AR barrel index pin??

[WestKentucky]

I’m putting together a new upper. Upper reciever is a BCA and the pin slot looks pretty narrow compared to what I’m used to. The barrel is an old carbine barrel that was laying around, and similarly the index pin looks a bit large. So tolerance stacking isn’t going my way right now because I believe both are likely in spec, just at the edge of spec. So how tight is too tight of a fit? Currently the barrel does not seat. The pin hits on the corners of the slot and it appears I have roughly 10-15 thousandths that need to be removed for a snug fit. Pic is terrible. I will try to get a pic with better lighting.

 

[someguy2800]

Is that a roll pin? If so that is your problem

 

[Charlie98]

Is that a roll pin? If so that is your problem

I wonder if someone sheared the pin… drilled it and substituted a roller?

 

[BreechFace]

Yeah there definitely shouldn’t be a roll pin there…

 

[NIGHTLORD40K]

Huh, yah never seen a roll pin used for that.....
You may be able to squeeze it slightly with needle-nose pliers as you slide it in, or a whack with a rubber mallet will probably drive it home too.
If those fail, maybe replace with a solid pin?

 

[WestKentucky]

That definitely looks like a roll pin. I didn’t even notice that. I don’t remember where I got this thing from but I know it was really cheap…like maybe I just paid shipping.

 

[12Bravo20]

I would say that Bubba made a repair to that barrel. One should not be using a roll pin for the indexing pin on an AR barrel.

 

[FL-NC]

There was a former AR company in Fatyetteville NC that was as shady as he could be- real unreliable junk. Soldiers from Ft Bragg were buying his kits and parts like crazy until they found out none of it worked. His barrels had roll pins like that.

 

[lysanderxiii]

Th index pin is 0.1255 -.0005" diameter.

The slot is 0.126 +.002" wide.

Slotted tubular spring pins are normally 0.131 to 0.135" diameter when free

 

[Robert]

I wonder if you could replace it with a proper index pin, or if the hole is hogged out now?

 

[12Bravo20]

I wonder if you could replace it with a proper index pin, or if the hole is hogged out now?

I would definitely pull the roll pin out and replace it with a precision ground dowel pin if it was me. That is the only way one will know if Bubba messed up the barrel. Note that even though dowel pin holes are finished with a precision ground reamer, a roll pin will normally fit in the reamed hole too.

 

[lysanderxiii]

I wonder if you could replace it with a proper index pin, or if the hole is hogged out now?

That would depend on how the original index pin was removed.

Roll pins will collapse down to under 0.1250", so there is a chance the hole is okay.

Just be very careful removing the existing pin.

 

[BreechFace]

Does the index pin hole and gas port hole even line up? That would be something one needs to confirm before spending much time working in it.

 

[someguy2800]

You sould be able to get a .125" pin at Ace Hardware.