I've owned a good number of Meriden shotguns and a few of their rifles.
One of the last SxS was a Model 58, a very high grade Wm Gough engraved 12ga that is now pictured on the Meriden F/A site.
All the Meriden shotguns I've had (12ga) had 2 5/8" length chambers.
That was standard (if there was such a thing before WW1).
Meriden remained in business thru WW1 and went bankrupt in 1918. But those WW1 years thru the end in late 1918 they were under the control of New England Westinghouse. Their output was war material, not sporting arms.
Anyway,,the Meriden/Aubrey shotguns are very solid SxS's as are the single shot break open shotguns.
The SxS's are thru side locks. They are often compared with the LC Smith and they do have some common traits in their looks and build. The LC gets the nod for a bit better quality as a rule. But not always.
No gauge markings on the Meriden/Aubreys.
No choke markings that I remember.
The 'S' does represent Steel Bbl's. The number along side it was the bbl length in inches when original. ( S30,,for example)
Other bbls were T (twist), L(laminated),,D(damascus)
The composition bbl's were sourced from Belgium, the normal choice in that time for just about every maker.
I think the steel bbl's may have been made here. But I don't know if they were made in the Meriden plant or by someone else in the US.
Butt Stocks can be fragile and crack easily,,just like the LCS. Not a lot of support for the action once the inletting is done and if it's not done well, it lends to weakness and damage from shooting.
With good bores/bbls and a good lock-up, the Meridens have always been great shooters for me.
I've always used 2 3/4" hulls and have reloaded my own ammo so as to keep the pressures down.
I do that for all my shotguns as they are in the same elderly group and some have the shorter chambers as well.
Earlier AH Fox SxS were 2 5/8 as well incl the Sterlingworth. Not many people get concerned about shooting over the counter ammo in those.
I shoot(shot) smokeless in the damascus & twist steel bbl'd Meridens as well. Again the loads were right out of the books. Pressures were in the 6000psi (+/-) which is equiv to what BP 12ga loads run.
Over the counter loads of today no matter what the payload or the brass length, ect are just going to be about 9000+psi. You can bet on it unless they are specialty loads from someplace like RST that state on the box that they are 'Low Pressure' for vintage guns.
Stay away from these in a short chambered gun or IMO any vintage shotgun regardless of proper chamber length or not.
These are 100y/o firearms, bhistory unkn.
Treat them kindly and they'll continue to serve you.
There are plenty of (re)load recipes that'll give you the same 1200fps as a 9000psi factory load, but at 6000psi and even lower.
Velocity does not necessarily need high pressure...
and what was a normal service load & psi in 1908 w/ early smokelesspowder of the day is usually a long way on the chart from what is considered a service load today.
Sold my last functioning Meriden not long ago, a Single Shot Hammerless Trap 12ga.
Only one left now is an 'in the white' complete metal but never stocked, plain 12ga hammer break open single. Steel bbl.
Too big to be a lunchbox special!