Rear Taper Pin Barely Penetrates Edge of Barrel. Is that a problem?

AR/M4 AR Technical Discussion
1

Recently, I decided to customize an upper I’ve had as a spare. In anticipation of shaving or replacing the front sight base, I removed it from the upper. After removing the FSB, I noticed that the rear taper pin barely penetrates the edge of the barrel:

In fact, there is a crack in the barrel along the axis of the taper pin.

Is that a problem? I am considering using a low-profile gas block that only uses the rear taper pin to hold it in place. Will that securely hold the taper pin?

Thanks for your thoughts on the matter.

2

Those taper pins are actually too deep.

They’re intended to be centered on the edge of the barrel.

A different gas block will generally not be able to reuse an existing pin hole.

Consider chopping down the FSB.

3

WYF? Never saw one like that before. Usually just tapered grooves on the barrel, not actually drilled into the barrel.

4

Why would you install a lo pro gas block on a barrel that already is drilled for taper pins?

Chop your FSB down and do it right.

5

Do what Clint said… Shave what you have. The odds of anything else lining up with what you have are slim to none.

6

Thanks for the information and suggestions. I will shave it and put the fsb back on!

7

Those are the deepest FSB taper pin holes I’ve ever seen. Are you sure they aren’t in the bore? Who made that barrel and/or installed that FSB? Just curious

8

There is just under 1/8" of clearance between the deeper pin hole and the bore. Is that acceptable?

Who made that barrel and/or installed that FSB? Just curious

Is it okay to mention that? I don’t want to violate site rules. I can say that it is a manufacturer that is very well-respected on this forum.

9

I’d imagine that 1/8” of clearance would be fine. I’m not sure if it violates site rules. I understand if you aren’t comfortable saying who made it.

Love your signature line, by the way

10

Wow…can’t say I’ve seen worse.

11

Agreed. Shaving the fsb is the best option as it’s already match drilled to the barrel. I’ve seen a few drilled like yours, OP. It should perform just fine.

12

Those are deep. Driving in a pin might cause a bulge in the bore. Contact the maker and see if they can help you out.

13

Old Bushmaster barrels were known for having taper pins drilled to deep just like on the OPs barrel.

This can’t be a Bushmaster barrel though because it’s finished under the FSB.