View Full Version : Frosty Bore on FN Mauser

January 19, 2002, 12:56 AM
After spending the better part of my spare time this winter working to restore (resurrect) a commercial FN Mauser .270 the prognosis is not too good at this point...

I hand polished the action and barrel which look great except for some tiny tiny pin hole pits around the FN cartouche which could be covered with scope mounts. The lettering is crisp, the edges are square... The bolt is excellent- super smooth and the face shows little if any wear... No problems.

The rifle was drilled and tapped for a 1 pc. mount. I don't think this was FN's practice- all I've seen have .500" rear bridge hole spacing. I think the rear hole is off center by as much as .100". My measurements could be suspect but it looks off. Naturally, I want a 2 pc. QD mounts like Talley or Warne... Could pose a problem.

The barrel was cut and roughly recrowned at 23.5" and the silver soldered factory ramp was removed. The area polished up well but will definitely have to be recrowned- I have the 11 degree crown cutter and I will get a .270 pilot . Minor problem with solution at hand.

I did a preliminary bore inspection before I started working and it seemed dirty but smooth. I ran a couple patches of Shooters Choice down the bore and they came out dirty but not too bad- except they kept coming out dirty. I got tough and ran an old .22 brush soaked with Sweets 7.62 solvent and let it sit for a few minutes and followed with a patch- the patch came out like a blue ink pen burst in the barrel...

Several sessions with the Sweets yielded a mirror bright bore when examined from the breech. From the muzzle, the grooves have some crispy frost "spots" and the lands are clean... I kept scrubbing hoping they would go away... I suspect I know why the rifle was cut and crowned... Heavy Frost at the muzzle- big problem.

I had big plans for this barrelled action! I was going to set it up as a British Express Style Rifle- a nice reddish Bastogne stock with short forend and ebony tip, pancake cheekpiece, red rubber recoil pad, barrel band swivel and front sight and a Marbles #20 rear (fits the step contour perfect) all with a nice rust blue...

So, am I beating a dead horse? Should I have just bought a plastic .270 Rem 700 ADL at MalMart and forgot about it? I love Mausers though- especially the FNs... I really don't want to rebarrel the gun as it would lose some appeal for me. I could cut off another 1" of barrel- the frost seems to be heaviest at the muzzle? I could TIG the hole in the rear bridge and redrill for .500" mount if I had a TIG welder? I could drill one more hole .500" from the other and hope the mounts align? I could not worry about the frost- hey it's going to be a fair weather hunting rifle, right? But I do want SOME accuracy... Or am I creating a very pretty fairly expensive trunk gun for shooting rocks at 50 yards???

Well, that was a long post. I guess I had to vent. Gunsmithing is tough-- I don't know how you guys do it for a living...

Any thoughts, inspiration or solutions to the above dilemmas would be appreciated...

January 19, 2002, 01:23 AM
I think a bit of test firing is in order. That frosting may or may not have any effect on accuracy.

Might also want to slug the barrel. Be nice if it is truly a .277 bore.


George Stringer
January 19, 2002, 09:25 AM
I agree Sam. After you crown put a few rounds down range. If it won't group I'd try bedding it and if it still won't group you can choose to rebarrel or not. George

January 22, 2002, 10:03 PM
Might he try lapping the bore a bit? At least that might help, too. Has any one done this, to a less than perfect (maybe mil surplus)barrel? Not "shot out" just a little rough...I'm curious 'cause I'm working on "experiment in gunsmithing" witha a decent but far from mint Mosin....

January 22, 2002, 10:30 PM
Highly reccommend testing before lapping. Some get better, some get worse.


January 24, 2002, 08:48 PM
What is a "frosty" bore? I have been shooting for 40 years and have never heard this term before.:confused:

January 25, 2002, 12:46 PM
OK, maybe I lost my mind...

The last 3" of the bore has a significant amount of frost with one small spot particularly bad (deep)... Fortunately, it's localized- I wander why? Or am I not seeing the rest of the bore as clearly?

Interestingly, the rifling does not seem to be affected to a large degree- it's still sharp and shows the factory toolmarks (microscopic chatter across the rifling)... Mirror chamber, good throat, 20" of good bore, low mileage bolt face, bank safe tight lockup...

I'm just going to downgrade my build design a bit- instead of a high end custom sporter, I'll go for a classic midgrade and keep my powder dry for the next big find...

And, I have not even shot it yet! Good point, gentlemen... I'm lucky when I can shoot a 1" group off the bench! Maybe the rifle will be a good match to my skill level. It's just the rifle is cleaned up so damned well, I hoped the bore would too... Used little, abused alot...

FROST: Small to microscopic corrosion in the bore of a rifle usually due to neglect, improper cleaning, or nitrocellulose powders. It looks like well, frost.