Lengthening barrel pin holes on Kibler SMR

[RocketMan58]

Working on my SMR kit and see that I'm supposed to oblong the barrel retaining pin holes a bit to relive stress as the barrel expands as it gets hot /cold. So my question to those with long gun building experience is, how and how much do you oblong those hole to allow for this longitudinal expansion. Jim's YouTube video shows him using a jewelers saw to complete this task but I'm not having much luck with this method. I'm thinking that maybe I should drill an additional hole offset to the rear of the existing one then connect them with the saw. .... I'm also thinking it shouldn't take more than a 1/16"" or so to accomplish the task but am not sure. Any advice/help from those in the know is greatly appreciated!

 

[wiscoaster]

No, you don't need to drill any more holes. That's overkill. Elongating the pin hole just a tad wider than the width of the jeweler's saw blade itself is sufficient. I found it was easier to use the jeweler's saw blade to elongate the holes if I just grasped the blade itself with my fingers and sawed without the saw frame. Mounting the blade in the frame and through the pin hole is a bit of a nuisance. If you have a pointed round diamond needle file you can use that to dress out the ends of the slot.

 

[RocketMan58]

Thank you Sir! BTW,, I did do a search on this topic before posting but came up MT. Then just now , I found this older thread in the list of Similar threads section below. I think I have what i need now.
Tight Groups,
Dave

 

[Hatchet-Jack]

I find using a jewelers saw like Jim does very tricky. My teacher taught me to drill a hole left and right of the pin hole so you have three then using a small jewelers file to remove the metal between and clean it up. This apparently is a pretty common way to go about it. Whatever you do don't be tempted to use a Dremel tool. That's a quick way to ruin your underlug.

 

[Hatchet-Jack]

 

[stubshaft]

That's how I've done mine for years.

 

[wiscoaster]

That's how I've done mine for years.

I don't quite frankly think that much elongation is necessary. I recommend following Jim Kibler's methods and advice.

 

[Hatchet-Jack]

I watched Jim cut the lugs on a SMR in person at the 2021 CLA. He cut them about the same length.

 

[Hatchet-Jack]

In Jim Kibler's video on assembling a SMR he elongates a slot to an oblong shape then finishes expanding it so the pin will slide freely with a small file. He says to make the slots progressively longer up the muzzle because you will get more expansion the further you go up the muzzle.

This starts approximately at 30:23

 

[waksupi]

Lots of overkill going on. I doubt a properly built rifle will ever recoil even .030 at most against the pins. The recoil should be at the breech. Only the front would need relieving, as that is where any recoil would work upon. I drill my holes, then use an old drill bit to worry a bit of metal from the front.

 

[wiscoaster]

Lots of overkill going on.

I agree.

 

[bptactical]

I agree with the agreements.
The barrel is only going to expand/contract a few thousandths, I’d be surprised if it was .015. Just a little elongation of the hole should be sufficient.
When you consider a 100’ bridge girder expands/contracts about 1” over its length from one extreme to the other a few thousandths on a barrel is plenty.

 

[2 shots]

if a barrel moves .030 theres a big problem. the pins should not take any recoil.

 

[Mgbruch]

I've learned it's' not the barrel, but the wood, that expands and contracts. Moister and temperature are always going to effect wood.

 

[RocketMan58]

Thanks to all that replied. After some experimentation I ended up using a spiral jewelers saw blade to get them elongated. I lengthened the front hole by about a good pins width. The others (progressing towards the breech) slightly less. I'm thinking that should give me the stress relief I need without overdoing it.

 

[wiscoaster]

Thanks to all that replied. After some experimentation I ended up using a spiral jewelers saw blade to get them elongated.....

Yes, nicely done!!

 

[waksupi]

I've learned it's' not the barrel, but the wood, that expands and contracts. Moister and temperature are always going to effect wood.

Which can be taken care of by a bit of wood removal.

 

[Rebel bull]

Which can be taken care of by a bit of wood removal.

I believe that if you seal all of the wood you won't get the expansion and movement I finish all of the wood on my builds and see no binding of the pins or expansion of the wood

 

[Larry (Omaha)]

Working on my SMR kit and see that I'm supposed to oblong the barrel retaining pin holes a bit to relive stress as the barrel expands as it gets hot /cold. So my question to those with long gun building experience is, how and how much do you oblong those hole to allow for this longitudinal expansion. Jim's YouTube video shows him using a jewelers saw to complete this task but I'm not having much luck with this method. I'm thinking that maybe I should drill an additional hole offset to the rear of the existing one then connect them with the saw. .... I'm also thinking it shouldn't take more than a 1/16"" or so to accomplish the task but am not sure. Any advice/help from those in the know is greatly appreciated!

You have a lot of good replies. I personally would not use a jewelers saw, just because it is not the easiest method for me. I would use a diamond impregnated dremel bit to open the hole on both sides. A dremel motor works the best, but a cordless dill will do for this small amount.
Larry

These can be purchased almost any decent hardware or tool store.

 

[tenngun]

I drill the hole 1/64 bigger and slightly bend the pins