M1 Carbine Barrel Question


February 5, 2014, 08:51 PM
My M1 carbine requires that the rear sight be moved quite a bit to the left to be properly zeroed.

How hard would it be to properly index this barrel?

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February 5, 2014, 09:28 PM
Would it not be easier just to remove the front sight pin and index the front sight, then refit the pin and locating hole ?

Carl N. Brown
February 6, 2014, 07:38 AM
I have the same problem as the opening post and I too would like to see an answer. I have the adjustible rear sight and the peep loop must be two full graduation marks to the left to be on the bullseye of the 100 yard standard target.

I have the original M2 style stock, an Italian repro of the M1A1 paratrooper stock, and a modern synthetic sporting rifle stock, and two barrel bands, one with bayonet lug and one without. My problem is not related to barrel bedding: same zero problem no matter what stock or barrel band is used. I have been told my best bet is to retire my 1943 IBM M1 Carbine to the gun collector case and buy a new Auto Ordnance clone. ;)

LAGS: Would it not be easier just to remove the front sight pin and index the front sight, then refit the pin and locating hole ?

Nope, not that simple. Front sight of the M1 carbine is pinned to an indexing key that is a tight fit in a slot in the top of the barrel. Remove the pin, you can drive the front sight forward off the muzzle, then lift out the key which has the hole for the pin. Even if the front sight is canted, relocating the front sight is not easy.

The military tech manual on basic armorer checks advises centering the rear sight with the adjustment knobs, re-zeroing the gun by drifting the rear sight in its dovetail. You must use a special adjustment tool, because the original sight is staked in place by using a centerpunch from the top to displace metal in both the sight and receiver. Just driving the sight left or right with a brass hammer runs the risk of damaging the sight housing, especially the stamped sight housing. Once zeroed, you must repunch the sight into the dovetail to prevent movement.

The usual reason found on the internet for M1 Carbines requiring rear sight extreme windage adjustment to the left was that the 1980s re-importer Blue Sky of Arlington VA stamped their importer mark on the barrels without proper support and bent their barrels. Google M1 carbine Blue Sky bent barrel. I suspect :) there.

Other reasons may be the barrel was bent in action (use with a bayonet, used as carry support, used as a pry bar) or the barrel was screwed in tighter when re-headspaced in an arsenal rebuild.

Some folks have reported going to the extreme of supporting the barrel on lead blocks and tapping the barrel with a lead hammer and bending the barrel itself to zero the front sight windage-wise. Lead supports and hammer to avoid damaging the steel barrel. So many ways to go wrong bending a barrel, I shudder at the thought of trying it myself.

A few have found relief by having a gunsmith recrown the barrel. That might cure the problem if the muzzle is off-square, but I can imagine it could compound it in some cases.

February 6, 2014, 10:21 AM
Assuming you have the correct tools it's not hard at all to turn the barrel. You really need the correct barrel tool for your vise and a good receiver wrench.
With that said I would first assume that the barrel is properly installed, clocked and head spaced. Turn the receiver over and put a level on the flat part and the flat part of the barrel and see if it's on the same plain.
Moving the rear sight base might be the easiest solution or don't worry about it. As long as you achieved proper windage it's GTG.

Peter M. Eick
February 8, 2014, 01:03 PM
Interesting. My Inland is the same way. Nearly 2 full turns left of center. It really bothers me that it is not closer to center, but I figure it was an arsenal rebuild and it works so why mess with it. I bought it for home protection and have no delusions about long range shooting with it so the sights are more cosmetic than practical for me. Reliability is good now so take that into consideration if you mess with yours.

February 8, 2014, 02:19 PM
If the rear sight has to be moved to the Left to get it on target, then that means that to index the barrel, you have to be moving your front sight to the right.
That means , you would be Unthreading the barrel, or you have to make almost a full turn tighter to get to the clocking that you want.
That would involve machining the stop point on your barrel, and then re- headspacing your rifle.
You didnt say how far off center you had to adjust your rear sight to correct at 100 yards.
Or how far to the right it is shooting at 100 yards with the rear sight set at Zero.
I have re- indexed the front sight by maching the Key Stop to allow the front sight to rotate to one side.
But the easiest if not too far off is to move the rear sight in the dovetail to the left a bit.
Then if that isnt far enough, then try re clocking the front sight.
If you split the differance in the front an rear sights, then the adjustments will not ne noticable.

Peter M. Eick
February 8, 2014, 06:20 PM
I had not really thought about it, but you are right. I would have to unthread the barrel to fix it. I guess when the armory rebuilt mine they just tightened on the new barrel a bit more than the old one and rechambered it.

Thanks for the insight. I have even less interest in fixing now!

Carl N. Brown
February 9, 2014, 09:44 AM
LAGS: But the easiest if not too far off is to move the rear sight in the dovetail to the left a bit.

Yes, the easiest thing to do is rear sight adjustment. Moving is the only option for the fixed type "L". First option with the adjustable sight is to use the windage screw; if the adjustment is too extreme, then you have to center the adjustments and re-zero by moving the rear sight base and all in the dovetail to the left a bit. That is difficult.

United States Government Printing
January : 1947
CARBINES, CAL. .30, Ml, M1A1, M2, and M3
TM 9 - 1276
The dovetail tapers slightly from right to left, tending to provide a tighter fit as the base is advanced. The base is held in place, when aligned, by staking the rear edge of the mounting slot in the receiver into two notches in the front edge of the dovetailed lug on the sight base.

Page 6. Photo of two types of adjustable sight. Help! Are my eyes deceiving me, or are both examples (machined and stamped) adjusted to the left off center a bit?

February 9, 2014, 09:51 AM
I have owned numerous Carbines over the years, and the majority of them needed notable left windage on the Type II or III rear sights to hit at 100m.

February 9, 2014, 09:56 AM
@ Carl N Brown
That is why I posed the question to the OP as to how far off zero the bullet is hitting at 100 yards.
With out specific information, we are all guessing , and recomending fixes that mey not be relevant.
But if it is more than a few clicks of adjustment to the left off zero on the rear sight, the rear sight should be the FIRST adjustment.
But we dont know if his rear sight has to be adjusted almost all the way to the left. And if that is the case, then resetting the front sight , or re-indexing the barrel is in order.

Carl N. Brown
February 9, 2014, 03:42 PM
It's been a while since I fired mine but I had it zeroed ready for the last match season. This ought to illustrate the amount of left adjust I have to use to get a windage zero at 100 yards:

| Index scale on aperature slide
| Center mark on sight base

If I had to crank it all the way left, with no adjustment left, and still could not get a zero, I guess I would really be hurting.

February 12, 2014, 11:31 AM
Doesn't the whole assembly install into a dovetail? I would drift the whole assembly a bit and live with it.

I would be leery of even small barrel clocking adjustments on a semi auto where there is an operating slide and gas system that could be impacted. The carbine is probably going to be OK with a little of that but right now you really don't have a problem other than the tick marks not lining up to an aesthetic satisfaction.

The reason that sight aperture is made to travel that far is so you can adjust it to obtain zero, and it sounds like you have done that.

February 14, 2014, 01:27 PM
What's wrong with remembering where the rifle zeros for you and leaving it alone once set? I might pick up your carbine and find it shoots to a different place than it does for you. That is, after all, why adjustable sights exist.

with a carbine there are plenty of reasons that one person might shoot a particular rifle to a different place on target than another person does. Hold on target, ho;d of rifle, pressure rearward or tightness of overall grip, etc., etc.

adjusting sights make one gun fit all shooters as far as a target is concerned.

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