M1a1 Sight Adjustment

[mp40 9mm]

my c&r wwii savage thompson m1a1 shoots high and to the right. anyone ever adjust their sights on these as unfortunately neither the front or rear is dovetailed.

 

the high part is not as bothersome to me as having to hold left. it is probably about 3-4" off at 25yrds.

 

compared to my mp40 it is quite hard to shoot accurately at steel plates as my mp40 hits dead on.

 

i have shot it from a sand bag rest in semi and the sights are definately off from point of aim. as a combat weapon this probably wouldn't make that much difference for what this gun was intended but it is annoying to me.

 

if anyone has some suggestions let me know. i don't want to mess the gun up, but someone may have a good suggestion. the rear sight doesn't look like you can bend it slightly to the left very easily to adjust point of aim (protected ears plus the way the sight is formed) and i think trying to bend the front sight to the right would make it look odd so i don't want to do that either.

 

thanks,

alan

[Bill in VA]

There isn't much you can do about adjusting the rear sight for windage. It sounds to me like maybe your front sight is canted a bit to the right and needs to be trued up.

[Bob B]

Assuming a front sight to rear sight dimension of 22 inches, a 3 inch deviation at 25 yards means a 0.073" sight adjustment is required; if the deviation is 4 inches at 25 yards the required adjustment is 0.098". These adjustments could be equalized between front and rear.

 

That still seems like an awful lot if the sights don't appear to the eye to be obviously out of whack. It's possible the barrel threads or the receiver-nose to barrel mating surfaces are worn or out of square, causing angular seating or allowing the barrel (and front sight) to rotate too far left (from the rear) when fully tightened. Squaring and/or shimming might help correct this if that's part of the problem. I'm not that familiar with Thompson ring sights, but is it possible the sight was ever replaced with one mismatched to the original pin hole? That could cause misalignment. On the rear sight I would try a piece of brass or hard aluminum of the correct size as a lever between the inside of the right wing and sight tab and carefully "spring" the tab slightly to the left. The object here is to JUST overcome the bending moment, so proceed carefully and by increments; keep in mind that depending on the steel, you may have to impose a 1/32"-1/16" flex to achieve a 1/64" permanent shift in sight position.

 

It might also be that the barrel is unevenly worn or slightly bent, or that the piece itself is out of axial alignment. Have you tried removing the bolt and other upper receiver internals and sighting through the pilot hole in the rear of the receiver, or using a perfectly straight piece of drill rod (or equivalent) to check this?

 

Not suggesting you attempt any of these fixes if you're uncomfortable with it. In that case it's certainly worth what a gunsmith would charge.

 

Hope this helped, and good luck!

 

Bob

[TSMGguy]

The gun should shoot high. The peep sight is for 100 yards, and the notch is for 250. Personally, I would not modify a TSMG for modern range work as it is poorly suited for it.

You can adjust your rear sight, though, being carefull not to mar it. The rear sight post is fairly easily bent. Note the small vertical holes just to the rear and to either side of the post. These serve to make the base of the post narrower to facilitate adjustment.

As Bob B. suggested, bending it only about 1/100" to the left should take care of your windage problem. This is such a small adjustment that you may not even be able to see it. Bending it forward (or back) will raise your point of aim. A little adjustment goes a long way!The metal of the "winged" sights is much thinner than the earlier "L" sights, and so is much more easily adjusted.

You can field strip your gun and peer down the barrel through the buffer pilot hole at a distant point until you have your adjustments in the ball park, then fine tune on the range.