spaniel
What powder to you plan on using? My experience with #11s and 777 was not good below freezing, but I think it was regular #11 and it was a sidelock (probably the WORST combination).
I would concurr , whether it be a #11, #11 mag, or Musket Cap when using T7-2f in a sidelock.
I have since switched to t7-3f and have not had a problem since even at 20 below..... You can get 3f out under the nipple so much easier than 2f.
In an inline, the #11 mag works well in cold weather even with 2f, well at least for me it does.