Can't see the Gov't issuing a weapon that was Unreliable!
Man they still issue one!
As for the problem at hand though,
Sounds like you have a partially blocked gas port.
Or a weak recoil spring.
Also sounds like a new Gunsmith way be needed.
The Iver Johnson is not an exact copy. Although some parts
will interchange, The Milspec tollerances were a bit looser.
The M2 (or full auto version) was notorious for jamming,
the M1 was not. Gun parts Corp should have the spring
The gas port you should be able to take care of yourself
with a field manual and a pipe cleaner or two.