Indexing pin loose

[mheimer_45]

While installing a brand new krieger I just received I noticed the indexing pin was loose. I’ve installed a lot of AR barrels but never had one with a loose indexing pin. I know the smith will take care of it.

But I guess I’m curious as to how most indexing pins are attached?

 

[kl3309]

Had a Kreiger do that 'bout 30 years ago. Good to see that they are as consistent as ever. See if your gunsmith can drive a slightly oversize, tapered pin in there. If you're really sweatin' it, have them green loktite the extension on and pin it (and measure your headspace).

 

[Yondering]

Had a Kreiger do that 'bout 30 years ago. Good to see that they are as consistent as ever. See if your gunsmith can drive a slightly oversize, tapered pin in there. If you're really sweatin' it, have them green loktite the extension on and pin it (and measure your headspace).

He doesn’t need to do anything to the extension; the pin doesn’t lock it to the barrel. All that’s needed is to Loctite the pin in place or drive another one in. You can make them from 1/8” drill rod, no big deal.

All that pin does is to locate the barrel extension in the receiver and keep it from rotating when you tighten the barrel nut. If you have another way of doing that you don’t even need the pin.

 

[kl3309]

He doesn’t need to do anything to the extension; the pin doesn’t lock it to the barrel. All that’s needed is to Loctite the pin in place or drive another one in. You can make them from 1/8” drill rod, no big deal.

All that pin does is to locate the barrel extension in the receiver and keep it from rotating when you tighten the barrel nut. If you have another way of doing that you don’t even need the pin.

OP didn't specify but my old Kreigers had threaded-on extensions and the pin locked it in place. With the pin loose or out, the barrel spun and/or flopped around in the extension.

Did your Kreiger AR barrels come with press-fit extensions?

 

[Yondering]

OP didn't specify but my old Kreigers had threaded-on extensions and the pin locked it in place. With the pin loose or out, the barrel spun and/or flopped around in the extension.

AR15 barrel extensions are always threaded on, but are usually installed with red loctite and torqued to 100-130 ft-lb. Obviously some do this differently than others, and some don't use loctite, etc, but if your barrel extension was loose because the pin came out, then the extension wasn't installed right to begin with. That's a much bigger problem than a loose indexing pin; the pin itself is no big deal but a loose extension is a major problem.

Generally speaking, the barrel itself isn't even drilled for that pin, it only goes into the extension. You'd have to drill through the hole in the extension into the barrel, and use an extra long pin to do it the way you describe.

 

[kl3309]

AR15 barrel extensions are always threaded on, but are usually installed with red loctite and torqued to 100-130 ft-lb. Obviously some do this differently than others, and some don't use loctite, etc, but if your barrel extension was loose because the pin came out, then the extension wasn't installed right to begin with. That's a much bigger problem than a loose indexing pin; the pin itself is no big deal but a loose extension is a major problem.

Generally speaking, the barrel itself isn't even drilled for that pin, it only goes into the extension. You'd have to drill through the hole in the extension into the barrel, and use an extra long pin to do it the way you describe.

Nope, the specific Kreiger I had this issue with was neither loktited nor was the extension torqued more than hand-tight, and the hole for the index pin was drilled right down into the shank.

 

[Constructor]

Nope, the specific Kreiger I had this issue with was neither loktited nor was the extension torqued more than hand-tight, and the hole for the index pin was drilled right down into the shank.

Whoever finished your Krieger blank screwed up.

 

[kl3309]

Whoever finished your Krieger blank screwed up.

Direct from Kreiger.

 

[Constructor]

I've been buying short chambered 223 DCM barrels from Krieger for almost 40 years. They have a little dimple on the barrel in front of the extension. The extension must be torqued to 150 ft lbs in order to line up with that dimple and the gas port. Since they are short chambered the extensions are not tight, there is no pin and they are not drilled into the threads. I don't know when Krieger started selling "finished" barrels.
If that barrel came straight from Krieger it must have been some morons first day. The gas ports are drilled between the lands before the chamber is finished or extension is installed so for it to not be tight and still line up with the gas port they would have had to face the shelf back to far.

 

[Yondering]

Nope, the specific Kreiger I had this issue with was neither loktited nor was the extension torqued more than hand-tight, and the hole for the index pin was drilled right down into the shank.

Then it definitely was not assembled right, in the normally accepted manner.

Barrels have to be torqued into barrel extensions the same way barrels have to be torqued into most bolt action receivers. There’s nothing else holding them in place. That’s definitely not the role of that little pin. It’s an indexing pin, not a retaining pin.

 

[kl3309]

Well, haven't heard anything back from the OP but maybe it was only a case where the indexing pin fell out. In my case, the pin was what was holding everything together and in alignment. I'd noticed that it was coming undone because the barrel had started to move up and down in the assembled upper. Whatever the cause (and because there was no indication that the extension had ever been torqued to a spec), the fix was to reassemble with green loktite and install a new pin.

 

[Yondering]

Sounds like a poor fix for a poor initial assembly. If it wasn’t torqued, it wasn’t right.

Sorry you got a bum barrel and didn’t have a good fix for it, but none of that accurately reflects how indexing pins work or what to do when they come loose. (Except as an example of what not to do I guess.) I sure hope the OP isn’t in the same boat or he’s got bigger problems.

 

[mheimer_45]

@Yondering is right. The pin is only drilled thru the extension. Not the barrel itself. Called the smith today and they said to locktite it in place and if that didn’t work to send it back. And you are correct again the extension didn’t come loose just the index pin. Btw this was a compass lake barrel on a vtor MUR receiver. Barrel nut was torqued at 32lbs. That’s when the PRI barrel nut lined up. Anymore than that and I was going to have to crank down hard.

 

[Yondering]

@Yondering is right. The pin is only drilled thru the extension. Not the barrel itself. Called the smith today and they said to locktite it in place and if that didn’t work to send it back. And you are correct again the extension didn’t come loose just the index pin. Btw this was a compass lake barrel on a vtor MUR receiver. Barrel nut was torqued at 32lbs. That’s when the PRI barrel nut lined up. Anymore than that and I was going to have to crank down hard.

Glad to hear you've got it figured out. Locktite should be all the pin needs, but if in doubt, just look at the alignment between your barrel extension and the M4 feed ramp grooves in the upper when it's all assembled (if your upper has those); as long as those are aligned you're good to go. Sounds like you've got the barrel nut figured out too.