"Untrained and un-toughened feet will blister."
- Yup.
I was never issued Mark 1s. I went from the old pebbled 'Ammunition Boots' to Mark 2s. I took a 9 1/2D.
When we went to the Mondo-point system in the early 80s, I was not properly fitted, and walked Auyuiituk National Park on Baffin Island it wet, ill fitting boots. A year later, I told the old guy behind the counter at Base QM at CFRS, and he tossed me a pair of 7 1/2 - 8C, and said "Try these!" Perfect. I could - and did - run for miles in them, with issue insoles and Socks, Wool, Grey.
Getting ready for a Nijmegan Team in Lahr, I was advised to trade in the two pair I had worn out on Forced March Team before training for Nijmegan. So I did. Special order due to the C width. back come two pair of Grebs. To tight across the top. All of my MKIIIs to that point were Sunbeams. The Grebs started to flatten my arch. I drew two pair of the next biggest size, and walked four days of 52 - 58 km in a new pair of boots that did not fit. Taught me a few lessons:
1. If at all possible, NEVER turn in both pair at once. Especially on Ops or Trg.
2. If sizes were perfect, boots would cost $1,000 a pair. Sizes fall into contractual specifications, the looser the specs, the lower the boot price. These 10Es don't fit and your last ones did? See if the mfr is the same. Yes? Try on another pair, then. If they came off a different machine, they might fit.
3. If you are going to experiment, do it in garrison, and give yourself lots of time before deploying - if you can. Try one NEW item at a time - not new insoles with different socks in new boots under a full ruck cross country: that would be a roll of the dice.
4. You can walk 200+ km in four days with ill-fitting boots, a ruck, a medic, and Motrin. Now that you have read that here, there is no need to try it yourself.
5. Once your feet get hardened to a particular boot/insole/sock(s) combo, keep them hardened.
When they gave me Vibram soles and orthotics, I started with broken in boots, had the Vibrams put on, broke the orthotics in slowly, had the boot upper stretched by QM, and when that combo worked, did Ruckmarches to prove the fit. After that, I got a knew pair of boots Vibramed, stretched, and broke them in on alternate days. Then I broke in my second pair of orthotics.
For the most part, I still wear Socks, Wool, Grey with the Mark 3s. I find the US Army OD socks I bought in Hohenfels in 1987 still work good as well.
Tom