Umarex Fusion 2 questions

I recently purchased an Umarex Fusion 2 air rifle. I've been having issues with what appears to be well known issue with this rifle... the bottom 12g CO2 cartridge not piercing. I've tried stacking 2-4 dimes between the cylinders, but even that's not helping. So I purchased 2-88g CO2 cylinders to eliminate that problem, provide a higher shot count and better consistency between shots. I understand the tube that the 12g cylinders go in has to be unscrewed, but how? It's so bloody tight and with it being close to the barrel, I can't really get a good grip on it. I certainly don't want to use any tools and risk damaging it. 

I've been doing some backyard plinking with Crossman 7,6g pellets, but certain I can get better accuracy with a higher quality pellet. What brand/weight pellet seems to perform best for this rifle?

Thanks!
 
batmanrobingamo.1610962838.jpg

 
No, they don't. I turns out that I needed to read the instruction manual and watch a YouTube video:

https://youtu.be/oLFo9aq0iC8?t=154.

However, it makes no odds at this point because that I'm now running Umarex 88g CO2 cylinders. I've noticed a marked increase in accuracy and the pellets seem to hit a lot harder, destroying such innocent things like empty beer cans at about 9.5 to 10m:



20210118_133425_HDR.1611069509.jpg
 
20210118_133505_HDR.1611069574.jpg


I'll get some grouping shot photos uploaded in the next day or two. All in all, I'm quite pleased with this rifle as my first air rifle purchase. No buyer's remorse here!


 
I had the problem of the bottom CO2 12gr cart not getting pierced so I bought some 88gr CO2. It wouldn't pierce either so I sent the gun off to Umarex for repair. $58 to ship. Got the gun back and the bottom CO2 cart gets pierced now but the 88gr still doesn't get pierced. Wrote to Umarex regarding their repair and never heard a word back from them. I'll be dam$#@ if I'll spend another $58 to ship it back for a repair they didn't complete. That puts it at more for shipping than the gun cost me. Can't find the part to replace it myself so I'll have to stick with the 12gr stack. I own 3 Umarex guns. This one, an SA10, and the P08 blowback. Both the Fusion 2 and the P08 had issues out of the box that required me to ship them off at my expense to have them repaired.
I don't think I'll be buying any more Umarex products. I can't afford their warrantee.