I am about to decide on pursuing modifying my Mini-14 GB folder to a 13" SBR - The gun is already been made into a rifle length AC556 clone with gas block sight and barrel shortened to about 14 3/4 so the pinned flash hider and oal on the bbl is over 16" long.

I haven't had to modify the gas port sizes and it runs fine - BUT If I go and cut the extra length off - I'm curious if I will hit the wall of the existing gas system and want to know what sizes the ports should be opened up to to run on the 13" length.  I figure as I get closer to the gas block there is more drop off much more.

What sizes would these be opened up to on a 13".

Also are 13" the actual length of the factory AC556K or is it something else?

Warning - once you make an SBR - you start wanting to do do more.

I cut my 18" down to 16 1/4" and it still runs on crap weak Ammo but I would think that down to 13" and you will have to open the gas bushing because when mine is really cold it barely cycles with weak ammo.
I'd probably go about .005 to .010 at a time.
Is that the Mini 14 I sold you several years back?

Yes!  I love this little gun.  I now live in the Free State of Georgia (left NY) and am doing a few SBR projects and really wanted to do an AC556.  It was either I do this as an SBR or consider a transferable AC556 and although Rugers can be had for less than many other transferable pre 86 MGs they are still typically over $10K.

I really wanted to SBR my Mini14 in 300blk, but with the factory folder stocks being so high, I figured it wasn't worth it. It'd still be a neat little package gun, but other projects moved up the list.

They have the adjustable gas thingees, so you could open it up, then use that to fine tune if you didn't want to keep opening it up a little at a time.