Bryce,
Yes the GG Website said 15lbs max. That means the pack can structurally handle that much weight without falling apart. It does not mean my shoulders are comfortable lugging 15lbs for 20+ miles :)
Typically my base weight with the Murmur was 4-5 lbs. Now add 3 days of food and the 4 liters of water I need at the start of each day where I typically hike, and it gets tiring at times. The pack is great where water is plentiful and it is a 3 day or less trip in 3 season weather.
I bought a zPacks Zero to test out the cuben before Dan McHale made my Bump. This light cuben held up well and the thicker cuben and hybrids should be fine in a pack.
Dan wanted to make the Bump out of his heavier cuben hybrid. Dan is confident the material will hold up, otherwise he wouldn't put his name on it. But I ended up getting the fine Dyneema grid, just wasn't 100% sold on cuben at that point — no science to it, just a feeling. I guess sometimes our old thoughts never die.
For me if my total pack weight is going to be much over 10lbs then I am thrilled to use a 3 or 4 lb McHale. Total pack weight is under 20lbs and the pack carries like a dream. Total pack weight is my key measurement. Base weight is more of a diagnostic procredure. An 18lb total pack weight with my Bump is like carrying a total weight of 6 lbs in the Murmur. The Zero is very similar to the Murmur. They are big stuff sacks with shoulder straps.
But these kinds of packs have their uses. I can't begin to count the number trips or miles I have on my two old school Murmurs and the Zero.
My Bump has a similar volume as the Mumur. The Zero is a size small and a lot less volume, but it is still taken on a lot of trips… But on most short trips the Bump is now my go to pack. All I need these days are my McHale LBP or Bump. The other packs I keep around in case someone needs to borrow one. Good news is that I think I will never buy another pack :)
I have given away several packs since I got the two McHales. I think I only have 2 UL packs left; a Mariposa plus and the Zero. Haven't used the Mariposa in about 3 years but have lent it out a lot… right now a good friend of mine has it.
Too bad the old Mumur is discontinued. At $80 is was a bargain for a 2 or 3 day UL trip. The new one costs almost twice as much. Oh well, I guess that is progress.