I am not a good modeller (or better put, an experienced one). Also, the only 3d modeller I have ever worked on is Milkshape. But here are a few things I can tell you :
1. 250 is a lot of polygons for something so simple. If you will play around, you will find out that reducing polygons on flat surfaces works wonders!!
2. Since its practice, I can understand. But for models made for games (I am just assuming) you can let the horizontal grooves (or whatever you call it) on the barrell go. It can be achieved using good texturing.
Again, this is what I think. But to be honest, if I were you, I wouldnt pay much heed to something said by a newbie to modelling
-- n00b at playing games...and now at making em too :p --