An American Handgunner story has me wondering.
http://americanhandgunner.com/a-tale-of-two-nines/


would one or the other help you choose which gun ?

why wouldn't they all be 1:12? and call it good.

1 : 10 is standard for copper jacket factory loads.= service/sd pistols.
1 : 16 is a compromise for copper jacket and lead projectiles. = plinker/sporter pistols.
1 : 20 is for lead projectiles = matchguns

we you 're a pretty handy guy to have around, thanks.

1. Georg Luger and DWM thought a 10 twist was suitable.

2. Colt thought a 16 twist was ample, it had worked in for John Browning in .38 Super.

3. S&W found an 18 3/4 twist adequate for .38 Special. Although they have reverted to 10 in recent production of 9mm.

I wonder if, when you special order a custom barrel,
can you stipulate which twist rate that you want?

sure you can. The question is what are you are expecting from the result and how much effort you want to put into the optimization of your ammo to get the result you desire. Optimizing ammo performance to a standard barrel will bring you as good results but its cheaper.

How custom are you talking about?
Individually machined out of a blank for huge cost? Any twist you want.

Specific name brand finished barrel? Not necessarily.

SOME finished barrel? A little choice by picking brand.

All Barstos are 16", don't know about Kart.
KKM has a selection although I don't know if all available for one particular caliber.

Bendable, I don't pretend to have independent knowledge about what twist is best, but I read a lot. Schumann Barrels has information that may be pertinent to your question, along with a variety of twist options available.