Should a new bolt for an M1A be a drop in part?  Or, does it need fitting?

I'm being informed that it must be fitted.  What say you?

Has to be fitted due to headspace.

Good Point.  Makes complete sense.  Thanks

It doesn't always have to be fitted. There is a chance it will drop in and be GTG.

Strip the new bolt and see if it closes on a "go" gauge, if it does, and doesn't close on the "no go" gauge your GTG. If it does close on the "no go" check it on the "field" gauge, if it doesn't close on that, your still GTG for a while.

On the other hand if it WON'T close on a "go" gauge, you will either have to have the chamber reamed until it does close, or if you have a chrome lined chamber/barrel, you will have to lap the bolt lugs to get it to close on a "go". You have to be very careful with lapping the bolt lugs that you don't lap too much and get through the hardened outer layer of steel on the lugs/locking surfaces.

The poor man's way of measuring headspace............and I am NOT recommending this, just throwing it out there.............is to strip the bolt, take a factory round, put it in the chamber, and see if the bolt will close on it. If it does you have "good enough" headspace to at least safely fire it and not worry about an OOB discharge. But I have seen this work/not work depending on the mfg. of the ammo too, that's why I am not for this method.

Every M1-A is headspaced to the current bolt it already has. The barrels are manufactured and "short chambered", meaning once it's torqued and timed to the receiver you have to finish ream the chamber to obtain proper headspace. A rod similar to a cleaning rod is run through the barrel and is attached to a finish reamer. It's turned until enough metal is removed from the chamber so the bolt will just close on a go gage.  

If anything you may have insufficient headspace if you replace your old bolt with a new one. This depends on whether your rifle has ever been rebarreled before. The bolt and receiver wears and mates with each other in use. Headspace grows over time. If your barrel won't close on a go gage with your new bolt you're in luck. A finish reamer will bring it into spec.

My first question would be, why do you feel that you need a new bolt?

If you want to try this at hone make sure you purchase a go gage and a no go gage. There are two different sizes, 7.62x51mm is considerably longer than standard .308. I can't remember for sure, but I think Clymer gages are the closest to military spec for an M1-A.

Well....I'm not a gunsmith, nor a machinist.  So I'm not going to mess with trying to do it myself.  In that regard, I am unqualified.

The bolt face has suffered from some serious erosion (etching) around the firing pin hole from either too hot loads or loose primers.  In any case, I will likely be replacing the bolt sometime this year, hence my original question.

Thanks for the education on the matter.
-ppknut

The fitting is not just for head space. Its a good idea to lap a new bolt for lug contact also.

Winchester standard large rifle primers have had gas leaks since they stopped nickel plating them close to ten years ago.

I would avoid them if possible.

Damn!  That may have led to the breech face pitting I've experienced.  WLR primers have been pretty much exclusively what I've used.

I will say that I've not seen the pitting using these same primers in my other large primer based cartridges (i.e., 03A3's, 6.5 CM - bolt guns).  Is the M1A possible more prone due to its being a semi?

Only if you're firing it more than the others.

That works, unless your chamber is chrome-lined.
If it's not too far out you can usually get there with lapping compound. Depends on how much lug contact you start with also.

There's no harm in checking with gauges yourself. As stated, you may get lucky and have a drop-in fit. In my experience it's fairly common.

If you can find a place with more than one bolt(like maybe at a gunshow), and if they will let you, test each bolt with a head space guage and see which one fits the best. Though you may have to do a little lapping to ge the lugs to fit right.
If you're looking for a USGI bolt, the TRW bolts might be a bit harder to fit, as many were made as replacement bolts.  Made to assumed specs.  "Assumed" based on the amount of wear that they assumed the rifle would do.....................................which did not happen.  So, they may be a bit hard to fit, as they may be a bit longer.

For what it's worth, I have a lot of pits on my bolt -TRW G.I. bolt in a LRB-due to the Winchester primers. It's like a door ding. 3K reloads later I'm not worried about how many pits are in the boltface now.

The pitting shown looks a bit more than "door dings"

I know that for the time being it shouldn't affect performance, but I think of it as damage that could get worse over time.  Hence why I'll probably replace it at some point:

This is true. I've experienced it myself. I've had two rifles damaged from this happening.

If this were a well documented occurrence, you'd think Winchester might want to change their manufacturing process.  If proven, wouldn't they be responsible for damages???

I know it'd be unlikely to change things up, but it makes it sound like a "known defect."

True, I ruined two bolts on a custom bolt gun because of them and I will no longer use them.

This is true for me. I have a M1A with a chrome lined barrel and I wanted a spare bolt. I bought two and one headspaced perfectly while the other did not.

M1 Garands are pretty much drop in bolts. I have bought several M1 Garand bolts and they all just dropped in and headpsaced correctly without me doing anything. I don't know if this is 100% true but from my own experience, M1 Garands seem to be drop in replacements.

I believe the problem with M1A is that the receivers are in different tolerances. No company actually makes the correct USGI receiver because it is too expensive to make. I do believe Smith has a forged M1A receiver but I don't know if it is within true USGI specs or not. Whereas most Garands are built on actual USGI receivers and nobody currently, to my knowledge, actually makes M1 Garand receivers.

Those are plasma burns. They usually come from either neglect or using reloads with bad primer seating.

Personally I wouldn't stress it too much and just keep shooting. I'd avoid using reloads.

FWIW, I've seen a number of Garands that needed to be checked with multiple bolts before finding one that had proper headspace.