Okay, I super cleaned my problem child .280 Mauser and slugged the bore. 3 times. Once from the chamber, twice from the muzzle end. There were no obvious felt tight or loose spots, but all 3 times the groove measurements were .285" and .286" across alternate grooves.

Too loose to even try and make it shoot? Some light pitting (looks like waterspots, just rough spots in an otherwise smooth bore no matter how hard I cleaned and scrubbed) was also apparent.

I'm giving up on this barrel unless someone has something else cheap to try...I'm wasting too much ammo for no obvious improvement!

How much of a problem child is it? How does it normally shoot? Have you ever encountered pressure signs with this barrel? A slightly oversized bore sometimes requires a little extra whack in pressure to force the bullet to seal and perform with any degree of accuracy.

Slug the bore again, but this time, if you haven't already done so, place another rod in the bore against the slug, to act as an anvil to force the soft lead slug tightly against the bore before running the slug down the bore.

I remember you asking about this rifle last year. Seems it was a rechambered military 7x57, wasn't it? I went through this with my first Mauser. No matter what I did to it, I just could not make it shoot. It may be time to say the hell with it and rebarrel. That is precisely what I did and I am much happier with it now.

I had a 7x57 Mauser once (some kind of surplus - can't remember now) that wouldn't keep 'em in a 3 foot circle......at 50 yards. I didn't slug the bore, but I suspect it would have been significantly oversize.

Huh - maybe I should have tried some .30 caliber bullets.

I had one like this.
I found that single shot pistol bullets worked great. Went from 5" and 6" groups at 100 down to 1.5-2" groups. They are of lighter construction and would "slug up" better.
I used Sierra 130SSP's.

Tex21, good memory. I've chopped and recrowned the barrel 3 times now, along with rebedding, rescoping, redoing the scope mounts twice, changed ammo many times, etc. It's still a 3" shooter.

I guess I'm too stubbon, and determined to get the @#$^% thing to shoot. It turns out that I've probably wasted half the rebarrel cost on ammo.

Live and learn. I think I'll strip the barrel off and stow the action the back of the safe for a while. Off to the gunshow this weekend with some cash in hand...

I think if you chamber a round with the barrel pointing down and the whole cartridge falls out of the muzzle that’s a clue that your bore is a bit oversized!

Nah Rick, Mausers a CRF. The extracter will hold it in!