I run my 7mag through my 300wby die. Fixes the issue every time. 300wby die is long enough if you have some loaded that aren't chambering, you can still run them through.
Post a photo of the opposing side of the belt. There should be sewn pockets for the bikini frame to slide into.
This belt will work for the duplex or the bikini if so.
Solid spotter for a great price. You may want better glass one day but for 350 that viper will work for a long while. You can always sell the viper for more than you paid to assist in upgrading to better glass one day.