I don’t like how dirty the interior of the rifle gets. The rifle needs to be run wet for best reliability and cleaning the interior is similar to wiping out an oil pan: a nasty combination of oil and combustion residue.
I prefer the open top exterior of the Garand/M14/M1 carbine. You can look down, instantly see what is going on. The openings are large enough that you can get you fingers in and remove jammed cartridges.
Serious AR competitors typically have a leatherman type tool on them or in their shooting stool. When you get a jam, and jams happen, or you get a blown primer rattling around the interior, you end up using the needle nosed plier to get things out of the loading port because it is too small for fingers. If you have a blown primer between the top of the bolt and the upper, the lack of a bolt handle makes it difficult to clear the primer. You can pull the bolt back with the charging handle but you can’t get it to go forward. The forward assist is basically useless for most of the bolt travel and does not provide much mechanical leverage.
Yesterday I had a blown primer eliminate me from a Highpower match. My trigger mechanism stopped resetting during the standing stage. I could drop the magazine, cycle the bolt, and get the trigger to work. As much as that disturbed my offhand sequence I got through it. However the trigger stopped resetting after my first sitting rapid fire sighter. I separated the halves and saw a primer in the trigger mechanism well. I knocked that out by wacking the lower on my shooting stool. During the rapid fire stage I shot three X’s and the trigger mechanism jammed again. I had to retire from the match and disassembled the trigger mechanism in the safe area. My trigger is a Rock River two stage. I wiped everything off, there was lots of grease and oil, no broken springs or parts, reassembled everything and was able to join the match at 600 yards. I don’t know what caused the reset problem, whatever it was either fell out when I removed the mechanism, or was wiped out. Still I was not confident in the thing, (every shot testing the trigger to see if it would release) only shot a 193-7X at long range, and I had a DNF in the two rapid fire sequences.
This mechanism traps primers, residue, in the trigger well. If something gets down there it does not come out. The Garand mechanism is so much better, you can pull out the trigger guard, the sides are open, so you can see everything and knock anything out with your finger.
As a semi auto target rifle the AR15 type is the best for absolute accuracy. However for a combat rifle I would want something better.
AR magazines have their issues. Even Government magazines malfunction given time. The shooter I was scoring, his first round on the reload came out of the magazine, ejecting from the port. He saw that and ejected the magazine. The next magazine auto ejected from the rifle, and I still don't know how he did that, even though I was watching this. He put the magazine in and hit the bolt release and the magazine ejected out. It looked latched till he hit the bolt release. When he got that magazine back in and relatched, he was so rattled that he shot those eight rounds at record speed, ruining his score.