Here goes. Not all will agree, surprise, but this has been my experience over many years and many different calibers. Probably one of the most extreme I own is a 17-224 Weatherby. 9 shots and you have to clean the barrel or you get exploding bullets.
Some basics that affect accuracy; throat wear, heat checking, carbon fouling and copper fouling.
1. Case capacity. The larger the case the faster bad things happen to barrel. It's the "you can't fool Mother Nature" thing.
2. rate of fire will add to or delay the issues with heat checking and fouling.
3. carbon fouling will affect pressure and accuracy.
Accuracy is affected by any build up in the barrel. As a smith I go to great lengths to build accurate rifles/barrels. Quality barrels, spec'd out reamers, concentric throats, smooth easy transitioning lead angles for the bullets. The reason is to do the least amount of damage to the bullet while it's in the barrel.
Some observations I've made over the years.
High performance cartridges come with a price to be paid. Heat checking is visible in 100 rounds in magnum size cases. Throat wear is in the neighborhood of .001" to .0015" per 100 rounds. Nothing is free if you want go fast or long.
308's can stand a lot of abuse and still shoot well but eventually they need maintenance also.
I'm a barrel cleaner. To manage heat checking, to manage powder fouling, to manage cooper fouling you have to clean the barrel. Now what kind of schedule and regime do you follow.
This is just a broad general recommendation as there are too many variables to give specific, as in exact round count recommendations.
308's I would
1. always push a dry patch down the barrel to get out the powder fouling before storing for any length of time. The reason is fouling attracts moisture and traps it against the barrel. I'll put a pic or two up that very plainly shows what happens if you don't get it out. This happens to S/S also just more slowly. 2. For the first 1500 rounds a rigorous cleaning every 100 if possible. After 1000-2000 rounds I would occasionally use a mild abrasive to manage the heat checking. This helps with carbon fouling also. After say 2000 I would be more aggressive and diligent with cleaning.
Here's two pic of LE rifles. One shows where powder fouling was laying in the groove and caused pitting the other has a lot of bad stuff going on. Pits that collected bullet jacket material.
Here's a pic of LE rifle, round count 5207. This is the throat area. You can see the neck on the right. On the left you can see the heat checking that has copper in the cracks. The heat checking extends down the barrel a ways.
HP rounds. Smaller bores with capacity of say 40 Grs. and up and then the magnums.
1.never put it away dirty. 2. For the first 300-400 rounds clean every 50-100 rounds. The more extreme a round the more frequently it requires attention. After 400 I would consider using abrasives. The more powder that's burned the more important it is. After 500-600 abrasives would part of my routine. Throats wear that's a fact of life. Barrels still shoot well but if carbon fouling, heat checking which leads to increased copper fouling get ahead of you accuracy will fall off quickly. Flyers will be more the norm than the exception.
One thing that shows up particularly with 338's is powder fouling between the case neck and the end of the neck area in the chamber. It can become a problem. On HP cartridges I insert my bore brush into the neck and give a couple of twists to clean this area.
This barrel is a 338 LAPUA Imp with 1173 rounds on it. It is a 1K yd. benchrest barrel that was well maintained until it's final days.
The first pic is 6" down the barrel.
This is 2" down the barrel. Notice the copper in the cracks and copper laying on top of the lands. Not good for accuracy.
This is a close up of the top of the land 1.5" down the barrel. Once copper gets into the cracks you can't get it out. Then consistent repeatable accuracy will fall off.
This is just in front of the freebore area.
This is the throat area.
As they say a picture is worth a thousand words.
YMMV