I am looking at installing a muzzle break on my 260. Will this negate the ladder testing I have done to date? I wouldnt think so, but wanted to ask before I did further development without the brake?
Probably not. Probably not enough, anyway, that you'll be able to shoot the difference. Every time I've installed/removed a brake, the old load shoots as well as it ever did - which is to say ~1/2 moa or so.
If it were a benchrest type rifle, it may make a legitimate difference (where thousandths of an inch count), but for a practical/tactical field rifle, I think not.
On a 260 and a 308 that I have installed brakes and removed them (I am always swapping things around) I have not noticed a change in accuracy nor needed to retune the load. You will see a change in point of impact.