samari...I'm a little taken aback by your statement that you could not get better than 1.5 moa for a .308....on a bad day all of mine don't go over moa...and on a good day they are under .5 moa... That is all jacked bullets in the 165-168 range... All my friends with .308s do the same and are shooting 168-175 grain bullets... Were your guns 1/12 or 1/10. That was the problem with the older .308...they had 1/12 twist whereas the 06 had 1/10... All my guns are 1/10...
I also have the same gun that the OP chose as do a couple of my friends. Have only shot it with factory 150 Federals but it will put 3 rounds in .8 moa. It is probably one of the best all-around hunting rifles I've ever had. Have not tried it with cast however...
My pick would be the same basic rifle in .358 Winchester. Besides jacketed rifle bullets, there are TONS of jacketed and cast pistol bullets for use on small game... My one .358 is a Ruger Frontier that shoots a MP 220 cast HP at 1800 fps to the tune of .9 moa. The one deer I've killed with it was with the Speer 220 FP...ran 30 yards and dropped. For small game I would just use a cast FP or 160-180 grain jacketed pistol bullet with enough UNIQUE to make .22 Magnum velocities... I have killed several grouse and rabbits with a .350 Remington Magnum using 160 grain Hornady XTPs with little meat damage...
Will be interesting to see if the OP has had success in his endeavor...
Bob