I guess the bore was fouled a bit

[603Country]

I can't speak for every situation regarding bore rust, but I can use my Dad's 270 as an example. To say that he was not into cleaning his rifle is an understatement. He might, on a very rare occasion, wipe down the outer metal, but in all the years he had the Ruger Ultralight, he NEVER cleaned the bore. As for how long that was, call it more than 15 years and less than 25 years. Every couple of years, I'd clean the bore for him, but if I didn't do it nobody did. When he passed on, I decided to give that poor old bore a good cleaning and there was no rust and no pitting at all. And it grouped like a champion.

His inattention to bore health did cause his old Marlin 336C in 30/30 to finally need a barrel replacement decades prior to his having the Ruger. Right or wrong, I put that down to the microgroove rifling, which is rather shallow.

 

[Brian Pfleuger]

...decades prior...

Corrosive primers?

 

[603Country]

No Brian, I doubt it was corrosive primers. I had a 35 in a 336T and my brother had a 30/30 in 336C and we never 'shot' the barrel out. We cleaned our barrels every now and then. Still, I never really understood why Dad's rifle barrel gave it up, but it surely did, and I just mark it up to years of use and mud and rain and no cleaning (and shallow rifling).

 

[kilotanker22]

I run a mop to get all the powder out of the bore and a little clp until accuracy begins to degrade. On almost all of my rifles they seem to shoot better with some copper fouling in the bore. I believe that the copper fills in the imperfections of the rifling.

The only two rifles I have ever needed to cleen the copper out of it was not until I had fired several hundred rounds.

I think that the quality of the bore makes a very big difference on how fouling effects accuracy.

 

[iraiam]

One of my most accurate rifles is a model 700 in 270 Win. I can regularly "clover leaf" the first 3 or 4 rounds at 200 yards. After this, the group will open up to about 1 MOA and maintain there.

After the rifle is cleaned, then I can get extreme accuracy for the first 3 or 4 rounds again. I discovered this on accident because I clean after every session.