The Mossberg 51M (no s) is a semi automatic .22 rifle, It was made from 1939-1946. It is an accurate target rifle, and has 3 sights- front, barrel mounted rear notch type, and a peep sight mounted at the back of the reciever. Values will vary based on condition, from about $75 to $250 for an excellent specimen.
They were originally made in New Haven Ct. Some are now made in South America. You can check with Mossberg Customer Service through their website.
There is a center fire and a rim fire.
A rim fire cartridge has the primer built into the rim of the shell casing. The casing must have a wide flat part at the back. A center fire has the primer in the center of the rear of the casing. The rim fire is less expensive to manufacture but is more prone to jamming. The rim fire is not suitable for rapid fire applications or rough handling.
The difference is explained in the name. A rim fire rifle uses ammunition where the hammer strikes the rim of the bullet. In a center fire rifle, the hammer hits the the center of the bullet. Rim fire ammunition is usually small, like a .22, and center fire ammo is generally larger.
Couple of problems- Spelling is Mossberg. Prior to the 1968 Gun Control Act, Mossberg .22s did not have a serial number, except for a few made for the US Military. The serial numbers I HAVE seen did not include letters. Is it possible that you have the Model number- since there WAS a Model 51M? Mossberg is still in business, and may be contacted through their customer service website. At the bottom of this page is a link to an excellent blog on Mossberg .22s that may help give you a range of dates for a particular model. PS- I collect older Mossberg 22s- they are GREAT shooting rifles.
Center fire- the firing pin is placed to strike the center of the cartridge. Rim fire- as the name implies- firing pin strikes the very edge of the rear of the cartridge- the rim.
in the rim of fire or the ring of fire
more then likely it's a center fire. rim fire cartridges are hard to find.
Marlin 31 is a shotgun. Marlin 81 is the rim fire .22.
CF
The Rim Fire which started in August of 2013 is not burning anymore. The fire was extinguished in October 2013, over two months after the start of it.
Rim fire, just like every other .22lr put out there.