The chambers on a DPMS and a Palmetto carbine failed to gauge properly on a 5.56mm NATO go/no-go... both had their tight chambers reamed to true 5.56mm. Both barrels were marked "5.56mm"... go figure.
The DPMS had out of spec gas rings, which were replaced (thanks SeanM your box of pieces parts is still making the world a better place).
Neither the DPMS nor the Palmetto had worthwhile markings on their bolts; I recommended replacement bolts of a known quantity.
Both the DPMS and Palmetto were carbine gas systems with 16" barrels, however they both had CAR buffers, which I consider suboptimal for that configuration. I recommended either H or preferably H2 buffer replacement.
The DPMS had no staking at all from receiver end plate to "castle nut", which I repaired with a spring-loaded center punch.
Astonishingly, both the DPMS and Palmetto guns had decently attached and staked carrier keys. Both also had proper inserts in the extractor spring. The Palmetto had both M4 feed ramps and barrel extensions, and the DPMS had rifle ramps/rifle extensions. This was fine for the A1 configuration.
After these tweaks, proper lubrication and function checks, both guns ran without issue and exhibited good accuracy.