I tried to light a 15 yr old flare and the ignition button broke off of the end. Tried another old one , the same... Used a torch to get them started and found that they dripped a hot white molten liquid that solidified when it hit the driveway.
Also tried an old 12 gage, old 25 gage and new extended 12 gage red flares. I believed that the 25 gage would be the best by far... Results were surprising. The older 12 and 25 gage only stayed aloft about 3 seconds, not much height . Yes the 25 gage was brighter. The new 12 gage extended flare was twice the height at least and was as bright as the 25 gage flare...I was surprised by this.
Being in the USA, I'll keep the old flares on board but also realize that they may be less than desirable and may not even work. I will keep fresh flares on board to count on should I ever need assistance.
Cal 9.2 #19 SilverSwan