Almost any .177 air rifle can be used for Supported Air Rifle Shooting but the recoilless types will give the best results.
SSP air rifles are a good choice to get started with and will work as well as any other type but they will have to be removed from the bar stand to cock them after every shot. This may not be a bad thing as this "break" will force the shooter to take more time between shots and we have found that this can help keep the concentration levels good.
CO2 and PCP rifles will not need to be removed from the bar to be reloaded and for many this will be seen as the most convenient option, but this speed of reloading can lead to shooting too fast and spoilt shots !
Any rifle can be used "as it comes" by just resting the front of the stock on the bar, but making a simple hard wooden "resting plate" to fit under the front of the stock will prevent any possible damage or wear marks to the rifles stock that may occur after extended use on the bar.
The "resting plate" can be made from any "hard" surface but wood (maximum 60mm wide) is the easiest to come by and the most simple to work with. We were given an old piece of water stained oak and that proved to be ideal and cleaned-up really well for our rifle rests, but it would have been just as practical to use any other sort of hard wood or even MDF to make a "resting plate" to fit under the front of your rifle stock - and MDF is probably a good idea when experimenting with shapes and fitting as it cheap and could always be copied at a later date in a more exotic wood or just sprayed matt black to look good.
The "resting plate" can be made to extend the length of the typical match rifles hand rest by making it fit immediately in front of it - but at the same height to give a smooth continuous lower support to the area under the main stock body. It would also be possible to simply replace the hand rest with a new longer one in much the same way as the manufacturers produce their specific "senior" rifles that are designed for bench rest shooting.( see Walther Anatomic Senior to get the idea).
The important thing about the "resting plate" is that it must be made from HARD wood as a soft wood will eventually "dent" in use and will then become illegal as this will give an unfair (and illegal) support as it begins to mould itself to the shape of the bar.
The contact point between the surface of the 50mm diameter hard bar and the 60mm wide (maximum) hard surface of the "resting plate" fitted to the front underside of the rifle has to be no more than a tangent when placed together. Any soft or "compliant" surface will help to hold and stabilise the rifle much more that the two hard tangental surfaces can achieve and so will give an unfair advantage to anyone whose equipment does comply with the ISSF rules
We have made our "resting plates" so they can be easily fixed to the front underside of the rifle stock and can be quickly removed again to return the rifle back to its standard form so it can be used for any other type of target shooting without compromise.