M1 Carbine Barrel/Receiver Witness Marks

[Lostinidaho]

The rear sight is turned to the left side and it still hitting to the right of the POA.

I understand the barrel might be turned into the receiver too much.

Where are the barrel and receive witness marks?

Thanks in Advance

[55fairlane]

Ok, let's start here

Military or commercial.........

hand loads or factory ammo?

How long have you owned this rifle? When did the rifle start doing this?

I think we need more info.....

Aaron

[Der Gebirgsjager]

Yes, more information would be helpful, and a photo of your sights would be even better. But.....

I own 5 of these, all have the adjustable rear sight, and just to look at them they all have the appearance of being offset to the left. Unless your barrel is obviously screwed in too far, which would be indicated by whether or not your front sight is vertical, then the best answer is to adjust the rear sight. If it is adjusted all the way to the left to move the POI to the left, and is still shooting right, the entire sight can be moved to the left in it's dovetail on the receiver. They're usually in pretty tight, so a solid bench vise with non-marring jaws and a brass drift punch is in order. The original, non-adjustable rear sights were also mounted in a dovetail and can be moved as needed, right or left for windage. The original, military version of the adjustable rear sight is staked into position, so once you overcome the staked areas by drifting the sight in the dovetail it may be necessary to re-stake the sight in it's new position to avoid future unwanted movement from recoil, dropping the carbine, etc.
Relatively easy job, done with a center punch.

Not to overlook another possibility, check the condition of the muzzle's crown for damage. A nick, dent, burr, anything other than a smooth even surface can deflect the bullet's path. If you become convinced that the barrel is actually defective for some reason such as being bent or bored off center, now is certainly the time to purchase and install a new barrel. There was a time period of about 15-20 years that replacement barrels were very difficult and expensive to come by. Currently, they are readily available as newly made replacement parts.

As a final option, before I started attempting to correct the POI by turning the barrel, I'd consider mounting a scope. I dislike drilling holes in historical military rifles that are in otherwise unmolested condition. There are mounts that utilize the existing rear sight dovetail, and one named UltiMak that fastens to the barrel forward of the receiver. I have two UltiMak mounts, one each on an M1 Carbine and one on an early production Mini-14. I tinkered (off and on) with these two rifles for years and could never get them to shoot well. Although the mount being attached to the barrel of such a short rifle is kind of clumsy looking and handling, one thing is for sure; the bullet will go where the barrel is pointed, even if it moves a bit between every shot, and much improved groups will result when the scope's picture and the bore are coordinated. If your specimen is a civilian version, then there are several other mounts available that can be side or top mounted, but which require drilling and tapping.

[Lostinidaho]

Its not my carbine, but this is what I know.

Receiver, trigger group are marked Winchester. Barrel is in 5.7 Spirtfire. Owners father is a fan of Melvin Johnson. Several nice Johnson rifles. Rear sight base is centered on the receiver. No damage to the crown. Cartridges are hand loaded and make a nice tight group to the right of the POA. 4.5" group at 100 yards

Leveled the barrel and receiver on the work bench bottom side up. When the level is placed on the flat part of the barrel (bottom). The level shows almost a 1/2 a bubble off level. If the threads are conventional it would indicate the barrel being to far into the receiver.

[Der Gebirgsjager]

Its not my carbine, but this is what I know.

Receiver, trigger group are marked Winchester. Barrel is in 5.7 Spirtfire. Owners father is a fan of Melvin Johnson. Several nice Johnson rifles. Rear sight base is centered on the receiver. No damage to the crown. Cartridges are hand loaded and make a nice tight group to the right of the POA. 4.5" group at 100 yards

Leveled the barrel and receiver on the work bench bottom side up. When the level is placed on the flat part of the barrel (bottom). The level shows almost a 1/2 a bubble off level. If the threads are conventional it would indicate the barrel being to far into the receiver.

This would have been good to know information up front.

So, the rifle is not in original GI condition. But, if as you state, the rear sight is centered on the receiver then it can be drifted left to compensate.

You might correct the POI by experiment with different loads.

The last paragraph, about leveling the barrel, etc., means nothing. Barrels have various profiles and whether they'll "level" on a bench has nothing to do with the threads. If the barrel was too far into the receiver it wouldn't headspace, and most receiver designs only allow a barrel to be screwed it just so far anyway. If you back the barrel out you'll create excessive headspace and the front sight will no longer be TDC. Accuracy has little to do with barrel profile. Round, half-round, octagon, bull, etc., all can shoot accurately. If the carbine in question is shooting satisfactory groups, just to the right, drift the rear sight to the left in its dovetail and call it good. Like I said before, most of the M1 Carbines I've seen look like the entire sight is over to the left of center the way they came from the arsenal. If yours looks centered, maybe somebody centered it because they didn't like the way it looked and said, "Oh-oh. I'll fix that!"

[Der Gebirgsjager]

In the way of an addendum, if you mean that the flat area behind the gas piston is not level side to side, (my original thought was that you meant front to rear) then how is the gun operational at all? The slide has projections that run in the grooves on either side of the flat area, and unless someone did a lot of tinkering and customizing the gun wouldn't function without the relationship of the projections and grooves being the way they're supposed to be. That's the important feature, this relationship, not if the flat itself is level.

Unless your barrel is lined, it is a replacement barrel, bored for the Johnson Spitfire cartridge, but the external dimensions and profile should be very similar to that of an original barrel. You're overthinking this. The gun functions, and the answer is to just move the sight.

[vzerone]

Has anyone mentioned if the face of the receiver is square?

[Larry Gibson]

Lostinidaho

You are correct, the barrel is turned in to far. No need, in my opinion, to over think the problem. You have a load that shoots well so "load adjustment" will not correct for how far off the sights are.

The barrel will need to be removed. Some will knurl the face of the receiver and the shoulder of the barrel then refitting the barrel to the receiver. I do not. I would make a small washer shim of .001 or .002 shim stock to fit over the barrel shank and fit the barrel to the action and see how close it comes to "plumb" using the same flats you did. Probably will have to +/- shims to get it plumb. Once plumb I would then make one shim the thickness needed and use that tightening up the barrel to the receiver and then test firing with the rear sight centered for windage adjustment.

[vzerone]

The rear sight is turned to the left side and it still hitting to the right of the POA.

I understand the barrel might be turned into the receiver too much.

Where are the barrel and receive witness marks?

Thanks in Advance

You talked about the flat on the barrel and how you put a level on it, but I haven't seen you mention if the front sight is perfect vertical or if it's canted to the left viewing from the rear of the rifle. If it's perfect vertical you have other problems.

[LAGS]

Why cant you just remove the pin on the front sight and re- index it with a narrower Key.
You can rotate it to one side and see if that helps.
To keep the sight in place while you play with it, and if it is rotated too far to re-insert the pin, then just crazy glue the front sight to the barrel. ( Acetone will disolve the glue later if need be )
That will give you an indication of how far your Barrel has to be rotated, or if it, depending on the rifle and condition, weather it is better to invest in moving the front sight on the barrel, or the money to have someone play with re Clocking the barrel.

[jimb16]

There are witness marks on the bottom of the barrel and on the front of the receiver. But it is more important to be sure that they barrel and receiver are properly aligned rather than that the witness marks line up. Mount the barrel lightly in a vise, up-side-down. balance a straight edge on the barrel flat. Next balance another straight edge on the flat at the front of the receiver. The two straight edges should be parallel if the alignment is correct.