Simple. For the original cost of the rifle, you can change it to use a different caliber.
Let's take the .270, either "color", as our example. I really love the iron sights but the caliber doesn't have as much power for taking down the animals I really like to hunt. So, I go to the store, choose the Huntsman and choose "custom caliber" then change it to .30-06 fir another 12k making the total cost 24k.
I won't even pretend, this is to combat the problem of having so many 4-8 weapons. Letting us change the calibers around will make sure we can use our favorite rifle with effective ammo no matter what gets added
(Let's be real, it's kinda boring to use the same gun all the time just because it works best)
I'm not giving up the fight either btw my 2nd overhaul is up finally after a few days 😅