GBBR barrel volume question

[venture]

Question for the GBBR doctors here. I have just acquired a KJ M4 and am starting the learning process.

Can an M4 GBBR in general, and the KJ TK designed M4A1 in particular, accommodate a 20 inch inner barrel? Can you even get one for a GBBR that long?

I am thinking about cylinder porting in aegs to prevent too much air blowing out the barrel. Are GBBR's calibrated to barrel length this way? Basically I would like to make an SPR or M16 out of it.

[Amos]

You're going to have INSANE velocity with a barrel that long. With a 363 mm barrel, and no velocity reducer, you're hitting in the mid 500's.

The velocity reducers can only do SO much.

You can put a long barrel into them, but at SOME point it'll stop benefiting the gun.. I'm not sure at what length vs what system... but there is a point.

[venture]

thanks amos.

[Eeyore]

But you could do it properly with a WE gbbr.

[ILLusion]

There technically isn't the same concern with "barrel suck" and porting that you'd have with a fixed volume pneumatic system like with AEG's or spring cock guns. With gas guns, you could generally install any length inner barrel you want, and the system will sort itself out. It will shut off the gas when appropriate. Thus, you could put in a 2 mile long inner barrel if you wanted.... although the gas in your mag might deplete before the BB leaves the barrel. LOL