Zeroing a TSMG - Question

[opsoff1]

I am interested in understanding how TSMG's were "zeroed" - in particular the 28A1's, M1's and M1A1's with the fixed rear sight.

There must have been some fixture in the production sequence that enabled the sights to be zeroed.

Obviously easy to do with an adjustable sight.

The fixed sight guns are interesting as it appears from any of the drawings, that there are no variations of rear sight height or location on the receiver or front sight height or even lateral dovetail to drift that for windage.

Also - how were guns rezeroed after a bbl replacement/rebuild?

Were the tolerances and dimensions such that the guns produced "minute of man" groups at 25yds / 50 yds and that was good enough?

or was it up to the shooter to correct with Kentucky windage / spray n' pray?

 

Thoughts?

[jim c 351]

I don't know the answer, but I fear that not much time was spent worrying about it.

My AO 28A1 shot 5 inches to the right at 25 yards. That may or may not have met US Army standards, but it wouldn't do for present day steel plate shooting.I solved the problem by installing a Lyman adjustable.

On my M1 I solved the problem by rotating the barrel a small amount. For this you will need a set of wrenches.

All Thompson I have shot group high at 25 yards. This was no doubt excellent for combat, but tough on plate shooters.

With my 28 I modified the Lyman sight so the gun would group lower. With the M1 I hold lower.

I do OK with both guns.

Good luck

Jim C

[opsoff1]

I tried to find an on line version of FM 23-40, but came up empty. The FM's usually have a great deal of info on marksmanship.

I wonder what the accuracy / acceptance standard was at AOC / Savage for the fixed sight guns?

[emmagee1917]

I had my original M1A1 Numrich sight crack at the ring and fall off . The replacement was pressed about half way on and then taken out and shot . I moved the ring around till it was on , then finished pressing it on . The rear was more of a challenge . Shot the gun , measured how much it needed to be moved , calculated how much the sight had to move to do that Measured the top of sight from deck of receiver and then taped the bloody you-know-what out of it . Used hammer , punches , pry bars , clamps , and other knick-knacks to change the bend at the bottom of the vertical post forward to lower and rearward to raise the peep in relation to the receiver deck . The real trick was to keep every thing clamped down to avoid any pressure on the rivets . When the top edge had moved enough , dragging the peep hole with it , it hit where it needed to .

Chris.

[Uncle Dudley]

http://www.machinegunboards.com/forums/index.php?showtopic=1318

 

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