to actually get the shoulder on the barrel (where the hand gaurd cap sits against) milled back ever so slightly so that the hole in the barrel lined up with the one in the gas block.
Now if the issue with yours is that the gas block sits too far forward (towards the muzzle) you could get the barrel shoulder trimmed back so the gas block taper pin holes line up with the barrel taper pin holes.
If you know a competent machinist or a gun smith who isn't a rip off, you may be able to get that done very easily/cheaply.
Just be aware that if you get a clamp on gas block you may encounter that problem anyway. Not saying it will happen but it could, I've seen it personally with a Norc barrel.
Hope any of that made sense or helped you out at all Sir.
 
Thanks for the help guys. I'm going to order the fsb from wolverine and hope that the hole for the gas block lines up. If not I guess I'll have to have it milled, unless it'll wind up being cheaper just being a new barrel.
 
Before I spent $$ on an armalite fsb for a Norc build, I would just install the one you have with loctite bushing adhesive.

That's how bushmaster does their DCM target rifles. Mine never fell off in a couple thousand rounds, I took it off with a heat gun to fool with the float tube and reinstalled it with green loctite and it hasnt moved in another thousand or so.
 
Out of curiosity Sir, can you slide the gas block on with the hand guard cap and take a close up macro picture of the holes out of alignment?
Post it to here, I can take a look at it and show it to a very knowledgeable friend who works technically with the AR15 design almost on a daily basis.
It would help greatly to assess what the issue might be.
 
rgv said:
Before I spent $$ on an armalite fsb for a Norc build, I would just install the one you have with loctite bushing adhesive.

That's how bushmaster does their DCM target rifles. Mine never fell off in a couple thousand rounds, I took it off with a heat gun to fool with the float tube and reinstalled it with green loctite and it hasnt moved in another thousand or so.
Click to expand...

It's held on with just loctite eh? I'll likely go with this method. Thanks.
 
Travis Bickle said:
Out of curiosity Sir, can you slide the gas block on with the hand guard cap and take a close up macro picture of the holes out of alignment?
Post it to here, I can take a look at it and show it to a very knowledgeable friend who works technically with the AR15 design almost on a daily basis.
It would help greatly to assess what the issue might be.
Click to expand...

I will do this when I get home. Thank you.
 
Alternately, just tap the holes used for the pin, and put some set screws in there - I think 8-32 did the job if I recall correctly. Took being pretty bored one evening and a few minutes of work.
 
Pictures as promised.

20150312_050322.jpg

20150312_050333.jpg
 
tavares86 said:
Pictures as promised.

20150312_050322.jpg

20150312_050333.jpg
Click to expand...

No that's way more than a little tap to get it settled.
If it's that far forward, I would be wondering how far off the gas hole in the barrel is from the gas hole in the gas block.
You have to think looking at the pic, if it's that far off, the two gas holes are probably misaligned the same amount as the taper pins.
You could have issues with the rifle having enough gas pressure to cycle properly especially with a very short barrel like that will have very little "dwell time" of pressure to cycle it properly. Then you would be right back to square one with a glued on gas block or expensive clamp on type and you would still have to get the barrel shoulder milled back to line up the holes.
The reason the taper pins and holes are on the barrel is to make sure the gas block is indexed properly for sight alignment as well as gas hole alignment.

If you have calipers you take some measurements from the handguard cap to the center of the gas hole on the barrel as precise as possible.
Then measure the distance from the area where the gas block would contact the handguard cap to the center of the gas hole in the gas block. If they line up/if the measurement says they are lined right up then proceed with glueing, set screws etc to simply hold it in place.
But looking at the pics I'm going to assume that when you measure, you're going to find that the holes aren't going to match up.
Take the advice how you want Sir, but if that was my rifle, I would get the shoulder milled back the same distance you would need to make those holes line up, that would mean to me that the gas hole is then in line with the hole in the gas block. Most of the clamp on sights seem to run $100 or plus that I can find, would probably cost the same or less to get 0.19" or so shaved back on the barrel shoulder by a half competent machine shop to make the taper pin holes and gas holes line up perfect.
Then you could simply hammer in the taper pins and good to go!
 
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Travis Bickle said:
No that's way more than a little tap to get it settled.
If it's that far forward, I would be wondering how far off the gas hole in the barrel is from the gas hole in the gas block.
You have to think looking at the pic, if it's that far off, the two gas holes are probably misaligned the same amount as the taper pins.
You could have issues with the rifle having enough gas pressure to cycle properly especially with a very short barrel like that will have very little "dwell time" of pressure to cycle it properly. Then you would be right back to square one with a glued on gas block or expensive clamp on type and you would still have to get the barrel shoulder milled back to line up the holes.
The reason the taper pins and holes are on the barrel is to make sure the gas block is indexed properly for sight alignment as well as gas hole alignment.

If you have calipers you take some measurements from the handguard cap to the center of the gas hole on the barrel as precise as possible.
Then measure the distance from the area where the gas block would contact the handguard cap to the center of the gas hole in the gas block. If they line up/if the measurement says they are lined right up then proceed with glueing, set screws etc to simply hold it in place.
But looking at the pics I'm going to assume that when you measure, you're going to find that the holes aren't going to match up.
Take the advice how you want Sir, but if that was my rifle, I would get the shoulder milled back the same distance you would need to make those holes line up, that would mean to me that the gas hole is then in line with the hole in the gas block. Most of the clamp on sights seem to run $100 or plus that I can find, would probably cost the same or less to get 0.19" or so shaved back on the barrel shoulder by a half competent machine shop to make the taper pin holes and gas holes line up perfect.
Then you could simply hammer in the taper pins and good to go!
Click to expand...

The gas hole in the fsb is drilled through the rear band from the bottom. All you need to do is hold them side by each in relative position and it will be clear to see. I'm fact you can stick it on upside down and see where the holes line up.

You don't need to measure anything.

In addition the hole in the fsb is far larger than the barrels gas port anyways and a bit of fore-aft variance won't affect gas flow.
 
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rgv said:
The gas hole in the fsb is drilled through the rear band from the bottom. All you need to do is hold them side by each in relative position and it will be clear to see. I'm fact you can stick it on upside down and see where the holes line up.

You don't need to measure anything.

In addition the hole in the fsb is far larger than the barrels gas port anyways and a bit of fore-aft variance won't affect gas flow.
Click to expand...

Good point, never though of putting it on upside down vice measuring.
Regardless. I've got a bad track record of doing things the long way lol
It seems to be much more than "a little off" though.
I have no other advice aside from that. I'm out!
 
With the gas block in place, just rotate the gas block 180° and see if the gas port on the barrel can be seen through the hole in the A2 block. If the gas port is visible and all's good, you are good to go.

To test, hold the gas block in place, plug the barrel extension end with either the palm of your hand or paper towel etc then blow into the muzzle end of the barrel and check to see if you can feel air coming out of the gas block/tube.
 
Good ideas with checking the gas port alignment. I didn't think of mounting the fsb upside down, but I did put it beside the barrel, by eye it looked pretty close. But I will try mounting it upside down to be sure.
Thanks for the help everyone.
 
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