barnbwt
member
- Joined
- Aug 14, 2011
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- 7,340
Yes; the shroud can be removed almost entirely except the stump which locks the sorta-quick change barrel in place. The compensator out front itself weighs a quarter pound and is entirely unnecessary (was added by committee, then removed by soldiers & during subsequent manufacture). The barrel is about 5/8" diameter, kinda fat for a 10" SMG barrel (especially on semi-auto) but allows for multiple drums to be run back to back into advancing Bolsheviks without issue.i wonder, can the KP31s weight be reduced at all? thinner stronger tube or shroud maybe? perhaps a lighter stock? any way to get it down closer to 8lbs?
The drum magazine is heavy, but trust me it's worth it; basically the best 9mm drums ever designed (which is why the Soviets copied them verbatim for the PPSH, not to mention the entire gun which became the 'PPD'). The stick mags are so good, B&T is still designing new civilian-marketed SMGs which use them. The stock is fairly dense beech, though I suspect much of that is cosmolene; it's a simple reproduction stock to make, though. The receiver is incredibly overbuilt; think RPD. It's on average about 1/4" thick, and the whole thing --tube and the trigger group section below the stock-- was machined out of one giant 30lb forging. The thickness makes the thing heavy of course, but also very tolerant of less than perfect welds --perfect for a first foray into building (I built the Hotchkiss first not the Suomi, since its tube is almost as beefy, but was saw-cut rather than torch cut). If you get one of the 'horizontal' cut kits which has the entire round portion of the receiver gone, you could easily use a new tube of smaller external diameter for the bulk of it (except the end-cap) to keep the weight down.
To be honest, though, if you want to cut the weight that badly (the Suomi was a defensive trench-broom like the Thompson; the weight was to allow for sustained full auto usage) you should go with the later KP44 with the folding stock, or even the Swedish K (of CIA infamy) which use the same mags but are much more lightly built for an 'assault' role. The Swedish K is about one-third the MP5 as far as price, but easily 2/3rds the gun.
All tube guns look alike, and all were emulating the MP18 Schmeisser early on (except the Thompson which was and remained its own thing). The two were developed & manufactured completely differently, and have very different recoil, FCG, & cocking handle setups. Thompson was almost all machined initially, the Suomi had a set of giant reamers that bored out all the cylindrical features at once. I believe the Thompson also had a rather funky mag release at first if memory serves, whereas the Suomi's is a more typical paddle. Cocking handle is nonreciprocating & located/shaped like a Mauser handle. The rate reducer was originally pneumatic; the bolt was so closely fitted to the receiver tube that a one-way valve in the rear caused a vacuum to develop on the return stroke. Sadly, not very effective when you gouge a big slot into the bolt for the semi-auto conversion.and looking at it closer it looks like the finnish just copied the thompson except put it in a round tube, the bolt with its long forward protruding section to eliminate the need to machine clearance for the magazine on the bolt, the section of receiver around the magazine well, the magazine well itself, its all thompson
BTW, the long 'snout' on all the early subguns was a safety & reliability feature; in the event of case-rupture, breech gases only impinged on a reduced area & did not as greatly exaggerate the force applied to the bolt. It also allows for a much narrower path from mag lips to chamber, with basically no way for the round to jam as it's fed straight in from the mag; incredibly reliable. There are still relief cuts for the mag lips, but not as pronounced as on, say, the STEN or M3A1. I suspect ammo (and chamber) quality improved by the second generation to the point case ruptures & mag issues were no longer so common as to require a feature that stretched the gun two whole inches.
TCB