first carbine unboxing

[painter777]

Get the mags tweaked asap.
Check any Trigger housing pin holes for excessive wear as stated by others.

Next I'd be looking for the longer type II mag catch / safety spring and plungers, using the later M stamped mag catch. This is what JackP is trying to point out.
Check bolt for burrs on the bottom front that push the casing forward. They can be lightly stoned.
Camming area on the hammer should be burr free and lightly greased.

Add: I like to lightly buff the feed ramp then a added drop of oil rubbed in with my finger.

** The longer Safety / Mag catch spring/plunger will push the later M stamped mag catches forward, which will raise the front of the mag.**

See TM9 1276 1947
http://www.90thidpg.us/Reference/Man...-1276_1947.pdf

Page 48 section J
27.) Check magazine catch spring plunger for retention on spring, wear,
and burs, and check spring for functioning, deformation, and set.
Free length of spring is 0.813 (approximately
7/8) inch. When assembled,
last coil of spring is contracted slightly and fits into groove in shank
of plunger for retention. Magazine catch (B7160470), and magazine
catch retainer plunger with safety plunger, assemblies (B7160472)
should be used. This is the catch that protrudes outward farther than
the old design, thereby providing greater engagement between the catch
and the nibs on the back of the magazine. It can be readily identified
by the letter "M " on the right-hand side.

Also on page 12:
(4) Chambering of cartridge. The bolt should chamber the cartridge
smoothly when released. If bullet ramp on receiver or barrel is rough,
or magazine loose so that it tips forward, the bullet may bind on ramp
or be deflected upward during chambering and strike the top of the
barrel and cause a stoppage.
(5) Position of cartridge in mouth of magazine. If magazine follower
does not position cartridge fully up against lips of magazine, the magazine spring may be weak or broken, or the tube or follower dented,
rusted, or burred, or the magazine incorrectly assembled. If dummy
cartridges are not available, depress follower to bottom of tube and
then allow it to rise. Inspect for smooth and positive functioning.

You'll figure it out soon enough. Good Luck,