Identification help

[Justin McKnight]

I need some help determining the grade of my shotgun. So far what I have learned is its
1927
vulcan steel
12ga
what confuses me is VH is marked above the serial which looks to indicate vulcan steel and V is marked under the serial.

also what is the NT or HT? (hard to read) and A marking for?

Thanks I am new. I have owned this shotgun for about 8 years now and my grandfather gave it to me right before he passed away. I hunted and shot clay with this shotgun until about 5 years ago when i decided I didn't want to abuse it anymore. Right about the time I realized what it was. That said. I also have an issue when its very cold out when I pull the trigger it will not hit the primer hard enough to fire. But only when its VERY cold out. I assume its got some gunk in it but I am scared to disassemble it myself. Is it something a user could do?