Umarex Colt 1911 problems and general questions

I recently switched my Gamo Black knight (29 joules) for a Umarex Colt 1911. I watched so many reviews of Umarex and they all came out pretty good. I was expecting (if I can believe the internet about 60-80 shots). 

First problem I encountered was the single shot didn't put the pellet in front of the barrel making it getting stuck into the gun and deformed. 
Second problem is that I only get 3 good mags out of it and 4 is dropping already. Less then 30 shots? 

I called the shop and I can get a new gun next week. First problem is obvious a fault in this gun but what about the co2? Is it normal for this gun?
I kind of feel bad I made the switch to co2... but again now it's much more compact, quiet and quicker to shoot. The gamo was a bit too big and loud.. (and overpowered for what I do)

---

Secondly as said, I can choose a new gun. I mainly focus on target shooting, I want economical in co2, accuracy and good fps (or just a good fps that remains consistent). I really liked the replica stuff but it isn't necessary. 
I've been only looking to Umarex as it's the only stuff that the shop has in stock. I probably can ask to order other guns too. So are there any "best guns / brands" for the stuff I want? 

--- 

Will a gun made out of plastic drop less in speed because steel gets colder easier?

Many thanks

Jesse