Champagne bottle woes

Howdy!

I need some help. Here's the deal: I have some american 750 mL green champagne bottles which I want to cap with crown caps. They look like these:

http://www.northernbrewer.com/winemaking/wine-equipment/wine-bottling/wine-bottles/750-green-champagne.html

The problem that I'm having is that I can't seem to get the bottles to cap right. I've tried the standard 26.5 mm caps, but when I push on them with my thumb they push off pretty easily (maybe this isn't a big deal). So, I tried the 29 mm caps - I can get these to seal, but the seal isn't great. If I shake the beer that I've bottled in these bottles, I get some beer which squirts out the side of the bottles.

I'm using a Red Baron capper. Is this the problem? Would I be better with a bench / floor model? I even bought a 29mm bell for the red baron to help with the 29mm caps, but it didn't work, I ended up capping the 29 mm caps with the 26.5 mm bell.

Any thoughts would be much appreciated!

Yes, you'd be better off with a bench capper.

I'll throw in a shameless plug for the Colonna Capper/Corker. The dual-mode model comes with the 26.5, and 29mm bells as well as a funnel and plunger for corking wine bottles. There's also enough reference on people using them for corking belgians.