I'm running a Colt Lower with my own upper at the moment.
- Colt Upper
- DD 14.5" barrel with a mid-length gas system
- DD BCG
- JP rifle length tubular handguard
I've been using it for 2 months now and have put about 2k rounds through it. Typical session is around 400 rounds. I've not yet cleaned it yet either.
Previously, I was running a LMT Carbine upper and never had a problem with it.
The why, I could not find a pre-built and readily available upper in the configuration I wanted. I tried other rifles and found that I prefer the mid-length gas system and the rifle length tubular rails on a shorter barrel. I went with the 14.5" barrel for the novelty of having a total length of 16" with a BattleComp 1.5 pinned to it. The barrel is a government profile, so it's fairly light and stays accurate under sustained heavy fire. My original Colt was a carbine with a pencil barrel and I found that accuracy went to shit on a hot day after putting through a few hundred rounds.
Initially, I was going to upgrade my Colt upper to a free float rail system. But looking at the cost of a rail/labor versus buying a new one. I found a brand new LMT with a blemish on it, sold the other upper and came out ahead.
As others have said, get quality magazines. I was getting FTFs and thought it was the rifle. But after running it in a free state with PMags, the problems ceased. This is what happens when you can only legally own magazines manufactured pre-94. After a while, the springs wear out, followers wear, bodies dent, floor plates come off and feed lips go to shit.