Effect of non-concentric OD w/ bore on shooting

[Milsurp Junkie]

Hey guys, I just got a MN 91/30 that was semi-bubba'd.

Anyways, the 91/30 was a 1943 in the middle of WWII and it shows. The finish work of the metal was definitely the last things on the minds of the Russians at that point. The bore looks pretty good, and the s/ns match on the receiver, bolt, and magazine floor plate. The prior owner cut off the barrel ~4" and re-crowned it. I did notice that the bore is definitely non concentric w/ the OD of the barrel.

My question is what effect that would have with shooting?

My original thought is that the muzzle blast is going to exert an uneven force on the bullet upon exit. As long as the effect is constant, this should be still useable.

My secondary thought is that the groups will more than likely move a lot as the barrel heats up, due to the different thickness of metal are going to expand differently. If this is a hunting rifle, again not a problem.

Obviously, I need to shoot the rifle to see.

Is there anything else I could try to fix the issue (cutting the barrel back more, and re-crowning to see if it is more concentric further back)? In order to fix it right, I guess it would require me to pull the barrel off and lathe it concentric (cost prohibitive).

If there is nothing I can do, I am okay with it as I bought the rifle mainly for the Boyd's Walnut stock it came with. And it is always good to have spare parts...

[Multigunner]

I once ran across a 91 Argentine Mauser carbine that had been rebarreled at some point with a long rifle barrel cut and turned to match the original barrel.
The bore was so far off center at the muzzle that it almost came through the barrel wall.

I've been told that Mauser did not straighten barrel blanks or finished barrels, so long as the bore was centered at the muzzle when it left the factory some bore wander was to be expected,and that the stepped barrel was in part intended to reduce the effect of unequal expansion of the barrel walls.

The British and the U S took much greater pains in making sure the bore didn't wander, and in straightening the barrel if there was even the slightest irregularity.
Later on the British dropped the labor intensive barrel straightening process, deciding that so long as the last six inches of bore was straight accuracy would be adequate.

Only way you'll know how much if any the accuracy is affected is to try it on paper.

[303Guy]

I suspect not many bores are concentric to the OD. I've fitted a few silencers and what a job simply because the OD runs out.

[Milsurp Junkie]

Looking down the bore, the rifle appears straight. It just does not follow in the center of the barrel. Which is unfortunate, because the bore looks great. I will try it this weekend or so and see how it does when fired cold, and fired warm. If it just doesn't shoot, then the action may be become a donor of something else. Does anyone know whether a 7.62x54r chamber reamer would work on a 308 chamber? Obviously, the pilot would have to be .308" as opposed to .310".

[Multigunner]

If you plan on rebarreling this action, I'd look into the various wildcat cartridges the Finns developed based on the 7.62X54r case.

I have a book here somewhere with information on these hunting cartridges. The 9mmX54r looks very promising, especially for cast boolit shooting.

A 7.62X54r with a .308 bore is not a bad idea, and the milspec 7.62 russian bullets appear to be designed to work fairly well in both undersized and over sized bores.
Articles from Finnland have told of Mosin Nagants being found to have bores as tight as .306 to a high of .316, which is likely why the Finns put so much effort into establishing their own tolerance standards and optimum bore size for replacement barrels.
They also developed a fine match grade bullet of .309 dia for use with both 7.62x54r and .308 bore western manufacture .30 caliber rifles such as 7.62x51 and .30-06 and the many .30 or .300 magnum rifles.

If Finn manufacture replacement barrels can be found, thats probably the overall best route to take.
I've seen MN replacement boltheads for sale at gunshows in the past, so it may be possible to tighten up headspace if necessary if a properly sized bolthead can be found. The MN bolthead unlike the LE bolthead bears the locking lugs, so a new bolt body by itself would have no effect on headspace.

If you chose to go whole hog on this, theres an alteration of the bolt body and receiver that sets the bolt handle to the rear of the bolt, to allow mounting receiver sights and simplify over bore scope mounting.

PS
Its possible to trim the outside of the barrel till concentric by hand filing, but its not easy.

[Milsurp Junkie]

Yeah, a 9mmx54r would be nice, but I would need to find a reamer and dies for it.
That is why I was looking at some of the 308 chambered heavy barrel blanks. I need to look over the cartridge dimensions, but I think that a 7.62x54r reamer would clean up the 308 chamber. Then it would be a matter of threading it to 1" 16TPI, threading it into the action, marking the extractor cutouts and be done with it. I have found some fairly inexpensive 357 magnum blanks ($80), but the 308 barrel is $36...

[Milsurp Junkie]

I have also found some interesting posts on sleaving the bolthead down to .473" with rings soft=soldered or epoxied in. They then move the extractor back a bit by inserting a shim in between the extractor and the bolthead. This was done on the bannerman 30-06 conversion as well as the Bindee 8mm conversion. Obviously I would want a new barrel/chamber and not try to make the existing barrel work...Which was the issue with the Bannerman conversions.

