Dating shotgun shells
You could always take it off and measure the length. I think that you are either looking at the identical Pro Mag Tri-Rail Forend on Ebay, .95 or the preferable combination Pro Mag, , PM168 - Mossberg 500/590 (12 Gauge) Tri-Rail Forend and .
the #10 most likely stands for 10 gauge a popular chambering. As for the age, without knowing the company, it is impossible to tell, but it is old.Alot of these were used very early on, a hunter might only own 4 of these shells and would handload them in the feild(the old blackpower type) they would make their shot, reload, then stop and reload the shells from supplies carried with them.these real early shells were not just tossed away and would be a rare find, I think yours are probably early to mid 1900's, but without more ID marking they could be from a vast time range.don't see much of a rim though could be an old battery casing? All brass shotshells started being manufactured in the USA in the mid 1870's.
Their popularity waned when the paper shells became more popular.I believe these came out mid 1800s because the paper shells would get wet.