I have a 280 ack imp rifle built on rem mod 78 action with a 26 " Shillen heavy barrel in a McMillan sporter stock. Believe the twist is one in ten. Would like to change the stock to one with a flat forend for shooting off a bench with a front rest and rear bag for deer and long range varmiting. By long range I mean 300 to 500 yards or even longer should I get the opportunity to go west for praire dogs.
I realize there are many guns and calibers that fill this role beside the 280 Ackley but this is what I have to work with.
Any comments and/or suggestions with reguard to stock, loads, bullet , & etc is appreciated.
Thanks, Chief.

When I used a 280 for varmits I started with the speer 115 hp and ended up with the Nosler 120 at that time it was a solid base now I'd look to the 120BT. It was a little heavier and held velocity a little better. I never tried any of the speer TNTs. For a deer and yote rd the 140s work well. I had good luck with Norma MRP (RL22)and IMR4831. With the light bullets RL19 and 4350 would be an option.

The McMillan Hunter Class BR stock makes a good platform for shooting off the bench, and is still usable for offhand shooting.

You might try here they have loading data for the 280AI lightest bullet they have is a 120gr
http://data.hodgdon.com/cartridge_load.asp You can also try H&S they may a flat bottom hunter and br stock style stock. I think Sierra makes a 100gr HP Varminter, Speers make a 110gr TNT, Hornady makes a 100gr HP. I'm using a 150gr TSX in my 280AI will be a good deer/elk round. Nosler reloading manual #5 also has loading data for the 280AI. You can call Sierra and maybe get a varmit load for their 100gr bullet. Well good luck

Chief - I built a 280 Ack for about the same thing as you have in mind. Mine has just slightly over a sporter weight barrel on a Shehane Tracker stock. I have swivels on it so I can pack it with a strap when I'm hunting big game and I can pull the swivels out if I want to shoot off the bench. I've only loaded 140 grs for it but have shot it out to 700-800 yds. I think it's made a pretty versatile rifle.