Mas 49 Conversion

I found a nice Syrian contract MAS 49 at the lgs today. It is mostly numbers matching, not import marked, and the wood is the nicest I have seen on a Syrian. The only thing not standard was a century-esqe stamping on the receiver denoting that this rifle was 7.62N. This is not my first converted mas 49, so I had some idea on what I was getting into.
I disassembled it on the bench at home and did a better inspection than the shop would allow, and found that this rifle does not close the bolt on a 7.62x51 like it said on the receiver. The cartridge is loose in the chamber, but does not go all the way down. It also completely swallows an x39 so it isn't that either.
Could this rifle be unconverted?
If this rifle was an unconverted 7.5 French, wouldn't the .308 still chamber, and bolt still close, just not safely

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Other thoughts, could this be a symptom of an old case head separation, left unfixed?

I cut the neck off of an empty case in an attempt to diagnose. It still doesn't fit.
I also attempted to tap in a case to see if by chance there was a burr. Try as I might, I cannot hammer the case in to a point where I can't effortlessly drop it out of the action

I'm not sure what to tell you. I did some investigating yesterday and all I found was this was the number 1 rifle to never buy because of these issues.

When in doubt, do a chamber cast.
Cerrosafe is easy to work with.

I like your idea about a case head separation, though. Do you have a way to look directly into the chamber? Borescope or little mirror or something?

I can look directly in, and I can run a wire down to feel the shoulder and throat. Nothing is in the way, and everything "feels" like it is where it should be for a 308.
The case stops far enough up that I might be able to cut the rim off and look directly down the brass to see what my obstruction is.
I was planning on making a chamber cast to see if that helps.

I know the 308 mas 49s and their reputation. This isn't my first. I had a Century 308 that I did some parts swapping, moderate modification and got to run like a clock. This rifle caught my eye because of the lack of import mark and overall condition. The 308 was just a bonus? that I don't need to hurt for 7.5 French.

Could it have a chamber adapter? Maybe short chambered? Do you have a full length sizing die for a .308?

Not as far as I can tell. Doesn't look like it has a bunch of freebore like an adapter.

I don't reload. I don't have dies, and the 7.62 I was testing with is commercial.

Many of those 308 conversions involved coils being cut off of the recoil spring. Maybe they removed too many coils from your spring and it doesn't create enough force to close the bolt all the way on your chambered cartridge? Good luck!

They allowed me to field strip in the shop. The recoil spring was one of the first things I checked. This is not a 49/56. It's not marked century arms anywhere on it, nor can I find an import mark. A quick internet search turns up no other full length mas 49 in .308. It may be a small shop conversion.
The cartridge physically does not fit in the chambe, when dropped in by hand with no bolt. It stops about 1/4" short, which in turn does not allow the bolt to close. By my best guess, the chamber is cut deep enough for 308, but the cartridge is getting hung up on the shoulder.
I brought it back to the lgs and they will diagnose and repair at no cost.

This gun is extremely dangerous and you should send it to me immediately so nobody gets hurt. I will pay shipping. :>)
Just kidding. I have seen a number of these on auction sites in .308N. I have bid on a few but they went for crazy price. Sounds like many have feeding problems depending on how the conversion was done/luck or whatever. I always liked the looks of it.

Do a chamber cast to see just what is not fitting. Chamber casting is easy cheap and will tell you the condition of your throat and rifling start. You can get from midway , brownells or Rotometals. https://www.rotometals.com/chamber-c...-low-158-190f/

Search on youtube for directions on how to use.....easy. good luck