Colt Peacemaker known issues?

[Sniper Pete]

I'm not a happy chappie.

My Colt Peacemaker SAA.45 Peacemaker (.177 pellet version) has just gone wrong for the 2nd time, apparently with the same problem.

I'd had a half dozen shots no problem and was on my second 6 shots. First shot great, bang on target and as I took the next shot a slight change of note... what's this? NO hole in my target? Impossible!
I opened the loading gate to find one empty shell (from the first shot) and one shell where the pellet had moved less than a quarter of an inch (I don't do metric) in the shell but unfired.

I'll spare you all the boring details, just to say I eliminated the possibility of duff pellets, or faulty Co2 cylinders, by process of elimination.

When I checked my records for this revolver, I noticed it had failed once before, with pretty much an IDENTICAL problem, after just 3 months!
On that occasion it was returned to the seller under warranty, who returned it to their supplier. It was returned to me fixed... (maybe not) a month later.

One year 3 months later it fails for the second time. Because it is out of warranty now I'm having to pay for it to be collected and will no doubt be without it for weeks until it gets repaired and returned.

I NEVER leave it loaded with a Co2 cylinder still installed, for fear of the seal being compromised.

What does puzzle me is - There was NO warning of anything going wrong. It had just fired 6, near perfect, shots.
Now, when I load 6 shells, the first will fire, but then the others won't. Another 6 shells same thing. SO, there is enough pressure to fire one shot, but not the rest. Very odd. It's as if something is stopping a good seal forming and insufficient gas is being expelled to fully fire a pellet.

When I gave up I released the pressure gently from the cylinder, which still had plenty of gas left in it.

I've spoken to the in-house gunsmith at the retailer where I bought it. He has no ideas what the cause is. (The last time it went wrong there was a different gunsmith).

Have any of you guys had the same failure with this revolver, and if so any idea of the cause? I'm no gunsmith and only have a basic knowledge of the mechanicals. I NEVER tamper with fixing anything myself. All I do is the occasional clean.

The only issue I've heard of is the BB version damaging the barrel.

Suggestions please?

UPDATE ADDED 3.8.18

For those of you who wanted to know, I got my revolver back today.

The problem was a tiny pin had broken off the hammer inside the gun itself.

I have (TRIED TO) attatch a parts diagram for the hammer assembly, and a picture of the pin itself, but for some (unknown) reason I have NO option to attatch pictures?