M1 Carbine rear sight adjustment

[The Freeholder]

I have a recently acquire M1 Carbine with the late model stamped adjustable rear sight. Shooting it for the first time this weekend, I'm shooting consistantly low at 100 yards. I've confirmed that the aperture is on the 1 (00) setting.

Does anyone know how to adjust the entire sight so that POA/POI will coincide at 100 and 200 yards? I think the 2.5 and 3 settings are a tad optimistic with that cartridge, so I won't get too concerned with those.

 

[dfariswheel]

The Carbine is sighted in by filing the front sight down.

New carbines were made with front sights too tall, then final targeted at the factory by shooting and filing until it grouped on a test target.
There's a picture of the special target used in the M1 Carbine Ordnance manual, but any target will do.

In your case, select GI-equivalent ammo and a narrow fine-cut file.

Shoot three round groups at 100 yards, and carefully file SMALL amounts off the top of the sight, until the groups come up to center.

Make sure to keep the top of the sight ABSOLUTELY level across the top, and very slightly slanted forward.

When you're on target, apply cold blue to touch up the top of the sight.

 

[Sunray]

"...POA/POI will coincide at 100 and 200 yards..." Ballistics won't allow that. With a 100 yard zero, a 110 grain bullet, out of Remington factory ammo, will drop 12.9" at 200. 4.2" at 150.
"...consistantly low at 100 yards..." Move the rear sight up. A reloading your of ammo may be in order too. Most factory and surplus ball is a tad anemic. 110 HP's with IMR4227 works well out of my rifle.

 

[The Freeholder]

Sunray, it's an adjustable rear sight. Adjustments are provided for 100, 200 and an optimistic 250 and 300 yards. If it was made correctly to start with, then if you zero for 100 and adjust the sight to 200, you should be relatively on target, right? I doubt it would be perfect, but within minute of looter, say. Or are the M1 Carbine sights that bad?

dfariswheel, you make an interesting point. I have to wonder if the ammo is that old and crappy, or if the gun was never properly sighted in. I'm going to try some new ammo (new, like current production) first, and then I'll see about filing the sight.

I think I'll also take a look at it under a scope and see if it shows signs of filing, just for curiosity's sake.

Thanks for the help.

 

[dfariswheel]

Just remember, your carbine was made in WWII, and has been through who knows how many hands since.

It's not at all unusual to find carbines with replaced front sights, that no one ever re-sighted.

Also, when the carbines were re-parkerized, any signs of filing would be blasted away by the bead blasting.

The bottom line is, if you're shooting good quality USGI spec ammo and it's shooting low, you would need to file the sight to target it.

The only watch-outs are to be careful not to file too much. Take tiny amounts off and shoot to check progress.

Next, be careful to keep the top of the sight level from right to left so you don't see a sight with one side higher than the other, and keep a slight down angle to the front so you don't get light reflection off the top of the sight.