in2anity wrote:
Getting back to bolts though, IMO barrel heat should be treated as another variable. For load development I take a second plinker to the range and let the barrel cool between groups; it's all about eliminating variables.
^^^ This ^^^
Also, as mentioned above, don't leave your rounds chambered while setting aim at the bench. Get set for your 'Natural Point of Aim' (NPA: this is where the rifle is at rest and pointing at your intended POI; even if you take your hands off the rifle in the rest, the cross hairs should stay on the bull). Chamber your round and take your shot. Immediately eject your round and leave the bolt open to allow air flow through the barrel & chamber. Re-set NPA. Chamber. Shoot. Eject. Repeat.
After your desired number of shots for the group, it is ideal if possible to stand the rifle up with the bolt open to allow the heat to rise and draw cool air in the chamber/receiver. This may not be allowed at the range but even having the muzzle higher than the chamber will help the 'chimney to draw' and cool more effectively.
As in2anity suggests, having a plinker to fore off some fun shots or another rifle to test and the same time will allow more time for the barrel to cool. Steady is the key in my book. Not too fast, not too slow.
I see people sitting with a round in a hot chamber while waiting for a shot and re-setting NPA and cringe just a little because all that hard work they are doing to pull a tight group is being counter acted by building fluctuating pressures from powders heating up to varying degrees in the chamber.
Again, this is just for precision shooting like in f-class or when testing loads & tuning rifles. Of course in many applications you will have a round chambered while taking aim. When testing loads you want to see how consistent it is and the only way to do that is to fire each round under as consistent conditions as possible. Once you are happy with your load, then you can do some rapid fire tests to observe how the load/rifle behaves in those situations (say in a rapid fire event or busting up a mob of ferals).