Uh Ohh... I (gun dealer really) have already sent out my .338 Sako action to Shilen for mounting of a 22 inch barrel. Should I have stipulated what twist rate I wanted?? I presume twist rate affects accuracy, but I thought the twist rate was based on some magic but standard formula which includes the weight of the bullet, length of the barrel, and what else?

A 1 in 8 twist would 'spin' more than a 1 in 12 twist. In my mind, a faster 'spinning' bullet would be more accurate, assuming of course that you could get the mass spinning before it leaves the barrel. I really have no idea how this works. Anyone with an explanation?!?!?!

Also, will Shilen automatically calculate the best twist rate for a .338 with a 22inch barrel, or should I start running to the phone???

Looks like they will give you a 1/10 automatically but I have never worked with them. They have a pretty good page on it.

http://www.shilen.com/calibers.htm

Why so short a barrel??? This rifle is going to be LOUD! And I should add a bit slow as well. Does 2 more inches or so of barrel bother you? Now as to twist, the heavier bullets need more spin for any given caliber, and velocity does play a small part in the stability factor. Regardless, dealing with reputable folks like Shilen should not leave you wanting.
Good luck, and good shooting

To stabilize a projectile [bullet] it has to spin . The amount of spin [twist rate ]depends on the length of the bullet [ and generally the weight],the longer the bullet the tighter the twist necessary.Too much twist and you overstabilize, too little and you under stabilize ,either is bad for accuracy.Typical 338twist is 1 in10" or 1 in 12".

Yeah, get a chin strap for your hat. The muzzle blast is going to be fierce. A little more barrel length will make that a much more pleasant shooting rifle... some would go as much as 26" on that kind of barrel, if that doesn't put weight out of the ballpark. Getting a barrel cut down and recrowned is not that expensive, if you decide you have erred on the long side.

Mete pretty well nailed the twist thing. You pretty much have to set twist for the heaviest bullet you want to shoot accurately. Lighter bullets will be spinning faster than they need to, and that will exaggerate any effects from bullet imbalance. I'd get on the phone with them, and get them to help you make your twist decision.

Let's be clear: the penalty for too much twist is very, very small indeed; the penalty for too little twist is enormous (no accuracy at all).

Too much twist has a potential accuracy penalty, but it is very minor, as in maybe a tenth of a MOA or so. High twist has also a minor benefit: it seems that bullets open up easier when spun a little faster. With a 338 with it's heavy hunting bullets, that can be a real benefit.

In varmint rifles, there can be a real penalty for too high a twist, as thin jacketed varmint bullets can actually tear apart in flight from too much spin. With a 338, that's not an issue.

Chances are, you'll get a one in 10, which will shoot just about any normal hunting bullet just fine. Exceptions would be much longer than standard custom bullets. HTH, Dutch.

Unless you are planning to shoot some kind of specialty bullet, like a 300 grain spitzer boattail, the more or less "standard" twist of 1:10 should be fine and is likely what you'll get if you don't specify otherwise.

I concur with others' advice that you should order your barrel at least a couple of inches longer and then whack it back if it doesn't suit you.

Dutch is absolutely correct. Accuracy problems stemming from spinning too fast (overstabilization) are dependednt upon the quality of the bullet. A bullet that is pefectly concentric, like a monolithic solid, may not demonstrate ANy degredation of accuracy due to spinning too fast. On the other hand, a bullet that is understabilized will tumble, and once this happens, forget hitting anything with it!