AR15 Pistol only shots 5.56
I'm new to ARs. Got 2 7.5" AR15 Pistols within the last 30 days. Bought one used and the other new. Both supposedly had 200 rounds through them. They both will only shoot 5.56 without any problems. I get FTEs after the first round of .223s are fired. I load only 25rds in 30rds Magpul G2&G3s. Cleaned & lubed per recommendations given by numerous YouTube experts. I did a Google search and didn't find similar problems. Could this be a buffer spring issue.
TIA,
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