My brothers new AR

[RancidSumo]

My brother bought a new Bushmaster AR-15 today and we went out to shoot it at night. It had no sights yet (it does now) and we were shooting tracers. We loaded up the 5 round clip that it came with and attempted to chamber a round. It loaded a round about 3/4 of the way and then the tip of the second round went in, causing it to jam. The mag wouldn't come out and neither would either round. After a few minutes, we were able to get the 2nd round out and clear the jam. Was this probably caused by the mag, ammo or gun?

 

[RNB65]

I'm guessing a tight mag spring. Keep the mag fully loaded to give the spring a chance to set and see if that doesn't fix the problem.

The same things happens sometime with 30rd mags. That's the reason that people often recommend only loading 28rnds into a 30rd mag. Usually a few solid love taps on the forward assist will close the bolt and it cycles fine after the first round is fired.
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[RancidSumo]

Ok, thanks.

 

[Tom Servo]

If it's a relatively new rifle, tracers aren't too good for the barrel.

They won't wreck it, but I'd suggest something a bit less...dramatic and dirty at first to break it in.