When you shoot it the gas all shoots out sometimes. It usually shoots okay on semi but it still happens then as well. But most times on full auto you get a few shots then boom all the gas shoots out. Not sure what's wrong not very familiar with gbbr. Selling AS IS to someone who knows how to properly fix it. Comes with what you see in the photos. This is a listing from East Coast Airsoft. We are a physical retail store located in Bel Air, Maryland. If you have any questions or concerns feel free to reach out to us any time. Either on here, Facebook, Instagram or you can give us a call at 410-838-6856. The store is open every day from 11AM to 8PM. ALL PRICES DO NOT INCLUDE SHIPPING, please message us your full shipping address for a quote. WE ONLY DO TRADE INS AT THE STORE, IF YOU ARE. NOT LOCAL WE ARE NOT INTERESTED IN TRADES!!!