I use damascus barrelled gun all teh time with modern loads. The key is to use a load suited to the gun. with american guns, you need to guess what will work and I'd expect most to err on teh safe side.
With British guns you just need to match the proof marks to teh ammunition myou are using. If the gun is still in proof and sound, it will be safe to use with the corresponding loads.No need to go ultra-low pressure, just stick to the correct loads n the correct length hulls.
I favour Game-bore 'Pure Gold' 2 1/2" loads in true 65mm cases loaded with 1oz of No.6 and fibre wads for almost everything except ducks and geese. Hull also produce a good fibre-wad 65mm shell and Eley Grand Prix is a load I use in my 16-bores with damascus barrels. All these guns have 2 1/2" chambers and corresponding proof marks.
