Feeding issues - FM Products Foxtrot Mike FM-9 Monolithic 9mm Upper Receiver

I used this in a USPSA match (PCC). It doesn't like longer mags (31 rounds or more). Endless feeding issues! It would slam the bullet but not feed it into the chamber. When you eject the round the bullet would be jammed 3/4 of the way into the brass casing. Works okay with 17 rounders. Tried 4 different 31 rounds or more mags and none worked. Unless I loaded them down to 25 rounds none of them worked so what is the point? Very disappointed and embarrassing at a match to have so many problems. The only upside was everyone in my squad and the squad behind us knows to stay away from this product.