for a 140 .284 bullet your gonna want a 1 in 11" barrel at a minimum. I like to go a little faster than that so 1 in 10" will be just fine, but 1 in 9" will enable you to shoot a heavier bullet later if you want to.
With regard to a Hart barreled 7x57- I found that the 1:10 twist produced one hole groups with 140 grain bullets at 1" groups at 100 yards with 162 grain bullets. The groups simply opened up gradually as bullet weights were increased to 154 and then 162 grains. I agree with Mike, the 1:9 twist is good if you one day decide you want to play with heavy projectiles. I like the 140 grain AB for general use, its a good projectile but you might find yourself in a situation where you want to tweak your loads for a certain application in the future. As an example, the 7mm08 shines with the 162 grain Amax, very explosive and very fast killing, good on lean animals.
Some of the heavy projectiles may seem slow on paper, but turn out to be shear dynamite out to 300 yards plus on game regardless of the low muzzle velocity. Its nice to have that option if you want to play later on.
I also prefer a fat barrel contour on a short barreled rifle. I have a .308 Tactical, 20" jobby, always thought it was very light till I weighed it and found it was the same weight as my long magnums. Point is, I was completely fooled by weight distribution as opposed to actual weight. Even with the heavy barrel, I/friends complain about losing the sight picture during recoil. That said, I load the little bugger balls to the walls. I think the fat barrel helps this a lot too, seems to shoot sub .5 with everything up till it gets fouled up or too hot to touch (culling in NZ).
I did some accurising work on a Sako Lightweight 21" barreled 7mm08 a while back, it was a real dog, I had to wait 30-40 seconds between shots and it couldn't handle a good fast load. Only gave sub MOA if I kept it dead cold and used just the right load- too finnicky for my tastes.
just to clarify, I only plan to shoot 140's( unless for unknown reason they wouldn't group out of this new barrel I have planned)
I have other guns, calibers for other stuff.
I currently have a 7mm08, in a different gun( just not sure on what twist it has, done very long ago, and my memory sucks any more!)
it is a #5 bbl on it at 24 inches, and shoot 140's like a champ!
I just wanted to build another one, just a tad lighter, going with a #4 bbl fluted, at 20 inches!( and hopefully can shoot same load with same or very close results!)
and was just looking for feed back of what you think the twist should be, since a few barrel companys, gave me different suggestions!
some said 1-11', some said, 1-9, and most said, 1-10.
so I was just wondering what anyone on here has used, and how it worked out!
But it looks like most here think 1-9 is the way to go, or 1-10, since I don't plan to use heavier than 140's,
do you feel i should still go to the 1-9, or use a 1-10??