IBM CARBINE BOLT

Riesch's book has Type III round bolts in IBM @ S/N 3,900,000.  NL-7 says all IBMs found above 3,898,000 were round which pretty well matches up with Riesch. I'd go with that.

my serial number is 3949745 doesn't sound like it has the right bolt? 

i haven't taken it apart yet, and didn't buy it as a shooter, as it is that clean, but i do plan to strip it, to see if the internals are correct. further posts to follow. i will say one thing, after owning a few auto ordnance repro's, this thing puts them to shame, and they were brand new! thats how nice it is!

IBM started using round bolts about 12-43 so I'm think you could get away with a round one, with a possible consideration for mixed use.

mikeurbas wrote: why would someone switch it to a flat bolt?

There are several reasons why it has a   flat bolt.

It is likely that if it was "corrected" that the person doing so just used correct manufacturers parts, or read a book with inaccurate information.

Once we have pictures posted we can discuss the other scenarios

mikeurbas wrote: one other question, how do i tell if i have an n14 bolt? thanks for all the help everyone!

I could have been more specific. National Postal Meter marked their bolts with and N and a number on the left bolt lug. I have had one crack and the more one scours forums and notices, the N14 turns up cracked more often that others. I have a friend and member of this forum doing a study on cracked N14's now. He will determine where they are soft or hard and what may have caused the numerous cracks reported. If I had a gun with an N14 in it...I'd just go ahead and replace it with a USGI or Post War contracted round bolt.

You need to ascertain the "exact" length of you laser-sight plug, from the rear of the case to the end of the case mouth. That dummy round should have a ridge on it where the case-mouth would contact the bottom of the chamber. Perfection would be 1.290, which is the go-gauge. Regardless....measure this distance. If it is shorter than 1.290, you can add pieces of scotch tape and build the base up to a point where it will not head-space (no-go). Most well-fired carbines I own/have owned no-go at 1.297. This sounds Bubba, but a razor-blade or a pin-knife will trim-off the excess tape and render a shim that matches the case rim.

You can also pull the bullet on a loaded round, measure the case-length on that round ad do the tape thing. Don't use a fired round, but there would be no problem firing the primed case in the gun to be safer if you desire. The fired-primer should not deform the case like a loaded round does.

Typically folks use a Field gauge for headspace and the GO, and NO-GO gauges for new barrel installations. Using a NO-GO may cause you to declare a rifle unsafe when it really is still good to go. If you're unfamiliar (and as a good refresher I use since I still get them all mixed up) here's a link to CMP explaining headspace: http://thecmp.org/training-tech/armorers-corner/headspace/  

mikeurbas wrote: so what i really ant o get is a field gauge, if i can locate one.  i am also going to see what bolt i have, and replace if need be, if i do decide to shoot my ibm. thanks everybody!

Yep...as stated by sling00 above, the field will be the longest gauge. If it closes on a field-gauge, it's deemed unsafe to fire.

Gauges can vary in actual length and everything machined has a tolerance of some kind. The gauges provide a rough-and-accepted safe-unsafe evaluation. If you ever want to truly know exactly what the head-space is, you have to measure it in detail. You don't plan to fire this gun much-at-all, so this likely is not a concern for you, which is just fine.

I like shortages of anything for the M1. Demand of carbine stuff is an indicator that the little gun remains popular. When you can purchase 7.62 x 33 at 38-special prices....that has to be a good thing and you can usually do that if you shop-around.