I love this discussion gents as one day I will be forced to sell everything and move into a condo and limit myself to (what I tell myself) will be 5-7 guns in total. So when that day comes... do I invest in a custom built ultra lightweight gun or do I just keep a couple that I have?
So a couple of points to consider... how many shots are you taking in the field? I have a pencil thin barrel on a 300 RUM that you can cover the distance between the first 2 shots with the finger nail on your pinky. The 3rd shot goes 6" high. BUT... after 2 shots it's either dead or doing mach chicken to another country!!! I couldn't care less in the world about that third shot.
Now one thing you guys haven't mentioned is bullet diameter and barrel composition (purities or impurities). I have 2 Browning Mountain Titanium rifles. A 7 WSM and a 325 WSM. There is over 1/4 lb difference between the 2 just on barrel clambering which absolutely blows my mind.
Now the other day I took the 7 WSM out to break rocks with it and I was amazed at how the barrel refused to really heat up and I kept plinking away until almost a full box was gone (kept 3 shells for coyotes on way home) and with very little time in between, the barrel never got really hot. The 325 after 3 shots will keep your hands warm all night.
Secondly it's hard to argue the cost of building versus buying when you can get such nice toys out there lol. These are my main lightweights in the pic. The lightest is the Browning Ti 325 at 6.3 lbs, then my Wby ultralight in 280 AI at 6.7 lbs, then Savage lightweight in 6.5x284 at 6.77 lbs and then the Browning Ti in 7 WSM at 6.8 lbs. But I'm learning as I get older and shot things that I have to drag out more and more by myself... lighter is worth ever penny lol.