Help IDing 16 gage double

[Apple a Day]

A buddy of mine brought me an old shotgun to see if I might be able to clean it up and look it over for him. He claimed it was a 28 gage but when I popped it open there was no way it was that small. I had a couple of old shells in the range bag and tested it: bigger than a 20 and smaller than 12.
Picture attached of underside of barrels once I removed the handguard and took down.
It has double triggers, exposed hammers, and free-floating firing pins. One of the 'pins is broken so I'm going to have to unscrew the nipple to get it out and replace it... once I find a replacement.
The diamond with the 16 makes me think my guess that it's a 16 gage is correct. The E L G in the oval with a crown on top is a Belgian proof mark?
Can anybody identify the manufacturer or give me an idea when it might have been made?
Much appreciated,
Apple

 

[451 Detonics]

Definitely Belgium, has the Mark for optional superior provisional proof. The candle stick indicates The Perron, sole proof mark until dropped in 1810, since 1853 used to indicate inspection or proof of breeching system. The ELG mark places it in the late 1800's early 1900's.