So...AR's are NOT 'direct impingement' operating systems

[zaitcev]

It's the cylinder which goes up and down. In the AR, the cylinder is the moving part, which is where many who look at it don't understand.

The linked tech note remarked upon that point, using the example of AR-180. Another common gun with a stationary piston is Mini-14.

Those of us who have owned HK91's suffered the same issue, gas directed around the brass case dirties up the action - not to forget the chamber is fluted to float the case out since the bolt head doesn't turn.

Just a minor point, fluting in HK action is necessary because, being a delayed blowback, the case moves while fully expanded by the internal pressure. It would not otherwise operate the action if it were stationary. The force of friction is applied at the walls, while the force moving it is applied at the case bottom. This can easily make the case rip. So, fluting is not linked to non-rotating bolts. The tilting bolt gas-operated actions, such as SKS, typically do without fluting. Maxim does not use fluting either

 

[zaitcev]

Motors of that type are generally called "rotary". The ones with stationary cylinders and rotating cranks are called "radial". I mean if words matter, and all that.

A rotary aircraft engine is a kind of a radial engine. All rotary aircraft engines are radials, although not all radials are rotaries. I suppose he didn't use the word "rotary" because it was stolen by Wankel to mean something else, just like the word "gay" was stolen to mean something else.

 

[chicharrones]

Mag, Clip, Mag, Clip,...................

Interesting discussion though.

Regarding the rotary engines and video clip, absolutely.

The gnashing of teeth caused by a technical note that was updated and re-released 6.5 years ago, not so much.

(Edit to add: Clearly, not everyone is gnashing.)

 

[Robert]

Yes it is, no it isn't... We appear to be going round and round on this one, so let's agree to disagree and call it a day.