5.7 MMJ Carbine PMC

While I can say for certain that Plainfield's standard became the 6 lands and grooves it applies only to their .30 cal. carbines. They may or may not have used the same for their 5.7mm Johnson caliber carbines. The few in 5.7mm Johnson I have info on do not include the number of lands and grooves.

I don't know of anyone who can tell the difference with the accuracy the 2, 4, 6, or 12 groove barrels with the .30 cal. carbine cartridge. Testing would need to be done with new carbines/barrels as used ones may have other contributing factors to performance and accuracy.

I haven't seen anything on the best number of lands and grooves for the 5.7mm cartridge. But someone somewhere may have.

Since the 5.7mm cartridge uses a neck downed .30 carbine casing the only difference between the carbines chambered for the 5.7mm and those chambered in .30 carbine is the barrel. All things considered, I think yours was probably originally assembled as a 5.7mm carbine but there is no way to determine if someone later swapped a .30 carbine barrel out for a 5.7mm barrel.

The past 4+ years I haven't continued buying commercial carbines for evaluation due to the amount of work I'm doing on the GI carbines and the USCarbineCal30.com website. I update and correct the M1CarbinesInc.com pages as more info becomes known.

I bought and paid for a Plaifield 5.7mm carbine about 7 or 8 years ago.





The seller failed to follow the laws so the deal fell thru. An exercise in frustration and a big disappointment.

Hope this helps.

Jim

An update on the number of lands and grooves for the 5.7mm Johnson barrels. I'm working on a web page for the Johnson Arms carbines. Found info the 5.7mm barrels used by Plainfield Machine and for the Johnson Arms carbines were 6 lands and grooves.

Jim

Also found a better pic of the Plainfield receiver markings. Forgot I took this one.