Quality ran from "not reliable" to "good shooter".

The Iver Johnson was built to the original GI design, with some modifications.
"Most" USGI parts could be installed, sometimes needing some fitting.
All you can do is shoot one to decide which end of the spectrum the rifle lays.

 

Pretty good

I was under the impression that all the parts were USGI in the Plainfield except the reciever. I thought the Universal was the one that only some USGI parts were used. I may be wrong as the last time I saw a Plainfield was a long time ago.

 

Iver Johnson/Plainfield Machine carbines ARE mostly all GI parts, and they shoot just as well and as reliably as any GI carbine...as do the early Universals. It's the later Universals that deviated from GI-pattern and went cheap. I've owned Iver Johnsons before--both M1 and M2--and there's nothing at all wrong with them. And looking at the value/replacement cost of my GI carbines these days, I wish I'd kept one of the Iver Johnsons back just as a shooter.

 

The very early Plainfield Carbines used 100% USGI parts assembled to a commercial cast steel receiver.

As time passed, the supply of USGI parts started drying up, and Plainfield started making "replica" parts from cast steel.
The first parts to be manufactured were barrels and wood.
Eventually, almost all the parts other than small pins and springs were new made.

Iver Johnson originally owned Universal as a subsidiary, and again, the early Universal was mostly USGI parts with a commercial cast steel receiver.
Again, as parts got harder to find, Universal began making more and more of their own parts from castings.
Finally, in the early 70's, Universal did a complete redesign of the Carbine, and it became more of a "look-alike" than a GI-spec Carbine.
These later rifles had the double recoil spring system, a different gas system and a stamped and welded operating rod handle assembly.

After Universal went broke, Iver Johnson bought them back, changed the design BACK to the original USGI design and made them up through the mid 1990's.
Again, most of the Iver Johnson Carbines had mostly new made cast parts, with only small springs and pins being GI.

As an interesting side note on the Plainfield Carbines:
At the end of WWII, the US government began selling surplus M1 Carbines parts as scrap.
They were selling most parts BY THE TON.
A buyer in Rock Island?? Illinois bought most of it.
When they started up Plainfield, he supplied the start up parts, and it was those parts used to build most of the Plainfield Carbines. When the original supply of parts began to run out, Plainfield started making new parts.

When the Vietnam War started heating up, the Government needed Carbine parts to use to keep the Carbines we'd given to the South Vietnamese in running order.
The government went to the man who'd bought the parts at the end of the war.
What he'd bought from the government by the ton, he sold back, BY THE PIECE.
He was said to have retired very wealthy.

 

Used to have one a few years ago. It was pretty well wore out and would double fire alot. Traded it for a russian sks.

 

dfariswheel:
No one has ever accused the government of being overly smart.

If you compare an "old model" IJ or a USGI carbine to the late Unis side by side, you can see the difference in the quality of the piece.
FWIW, a local dealer is selling a newer Universal Carbine as a "rare" gun after stamping it with several US markings. Be aware of what you are buying.

mark