I bought a Interarms 458 Win Mag at an auction. I wasn't happy with the recoil pad so I took the action out of the stock to fit a new pad.

What I found when I removed the action was that someone had installed a CZ 550 style recoil lug forward of the receiver directly into the barrel. Now the lug was attached with a screw and fricking epoxy so that got me a mite bit concerned that Bubba has had his way with my rifle.

I removed the lug to check the depth of the hole and how much barrel steel was left between the chamber and this unintentional potential gas port.

The barrel is 1.110" thick at the location of the hole. The depth of the slot is 0.093" and the threaded hole is 0.042" which gives a total penetration of 0.135". The barrel diameter (1.110") minus the bore dimension (0.458") x 0.5 minus depth of hole (0.135") which is ((1.11 -.458) * 0.5) - .135) gives the barrel thickness remaining of 0.191".

Now the hole is at 3.500" from the bolt face which puts it vey close to the throat and peak pressure at ignition. The question is there enough steel at the chamber in a 62kpsi cartridge?

My gut feeling is that holes in barrels near the chamber are bad, and I bought myself a rather expensive action needing a new barrel.

Thoughts?

I believe many of those lugs were done at the factory. Mostly on later versions. I take it this is a Mark X with the Interarms stamp on it?

I have seen one from Manchester (no inter arms stamp) that did not have the lug, but think they were added later.


Edit: sorry - I see you mention interarms above now.

Don't understand your math or your formula for using a case wall thickness. You do not have half inch (.517) of steel over your bore.
Here is what I see; Your barrel wall over the bore is .321.
If you drill a .092 hole into it, you are left with .186 of steel left over the bore.
Plenty, and don't worry about it.
For reference, look at a Ruger #1 barrel; rib holes are over the chamber and have very little wall thickness left.

Yes...it does have an Interarms stamp on the receiver.

It was the epoxy that threw me. I would have though it would be silver soldered on and the lug itself would have a radius that matched the barrel. This lug is a square of steel with epoxy filling the gaps between the barrel radius and the flat of the lug.

Yes, my math was wrong. I was being dense. That said how do you get the barrel small of .321"?

I thought the following for a .458 Win Mag:
Bore = .450"
Groove = .458"

Given that it would be barrel diameter - groove dimension x 0.5 and in this case (1.11" - 0.458") * 0.5 = .326"

Then subtract the 0.135" of the hole leaves 0.191"

quote:

Originally posted by webfeet:

My MK10 has the same lug and 200+ 400g rounds I have put through it not an issue. YMMV

Does your lug look like this? My other Mark X did not have a secondary lug. I have heard some have them but I have not seen one. If it was factory work then I am not going to worry about it.

The rifle was getting a replacement Bell and Carlson stock. The stock has the aluminum bedding block, but I don't think it has the recoil lug cut out.

Is that regular recoil lug slot big enough with a bedding block or should I replace/reattach the lug and then open and glass-bed the stock for the lug?

Does anyone know if the synthetic stocked CZ 550 big bores have secondary recoil lugs on them? All of my wood stocked 550s do from 9.3x62 up to 458 WM, but I haven't owned a synthetic stocked 550.

and thanks for the replies.

Because I just used 1.1 for your barrel OD in my math.
The word, Small, was supposed to be Wall. Barrel wall thickness. I was in a hurry.
I would solder the lug back on, better yet, I would cut a dovetail in it and fit a new one. No screw.

I like the idea of the dovetail and solder rather than the screw and epoxy. I don't know...it seems somehow more professional.

I'll mill a new lug out of some stock that will actually get it to fit the barrel contour then I'll pull the barrel and solder it on. Finally I'll mill a slot in the barrel channel for the lug and then bed it with Devcon.

Thanks for your help everyone. I just saw what they did and it looked sketchy to me. I figured that I needed to check it was still safe.

Actually if you dovetail it, you won't need the solder.

And JB Weld the screw hole full?

I'd use old chewing gum.

quote:

Originally posted by webfeet:
This lug is a square of steel with epoxy filling the gaps between the *barrel radius* and the flat of the lug.

Maybe it’s the lighting in the photo, but it looks to me like a flat spot for the lug was milled or filed into the barrel…

quote:

Originally posted by montea6b:

quote:

Originally posted by webfeet:
This lug is a square of steel with epoxy filling the gaps between the *barrel radius* and the flat of the lug.

