How to check caliber of a rifle...

[MicroPilot]

Is there any way to determine what caliber a rifle is chambered for?

My Dad gave me a really beat up looking MAS 36. The shells he had for this gun are 7mm. The MAS is supposed to shoot (very hard to find) 7.5mmx54 cartidges. I acquired a box of the 7.5 MAS cartridges and when fired it seems that there is gas escaping around the case and coming back toward the shooter. I have not tried the 7mm shells that came with it as I expected this to happen with those shells.

Is it possible that someone has used a MAS receiver and put some other barrel on it. The barrel is too short, the front sight, and the stock are different than pictures of the MAS 39's I've seen on the web.

[cimmaronkid]

Yes, there is a way to tell what the rifle is chambered for. You need to get some cerrosafe from Brownells and cast the chamber to see what you have. Stuff is easy to use and then you can measure and see what you have.

A lot of the Mas 39 rifles were converted to 308 just like their replacement, the 49/56 were and not done correctly. Not seeing the chamber cast, I would bet that the rifle was rebarreled into something different and would not shoot it until you knew exactly what it was. It could also have excessive headspace in which case the above applies again.

Also, post some pics so we can see what you have.

[okie shooter]

Micropilot, does the rifle have an sks type safety in the trigger guard to prevent movement of the trigger, it maybe a converson to 7.62x51(.308 winchester) where century setback the barrel, rechambered the rifle and added the safety. Look for markings on the receiver or barrel denoteing the change.

[MicroPilot]

No trigger SKS type saftey, but there is a device under the rear of the bolt/receiver that acts as a safety. My understanding is this is not typical for a MAS 36.

[MicroPilot]

http://lh4.google.com/image/rghunley1/RgpvxFnd5tI/AAAAAAAADHA/1d2_XqxKVOk/IMG_0312.jpg?imgmax=512

http://www.militaryfirearm.com/Forum/picture.php?albumid=1&pictureid=158

[okie shooter]

Looking at your pictures, thats been converted as a sporting/hunting rifle, I am not sure what round it maybe chambered in. I would recomend the chamber casting to ensure that you have the right ammunition. Does it look like the barrel has been shortened after rechambering? That at least would lead me to think its been converted to a shorter cartrage.

Upon second thought of your problem and the fact it leaked gas but chambered the 7.5x54 cartrage(thus the barrel wasnt refaced and shortened at the chamber end), it couldnt have been rechambered for 7.62x51 nato, you could never get the longer french round into the chamber. Hmmmm maybe 30-06 or something longer than the french cartridge. If you had a spent 30-06 cartrage you might try to see if it would go into the chamber, NOTE, spent cartrage or snap cap for 30-06. Do not force it to chamber.

Another thought, compare the shot cartrage to a unshot 7.5 and see if they are different, if it is 30-06(or something longer) the cartrage would try to fireform to that shape and maybe crack but would look different than a virgin round.

Another interesting thought is you said, it came with 7mm rounds, have you tried to measure with a mic the bore at the throat. I would think if it had been lined or barreled with a different but smaller caliber you wouldnt have been able to chamber the larger round or atleast closeing the bolt might have been really tight.

[cimmaronkid]

Are those steps I see on that barrel? How about a couple of pictures of the fired cases? Do a chamber cast because it could have been done in 8mm Mauser as the picture looks like a cut down mauser barrel. Good luck.

[okie shooter]

On hand guns you could force a slug of hard wax thur the barrel with a wooden dowel and get a good idea of the diameter of the lands and grooves, this might be alot harder on a rifle though but if you wanted to do it from the muzzle to the chamber and catch it and measure carefully with a caliper or micrometer.

[k98k792]

I think CK has a winner. Looks like a Mauser barrel to me too.

[turbothis]

i bought my mas 36 sported just like that. lol. got some new old wood and noticed they chopped the end of the barrel off. bastards! mine is 7.5 and shoots nice when i can find bullets for it. no gas to the eyes like his. would it be geek to get it chambered to .308?

[cimmaronkid]

Not geek to get it chambered to 308 as a lot were, but why do it? This is not a particular gun that lends itself well to customizing and would not increase the value of the gun and in fact make it less. If you can do the work yourself, then fine, but otherwise I really feel you would be chasing good money after bad.

[turbothis]

i actually saw a old 36 that had a huge stainless barrel on it at the pawn shop that said 22-250 0n it. big old scope too. they wanted 250$ for it, i thought it was kinda neat but a bit of money for me.

[okie shooter]

The problem of converting this rifle to .308 winchester, is that you have to shorten the barrel, then refit to the receiver. Mine was done by our friends at century and now the forewood is slightly loose but other than that I have the funky self storeing spike bayonet and the new and improved Century added sks type of safety. It would be far easier to make it into 30-06 if there was enough barrel reinforcement where you have to reem the chamber longer.

[turbothis]

i kinda like mine to be the real frenchy that it is so i will leave it alone. poor little thing, barely made it this far.

[cimmaronkid]

Gotta remember that it is a FRENCH rifle and has probably only been dropped once or twice!

[MicroPilot]

Heres a pic of a fired 7.5 MAS casing from this rifle.

Pic deleted (DOH)

[turbothis]

maybe the chamber has some good pitting to cause the gas to go around the casing?

[tanstaafl4y]

cimmaronkid nailed it with the chamber cast.

okie suggestion of slugging the barrel is also an important peice of information.

Alternatly you could take the rifle to a competant gunsmith and pay him to cast the chamber and slug the barrel.

/I had a similar situation with a Llama pistol that was sold to my father as a 9mm (nato implied)....It shot fine for him for 20+ years, it wasn't until he recently moved to virginia and gave the pistol to me that I informed him it was a 9mm Largo (and it only took me 3 days of research to figure that one out.)

[okie shooter]

Sounds like dad had a extractor strong enough to hold the rim and not let go when the fireing pin hit. They say the astra 400's will shoot all sorts of rounds, but I need to get some largo to feed mine.