[Milsurp Junkie]

Multigunner, can you describe the hand filing procedure? Can it be done with the barrel still attached to the action?

[303Guy]

You know, Milsurp Junkie, it's not that difficult to skim the OD of the barrel to even it out. I've done it to 22 and although for me it was slow, the end result was great. (It was slow because I had to manually control the contour). The barrel ends up slimmer but the finish is a nice as one cares to make it.

[bob208]

the bore being off center will not effect the shooting at all. i have a muzzleloader that the bore is way off center but it is stright. i have won many matches with it.

the way i would get the bore and the out side on center would be to hold it between centers in a lathe and take a cut. but then the barrel mite get too thin and whippy.

[Milsurp Junkie]

I will have to measure it this weekend. It is noticeable in the daylight. Unfortunately, I picked it up at night.
I will also load it up and see how it shoots. Unfortunately, I need to drill out a set screw and knock out the pin in the rear sight mount. To mount my scout scope on.
As I said worst case scenario, is that I broke even with the stock, and have extra parts if needed. I also have an action that I would not feel bad about converting into something else for a later project.

[303Guy]

This may be a different kettle of fish altogether but I picked up this rusted bore two-groove No4 specifically to cut down and make my pig gun. I decided to first see just how it shoots first and did a bit of fire-lapping and re-crowning, taking off about ½ inch. It turned out to be so accurate I picked another gun for the pig gun project. (Now that one was rusted!) Yours might turn out the same - scary accurate. But don't blame the barrel too quickly - it could be the bedding or something.

If you do consider profiling it you might want to do only the end bit and blend it in. Polishing hides the transition. That way you don't lose the existing barrel rigidity.

[Multigunner]

Multigunner, can you describe the hand filing procedure? Can it be done with the barrel still attached to the action?

Not really, hand filing would require that you eyeball at every step. Like whittling, you either have the natural skill or not.
Think of whittling a straight tapered pool cue or cane from a treebranch, then translate that into filing a gun barrel.
I've been hand crafting parts for half a century, so this sort of thing is fairly easy for me, but others might have a hard time with it.

If something looks straight it generally is straight enough, and as it is the barrel left the factory in worse shape than it would be if you gave filing it a go.

[Gtek]

Put the whole thing in Lathe and do run out check before you decide. Screwing up a Mosin is not going to be the end of the world. If barrel gets to thin in turning, cut back to 38/44 length- TA-DA carbine. Turn OD at muzzle for sight base re-install, Scout Scope set-up, where ever your brain takes you. Have Fun! Gtek

[leadman]

A MN in 308 would be almost just like the 30-40 Krag.
I bought a CVA muzzleloader kit in 1974 to make a Kentucky rifle. did not have much gun savvy at all then so didn't notice the hole was way off center at the muzzle. When I put it all together it shot about 10 feet to the left at 50 yards with the sight almost out of the dovetail.
Called CVA and the guy apoligized and said he would test fire one and send it to me. That barrel was a tackdriver.

If your MN shoots too far to one side just tweak the barrel a bit until it shoots good.
I bought a Universal m-1 carbine once cheap and it shot too far off to adjust the sights. I took the gun out of the stock and me and the SO noticed it was bent. He about s*** when I put the muzzle on the cement and stepped on the barrel. Took a couple of times but I got it shooting to the sights.

[madsenshooter]

A different ball game, but my old Stevens 22 is noticeably off center at the muzzle, but it'll drive roofing nails at 50yd. Try it first, then you have an excuse if it doesn't work good.

[Bob S]

Barrel with an off-center bore will walk its shots as it heats up. This was a problem with some WW I era barrels for the M1903.

Resp'y,
Bob S.

[Linstrum]

When threading a barrel for a Mosin-Nagant, make sure to cut the threads at a 55º profile instead of 60º. Mausers and Mosin-Nagants all originally used Whitworth System threads, which have a 55º angle profile and inch-pitch. I recently made adapter bushings to hold Mosin-Nagant and Swedish Mauser barrels in a universal receiver and I had to re-grind my lathe internal threading tool to 55º.

rl 1071

[Milsurp Junkie]

Finally removed the rear sight base. Everyone says that they did not solder the base down during WWII...wrong.

Two pins (requiring a 2.5 lb hammer to remove), one set screw that I had to drill out (I am still trying to figure out how they got it in there, as the "screw head" looks like a scratch on the surface. Heated with a propane torch and knocked the base off with a brass chisel and a 2.5 pound sledge.

Got the scope mounted on it, and it seems exceedingly solid. Now to inlet the plastic stock for the barrel (action fits fine), and polish up the bolt sear and rear cocking piece to smooth the trigger. I might be done by this weekend to see how it shoots.