I am looking at a Belgian .450 express, double gun, boxlock. It seems a little light at just under 8lbs. I can decipher all markings except B. Plomb. I think that means proofed with lead bullets. It had definitive nitro proof markings, but someone on another site suggested that this gun may not be meant to handle standard NITRO .450 loads...seems unlikely to me, but looking for further affirmation.

It is most likely built for a NFB round. You would not want to shoot full boat, 480 grains bullets at 2150 FPS in such a light weight gun. Both you and it are likely to be damaged. Let us see the proofs to be sure.

For sure, it is a .450 BPE gun, and not a NE full load.
"B.Plomb" means "lead bullet" which indicates the former.
"B. Blindee" i.e. "jacketed bullet" would be required for the latter.

Don't shoot a full load in that double. At the least you'll have a very sore shoulder. In the worst case, you'll have gun and body parts laying around.

Best regards,
WC-

You may want to reference some belgian ammo catalogs for a medium to light load to start with. Definitely far less than 480grns at 2100 FPS

I load either 48gr of 4198 or 46 gr of RL#7, 285 to 300 gr
cast Valiant or Laser Cast Bullet with 14gr of Dacron to yield between 1800 and 1850 fps.
The 285 gr bullet starts as 300 and is "hollow pointed" for more expansion.
Every shot looks like a snow storm with the Dacron.
Works good as picture shows!!
Bob Jurewicz

http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=271431&page=1

Bob Jurewicz

Many doubles were made for the 450 No. 1 Express, AKA 500/450 No. 1 Express. Do any of the marks indicate a 2-3/4" case?

The gun was Nitro proofed. I would not want to fire a full power load... My 375 H&H is enough for me.

Pete