Can you shoot a 2" shell in a 2.5 gun and pretend it's a 20?
 

I've never heard of anyone doing this, but can one shoot a 2" shell in a 2.5 for longer gun to pretend you are shooting a 20 gauge? RST offers the shells. It would work. Might pattern nicely too. Anyway, just thinking...

If its a 20 gauge gun, you wouldn't have to pretend.

A 20 gauge feels distinctly different in your hand. No amount of pretending will compensate for that.

I'm not even remotely sure I understand the question.

So if I load a 3/4oz 12g shell in 2 3/4" (which I do at times) can I pretend it's a 28g gun with 2 3/4" chambers???? ???

Something like that...

I reckon....

SOLUTION
 

Cheapest alternative.

Short answer, yes. That said, it really doesn’t get you anything other than an expensive shell. There are lots of other cheaper options that are close in shot weight and velocity. Even RST 1oz or 7/8 oz are cheaper.

Also, RST request that only people with 2 inch guns buy 2 inch shells as they are very limited run with no known re-run timeframe. If that matters to you

You can always cut down some shells and use 2 1/2" data to load them. I've made a few with roll crimps that came out nice. More work than I care to do too often, but they work.

Proprietary offerings of 2" shells in UK use card and felt wads with RTO closure.
This type of load configuration is more prone to pattern degradation due to inefficient obturation in longer chamber guns. If plastic wads are used in place of card+felt then there is less likelihood of gas "blow-by" however load data for the 2" hull utilising plastic wad and finishe with a crimp closure is pretty scant.