Cleaning firearms
On some new firearms the barrels have a layer of grease or oil inside to prevent rust. If you fire a round without first cleaning out the grease the additional pressure build up could create a tiny bulge in the barrel that would affect accuracy.
This might not apply if you are shooting shot as opposed to slugs but my advice would be to run a tight cloth through the barrel to clean out any grease or oil before firing.
I would clean any barrel of any firearm that is NEW TO ME. This applies to new in box or second hand used firearms. First of all, it is a simple procedure that takes only a few minutes, it is a Safety precaution, and the only reason for not doing so is being lazy.
You never know just what might be in a barrel. I have seen bullets lodged into .22 rifles, cleaning patches, a cleaning rod tip, a shotgun wad, and part of a paper hull in barrels. New firearms, especially foreign or military rifles generally have a preservative in the barrel, and a large numbers of the surplus rifles available have been pulled from long term storage where they have been well greased to preserve them.
A small bit of grease in a barrel can raise pressures enormously. In fact, after WWI, several 1903 Springfield rifles on target ranges blew up because shooters dipped the nose of the cartridge in grease to prevent barrel fouling. This grease also migrated to the chamber of the rifle, and coated the surface of the chamber, so the brass cartridge did not have enough friction to momentarily stick to the walls of the chamber. This made for higher pressures when fired.
For the few minutes it takes to field strip and clean a firearm, it is worth the effort to clean and lubricate it so that it will function properly.
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