doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Advantages of the top rib extension bolt

In 1921, Charles Askins wrote in The American Shotgun
"It remained for America to have the final word in bolting mechanisms. Lug bolts located on or as part of the barrels were in the wrong place. The hinge-joint of the barrels acts as a fulcrum of a lever, upon which, the barrels rest and pry at the bolts. It takes three times as much strength in bolts, to withstand the pressure if they are placed an inch from the joint, as it would should the fastening be accomplished three inches further away.
Alex Brown moved his locking bolts from the lug and placed them in the extension rib, which is undoubtedly the right position for them mechanically. Throughout the world no other locking devise should be used on a shotgun save the rotary bolt."



The whole world had not taken Askins’ advice at that point in time, but some form of primary or secondary top fastening system was used by Westley Richards, Greener, Rigby, and Beesley in England, Merkel and most German-Austrian makers, the Manufrance Ideal, and in the U.S. by L.C. Smith, D.M Lefever, William Baker designed Ithaca and later models, Baker and Hollenbeck designed Baker Gun & Forging guns, Remington 1893 and 1894, and A.H. Fox.







William Wellington Greener in The Gun and Its Development 1907 provides an historical perspective on bolting mechanisms.
Page 145 "The Westley Richards' Breech-Loader"
"This gun is one of the first, if not the first, of the top breech-bolt mechanisms, and was patented in 1862. In addition to the lump underneath the barrels, upon which they turn, here is a lump projecting from the breech ends at the top of the barrels. This lump is of dovetail shape and has a hook; the projection fits into a correspondingly shaped slot in the top of the standing breech, and is secured there by a holding-down bolt sliding to and fro in the line of the barrels.
This bolt is pushed forward by a spring behind it, and is withdrawn by pressing the lever lying between the hammers to the right. The object of this particular arrangement is to prevent the standing breech from springing back at the moment of firing, and was undoubtedly a step in the right direction.
In 1865 the author invented a top cross-bolt, which passed through an extension of the top rib, thus wedging the barrels to the standing breech."

Chapter 15 of Shotgun Technicana by Michael McIntosh and David Trevallion discusses "Top Fasteners" specifically the Alexander Brown patent, and the almost identical Ansley Fox patent.
"The most basic principle in fastening any hinge is that the farther the fastener is from the hinge itself, the greater the mechanical advantage. That’s why door latches are placed where they are. In a gun, the action bar and breech face form two sides of a right triangle, so that the top or the breech face is farther from the hinge pin, in straight-line distance, than the bottom. In a side-by-side gun
there’s an additional advantage in that a top fastener is a bit more efficient in overcoming the effects of barrel flip-for the gun, if not for the shooter. With a top fastener, the barrels still flip downward on firing, but the action bar flexes less, and the fastener keeps the top of the barrels from pulling away from the breech face."
"The most interesting of the American top fasteners is the L.C. Smith’s patented by Alexander Brown in 1883. Where all the others used either Greener’s transverse bolt, some sort of flat bolt or hook on the front end of the top lever, or both, Brown designed his bolt as a steel cylinder that turns on a horizontal axis. A slot filed into the cylinder forms the actual hook, which fits into a slot in the rib
extension. The cylinder also engages a lip at the rear of the extension as a secondary bite. L.C. Smith described this arrangement as a double cross-bolt, although double rotary bolt would be more accurate."
They also discussed some disadvantages of the rotary bolt, with examples of actions shot loose with time (and magnum loads), but did agree that "...the top fastener mechanism…makes excellent sense."

Fox HE

What makes a rotary bolt better than, for instance, a Greener cross bolt?

All this rhetoric is fine, except that thousands of heavily used guns without rotary or Greener bolts are still going strong and are still tight. Parkers, Model 21 Winchesters, and Purdeys are examples. Mr. Greener seems to imply that there is a second locking bolt on a Westley Richards in the 1862 patent. There is not a second bolt, only the bolt that extends into the extension rib. I'm sure he was aware of that.

Thanks Dr. Drew! A timely article (certainly for me these days). The rotary bolt seems to be almost exclusively an American application. Smith, Baker, Fox, and Ithaca employed them endlessly and as the years pass, they keep on doing the job. Alex Brown's 1883 design is good one and in a mostly machine-made gun, they are hard to argue with. The Brits don't use them on anything "bespoke" (unless you consider the Greener cross-bolt or a 3rd-bite a variant) because they generally criticize any rib extension as another "unnecessary-encumbrance" to accessing the barrels for the loading process, and for London "Best" guns "they simply won't do". Allright...very different economic situations(!) and the Brits clearly know their market well (and make sure to build accordingly). With only a few exceptions, American guns have always tended more towards the unadorned "general-use" category anyway (historically, most American families could only afford one shotgun & it had to do it all, i.e. hunting & defense). If there was the luxury of another weapon at home, it was likely a rifle (or occasionally, a pistol) and similarly unadorned.

It was and is a purely economic game and that really is "the final word". Col. Askins was simply schilling for the home team (because "he knew where his bread was buttered"- to quote my maternal grandmother).

Stevens also used the rotary bolt on their early doubles.

All right, from a mechanical point of view a properly fitted, and I stress properly fitted Brown rotary bolt is attractive. Simply this. It holds the barrels down towards the frame while holding the barrels back against the breach. Self adjusts for wear and is a very simple mechanism. Double underlugs hold the barrels to the frame nicely. The holding to the breach is a function of the fore end I think. A cross bolt would work much the same as the rotary bolt. Needs a lot more fitting than the Brown patent. A double underlug with crossbolt such as a Merkel SXS is just overkill. either method would be more than fine. Lots of low enders work just great with a inclined slot on the barrel extension, lots of them.

In practice all work just fine. Clean the pin, lube the pin, shoot the gun!

Chief

Drew, please explain the picture of the HE Fox. It appears that the extension rib is broken. Am I mistaken or is that really the case? If so, how did that happen?

I believe Damascus has a hammer Purdey that he has owned most of his life, that has no extension and but a single locking lug on the barrel.

There does not seem to be an issue with it holding the gun closed. Properly fitted, they all do that, and a rotary bolt was no better and no worse than any other bolt.

Best,
Ted

David Trevallion sent me that, and this, pic long ago



A 2 3/4" chamber HE was used extensively with 3" 1 3/8 oz. at 1295 fps Super-X 'Record' shells.

Ouch!

I certainly don't think Merkels or Greeners with three locking mechanisms are over built.