Background:
I purchased a Bushmaster Carbon 15 Type 97 in July. I really haven't had the chance to shoot it much; I may have put 100 rounds through it before today. Probably, the round count is more like 60. I have never cleaned the gun and the only lube I've used is a graphite spray from Birchwood Casey.

Ammo/Mags:
So I took it to the range today with 240 rounds (40 rounds of 69 grain PMC with Sierra MatchKing bullets, the rest 55gr Winchester White Box). The PMC is the heaviest bullet I can find commercially in my area. I have SS-109 from Spain, but the range I was shooting at will not allow them.
I had 4 Colt 20 round mags, 1 30 round LaBelle, 1 30 round Adventure Line, 1 30 round Parsons, 1 30 round Orlite batch 0/22. All magazines are of pre-ban manufacture. The LaBelle, Adventure Line, and Parsons all have green followers and have been refinished at some point. The Colts are old and worn.  

Range/Targets:
I was shooting indoors at 25 yards. I alternated targets between a B-24 and US Navy 25 yard qualification targets (they simulate an 100 yard silouhette). I made no effort to measure groups. In my view there is really no point since it is 25 yards. Besides the gun shoots better than I can.

Optics/Mods:
The optic was a first generation Bushnell Holosight. This has been the best investment I've made as far as red dot sights. I've had a Simmons and a BSA both were complete junk. They maybe lasted 3 shooting session before they would not hold zero.
Before I even shot the gun I ordered a youth stock and an ambidexterous safety. Both were easy to install. Even though I'm a lefty, I don't find the ambidexterous safety to be instinctual. I guess I've shot too many righty guns in my life. I still reach around the grip with my thumb to take the safety off.  The youth stock gives the gun a length of pull similar to the A1 stock. I prefer shooting ARs with either entry stocks or collapsible stocks all the way collapsed, nose to charging handle, off hand.

Shooting impressions:
The gun has a huge muzzle blast. I didn't notice this until today. I guess it's because I had shot my other Bushmaster last week with an A1 flash hider. The fireball had to be three feet in diameter if it was an inch.

The fiber stock has NO give. I'd rather shoot a shotgun all day than shoot more than 200 rounds through this gun as is. The last 40 rounds were painful. So much so, I'm ordering a rubber slip-on next payday. The first 180 or so rounds were fun.

The carbon fiber handguards get HOT. And I mean damned hot! I shot all 240 rounds in less than 45 minutes and the heat just kept building and building. It was still hot after I took it home and I live 45 minutes from the range.

The brass deflector looked like it was experiencing some deformation. Bushmaster expected that I think. The brass deflector attaches with an allen head screw, so replacement should be possible.

I think the lightweight bolt/carrier vents gases in weird ways. Take a look at the pics of the bolt below and you'll see what I mean.

Overall, the gun was fun to shoot. It would keep the rounds on the target if I did my part. The trigger seems lighter than my other Bushmaster. I think I shoot iron sights better than I shoot a red dot, not sure why that is. If I had it to do all over again, I'd buy two Aimpoints instead of another gun.

Reliability:
All mags were completely loaded at least once. The 69 grain loads were fired from the Colt 20 rounders with zeor malfs. The gun functioned perfectly through the first 211 rounds. On the last mag, the Adventure Line, the second round failed to feed from the left side. The nose of the bullet wedged itself between the lower receiver and the barrel extension. I locked the bolt to the rear, dropped the mag, reloaded the round and successfully loaded the same round from the same mag by just releasing the bolt hold back device. I believe the heat was the indirect cause of this. I could no longer grab onto the handguards due to the heat, nor could I use the magwell as a handle, it was burning the top of my off hand. So I used the magazine as a handle. The Adventure Line has more play than any of the other mags, so I think by using the mag as a handle I forced the round to nose dive.  I moved my hand up to the magwell, careful not to brush up against the handguard, and no more malfs were experienced. I did not notice any deformation of the carbon from the round that failed to feed.

Recommendations:
The rubber butt is a must. Something has to be done about the heat build up in the handguards. Not sure what that something is yet. The muzzle brake is getting replaced with a flash hider ASAP.  I'm not sure if I should dremel the feed ramps to try to prevent a future malf like the one I experienced. Perhaps, some homemade M4 cuts?

Pics!
C15 T97 field stripped:


Bolt/Carrier left side:


Bolt/Carrier right side:


Brass deflector:


Feed ramp: