I found this info about jammings and misfeads from a wholesalers website, very interesting and it sounds like it is the problem that you might be having with your T77;
http://www.airsoftgunsusa.com/shop/p...&cat=18&page=1
PLEASE READ DO NOT USE UHC GREEN GAS WITHOUT READING THIS NOTICE
If you use green gas with silicone (UHC G-1000) included you will need to clean the magazine, and BB holding O-Ring often (every 40 rounds) to minimize excess oil in chamber area. Excess oil can cause jams, misfire, short shooting, and/or shorten life of product. We suggest gas with little or no silicone fired through this product. You may introduce into the magazine a small amount of silicone to maintain seals. Ask your retailer to show you how to correctly clean this product. Use a clean Q-tip with very small amount of silicone to clean, and lube the O-Ring inside chamber. Then use a dry Q-tip to remove excess oil. Very light circular pressure should be applied to avoid damage to ring. Also periodic use of gun cleaning rod to remove build up inside barrel is recommended. Damage caused to product by customer voids warranty.