A question that I have is will your optimum load (for accuracy) change with the wear/number of rounds through your barrel?
I know this is a theoretical question and I am referring to .243 but you can comment on any round. I was shooting roos the other evening and this question popped into my little head. I am currently using a T3 Stainless Varmint in 243 and have put over 1000 rounds through it at this stage. All reloads are soft, minimum ADI recommendation for 2208/2209. So was wondering if I would have to revisit load development later on in rifles life.
I know when I had my 220 Swift the accuracy dropped off a little as the barrel wore. Admittedly I was running hot loads so that wouldn’t have helped as they are known as barrel burners.
I think load is a moot point given the question. I would think that it would be more reasonable to think about bullet diamter, rather than load. As your barrel wears out, you’d be looking for a larger diamter projectile to better engage the rifling. Load or charge would then be something you’d develop for the new projectile diamter.
The biggest issue is going to be throat errosion creating a longer freebore/leade for the bullet. This will require some ‘chasing the lands’? Ie: experimenting with longer seating depth. In doing so it may pay to run a few tests for charge weight as well. Eventually the rifle will drop off to the point where you can’t load the bullet out far enough for good accuracy and still be in the max mag length. At this stage, depending on barrel profile, you’ll be a ble to have the chamber reamed and barrel set back (shortened at chamber end) so that you effectively cut out the throat errosion. At this stage you will have to deverlop a new load as you will have both a new barrel length with new harmonics and also a different chamber.
Not something i have had to do as yet so some of the details may need to be clarified by someone with 1st hand experience but the issue is well documented.
Some people don’t bother and just get a new barrel, while others flog off the rifle and buy a new one (usually budget rifles).
There are a couple of train of thought on the matter. As there seems to be with everything firearm related. Certainly as Gwion pointed out the throat does wear no one disputes that and seating depth does have an effect on accuracy, so perhaps you may need to seat projectiles longer. The velocity will change slightly due to this. Changing the charge to get the same velocity as before would require a new load. But it may also be within the normal variance of shot to shot. Getting the same velocity as before most likely is not needed to get the same accuracy