To go from a loader to a stock class feed, you need to buy these parts:
- Stock Class Breech ($28)
- Horizontal Feed ($15 black, $20 clear)
- Screw for Horizontal Feed ($0.25)
- 10 or 15 round feed tube ($11.99 or $12.99)
- Feed cap ($3.85 black, $5.99 clear)
- Ball retainer ($0.50)
So total would be $59.59 - $67.73 (depending on feed tube length and color) to convert it to stock class if you want to down the road. Installing the parts themselves is cake.
I took those prices from Wevo
http://www.wevopaintball.com/pumppaintball.html, but Otter's will be about the same.