Balls!

[Aimstraight]

Presumably the solid ball does not spread out as much on first impact, whereas the mass of the pellet is distributed along the weaker head and skirt?

Did you strip the pistol because it feels rough from new? Good pistol though, with quite a light trigger.

[Modski66]

Mine was nearly-new, but in perfect condition; I saw a US blog where one was stripped and lightly tweaked and a post on the UBC from a guy in Canada who had fitted a weaver rail to replace the original sights, which I fancied doing too.
When I got it apart, I realised how agricultural it was inside, so thought I might as well have a go at making it a bit smoother. My model did not have the trigger adjusting screw found on the earlier versions, so I drilled and tapped the mounting lug, which has made the trigger better.

[AdeC]

The weight of the pellet/ball will also affect the penetration.
Remember... Power is nothing without control (accuracy)!

[Hsing-ee]

Hmm. Are the spherical projectiles a really tight fit in the bore? In which case you may be getting some diesel-assist as the pressure builds up so much before they move that the oil vapour from your rebuilding is detonating.

How accurate is that little Russkie? It seems very keenly priced.

[Geezer]

My theory is that hitting the can causes the diabolo pellet to lose stability and tumble, reducing penetration when it hits the far side sideways-on. The ball probably also loses stability, but still hits ball-side on, because it is a ball.

[Modski66]

In reply to the last two comments, the Gamo balls are probably not as tight as pellets, but stop at the rifling after the breech lead-in.
It is an accurate pistol but a bit rough around the edges, my attempt at giving it a light tune and lube has made the firing cycle more pleasant. The hard thing for me is getting used to the front-heavy balance and ambidextrous grip compared to my target pistol. However, I am really enjoying the change and challenge of mastering it, I am hopefully getting a 2x pistol scope at the weekend which I am looking forward to trying.

As for the can bashing, I think one of the earlier posts got it right about the hardness of the balls being greater than that of the pellets; they certainly don't deform to the same extent.

[averageplinker]

So does the MP-53 have a scope rail? I didn't think it did which has put me off buying one to date.
Rich

[Aimstraight]

Hmm. Are the spherical projectiles a really tight fit in the bore? In which case you may be getting some diesel-assist as the pressure builds up so much before they move that the oil vapour from your rebuilding is detonating.

How accurate is that little Russkie? It seems very keenly priced.

It is accurate, the mechanism is very basic but strangely enough the trigger is pretty good. The rear sight has a bit of slop in it, but that can be remedied. The cocking action on a new one sounds like an old bed spring (it also includes an ABT ratchet), but the pistol shoots well with decent velocity.

Pretty sure Ian.KD did a review on bbs a while back (including strip and re-lube), but often is the case I cannot find that now

They were available from Europe at a ridiculous knock down price a year or so ago.