M1 Carbine Rear Sight Drift and Sight Picture

[The Grand Baboon]

Hello, friends.

I've inherited a 1942 Inland M1 Carbine and decent amount of original ammunition.

When zeroing it this last weekend, I was quite surprised to find how far the rear sight had to be drifted to attain a POA/POI windage zero. I was also surprised at how much of the front sight I had to file off to attain a precise 100-yard elevation zero.

I have two questions:

1) The rear sight isn't out of the dovetail in any capacity, but it is shifted to the left enough to cause me some amount of frustration in the aesthetic department. At 25 yards, the gun printed groups at least 8" to the right of my POA with the rear sight centered on the receiver. Is this normal?

2) The top handguard obscures so much of the front sight that, upon attaining a correct sight picture at any BDC setting, I can only see about the top quarter of the front sight and the two protective wings. As compared to my M1 Garand, it's not quite...optimal. Is this normal too?

Both of these problems, to me, seem like they would be par for the course for this firearm given its task and purpose (in addition to the flip to slider rear sight retrofit). But I don't have much knowledge on historical firearms.

On a good note, this little gun is surprisingly accurate. I expected 4-5" groups, but am getting right around 3" at 100 yards. Quite excellent for it's intended purpose as a sub 100 yard prairie-dog blaster.

 

[trackskippy]

Not sure I understand which rear sight you have. Is it the original, small "flip" sight, or the latter adjustable?

The latter adjustable rear sights when properly set and staked in the dovetail, do look like they are off to the left. Ive had to reset and restake all of the rear sights on the guns Ive had. Its kind of deceptive too, as the hash marks are lined up as centered, but it doesn't really "look" it.

As far as the handguard goes, Ive had 5 Carbines and still have a couple, and as best I can remember, with all of them, when you sight down the barrel, the channel in the handguard is right at the "flat" base of the post on the front sight.

I do remember seeing a couple over the years where it seemed like the channel was higher, but I haven't seen one like that in a long time.

I had to file the front sights on a couple of my guns to get the zeros to match the settings on the rear sights. My understanding is, when they went back to the arsenal after the war, and had the bayo lug and rear sights fitted, they didnt always, if ever, rezero the new front sight.

And I agree, they are decent and fun shooters.

 

[hps1]

1) The rear sight isn't out of the dovetail in any capacity, but it is shifted to the left enough to cause me some amount of frustration in the aesthetic department. At 25 yards, the gun printed groups at least 8" to the left of my POA with the rear sight centered on the receiver.

If POI is to the left of POA, you need to move the rear sight to the right.
(Move rear sight in the direction you wish to move the POI.)

Regrds,
hps

 

[The Grand Baboon]

Not sure I understand which rear sight you have. Is it the original, small "flip" sight, or the latter adjustable?

It's the 100 to 300 yard adjustable.

The latter adjustable rear sights when properly set and staked in the dovetail, do look like they are off to the left. Ive had to reset and restake all of the rear sights on the guns Ive had. Its kind of deceptive too, as the hash marks are lined up as centered, but it doesn't really "look" it.

Awesome. Thank you! I think this is some of the OCD of being used to modern, CNC produced firearms in which generally everything just...lines up.

As far as the handguard goes, Ive had 5 Carbines and still have a couple, and as best I can remember, with all of them, when you sight down the barrel, the channel in the handguard is right at the "flat" base of the post on the front sight.

Again, thank you. Looks like everything is right in line with what I'm experiencing.

If POI is to the left of POA....

Sorry, a typo on my part. POI was right of the POA. Editing the OP now.

 

[Carl N. Brown]

What you have with alignment of an M1 Carbine is a stack of tolerances
_ in fit of the receiver hook with the recoil plate (with no other contact of receiver to stock per CMP website),
_ in the rear sight base,
_ in the barrel itself,
_ in the barrel band (holding the barrel within its clamp with no other contact of barrel to stock per CMP website),
_ in the front sight key slot in the barrel.
_ in the front sight itself.

When I bought my M1 Carbine in 1990, it was an import from South Korea, came with a 30 shot magazine, and had been freshly parkerized.
I checked zero first at 25 yards using the biggest paper target I had.

