anyway to re blue a barrel without taking old finish off an polishing

[ben_tucka]

Hammerite is good for mimicking the lacquered finish of some vintage airguns but you need to keep cutting it back, like you would when painting a car. You'll end up with a mirror finish.

Just for clarification hammerite paint is going nowhere near this rifle, hammerite in my opinion is limited to fences and gates.

[air-tech]

Just for clarification hammerite paint is going nowhere near this rifle, hammerite in my opinion is limited to fences and gates.

Spoilsport!

That aside, buy nitro thinners or aerosol brake cleaner to degrease, latter is probably better.

[njaw]

Just for clarification hammerite paint is going nowhere near this rifle, hammerite in my opinion is limited to fences and gates.

Your choice, but I have replicated a BSA 70's lacquer finish using careful application of spray-can Hammerite (with plenty of cutting back) and a seasoned collector friend couldn't tell the difference. Obviously, this is if the gun was originally lacquered, not blued!
Like I said, mirror finish, tougher than the original. Still, each to their own...

[junglie]

IMHO while no cold blue will ever last as long (or, perhaps, even "last") it's ideal for what you need it for, as long as you accept that you will need to re-apply every so often.

The really, really important thing is that you must degrease very thoroughly.

this & with some cold blues I've found warming the part first to about 70deg c helps get a much longer lasting finish.

[ben_tucka]

Spoilsport!

That aside, buy nitro thinners or aerosol brake cleaner to degrease, latter is probably better.

Well thats good news, I've got loads of brake and clutch cleaner from car maintenance