I have had that back pack as a GHB for about three months. I replaced a mid size duffle bag with the back pack b/c I decided if I needed to walk a back pack was better than a duffle. The back pack is well made, but somewhat stiff to work with. If you like a lot of nooks and sleeves for your things, this is the bag for you. If you prefer to pack with larger items and would prefer a larger open style like a large Alice pack, this is not the bag for you. The back plate sleeve is not suitable for a lap top IMHO. Hope this helps.
You have three choices; Buy an adjustable gas plug from MidwayUSA or someplace similar. Your rifle will then be able to shoot current production commercial ammunition. You risk injury or damaging your Garand shooting commercial ammunition without an adjustable gas plug. The only exception is Hornady is now making a load specfically for the M1 Garand. Your other choice is to join CMP and buy surplus HXP ammunition from them. HXP is made for the Garand and does not require an adjustable gas plug. A third choice; go to gun shows and buy CMP ammo. at a huge premium from someone who purchased the ammo. from CMP.