Maybe it’s the lighting in the photo, but it looks to me like a flat spot for the lug was milled or filed into the barrel…

There is a flat spot on the barrel for the lug. Don't know if it was milled, filed, or both. I imagine both given the cut and finished surfaces. I had the dimensions for the cut and the drill hole / tapped hole depth in my math. I will deepen the flat spot to a dovetail and reattach the lug.

With the original design the lug should fit into the shoulder of the flat spot so the shoulder takes the sheer force of the recoil. I see now that was how it was designed although I don't think they removed enough for the shoulder. The epoxy they used was to support the sides not so much to resist the sheer forces generated by recoil.

I do realize that I Bubba'd my own rifle in removing the recoil lug, but I also knew it was nothing that I could not fix doing it. I can tighten a 8-32 thread machine screw and apply two part epoxy with the best of them. Hardly a stretch...but I was kind of concerned with a unknown depth hole in the barrel right over the throat of the barrel.

All I know is epoxy does NOT stick well to smooth metals no matter what flavor. The more abraided the surface (within reason) the better. Also, all oils, waxes, etc need to be absent. Probably picking the surfaces with a very small diameter drill would help, increasing surface area and shear even though epoxy is not that great in shear. I don't think I'd go the trouble of making a dovetail fit. How will you do that anyway? If I understand, you have a slot that a lug fits to. Seems to me you have to make a new lug if you now have a different (dovetail) slot? Relying on epoxy to make the male part of the dovetail is useless, IMO.

The epoxy was just to keep the lug and screw from vibrating loose and has nothing to do with the function of the lug. It sits into a slot in the barrel. Anyway, I think I read that you will DT a new lug in, in which case you do not need any adhesive or solder of any kind.

Thank you for clarifying the purpose of the epoxy and screw.

The original job just looked crappy to me and it threw me. I didn't expect epoxy attachment on metal to be factory work.

I will make a new lug with a male dovetail profile and female dovetail the barrel with a dovetail cutter for an interference fit with the lug features. I won't solder them together.

Then I will re-bed the lug as the original has tapered sections front to rear and up and down. Matching those tapers exactly to fit with the new lug will take longer than re-bedding.

I wouldn't worry about the exact shape; you are going to re-bed it anyway, and it only needs to bear on the rear surface. In fact, I put tape on the front and sides; otherwise it is hard to remove from the stock.
I use Paste wax for release agent.

I just realized why they might not have used a dovetail joint. In creating a dovetail and then bedding it, they would create the possibility of bedding compound seeping above the dovetail and creating a mechanical joint so the stock and action are fixed in position.

I will just deepen the slot and screw hole slightly and use it like that. If the slot is an interference fit with the lug and the screw just holds it in position, there should be plenty of resistance to sheer.

The epoxy from the factory may have not been for adhesion of the lug to barrel at all. It may be there to prevent bedding compound from creating a mechanical lock much as how I explained the dovetail might. Now if they had created a lug that fit the barrel contour they would not have needed to do that, but they didn't.

Nope; you use modeling clay in the DT joint to prevent it from being locked in; just like you do in any bedding job.
Stick with your original idea. Or you can deepen the slot. But if there is a part of the lug that creates a locking surface, then use clay to prevent bedding from getting above it anyway.
That was not their reason to use adhesive on it in the first place though.

Makes sense. I have used that blue stuff you stick up photos or posters on a wall to fill holes when bedding. Modeling clay probably works better because it hardens, but you can still remove it afterwards. The blue stuff stays soft.

I deepened the slot and the screw hole 0.015" on the mill and tapped the hole again. The fit was pretty good and there was no movement back or forward in line of the recoil force without the screw in it. I then put the screw in with a dab blue Locktite on the screw to hold it in place and torqued to 20 inch pounds.

I think I am just going to shoot it and see what happens. I don't think the lug is going anywhere with that ledge cut into the barrel. If the screw gets loose I will address it further. The worst case is that I put the dovetail in it after all.

The main gain from this exercise is that I feel safe about the rifle at this point. I didn't when I started. I really appreciate all the tips and advice. Thank you all!