I do not have a custom rifle. I currently have a Browning M-1000 Eclipse. It has a 26" heavy barrel with a 1 in 10" twist. It is a heavier rifle, I have no problems shooting it all day long with nothing but a t-shirt on. Thanks for the advice guys. I have shot at a 22"x32" steel plate at a 1000 yards. I think I hit it 3/10 times with factory winchester ammo. I used info from my chronograph as well as a weathermate and isnipe ballistic calculator (which I never found very accurate). Shooting off a bipod you realize how much you shake around looking at a target at 1000 yards haha. It is very tough to do accurately but a lot of fun no doubt.
Bed this action properly - nothing else has as dramatic an impact on a factory rifle.
Load up some good quality match bullets using proper load tech. Pretty hard to shoot sub MOA if the bullet you use can't do better then 1.5MOA.
Shooting off a bipod like a Harris is really hard to do well and is a learnt skill. A pedestal rest and proper rear bags will improve your LR accuracy tremendously.
Something like a Remple pod works superbly if you prefer a pod.
Visit my website and look in the Tech section where you will find load tuning info. When you get a quality bullet shooting consistently sub MOA at 200yds, 1000yds will be simply a matter of holding into the wind.
The Hrn Amax line is likely the least expensive target bullet you can choose. I use these alot but compete with Bergers and Lapua.
Sierra, and Nosler are other options that have worked really well for others.
Good optics help too and higher mag is a great aid.
With good bullets, properly bedded actions, well tuned ammo, Optics and nice solid rests, that gong of yours is going to get pretty darn big.
Think 10X10 @ 800yds and eventually at 1000yds.
Jerry