I think Col. Ducrest thought that problem through with the 65mm Mle 1906. The wheels are a long way forward of the trunnions which should give considerable stability to the gun
even if there is a hangfire. The Deport gun looks like a very early example of a concentric recoil absorber - very few guns have adopted this idea.
The 75mm M6 gun used on the M24 Chaffee tank and B-25H medium bomber is the only example I can think of.
The argument Hogg makes about the Deport gun and hangfires ignores the effect of the buffer which is designed to prevent excessive forces being transmitted to the gun structure when
Talk of the "differential recoil" systems (or "soft recoil" as it was later known) used in some mountain guns put into service immediately before the war in the topic http://landships.activeboard.com/t52315836/french-canon-de-65m-montagne-modele-1906-65mm-mountain-gun/ reminded me of something - turns out it was what Ian Hogg calls the French 75mm Deport Mountain Gun of 1910 which used an unusually evident version of such a system. A reproduction of the drawing of this unlikely-looking gun in his book A History of Artillery:
Aplogies if this is covered elsewhere in the forum - I can't find if it is. Hogg, the old Master Gunner, evidently has some reservations about this "peculiar" form of recoil system (that is any and all differential systems which fire the gun as its barrel and breech run forward from the fully recoiled position) but admits it "is in fact based on very sound principles". He mentions some practical aspects to be considered in operating these weapons, the most serious being the management of a hangfire (the whole cannon probably being tipped on its nose by the unrestrained mometum of the forward-moving mass, then the propellant belatedly fires ...). "Highly embarrassing," is his asessment of such an occurrence (should it take place).
Quite unsure when and where these might have been used - or whether or not they or any other of the differential recoil guns suffered the "embarrassment" of a hangfire.
Marvellous resource - copy retained, thanks Charlie! Don't know why this stuff interests me so, my dad was the gunner, I was a sapper. Oh well, very loud *bangs* I suppose.
http://www.network54.com/Forum/330333/thread/1209982679/belgian+museum+guns and http://www.network54.com/Forum/330333/thread/1219676444/Belgian+Artillery+Adventures+%281%29
and 1910 (third) edition of Henry Bethell's Modern Guns and Gunnery.
I think there's plenty of information about the Canon de Montagne 1913 Saint-Chamond/Deport for an article on Landships II. The gun had a fair career given the tiny numbers made.
It was actually a smarter design than the Ducrest design since it didn't have a hydraulic recoil absorber just a large spring - just takes a little more study to figure out how it worked.