AR Pinned Gas Block Replacement If Barrel Already Pinned

[Sanch]

Suppose I source an AR barrel that comes with a pinned gas block from the factory. And I want to replace the gas block. The factory drilled the barrel to secure the pin relative to the included gas block. My assumption would be replacing the gas block might result in needing to re-drill the barrel to line the new gas block up properly. And may be impossible if the new gas block needs to be to slightly shifted that you can’t really drill a new “hole” /dimple ‘ groove into the barrel without elongating the existing one.

Or are all pinned gas blocks specced the same so that the hole for the pin always matches up with the opposite side hole for the gas in such a way that you can pop the pin on the old gas block, get any other brand gas block, slide it in, and be repinned without drilling?

Also, what’s the name for this groove in the barrel that gets drilled out, where the pin fits through?

Is there a generic name in machinist lingo for the resultant “hole” / groove that results when drilling along the edge of a material like the barrel to secure something with pins? Wondering if the name aligns with the name in gunsmithing or differs.

Thanks in advance fellas.

[rob_s]

Drilled and pinned gas blocks are not typically interchangeable. The holes are supposed to be drilled with the GB in place, and the taper line inserted to pull down on the GB against the top of the barrel to help make the seal.

Not sure what the particular circumstances are here, but if you have an old-school pinned gas block that looks like a cut down FSB with two pins (or, for that matter, an actual FSB) you could theoretically replace it with a low-profile GB that has a single continuous point of contact with the barrel and have a new hole drilled.

However, if I had a fixed FSB and I wanted a low-profile gas block I would, and have in the last, cut it down. I’ve done this with thenGB in place on the barrel (carefully) and with it removed (less careful, more pain in the ass to remove a good FSB).

[HeavyDuty]

What Rob said, with the possible additional option of replacing it with one that uses set screws if they line up properly. But cutting down the original is the way I’d go.