Could anyone explain what does unchoked barrel mean? I found the so called "prometheus plastic pellets" and it says thay they are suitable for unchoked barrels. Does this mean that they are not suitable for my RWS 48 ? Any reply will be strongly appreciated. Thanks.

The ckocke is a small reduction on the inside diameter of the barrel at the muzle .There are many technical reasons for it to be there,but the piont is that it makes a more accurate gun.As for Prometeus pellets out of your 48 , they go supersonic (report sa loud as a .22lr)and they are not accurate at all.
On the flip side ,they are great for tricks.You shoot a penny at 10 feet and they go thru like butter, your buddy will think you have the most powerfull airgun in the world!

Sorry , I kind of miss the point.A unchocked barrel is a parallel barrel , same diameter all the way thru.As for the pellets ,if you take them apart and the metal point falls thru your barrel easily, is safe to say you're ok to go.
Just in case have something handy to CAREFULLY push the pellet out.DO NOT push it thru the muzle if it gets stuck.They are ok on my 52 so is probably unlikely youll ecounter any problems.They are a killer on the spring, so I only use them for the penny trick.

Thanks for your replies Otto. Why are they killers on the spring? As long as i remove their plastic and the bore wont get damaged, how could they affect the spring?

On a powerfull gun they crate little resistance and they start moving before an optimal cushion of air is built in front of the piston.That creates the piston to slam violently at the end of its travel.
I dont' mean to take appart the pellets to shoot them, what I meant is to take only one appart to make shure that te metal core can fall thru the barrel by gravity ,so wen you fire a complete pellet there will be no chance for the metal to tuch the barrel.Be carefull with ricochets , they are allmost like BBs on hard surfaces.

in a chocked barrel is the plastic sabot stays in the barrel or causes a major restriction as the pellet exits and the plastic has to compress. Plastic does not deform or compress as easy as lead does. The reports I hear are these pellets are not very accurate and I can tell you from exerience they rocochet off metal or hard surfaces to a great extent. As the instructions for BB's state "Do not use these on metal targets". Some use a zinc type of metal, the ones I have are steel. They do increase the velocity.