Because it takes the PO less time to crush a mag tube with a punch and hammer so it only holds 2 shells instead of whittling a dowel, I have to change the mag tube.  I have a new tube in the white.  My question is what finish to protect the new tube, coatings are out since it is part of the action with the friction parts sliding on it and what not.  If it needs rust blue, any place i can send it that is fast and reputable?  Thanks

All of the A5s I have a Browning blue magazine tube as from the factory. Might give Browning a call and see who they recommend. I know there is atleast one Browning authorized outfit here in the US as I have a shooting buddy who had one of the so-called "Salt Guns" reblued awhile back. Will ask him and see if he remembers where he sent it and get back to you.

ETA: "Artsgunshop.com"    in Hillsboro Missouri is the place you seek. They do great work based on a sample of two that I have knowledge of them doing. Hope it helps.

Blued from the factory, however it's a part no one sees. If this isn't a heirloom that sits in a collection, go ahead and leave it in the white. Keep it cleaned and well oiled.

Op, rust blueing  that tube would be a very simple DYI project. I’ve done s lot of rust bluing, very successfully. Solution, 4OOOO steel wool, some distilled water and something to boil the part in. Slow speed operation. Rust , boil, card ( steel wool), rust , boil, card, until it’s dark enough for you or stops rusting. then dunk it in oil.

My go to cheap solution, don’t be put off by the name, blueing and browning are essentially the same operation .

https://www.midwayusa.com/product/1006393653/laurel-mountain-barrel-brown-and-degreaser-2-1-2-oz-liquid

http://www.laurelmountainforge.com/barrel_brown_inst.htm

We always left them in the white at the gunsmith shops I worked at, unless the whole gun got sent off to be re-blued. I don't recall anyone asking to finish just the tube.

We put a very light coat of RIG on them for rust prevention (with more around the threads), passed a lightly oiled rag through the interior, and that was it.

Thanks for the replies, never considered just leaving it in the white.