My dad has a Topper 48 in .410 "guage". That is the shotgun I first hunted with and the thing is dead accurate. We could put slugs in it and kill 'chucks anytime out to 100yds.
I am curious as to what year this shotgun was made. I looked all over for a SN and finally found it at the front of the receiver with the forestock removed. The metal there is curved, so the top of the numbers are very lightly stamped. It's also possible that the first "letter" isn't really part of the SN, but just happens to be markings in the cast (the inside of the receiver looks like it was cast steel), as it is much more lightly stamped than the other numbers.
I found: J03617
The J is the character that might not even be part of the SN. The 0/O fades out toward the top (like the 3617 do) and could actually be a U. It has an H&R buttplate on the stock, a modern looking grip on the stock, a snap-on forestock, and a forestock pin which is brazed (gold colored) to the barrel. If it should help, the receiver has 4 pins in it: smaller ones at the front of the trigger guard and above the trigger, and larger ones higher up (likely the hammer and barrel lock pivots), and the barrel release is a side-to-side lever rather than the push down release of the modern H&R/NEFs.
If anyone can help me date this shotgun, I'd appreciate it.