I've used the Birchwood Casey kit to reblue an old Sportco. It's a good kit and works well if you do things properly. Still, it's never going to be as nice as a proper hot blue.
Here's some things I learnt:
1. Clean everything spotlessly! Obviously removal all rust, oils/greases, and old bluing (the bluing remover is excellent, so keep it away once you start bluing).
2. When prepping the bare metal you want to get it looking as polished/smooth as possible! This will ensure the finish is consistent, without any patchiness.
3. Disassemble everything you want to blue, don't cheat and try to do assemblies. For example, take the front and rear sights off the barrel/receiver rather than trying to treat it as one item.
4. I used the oven on it's lowest temperature to dry parts as I clean them. I also do this to warm parts before applying the liquid blue, and later to 'cure' it.
5. Your rifle will probably use a few different metals, expect some parts to blue easier than others.
6. Don't forget to blue ALL the screws and other minor hardware as you go. It makes a big difference to the overall finish. I cleaned up screws heads with a file and disassembled my factory swivels.
7. On less than pristine metal (eg. old Sportco's), you may get a bit of an antiqued look to the blue. I don't mind it.
8. Birchwood Casey also sell a bluing paste. Occaisionally I'll strip the oil from the metal and rub some paste in to enhance the bluing. It's not as effective as the liquid blue but makes for easy touchups.
9. Despite all the cold bluing products/videos on the internet, don't expect the same miracle results they often show.
If you want to blue your 303, I think you'll like the finish the kit gives. It will suit the rifle and it's age without looking too perfect/artificial.
You can see my reblue of the Sportco in the Gallery, noting I could do a better job the second time around.
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