There is some very nice wood in that rifle! More pictures would be great.
I have a Hawken full stock with a .54 caliber x 1" x 36" barrel. It is heavy. If you want to shoot it offhand, you need to "draw a bead an touch 'er off" pretty quick, because it's too much to hold up for very long. However, twelve pounds was not unusual for original mountain rifles, and some, such as the Hoffman & Campbell rifle carried by Francis Parkman, were fourteen pounds. Most of the period references I have read indicate the marksman would "drop to his knee," or prop the rifle on his wiping stick, or rest it on whatever natural object was available whenever possible for shooting.
Regarding the transfer of photos from your iPhone to your computer, I just email them to myself. Next time I'm on the computer, I save the images from the email to a folder. Sometimes, when I just want to plug a picture into a post on the forum and don't necessarily want to keep it, I save the image to the "desktop," insert it into my post, and then delete it from the desktop.
Now, back to that good-looking rifle...
Notchy Bob