BLUF: MidwayUSA seems to be the Factory Seconds liquidator for Hornady and whoever makes Shockwaves for T/C (seem identical to SSTs except for different colored tip, but I haven't cut any open to compare gizzards). If you like SSTs and/or Shockwaves, I recommend signing up for MidwayUSA emails. If you have an account with them, go to your "My Account" page and select Hunting/Big Game/Muzzleloader, and Reloading, so Factory Seconds bullets will go into your "Custom Shopping Experience" emails. I've seen 250 grain Factory Seconds bullets matching Hornady SST-ML and FTX bullets in my email as recently as this past fall.
Background: In 2011, MidwayUSA offered "Factory Second Muzzleloading Bullets, 45 Caliber (452 Diameter), 250 Grain Polymer Tip Spitzer, for use with 50 Caliber Sabot, Box of 50 (Bulk Packaged)" for $4.41. I bought 32 boxes (1,600 bullets) for about $170 with shipping. They are definitely Shockwaves; yellow tips and same geometry as 250 Shockwaves I'd previously bought in T/C packaging. I have no idea what the defect is that made them Factory Seconds, other than some discoloration of jackets. A year or so later, I ordered a similarly described Factory Seconds shipment of 10 boxes, 50 bullets each, $7.00/box that were red-tipped Hornady 250 SST-MLs when I got the package opened. Again, no visually-detectable functional defects found. Shortly after that, they had 50 packs of Harvester black Crush Ribs for $3.99 and I ordered 40 packs. I've seen that same SST-type bullet in Factory Seconds sale emails several times since then, though I haven't paid much attention to them since I'm still sitting on about 1,200 "Second" Shockwaves and about 350 "Second" 250 grain SST-MLs. I got about 200 Factory Seconds 300 grain SST-MLs as well, $3/20 count. All of those Factory Seconds bullets from MidwayUSA came in sturdy blue plastic bullet tubs with MidwayUSA labeling. That's probably my lifetime supply, for inline muzzleloaders at least. 77 grains (by weight) of BH209 and CCI Magnum primers in my Frankenrifle will group 3 of either of those bullets at or under an inch at 100 yards if I'm doing my part on a calm day, same POI/POA for both at 100 and 200 yards. In other words, I haven't shopped for inline bullets/sabots in about 7-1/2 years and might never need to do so again in the future.