Three years ago I personally had two occasions on which T7 (50grx2) pellets did not ignite. The rifle is a .50cal Knight Disc Elite. I was using Winchester 209 primers. Both occasions occurred in the field and they both cost me a deer - one a dandy buck. In both cases, I got a "pop" from my primer and then watched my sabot/bullet dribble out of the bore of my rifle. Both occurred on down right miserable days. I'm talking, cold, wet snow coming down pretty hard. I'm certain I got moisture in the bore and during the course of the day it made its way down the rifling to the pellets.
Now, I use loose T7 and cover my bore with a finger cot if the weather is inclimate. Had I been using loose T7 3 yrs ago would my rifle have went off in those two situations? Impossible to know. I do know this though, shooting two 50gr pellets over a 300gr Barnes Expander consistently produces between 80-100 fps lower velocity out of my rifle than 100gr of loose T7 under the same bullet. That tells me that either the pellets don't burn as well or they are a little shy of 100gr. Either way, I still have a full box of T7 50 gr pellets on the shelf that will never see the bore of my rifle. If anyone is in the mid-Michigan area, I'd make ya a heck of a deal on them (hazmat prevents shipping).