I seem to have read somewhere about people having problems traveling with sporteized military rifles or even rifles in "military" calibers. Is there anything to this rumor? I had Mark Skaggs in OR put a "new" stepped military barrel on a 98 action for me. He also put a bold trigger on it reblued it after removing the sights and dropped it in an aftermarked stock for me. I was going to take it to Africa as my PG back up rifle.
Will this be considered a "custom" or could it be considered a military rifle because of the action, barrel and caliber (8x57)?

Anyone have experience with this?

No experience; the only factor is caliber; if the country you are going to does not allow former or current military calibers, you might not get the rifle in. None of the other factors you mention matter; in fact, what is the difference in a vintage Mauser sporter action and a military one? Usually, none. Check whichever country you will hunt in and ask about restricted/banned calibers.

it depends - and you should contact the hosting country on the matter -- mexico, for example, has strong laws on military calibers, which means ANYTHING their military has every had in inventory

OK thanks. I thought I had read something about problems with import permits based on the rifle being a sporterized military rifle, whether in the original caliber or not.
I'm heading to Namibia this spring but since they have only been independent for a couple of decades I can't imagine they have issued 8MM mauser rifles to their troops.

I might just take a second 375 as backup and not worry about it.

Ditto W/Jeff concerning Mexico. 06 is a Federale round. So is .45 ACP,although I doubt you'd be taking a pistol into Mexico period!Also if you are a hand loader/wildcatter do NOTHING on an 06 case;same things apply;they only read the headstamps.I have buds who still hunt in old mexico + leave their rifles there year round to avoid the import hassle.Have another buddy that did the same + when he went down;new sheriff in town.Confiscated guns with no recourse,ad nauseum.Bad business. Also watch Heathrow as there have numerous reports of the antis damaging luggage of Africa bound hunters.Not meaning to make you worry,only be aware.