The keys to a reliable M1 carbine are:
1. A USGI (NOT a commercial copy) that's in GOOD condition.
Remember, the last carbine was built at least 60 years ago, has been "through the wars" both as a military issue rifle AND through who knows how many civilian hands.
A worn carbine with possible "replica" non-USGI parts, or one that has a gas cylinder full of 60 years of burned lube and fouling isn't going to work well.
2. GOOD USGI type ammo.
Many people complain about unreliable operation, then we find they're using "Billy Bob's Budget Brand Ammo, $2.99 per 500 rounds".
The carbine was designed and built to work with USGI carbine ammo, not commercial ammo with different powders, steel cases, or soft-point ammo.
Some carbines WILL feed soft point ammo, but again, they weren't designed for it.
3. GOOD USGI magazines.
Most carbine problems are traced to worn-out carbine magazines or commercial "replica" magazines.
The 30 round magazines are particularly bad about problems, since almost all 30 round mags are either worn out or abused GI, or worse, bad commercial replicas.
So, if you want a reliable, accurate carbine, buy a USGI in good condition, then have it checked out/repaired/rebuilt by a qualified carbine gunsmith.
Use high quality USGI specification ammo, and use USGI magazines in good condition.
If you can find good USGI 30 round mags, fine, but otherwise stick with USGI 15 round mags, which can still be found new-in-the-wrap.
Do this, and you'll have the same reliable battle carbine that was favored over all other weapons by such experts as Audi Murphy.