Researchers at Purdue University took high speed video of metal sliding over each other and discovered a strange swirling fluid-like behaviour not normally associated with solids.

This research might have major implications for the gun industry. Guns are essentially a collection of sliding metal parts. If this fluid behaviour can be reduced in the barrel, maybe the barrel life can be significantly extended.

The reader who emailed us about this research pointed out that this may be one of the pricinples behind the Blish Lock phenomenon that was exploited in the Thompson Autorifle and the original Thompson SMG. John Bell Blish discovered that “certain dissimilar metals will resist movement with a force greater than normal friction laws would predict” from observing naval gun breeches which unlocked when firing weak charges but not heavy charges.

Thompson Autorifle. Drawing from Hatchers Notebook 2nd Ed, 1957, p. 45

The Thompson Autorifle was just about the simplest fullpower semi-automatic rifle ever made. It’s action was not much more than a rotating bolt which resisted being unscrewed when the barrel pressure was high but would unscrew when the pressure decreased. It was a very clever invention but required a lot of lubrication and ejected brass violently (the latter being a common problem with all delayed blowback rifles).

[ Many thanks to Frank to the tip. ]