What is the purpose of a threaded barrel on nelson units?

Is it for different ammo? I was looking at their site and they say to specify what ammo you are using. The ammo I'm using is cci std velocity. If I wanted to try something else, would it work. What do they do when you tell them your ammo choice? Is it a spring change, or is there a headspace difference?

Nelson has 3 different chambering for their conversion.  Depending on what ammo you plan on shooting determines chamber cut. Threads are for silencer if you live a state that allows it. They're very nice units.
Jon

Suppressors are nice. Some will actually help the guns accuracy.

On my Marvel Unit 1, which is lighter than my Nelson, I put a steel compensator on it to give it some weight.  When I ordered the Nelson I got the threaded barrel thinking I'd have to put one on it as well, but because the Nelson uses a steel optic rail I didn't need to.

- Dave

On the hit man forum they all buy that model...