12.75" barrel for BRP Stemple Takedown Guns.
The extractor relief on this barrel is setup for the BRP-Stemple extractors and would have to be enlarged to accommodate the KP31 extractor for full auto and semi auto KP31 variants.
HEADSPACE on Closed Bolt Guns vs Open Bolt / Fixed Firing Pin Blow Back Guns
Case exposed on rear: .12" - .125" (chamber depth may have to be deepened for semi auto setups to match the pocket depth in the bolt). Some semi auto KP31s use modified original KP31 bolts with a bolt face pocket depth of .09". Since these SMG (as well as the Stemple / BRP SMGs) are fixed firing pin / blow back guns, the bolt stops on the back of the case rather than the rear of the barrel. The final critical stage of Open Bolt / Fixed Firing Pin Blow Back SMG process is when the mouth of the case makes a firm and crisp stop on the inside cutout of the chamber. At this instant, the extractor snaps over the case rim and allows the firing pin to contact the primer and detonate the cartridge.
For use in a semi auto / closed bolt gun, the chamber should be deepened to so the case exposed on the rear is just a few thousandths less than the pocket depth on the bolt face. This way the bolt would actually be stopping its forward movement on the back of the barrel rather than on the back of the case.
Designed to work with original KP31 Suomi M31 barrel shrouds.
4140 Alloy Steel
Parkerized Metal Finish
Twist Rate: 1:10
Muzzle Diamter: 19mm (same as original)
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fantastic quality and accurate