Frosted bore

[Major Tom]

I was looking at a very nice 1939 Mauser luger, but, it has a frosted bore. Does this affect accuracy? What causes a frosted bore? And finally, can the frosting be removed?
Thanks

[Chickenthief]

Corrosive primers and no cleaning.
Most all switched to non corrosive sometime in the 50's, the eastern block took (way) longer.
There is little need for "repairs" and it will shoot just fine.

My 7.65 is butt ugly and shoots way beter than i ever will, both with jacketed and cast bullets.

[Olle]

Many (maybe most) guns with frosted bores will still shoot very well. Frosting and pitting is often located in the grooves only, and you won't have a problem as long as the lands are fairly smooth and well defined. Some corrosion on the lands won't hurt much either, their function is to guide the bullet and make it spin, so frosting and a few small pits won't hurt the performance. I have shot some guns with deep pitting, and they performed surprisingly well. As a matter of fact, I have one Dreyse 1907 with a pitted bore and one with a perfect bore, and strange as it sounds: The pitted one actually shoots much better.

There are no good ways of removing it, and it's better to leave it alone. It's etched into the surface of the bore so any method you use would require that you remove material from the bore and that will affect the accuracy for sure. I know that some have done it just to make a bad bore look better (like using a patch and coarse polishing compound), but that's for show only and will be detrimental to the accuracy.

You may want to take a closer look though, and make sure the rifling is sharp (which is the most important factor). I have seen some guns where the owner had tried to clean up a bad bore with different methods, and the tell tale sign of this was that the lands were rounded off. I would stay away from a gun like that, especially if I wanted to shoot it.

[DonVoigt]

"Frosting" is a marketing word, invented to make a corroded/pitted/rusty bore sound better.

There are many degrees of "frosting", but we should really call it what is is- corrosion from whatever source. JMHO.

A pistol with a "frosted" bore is worth less than one with a clean, bright bore- all else being equal.

[Edward Tinker]

My terms, to me

Frosted bore - has funny spots - you see a speckled look on many sideplates, same type of look

Frosted boore that is worse - turning slightly dark from corrosion, but strong rifling

Dark bore - worse than above

Slightly pitted - just as it says, but has strong / good rifling

pitted - pitted and dark but still shootable

sewer pipe - sometimes shoots remarkably well

------------
much depends on interpretation - I know several collectors who insist on a shiny, almost new bore on a pre-1944 barrel - lots of them out there, but come on - its a 70 yr old barrel

many times, extra cleaning will make a poor barrel look pretty darn good

[mccaslyn]

There is not much you can do i have a 1917 enfield with original barrel and it is frosted still shoots great but will collect copper and just generally be dirtier after shot

[Major Tom]

At the range, this luger with frosted bore shoots very well and is accurate. The pistol is remarkably in very good condition finish wise and with all matching numbers. Someone took very good care of it and I wonder why they didn't take care of the bore too.

[mrerick]

They stopped using corrosive promers in ammunition a long time ago in the West. Probably the last of the corrosive ammo was just after WW-II.

The person the Luger was issued to may have paid much poorer attention to maintenance than the GI that captured it and brought it home as a war trophy.

[4 Scale]

My theory is that corrosion ("frosting", "rust", etc.), adds nothing to the bore that can obstruct or alter the path of the projectile as rust is softer than the metal it formed on. Rust by definition is a transformation and a net subtraction in terms of mass.

Due to the length of the bullet in relation to the relatively small size of individual corrosion patches such as pits, the corrosion itself will not degrade the bullet path or its spin. For the same reason, even in poor bores, gas cannot escape enough to decrease bullet velocity.

Phrased differently, as long as you can see rifling it doesn't matter how worn and corroded the bore is, it will be accurate.

I wish there was a way to test or substantiate this theory. The fact is I cannot tell any accuracy difference between excellent and poor bores.

[DavidJayUden]

I would think that the frost should go away with the use of jacketed bullets, possibly leaving behind pitting. No?
dju

[mrerick]

A frosted steel surface is one that has been etched by a corrosive compound. It is no longer smooth polished steel (iron and carbon) grains.

Polished steel grain on gliding (bullet bearing) bullet surfaces change to rough steel and oxide pits on gliding surfaces - this changes the friction coefficient of the relationship and changes the ballistics of the barrel.

Frosting would logically slow the bullet down slightly, generate more heat and leave more residue on a frosted surface. Is it significant? Probably not at close range. Probably not when just firing a few rounds...

[DonVoigt]

What - ever it is, it is not "desirable".

And as said before, it is a "euphemism" for "rust"- which itself is a type of "corrosion".
Even if not "exactly" rust- it is still an imperfection from another cause.