When M1 Carbines were first manufactured, they were zeroed before they left the factory.
Whenever possible in repair or rebuild they replaced the M1 or M1A1 stock with the M2 stock, the "L" flip rear sight with the adjustable sight, the plain early barrel bands with the barrel band with bayonet lug. These may have been repairs in the field in an armorer's work truck, or a rebuild in a fully equipped arsenal. I suspect that M1 Carbines in field repair or even in arsenal upgrade were not always rezeroed.when parts that would affect zero were changed. I also suspect when Carbines were inspected and cleaned to be put in reserve storage, they were not always rezeroed.

 

[hps1]

^^^^^this!
I was issued my first (of several) M1 carbines in the mid '50's. Not my favorite individual weapon, the Garand is much more accurate. 3" @ 100 yds. is about as good as it gets.

I've often thought I would experiment w/trying to accurize mine by tightening up the (sloppy) fit of the receiver hook within recoil plate by either "bedding" the plate or use of a set screw and shimming or bedding the barrel under the barrel band. I suspect these two tweaks would help accuracy quite a lot.

However, M1 carbines typically can hold their shots in just 3" to 5" at 100 yards. Maybe one of these days I'll get around to it.
https://www.americanrifleman.org/content/the-30-carbine-history-performance/

Some interesting info on the many changes to the bolt assembly @ http://www.uscarbinecal30.com/bolts.html
I can attest to the fact that bolt failures described in above article do occur.

The carbine would not be my choice if the targets were shooting back, but they are a fun little rifle to shoot.

Regards,
hps

 

[Carl N. Brown]

This off center with a zeroed rear sight is supposed to be common with Carbines:

 

[Slamfire]

^^^^^this!

Some interesting info on the many changes to the bolt assembly @ http://www.uscarbinecal30.com/bolts.html
I can attest to the fact that bolt failures described in above article do occur.

Regards,
hps

I will disagree with this statement found on that site:

"Along with the design of the rear of the bolt and face of the hammer this was intended to prevent out-of-battery discharges."

He is talking about the receiver bridge on the M1 carbine.


My M1 carbine TM correctly calls this the "firing pin retraction cam". Its function as a firing pin retraction cam is obvious as firing pin retraction is important in rotating bolt mechanisms. Given firing pin hit offset, sometimes so out of tolerance that misfires happen



you can imagine that a bolt rotating in a circle, with the firing pin offset, and stuck in a primer pocket, is going to break the firing pin tip.

While there are those who claim the receiver bridge is some sort of firing pin block, well if it is, it is a poor design as it provides next to no protection from out of battery or in battery slamfires.



the fact of the matter is, the only thing preventing in battery and out of battery incidents in Garand type mechanism is primer sensitivity. If the primer is insensitive enough, the primer will not ignite when the firing pin rebounds off it. If the primer is sensitive enough, it will ignite when the firing pin rebounds off the primer. I collected web reports of in battery and out of battery incidents in the M1 carbine, with factory ammunition. So they happen.

The greatest probability of an out of battery slamfire incident occurs when a fat, or over long case is chambered. If the bolt has to stop, or slow down to crunch fit a case to the chamber, and the lugs are not engaged, that firing pin is rebounding off the primer at the highest velocity possible in the mechanism. And if a sensitive primer is hit, they occasionally ignite.

 

[hps1]

@Carl Brown, first such sheet metal cap I've seen on a carbine. Looks like the purpose may be to hold the back end of receiver down snug into the recoil plate??? Is that the case?

Regards,
hps

 

[The Grand Baboon]

Upon further inspection at home, it appears that the entire front sight assembly is slightly rotated to the left (counterclockwise) from the shooter's perspective. If vertical is 12 o'clock, it's sitting at about 11:45.

Due to so much of the front sight being obscured by the top hand guard, I didn't really notice at the range.

So, the dilemma is now thus: Do I just leave it as-is, or do I attempt to rotate the barrel clockwise to get it all lined up?

As good as the gun is shooting, both from a reliability and accuracy standpoint, I'm somewhat partial to a "let sleeping dogs lie" solution.

 

[GBExpat]

I bought 2 Inlands from The CMP when they first became available in Summer '07.

Both required the later-version rear aperture sights to be moved to the far left (14-15 clicks, IIRC) for Zero.

BTW, in my hands, when I received them, both were capable of <3moa from rest. Unfortunately, my eyes are no longer capable of producing such results (presbyopia).

I was quite surprised & pleased to find how accurate those little rifles are.