Is it true/What's the physics behind a dirtier rifle shooting better?

you should know

you're wearing the helmet


and aren't you smart?

I would think it's the same reason a hot barrel is less accurate.

tighter fit.

I would think it should expand fairly evenly unless it's a poor quality metal.

The biggest factor imo is just the diameter increasing with the metal's expansion and having a greater tolerance for the bullet to pass through.

Every machining process has some sort of tolerance and if you happen to get one on the upper end, getting a little crud in there could have the opposite effect. That's strictly speculation though.

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My theory is that clean barrels don't group because they aren't clean after the first shot and get progessivly dirtier to a certain point, where as a dirty barrel after x amount of shots will have pretty much even fouling for the next shots, as only so much will accumulate without the bullet bringing it out with it.

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Ahh. So the build up of gunk is needed where each shot will have the same pattern because they are cleaning/causing the same amount of residue each shot. So you basically have to get up to that level of gunk before you're back at precision.

It makes sense I guess. Rifle accuracy is about repeatable harmonics, and it seems like a changing amount of shite in the barrel between shots would have a negative effect on that.

I'm sure kengal or one of the other rifle geeks will be here with a better answer eventually. They'll all night walkers.

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My theory is that clean barrels don't group because they aren't clean after the first shot and get progessivly dirtier to a certain point, where as a dirty barrel after x amount of shots will have pretty much even fouling for the next shots, as only so much will accumulate without the bullet bringing it out with it.

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This is correct.

I agree with infidel.

It seems like some bores have slight imperfections that must be filled in. Once they're filled, the rifling is consistent.

The idea makes sense...but the next question is- when should a rifle be cleaned? After a while, that buildup will become too much

I agree with downshift for the most part.

If it's a deer rifle that gets shot 2-3 times a year, it probably won't matter too much. But if you have a few range outings to test new loads, you may need to use a copper solvent to get rid of some of the fouling. Once the lands and grooves don't grip a bullet well enough your accuracy goes to shite.