doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com SPRING STRENGTH

Hold the trigger group of any auto and try to cock the hammer using your pinky. It is doable in almost all autos and pumps.

Now compare that tension with the V or coil springs in any break open gun and the inevitable question is why so much stifness.

The auto hammer has to overcome a heavy, usually spring loaded firing pin, and it does it reliably, the break open springs move less mass, yet it is incompressible by hand.

Can the gunsmith posters enlighten us on this spring strength difference?

something to do with lock time in having to overcome inertia to move large masses of metal in heavy striker/hammer/tumbler/sear assemblies quickly? Or not? I dunno.

Good question. Possibly a carryover from the days when a very strong spring was necessary to fire a percussion cap. I know from experience with percussion guns that a weak hammer spring can cause failure to fire. It seems that the design of a firing pin, striking a primer, requires much less force than that required to ignite a percussion cap.

I hope some of our gunsmith posters address this, too.

SRH

There's a minimum striking force needed to reliably set off the primer. I bet the auto is closer to that minimum. The auto with the softer spring will likely have a longer lock time as well.

If both were of the same striking force, yet each different in spring force, the amount of travel and moment of inertia of the hammer would have to make up the difference in spring force.

Chuck is very much on the right track. I'd add that pump and auto guns have firing pin travel in a straight line whereas most double guns utilize rotary motion within the firing train. If one knows the required impulse to ignite the primer (something the manufacturer would know), one can back calculate the required spring constant and travel to generate the needed impulse at the firing pin tip. Straight line force and travel are easier to deal with than is rotary motion. Older double gun spring stiffness and travel was most likely established by trial and error. Modern guns are most likely calculated, tested, and adjusted as necessary.

Lock timed depends on the whole train from spring to firing pin; weights, frictions, and travels.

DDA

Many, if not most, double guns have straight-line firing pin travel, Don. The ones who don't have the firing pin integral with the hammer, in one piece. Even autos and pumps have a hammer that travels in an arc and strikes the firing pin. I can't see much difference in that regard. Maybe I misunderstood your meaning?

SRH

Isn't the new benelli O/U a new system involving striker firing?...Geo

I wondered too if it was apples to apples comparison. If the spring were out of the autoloader, it probably would be difficult to hand compress. Also, is the spring in the break action storing energy for other operations that the autoloader taps off of a shell being fired.

The most familiar SXS actions, the Holland type sidelock and A-D boxlock do not utilise the main spring for anything other than primer striking. Other actions, notably the Beesley, Baker (12/20), utilise the main spring for opening after the primers have been struck.

Evn out of the action the pump and auto main springs are fairly mild compared to the stifness of double gun springs, and that goes for both coil and V types.

Somewhere there is a video of a SXS hammer gun tuned for cowboy action shooting. Its hammers can be easily cocked with the sweep of one hand. It is is probable that it strikes primers OK.

I see a lot more misfires with autoloaders. Probably because everything in their mechanisms has to be tuned and in harmony so closely. They're usually light strikes, where the primer is lightly dented and does not fire. In 99% of these cases the same shell that misfired can be fired the first time in a fixed breech gun. I agree with Chuck that the auto is probably closer to the minimum necessary to fire the primer. They are trying to keep the resistance to the breech block traveling rearward at a minimum to facilitate reliable ejection and feeding. Remember, it is the breech block moving rearward that recocks the hammer each time it cycles. The fixed breech gun can utilize stronger springs than are actually necessary because it is not limited except by the force required to recock them when opening (or closing in some cases) the action. IMO, the extra strength in hammer springs in fixed breech guns is a "just to be sure" measure. Remember which genre of shotgunners almost never use autos .............. those with big money riding on a shot. Pigeon shooters. NSCA competitions allow two misfires, or gun malfunctions, in a round of 100 before it costs the shooter a lost bird. Not so with flyers.

It stands to reason that less force should be required than with a percussion cap. The p.cap has to be forced down upon the ring of steel at the top of the nipple with enough force to detonate the fulminate. With shotshells, not nearly as much force is needed by the firing pin to make the very small indentation in the primer necessary to fire it.

SRH