Chopping 20" SFAR down to 16"

[MarksmanJelly]

Just got my new 20" SFAR. My question is, would any issues come from taking the barrel length down to 16", considering it came with a rifle-length gas system? My reasoning for doing this is because I plan on throwing a suppressor on it and a 20" barrel + suppressor length is just too long for my liking.

 

[hittman]

Considering the problems some have had with the gas adjustment I'd wonder if shortening it would create a problem in reliability.
Why not just sell it and buy their 16 inch model?

Welcome to the forum.

 

[MarksmanJelly]

I've seen a lot of these issues with the gas adjustment and 99% of what I find are with the mid-length gas system that comes with the 16". I was wondering if these problems could be easier to fix or even solved if I had the rifle-length gas system on a 16" barrel. Just as long as it wouldn't be too undergassed with only 4" between the gas block and the end of the barrel when cut down to 16".

 

[Mobuck]

I don't own a SFAR(never even handled one) but I do have a fair amount of experience with the common AR platform.
Here's what happens when you try to run a rifle gas on a 16" barrel: the 'dwell time' is often insufficient to achieve proper cycling. Dwell time is a function of bore diameter, gas port size, gas volume(of the cartridge used), and the distance the bullet moves beyond the gas port which what maintains gas pressure in the gas tube long enough to provide the force to cycle the bolt.
I've had excellent results using rifle length gas and a .223 18" barrel but this might not work with a different cartridge. Using a rifle gas with a 16" barrel cuts the dwell time to nearly nothing and function would be questionable IMHO. At the very least, the gas port would have to be larger to get more gas quicker--very tricky process.

 

[s4s4u]

Just got my new 20" SFAR. My question is, would any issues come from taking the barrel length down to 16", considering it came with a rifle-length gas system? My reasoning for doing this is because I plan on throwing a suppressor on it and a 20" barrel + suppressor length is just too long for my liking.

Been done by several folks with success. If using a suppressor you are adding effective dwell time to make up for the barrel length loss.