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Semi Versus SMG Thompson Receiver Dimensions

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#1 Wolfer69


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Posted 30 December 2017 - 12:53 PM

Merry Christmas to all. I sold my West Hurley M1A a number of years ago which I still regret. I have picked up a Kahr 1927 which I am in the process of SBR'ing. It is my understanding that the interior receiver dimensions (bolt travel) is different on the semi and SMG guns. I am contemplating machining some of the excess meat out of the back of the Kahr so I could have more bolt travel, and lower the incredible spring load they have on this beast. 


Could I impose on someone to take some measurements for me. On your 1927 or M1 with the upper off the lower, and the bolt group still in - how much free travel do you have to the interior back wall of the upper? So measured from the back face of the bolt to the front edge of the bolt cavity?


I appreciate the help.   

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#2 bob241


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Posted 30 December 2017 - 04:11 PM

This may help, on a M1 thompson, measureing from the inside of the front wall to the inside of the rear wall, the print shows 8.950 inches.

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#3 Wolfer69


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Posted 30 December 2017 - 04:35 PM

Thank you! I should be able to backtrack subtracting the bolt length.  

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#4 deerslayer


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Posted 30 December 2017 - 07:20 PM

I've milled out the back... your spring pilot guide will then sit further back..something to consider. I've added buffers, shortened hammers, lengthened the guide... also your bolt knob will then need more clearance milled in the top slot.

If you mill just far enough to put in a buffer that works pretty good without the other modifications rearing their head.
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#5 Paladin601


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Posted 30 December 2017 - 11:14 PM

Why increase bolt travel to ease spring load? Just use EZ pull springs to lighten the pull.



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#6 Colt21



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Posted 15 January 2018 - 06:50 PM

   I am pretty sure that receiver depth between the TSMG and the semi auto is different with the Semi receiver being about 1/10 inch shallower which was done so that a TSMG bolt couldn't readily be used. I have an early West Hurley 27A1 that I can measure the bolt travel in if you want.

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