Winchester Subsonic 42 Max is made by Winchester in Australia. This small game hunting and pest control ammunition features a "heavier than most" 42 grain lead hollow point bullet. Pushed to subsonic velocities, it is also quieter than high velocity 22LR rounds. Packed in boxes of 50, I found this ammunition available by the brick at Bass Pro back in February 2017. This test should be representative of ammunition currently available at your local retailer. Expect to pay $5 to $7 per box of 50 at current retail price levels.
Velocity, accuracy, function, and terminal performance testing were all done in a Ruger 10/22 Carbine with 18.5 inch barrel at a distance of 25 yards. The testing results are documented in the video and data sheet immediately below. You may need to click on the data sheet image to enlarge it for better visibility.
Direct Link to Video On YouTube
The greatest concern when using subsonic ammunition in semi-auto rifles is reliable function. I am happy to report that 42 Max fed, fired, and extracted perfectly in my mostly stock Ruger 10/22. 25 yard velocity averaged 1042 feet per second, which is right in line with the 1065 fps muzzle velocity published for this ammunition. Downrange energy at 25 yards was right around 100 ft/lbs. Perfect for small game and nuisance pest control.
Terminal performance was very good. This load expanded like a high velocity hollow point, but did so at subsonic velocity. Penetration was also greater than we have seen with other subsonic hollow point ammunition I've previously tested. I believe this is due to the slightly heavier bullet Winchester uses in this loading.
My only quibble with the overall performance of this load was demonstrated accuracy. We've seen this rifle turn in smaller groups with other brands and bullet weights of subsonic ammunition. Rimfire rifles are notoriously picky about the ammunition that produces their smallest groups. At 25 yards the ammunition delivers acceptable accuracy for small game hunting and pest control. I would be reluctant to push distances to 50 yards and beyond with this rifle and ammunition combination.