I'm converting a Browning A bolt 243 Win into a 308 Win to run as a compact 20" suppressed hunting rifle capable of making consistent sub MOA hits at 1000 yards.
That'll be hard to do with a 20 inch barrel. There may be powders that'll push your bullet choises out fast enough, but not with a low enough muzzle velocity spread to shoot no worse than 1 MOA from shoulder fired rifles in hunting environments. The rifle and its ammo will have to shoot no worse than 1/2 MOA at 1000 to do that. Note the very best benchrest 1000 yard rifles don't do that well. The record for shoulder fired high power prone shooting with a scope's 1000 yards is 19 out of 20 shots in 1 MOA; with a .300 magnum. Even the top classified folks rarely get more than 12 or 13 shots out of 20 in the 10 inch scoring ring on the long range target. Adding a supressor will degrade accuracy a little bit; a lot if it's a bad one.
I have a maximum magazine length of 2.815" and I prefer to keep it as a repeater.
That limits the powder you can put in a case. When the .308 was "the" round for NRA high power competition, 190 and 200 grain bullets were seated out to about 2.9 inch OAL and single loaded. 26 and 28 inch barrels were used shooting the 190's at about 2560 fps and the 200's about 2470 fps.
I'm planning to run 175 - 200 grain bullets with a 1 in 10 twist.
That's a good choice for 24 inch or longer barrels, but the 200's may not stabilize to well with the lower velocity a 20 inch barrel will produce with sub MOA accuracy at 36,000 inches down range.
How have you guys been setting up your 308 chambers to suit this type of shooting? Is a Saami spec chamber versatile enough to perform well in this application?
SAAMI spec .308 Win. chambers (or virtual copies thereof) with standard .344" necks were used to win virually the matches and set the records from 1963 until recently when the 26 and 24 caliber match bullets finally became competitive.
What are your recommendations for a tack driving 308?
I don't know what the Browning action's abilities are and track record is for super accurate rifle shooting. Instead, get a cheap, used Winchester Model 70 (or 670, 770), square the bolt and receiver faces, lap its locking lugs to the receiver, then fit a 26 inch Kreiger 1:11 .2980 x .3075 bored/rifled barrel in a medium-light weight taper. Replace the firing pin spring with a new 26 or 28 pound one. Put in a Jewel trigger with a 1 to 2 pound pull. Epoxy bed only the receiver in a stock of your choice. Attach the scope of your choice.
Next, learn what processes, techniques, tools and components to use for sub MOA acuracy in reloaded ammo. Then go buy, use and test them.
Then you'll have to learn how to hold you sights in an aiming area under 1/2 MOA on that 1000 yard target, dope the wind correctly and finally shoot the rifle well enough to meet your objecdtive. It's been done by others but they usually wear out at least one barrel in the process. Best wishes in your endeavor.