I don't like recoil - the reason for 3/4 and 1oz loads. I went from 1 1/8oz 12ga loads to 1oz, 7/8, and then 3/4oz loads and never saw a difference in my scores. International skeet and trap only allow a load close to 7/8 oz [ 24 gm ] - about 11 of #8 shot lighter. Both of those games are much harder than ours here in the USA. FITASC use to allow 1 1/4 oz of shot and went to 1 oz. Everyone complained but their scores went higher. The less shot, the shorter the shot column, the less set back, so more of the shot at the bottom stays round. This means more of the shot stays in the pattern. 1 oz of shot in a 12ga is only .690 high, in a 10ga it's .610 high. Both of those are way better than the great square load a lot of people promote. Claybuster wads use to [ and still may ] have a sheet of reloading data in their 3/4 oz bags of wads. Here's two, one for RD and one for CD. The wad is CB0175-12, 3/4oz of shot, Clay Dot, Red Dot [ or Promo is the same as RD only cheaper ] at 15.2 grs gives 1200fps at 5500 to 5900ps. At these pressures it wouldn't really matter what primer you used.
You won't find light 10ga loads. Go on here to Pete Lesters chart or just chose a mid 12ga load, say something around 8500 psi. In a 10ga it'll drop more than enough to where you're safe. Mine is 23.5grs of Green dot in any 10ga shell, any primer, 1oz of shot, and a Rem SP-10 plastic wad with enough 16ga fiber cushion wads in it first to make the shot column high enough for a good crimp. I've also used the same for 1 1/16 or 1 1/8oz of shot. You can cut the cushion wad any thickness necessary. BPI has paper and plastic wads. RST claims to use the Remington wad for a little more blow by for less pressures. And, you don't need all the junk BPI wants to sell you for cut shells. The regular Mec start crimp works just fine. No skiving is necessary. If you want to roll crimp I feel Precision Reloading has the best one. Have fun - Paul

In your case, I would use only loads published in the reloading manuals, offered free by the powder companies. Yes, the bigger the hole, the lower the pressure, assuming identical loads. Your question about "does it come out faster because of more powder" depends on how much powder you are talking about and the rate of ignition, which can be slower in a bigger hole. It is better to consider specific loads rather than making generalizations.

Just to clarify, Paul's ".100 to .120 around the breech end" would refer to the end of chamber wall thickness.
I just measured the at the very end of the breech WT of a 10g Ithaca at .230", a 12g 00 Smith at .210", and a 16g 0 Regular frame Smith at .200".

I saw the chart and downloaded it. I was only worrying about pressure. People go wild when I mention a Damascus barrel.

Kevin: before using the gun with any load, the wall thickness needs to be measured from breech to muzzle. Please share the numbers with us after having it measured.

I already shot it. Works good. There is a bit of rust in the barrels but nothing crazy. I dont even know how to measure the chamber thickness? I can put calippers at the end of the muzzle to measure the thickness but no idea how to get the chamber thickness.

You can get close by using a scale to measure the thickness of the wall where the shell goes in. Measuring the thickness of the walls from breech to muzzles is the ideal thing to do, but sorry to say, I've never done that and have owned over 25 or 30 different Damascus barreled guns. Four or five friends at the club have also owned many Damascus guns and no one has ever measured barrel thickness. I don't measure chamber length either. As for "published data " for the 10ga, Hodgdons has just put out one 10ga low pressure load and then there's Petes' data. That's about it. Low pressure loads to me are more about common sense than anything else. If it'll work in a 12, it'll work in a 10, with lower pressure. I'm not a collage grad, but I think it has to do with the volume the pressure has to work against. The bigger the volume, the less pressure. JMHO

Paul, I'm not picking on you but I don't think that's good advice for somebody just getting into old shotguns, especially classic old side-by-sides.
There are enough of them out there that have been honed nearly to death and the chambers lengthened to dangerous wall thicknesses that are literally "time bombs" and shouldn't be shot with ANY shell. Although I have done the same as you, I would never advocate an attitude of 'just go ahead and shoot it - it will probably be fine' - rather I would give the strong advice to have the wall thickness measured by somebody who knows how to do it...... especially in this case where the poster says "There is a bit of rust in the barrels but nothing crazy." where we have no idea of his definition of "nothing crazy".





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Manson wall thickness gauge, $160.99, retail, don't know the dealer price. I paid about $100.00 for mine maybe ten years ago. That $160.99 item will probably sell for a bit more at the estate sale. Mine has already appreciated 61%.

Dean, I get picked on so much over in the shotgun room at the club a little here won't make any difference. Maybe I should have put a disclaimer in my post. You're right, it would be nice to measure the wall thickness. I'm use to looking at American made SxSs, which are a bit thicker than our English cousins. Over there the guns were usually gone through at the end of hunting season, and that could mean a honing of the barrels. Back here the gun was usually just oiled up and put in the closet, no honing. I'm use to looking at muzzles with .040 to .060 wall thickness. With that in mind I assume, right or wrong, the rest of the barrels are still factory specs. I believe over there .020 at the muzzle and they'll still proof load and test it. I wouldn't shoot a gun with .020 at the muzzle with your fingers. No offense taken by your post - I think we're on the same page.