There are a number of methods other than ‘krylon’ available to the do it yourself’er.

Cerakoat is available in both air-dry and oven-dry versions that can be sprayed with a automotive touch-up sprayer.
You need to bead/sand blast the gun first for best adherence, but you can get a good finish assuming you degrease and rough up the surface. It’s liquid only, no premade cans, and costs more than the others, but lasts better also.

GunKote is available in rattle cans, the same applies to blasting and degreasing but it’s oven sure only. It’s a little easier to spray and is more forgiving to the hobbyist, but is oven cure only.

AlumaHyde II, is also available in rattle cans, is suitable for firearm exteriors only, as it’s a thick coating but it goes on fairly easy. Roughing the surface helps but you don’t have to although the finish won’t adhere as well. It like the air-dry Cerakote, can be applied to wood, plastic and scopes as it’s air dry.

CeramaCoat, is not recommended, it’s oven-cure and hasn’t held up well in my experience.

Dura-Coat is basically nothing more than rebranded Sherwin-Williams Polane-T epoxy paint. Like the AlumaHyde it’s thick and only really suitable for exteriors. But it’s also available now in rattle cans, @$35 a can though.

I do a couple of finish jobs every couple of weeks.
Recommendations, degrease, bake, degrease, bake degrease, bake, degrease, warm, spray.
Allow to cure then either bake the part or leave it alone for a week for it to cure (air dry).

Hot summer day? Leave the gun/parts in the sun for a while to warm up for spraying.

You can’t degrease enough, especially with old mil-surp guns.

Me, I’m running mostly GunKote and Alumahyde II on my/our guns.
I’ve tried the rest, the Cerakote is becoming a favorite both for colors available and durability but it’s more difficult to work with, unlike the GunKote it doesn’t harden before you ‘bake’ it and the slightest touch will mar the finish before its baked/cured.
The GunKote you can let dry, then handle carefully when/before baking.

One word of caution, the AlumaHyde II can be removed with liberal applications of DEET. (Oops)
Haven’t tried it again though.

High temperature automotive paint and high temp Bar-B-Que paint is popular but is often too shiny and definitely too ‘brittle’ for hard use.

A little info that may help: