Low Brass has nothing to do with low pressure! Low brass shells often generate higher chamber pressures than high brass loads because these so-called promotional or Wally World loads will use a smaller charge of faster burning powder which generates higher chamber pressures. You can handload to keep pressures below 7500 psi or you can buy commercial low pressure ammo from RST or other sources. Also, there is nothing on your barrel markings to suggest that your gun was originally built with 70 m/m or 2 3/4" chambers. So until you get better info to the contrary, it would be wise to have your barrel wall thickness evaluated by a good double gunsmith who is familiar with vintage doubles.
Thanks for your input, Keith.
My chamber measurement is accurate @ 2-3/4", and the chambers appear to be original/unaltered.
I already knew about pressures, etc, and I was simply expressing my hope that I could use ammo I had on hand for my other 20ga's (a Stevens 311 & an Ithaca M-37 Deerslayer).
I have some 2-1/2" low-pressure RST's on order as we speak - but on my cardiologist's orders, no long gun shooting for at least another 90 days (I recently underwent heart bypass surgery for 5 blockages), which puts this year's hunting season beyond the pale for me.
I haven't had much luck in determining the maker or the date (year) of manufacture, though - but still have high hopes for finding out the same.
.
