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Posted: 12/31/2025 2:56:51 PM EDT
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This is an 11.5" barrel that had the gas block pinned with taper pin. Taper pin was partially installed upon receipt. Just a quick preface, I have removed installed multiple FSB's and dealt with their taper pins as well as low-profile gas blocks. In this case, I attempted the following: 1. Leaving pin in freezer for a couple days 2. Heating gas block w/ torch 3. Using quality steel punches and attempted install with 12oz hammer as well as 1.5lb mallet 4. Gas block was secured multiple iterations with Forward Control GBU, Generic urethane blocks 5. Even attempted a press contraption using vice. Nothing worked. This taper pin will get about 75% of the way and just hard stop, regardless of method. Gas block looks like hell from variety of methods and out of the dozens of taper pin low-profile gas blocks and FSB I've worked on, this is the only one I've had trouble with. MY QUESTION: To my eyes, the exit side of drilling has resulted in the barrel and gas block being misaligned. Wouldn't the force just cause the gas block to sit crooked once pin driven all the way through? Or is it so tight since the barrel doesn't line up with gas block that it physically won't allow pin to sit further in? 
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If available, have you tried either a different pin or gas block to rule out one that is maybe out of spec? Is it possible to maybe reshape the taper pin to work with the drilled hole? From the picture provided I can’t say definitive if it would cause the block to be mis aligned. From my experience it is a maybe. |
| I had one that would not seat evenly. I tried several things, like you did. Finally, I took my taper pin reamer and gave it a very light ream by hand, not drill. The pin settled in further. I did another iteration but stopped short to allow the pin to be driven in enough to be tight in the barrel and GB and pretty well centered. A little at a time was the plan to not over ream. It is hard to unream a taper pin hole. |
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There should not be enough clearance between the I.D. of the GB and the O.D. of the barrel journal to force the GB crooked with a taper pin. I would likely source another GB and start over personally. You may get lucky using a needle file to fit things enough to get it together but the end result likely will not be cosmetically pleasing. A taper reamer is another option. Amazon sells a decent offering. (Is the hole in the GB oblong? It appears so in your pic, but may be an optical illusion.) |
"All welchers should be removed from the EE".-Aimless
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Originally Posted By ducati650: I had one that would not seat evenly. I tried several things, like you did. Finally, I took my taper pin reamer and gave it a very light ream by hand, not drill. The pin settled in further. I did another iteration but stopped short to allow the pin to be driven in enough to be tight in the barrel and GB and pretty well centered. A little at a time was the plan to not over ream. It is hard to unream a taper pin hole. This is where I would start. Possible the hole got a burr or slightly peened and just needs to be cleaned up. |
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We cover how to fix this in our Advanced Armorer courses. Most front sight bases and gas blocks that are installed using a taper pin are first drilled with a 1/8" drill bit. Then a 2/0 taper pin reamer is then run through the hole to ream it out for the 2/0 taper pin to be installed. So in your case, have you tried to just install just the taper in into the gas block while it is off the barrel, to see if the taper pin will go through the gas block, as the holes in the gas block for pin would be slightly large on one side and smaller on the other? Another way to check things would be to install the gas block onto the barrel, then put a 1/8" roll pin though the pin hole to see if things line up, if they do and the pin is installed, check visually around where the roll pin sits in the hole on each side to see if there is any gap (space) showing that the hole is actually reamed out for a taper pin, or was it just drilled out straight across and not taper reamed. If it wasn't reamed out for the taper pin, you could just use a 1/8" roll pin. The other option as already mentioned is to ream it out to the correct dimensions with a 2/0 taper pin reamer to make it correct. Or send it back to the manufacturer or place you purchased it from and put it back into their hands is always a good option, as if their machining is off or wasn't done correctly, then let them fix or replace it. CY6 Greg Sullivan "Sully" WeaponsArmorer SLR15 Rifles TheDefensiveEdge.com (763) 712-0123 |
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Originally Posted By MJ11B4P: This is where I would start. Possible the hole got a burr or slightly peened and just needs to be cleaned up. This is what I think the situation was with mine. It took very little effort with a hand taper pin reamer to get mine where I wanted it. This was on a factory drilled and pinned DD barrel for my MK18 build. |
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Good on DD for dealing with the problem, Being that each FCB is drilled for the barrel is going on (not interchangeable between different barrels) ,and in the above case, that is not the FSB that was drilled/ taper reamed for that barrel. |
Posted By PlaymoreMinds:
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...
<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...
<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
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