Powder burns on outside of rimfire case?????

[nrb]

I have one rimfire rifle that shows heavy powder burn on the outside of one side of the cartridge cases after firing. Some ammo brands show heavy burns some show little. This is a modern, well made rifle from a well regarded maker.

What is your opinion of the cause of these powder burns????

Thank you in advance.

nrb

 

[Don]

I have one rimfire rifle that shows heavy powder burn on the outside of one side of the cartridge cases after firing. Some ammo brands show heavy burns some show little. This is a modern, well made rifle from a well regarded maker.

What is your opinion of the cause of these powder burns????

Thank you in advance.

nrb

Cartridge brass is not sealing against the chamber walls in a timely enough fashion allowing for some gas reward leakage. Possible causes;

-excess lead build up at cartridge lip

-too large chamber diameter

-excess headspace

-excess freebore

Borescope/chamber cast chamber and bore area to determine problem..................Don

 

[nrb]

Thank you Don

I saved a bunch of fired cases from different manufacturers and different rifles and measured the outside diameters after firing. The fired cases from this rifle are out of round and larger diameter than cases from a normal rifle. I think the chamber is bad.
Back to the factory she goes.

best, nrb