Re: New Barrel for .220 swift
It's well documented that properly designed heavier bullets are generally more accurate at longer distances. The more velocity one can achieve, the better because it is in the air for less time, the conditions have less influence because they don't have as much time to push things around.
not rocket science.
I think you should go with a 1-8 twist barrel personally. there is a great deal of test data floating around that supports this twist rate in 22 caliber centerfire cartridges. The USMC Reserve Service Rifle Team uses 1-8 in their gas guns because they have proven that it's effective on 80 grain VLD Bergers. Sierra's too.
I'd like to offer a suggestion though. Select your barrel carefully. The 223 that an AR or M-16 uses is only going to get you around 2700 fps. Give or take. they work in a finite set of rules. The barrel has to be so long, etc. . .
You don't have these limitations. It can work for you or against you.
A 220 swift has a lot of steam. You can more than likely get to 3300 fps with this cartridge or perhaps a bit more before centrifical force takes over and starts pulling the thing apart.
The way the lands and grooves are formed/cut/machined are what I would consider paying attention to.
It's well documented that 5R or "polygonal" rifling is gentler on a bullet. There are no 90 corners on the features. Weakest part of a house? The corner. If you "cut" or form a 90 corner in a bullet whizzing at 300,000 RPM and if it fails, it is more than likely going to be along that crease formed by the lands/grooves.
A polygonal configuration reduces this effect. The jacket material retains more of its structural integrity. It has a higher resistance to mid flight jacket failure. They are also supposedly more resistant to fouling because the crap cant hide in the corners as well. There are no corners!
Boots Obermyer makes a damn fine barrel and is a sharp ol cat with a lot of years under his belt as a barrel maker and shooter. Just something to consider.
Bottom line, the 1-8 twist with those bullet weights is well established. Something else might work, but we all know this will work.
If you shoot VLD bullets, condsider having the reamer made for it. There is a difference. David Kiff at Pacific Tool and gauge is one stop shopping for great tooling. He's well versed on making a reamer for a specific application. Throat lengths and angles become fairly important with what you are wanting. He know's how to do this better than anyone in my opinion.
Hope this helped.