Well I'm most likely not the one to be helping you, but first off don't forget to make a introduction post. anyway fittle around with the hop-up, Try using different gram bb's mabey? Last but not least I heard that propane makes gas rifles gods out on the field.
But anyway most of this is all If heard or just suggesting I personally want to get into some gas rifles too but I have very, very little experience with gas rifles.
Well, you're using 134A green gas I assume. Try using a propane or something with not as much lubricant already inside the bottle.
What's probably happenening is as that power shot is being released, the little amounts of silicon that they put in each bottle is getting misted on that hop up, and making it slippery to the point of ineffectiveness.
I'd suggest running a swab or paper towel or what-have-you in the barrel and seeing if you have a lot of lubricant inside there. That's the only real problem I can see with the accuracy, having something in the barrel such as a semi-cracked bb fragment or even too much silicon will greatly effect accuracy.
If that is the problem, I'd suggest switching over to propane, while only putting a set amount of lubricant before every game, as well as a little bit onto the tip of the can, so that it helps keep the seal good inside the mag.
I use green gas in my tanaka m40 and have had no problems with accuracy until you have fired 20-30 mags. Then the hop and barrel do get a fair amount of gunk in, but its easy to clean (due to just taking the bolt out )
My rifle is very very accurate on green gas and I think the lack of silicone in propane is not the cause of your problems.
When you got the L96 did you clean the excess of oil that was on the action?
If not the oil/grease will have found its way into the hop/barrel and be degrading your accuracy. Clean everything and only lightly grease the bolt's exterior.
Tanaka rifles do not work well out of the box and require running in before performance picks up. Some Tanaka rifles just shoot better than others (we bought several m40a1 and LTR at the same time and some were better than others).
The barrel change will help. Once fitted use 0.29g SGM they ARE worth it if you want maximum accuracy in my experience compared to 0.36g STRAIGHTS.
If nothing improves just try reseating the HOP rubber. Also take note that the tanaka hop system is more accurate with less hop applied then you would want.
I just wanted to inform you about the news.
Now I completely disassembled the hopup to clean it and what did I see? There was the mini-rubber missing, that ist pushing onto the sealchamber. I guess, it was just forgotten to build in? I took a small piece of rubber in the right size from a thin audiocable and now the accuracy is much better. I guess, after "running in" the "new" hopup and with the use of the modified tightbore it will be close to perfect - as a Tanaka should be.
Thnx a lot again for your help and best wishes,