Plainfield Carbine Slide Lock Problem

[Richard H Brown Jr]

Greetings:

Just a question. Do *most* Plainfield made carbines have a problem with the slide lock not holding the slide back?

I have a Plainfield, and the milled out section on the receiver won't hold the op rod/slide back, after emptying a mag, or manually locking the slide/op rod back. To the point, that if you manually lock the slide/op rod back, and slap the side of the stock, the slide/op rod and bolt go forward.

Going to take it to my favorite gunsmith sometime real soon.

RHB

[dave]

A lot of carbines may have that problem (Plainfield or not) even the ones which stay back are not tightly held! Once the pin or hole wear a little they tend to not lock good. I never trust any of them!

[kcw]

It should be EZ enough to examine the forward edge of the recess in the receiver to see if it looks worn. Most of the time however it will be the "stop" (pin) in the slide which worn and wants to override the sharp edge of receiver recess. Plainfield used A LOT of NOS USGI parts which were of the original designs, parts which were subsequently substituted with newer, better functioning designs by the military. TM9-1276 reads in section V.-39-b.-(2): "For depot maintenance, check to assure that stop 7312452 and spring 7212453 are used. For field maintenance, old type is satisfactory if it functions properly".
The stop is not designed to automatically hold the slide back when a magazine is emptied. The slide must be manually held back while the stop is then pressed down into the receiver recess with the thumb. If the receiver recess looks good, I believe that you can spin the stop around 180 degrees while it is in the slide. That would expose the current backside of the stop (less worn?) to the recess in the receiver. Another issue is with the spring, which should it fail, will allow the stop to unexpectedly drop into the receiver recess during firing, thus causing the slide to "hang up" and put the carbine out of action. Accumulated dirt around the spring/stop in the slide can also be an issue. If you don't already have it, USGI Tech manual TM9-1276 is an excellent guide for Plainfield owners.

[n64atlas]

As stated, the slide isn't help back on the last round unless you are using 30 round magazines. They had a razed portion on the follower that held the bolt open. The 15 round mags didn't have this feature.
http://img.photobucket.com/albums/0603/n64atlas/Carbine%20mags/follower.jpg

[Tuna]

Sometimes as stated you can turn the pin 180 degrees and it will work fine. If not then remove the pin and file it to reshape the edge and try it again. But with a lot of carbines the edge in the receiver is also worn. A dermal tool can be used to reshape the end of the slot. Just be careful not to cut down into the receiver. You can get a new pin from parts suppliers.

[Richard H Brown Jr]

Update #1:

Took the carbine to the smith yesterday afternoon, and he basically mentioned all the problems you guys suspect.

He even looked at the two spare slide lock pins and springs I brought along, and caught that one of them had the rounded over area where it is *supposed* to go into the slot.

Basically he's got other guns on his lathe/mill but he's going to recut the slot. The idiot Plainfield slot was fronted with a round area from some sort of drill cut, and it was above the rest of the milled slot. So *maybe* recutting the slot and checking the pin and spring in the slide will fix the problem.

Atleast I'll know in about a week.

RHB

[Sunray]

No last shot hold open with a Plainfield with or without a 30 rounder. If the bolt doesn't stay open manually operating the slide stop, it's either dirty or the wee, tiny, small, itty-bitty spring is busted. Gunparts wants $2.45 for one(their part #542210B.). Just to make things interesting they sell 2 types of slide lock. Don't think it matters which you have.
http://stevespages.com/pdf/plainfield_m1_carbine.pdf

[Richard H Brown Jr]

Final Entry; Picked it up from the smith today. He milled the slot forward a few thousandths of an inch, and recut the front edge. And now it locks the op rod and bolt back really good.


RHB

[Sunray]

Hi. That one of the Plainfields made and sold by IJ? IJ bought PMC in 1975. Just curious. Never had any issues with my Plainfield a bath didn't fix.
http://www.m1carbinesinc.com/carbine_plainfield.html