I'm not too worried about it, to be honest. I shone a light down the barrel and it looks fine - no scratches or bulges or anything.

My 249's gone through 3 brass barrels so far, so don't tell me BB's can't mess up barrels lol

Just an update for posterity, in case any other noobs have this problem. I loaded it with .2s (the sample pack, but probably still better quality ammo than Wal-Mart .12s) and it functioned flawlessly. Thanks to everyone who posted in this thread for their patience and input!

EDIT: I may have spoken too soon. I'm still experiencing stoppages every now and again but nowhere near as badly as with the .12s. Maybe these will be fixed with higher-quality ammo.

take your barrel out and try dropping .20s through it by hand and see if they get hung up anywhere

I had similar issues with mine. ended up changing the hop up unit, hop up rubber and nub and the barrel. The original barrel was warped, and the hop up leaked and was causing the misfeeds. I also wasn't getting any hop up on the bbs till I put one of those bridge type nubs in. Not my best gun after all that, but its pretty consistent and reliable.

Dropping BBs manually down the front, are they supposed to fall right out the other side? I experience no stoppages in the barrel itself but the BB gets caught on the red rubber ring (the bucking?) which prevents it from falling straight through.

ts10z: Yeah, I'm not using this gun for serious skirmishing or anything so I don't need it to be a tack driver. I just want to be able to plink with it and maybe play some informal pick-up games every now and again.

If you are dropping them in from the muzzle end then they should be caught on the hop-up rubber. But if the "entry ring" (on the chamber end) of the hop-up rubber being too tight for BBs that can cause jamming.
So your barrel should be no problems now.
Try to figure out where the BBs are stuck when you had a FIRST jam (stop shooting after you found first jam as the later BB will push the jamming one out of position), they should no longer stuck in the barrel (unless the problem is caused by few bad BBs).

It's the flash hider. I remember now. BBs were shattering on it's way out at one point. Try shooting without the hider and see how it performs.

It seems to perform a little better without the flash hider but I still experienced a stoppage after about 20 rounds. This time, the stoppage seemed to originate at the "entry ring" of the chamber, as ccyg8774 described it. Perhaps that particular BB was out of spec?

You may need a new rubber.

I've seen improperly molded rubber before that were too tight on the sealing ring and had to be bored out a little bit because they were causing jams.
Cheaper to get a new rubber though

So what type of rubber would you guys recommend I get, then? I can see different choices like 60°, 70°, 80°, hard type and soft type. I have no idea what any of these descriptors mean and which one would be right for my gun.

PDI-W

Well, I've had good experiences with Maple Leaf buckings and the PDI W-Hold. Many players also recommend a Guarder clear bucking. As for the different degrees and such, the correct bucking to use depends on the FPS and ROF of the gun. Generally you want to use a lower degree for a lower FPS. For example if your gun is shooting around the 360 mark get a 60 to 75 degree 'soft' rubber, likewise if it's shooting over 400 FPS it's best to purchase a 'hard' bucking.

Well, my gun is supposed to be shooting at 450 but last time I chrono'd it, it was shooting at 290, so yeah... Not sure what to choose in this case. :P