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5.7 MMJ Carbine PMC

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mjholden57 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mjholden57 Quote  Post ReplyReply Direct Link To This Post Posted: Mar 16 2022 at 2:48pm
Not sure if that is good or not, 6 lands and grooves, but at least it meets the criteria of the barrels that came standard. Really just want to confirm it's an original MMJ 5.7 carbine.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sleeplessnashadow Quote  Post ReplyReply Direct Link To This Post Posted: Mar 16 2022 at 11:02pm
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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mjholden57 Quote  Post ReplyReply Direct Link To This Post Posted: Mar 18 2022 at 3:00pm
Thanks for all the info and your time. All in all I'm okay with the rifle and at a minimum it's in a awesome caliber and at best it's a legitimate MMJ carbine. 
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Post Options Post Options   Thanks (1) Thanks(1)   Quote sleeplessnashadow Quote  Post ReplyReply Direct Link To This Post Posted: Mar 29 2022 at 5:47am
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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sleeplessnashadow Quote  Post ReplyReply Direct Link To This Post Posted: Apr 12 2022 at 9:12am
A web page devoted to Johnson Arms is now online for those interested in the 5.7mm Johnson cartridge and carbines that shoot them.

http://www.m1carbinesinc.com/carbine_Johnson.html
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sleeplessnashadow Quote  Post ReplyReply Direct Link To This Post Posted: Apr 12 2022 at 4:01pm
Also found a better pic of the Plainfield receiver markings. Forgot I took this one.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote eb in oregon Quote  Post ReplyReply Direct Link To This Post Posted: Jul 13 2022 at 10:22am
Originally posted by mjholden57 mjholden57 wrote:

Not sure if that is good or not, 6 lands and grooves, but at least it meets the criteria of the barrels that came standard. Really just want to confirm it's an original MMJ 5.7 carbine.

If the receiver is marked with any other name than Johnson Arms it is not an original, unless it was made by another company after Johnson Arms folded. As far as I can determine (as I've not examined a specimen of all manufacturers) the Johnson Arms receiver was originally a modified unmarked Plainfield receiver and then became a special order receiver with a modified ramp. I'm pretty sure that the company's that made carbines in 5.7 used the original M1 ramp profile. The one Johnson used will feed anything from 35 grain Hornady's to 40 grain open tipped match style bullets. The standard M1 carbine ramp (in my experience) will feed semi-spitzers only. The company's I know of that made 5.7 carbines would be Johnson Arms, IAI, Iver Johnson, and Fulton Armory for a short time. I've never seen a different type of ramp (outside of Johnson Arms) that used a feed ramp other than standard.




"You are what you do when it counts."
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