I measured two factory small shank .308 barrel tenon threads and all of them are around 1.650" long.
I had no issue trying to head space the barrels in an extension while I have my predator apart for a severe cleaning.
I had a couple of short shanked thread barrels that wouldn't headspace correctly.
They were threaded to fit a zermatt receiver.
I put the barrel in a barrel vise, used a lot of cutting fluid and chased the threads with a 1-1/16"- 20 hex die like this till I was able to headspace.
https://metalcities.top/product/1-1-...6-20-tpi-sn-3/


SJC