In his "Gun Book" British author Gough Thomas describes an imperical test he used to define the "balance" of a shotgun, by which he meant a traditional British side by side. He said that the measurements he made included weight, point of static balance, least transverse moment of inertia and radius of gyration.

The purpose of the test was to quantify the amount of effort required to swing the shotgun in question.

He included a photo of the device he used, which appears to be a cradle for holding a shotgun inverted while suspended from above by what appears to be a thin rod or wire.

He offered no explanation as to how this measuring device was used, although there is a stop watch included in the photo, so evidently accurately measuring time is part of the procedure.

Can anyone shed light on what the measurements consisted of, how they were arrived at, and how the figures obtained are to be used?

Rocketman, where are you?

Basically, the whole contraption pivots around the suspension wire. The operator rotates the pendulum a small amount, say 10 deg., and starts it oscillating. The period "T" of the oscillation is established and plugged into the moment of inertia formula. The formula used for a two wire pendulum is I=(M*g*T^2*b^2)/(4*pi^2*L), where I=moment of inertia, M = mass (kg), g = acceleration of gravity (9.81 m/sec^2), T = period of oscillation (sec), b = distance from suspension wire to center of gravity (m), L = length of suspension wires (m).

I believe, that since T^2 and M are the only variables in the equation, one could simply make that calculation and be able to directly compare different guns. Moment of Inertia, I, is an indication of the energy required to change the orientation of an object; so a low figure would indicate a "lively" gun. A high figure would indicate just the opposite.

Ah physics. I think I'll just stick to shooting the gun and see how it feels. My cousin is a engineer and he loves this kind of stuff. Quantitative analysis is his thing. I am a medical professional and have a much more philosophical/abstract mind.

James

Here I yam, Builder!

xausa, I have been providing this measure for some 12 years now, although with a differing measuring device. I use a constant torque turntable with one revolution timed from start to completion. My current database is over 600 guns with gun description, weight, balance (teeter-totter point balance = CG, not some magical feel sort of thing), unmounted swing effort (MOI at CG), mounted swing effort (MOI at butt), and half weight radius (compactness). The turntable is kept calibrated via metal bars of calculated MOI; several differing MOI's are used to make a chart with a regression line (R squares are very high indicating a high degree of accuracy).

Thomas's device was based on a torsional pendulem. It is sufficiently accurate, but does not lend itself to "production" of data. My data fits well with Thomas's.

What more would you like to know?

DDA

Rocketman,

Thank you for your response, although as someone who barely made it through calculus 55 years ago, I don't pretend to understand the details of what you and Carpetsahib are laying out, except in the broadest terms.

However, my original inquiry was just a lead-in to a more basic question, which is a request for a comparison between what I have been led to believe are the top level American made doubles, such as Fox, Lefever, Parker, Ithaca and the Winchester Model 21 as opposed to British and Continental "best" doubles, in terms not only of "balance", but also of stock design, action strength, durability and robustness, and sophistication of locks in terms of ease of cocking, resistance to doubling, weight of trigger pull, and lock time.

Since my experience over the years has been primarily with over and under shotguns, starting with Brownings and progressing through Perazzis to the SO series Berettas, I have very little first hand experience with side by side guns and would greatly appreciate whatever crumbs from your table of expertese you would care to brush off in my direction.

Rocketman, will you be at the Vintage Cup in Rhode Island this year?

Builder, I working on a viable plan to do just thst. Will let you know.

DDA

xausa, next "pearl of wisdom."

I assume you understand stock measurements and would agree that they can't be "summed up" by any one measurement or descriptor. Consider that handling dynamicas are the same in that it takes four measurements to describe any particular gun's handling. Also, consider that, just like stock dimensions, handling dimensions need to be "fitted" to the individual shooter.

All for the moment. Let me know if the above "computes" for you

DDA

This is highly interesting. How do you mount a gun to determine the MOI at the butt?

You don't need to measure MOI at butt as it is easily calculated. Therefore no need to monut the gun at butt in a MOI measuring device.

Parallel axis theorm: any axis of rotation through the CG will have a parallel axis through the butt. The MOI at butt is calculated by mass (weight/32.2) X length in feet from CG to butt (balance point to trigger + LOP qty / 12 in/ft) qty squared qty + MOI at CG.

If anyone doesn't get this or wants to see a sample proble, post back.

DDA

xausa - you're asking about 100 year old guns that were cared for differently. Some are gonna be in great condition and others will need a lot of repairs reguardless of design. All box locks are basicly the same - and from my experince the Remingtons and Ithacas the easiest to work on. Most American stocks have more drop in them than their European counterparts. Most American guns are heavier but still balance good which is nice if you're going to be shooting clays, not so for carrying all day in the field. If buying one for the first time you'll first have to handle it to see how it fits and feels. Then have a double gunsmith check it out for any repairs and parts. Will he have to bend the stock or add a recoil pad - can he get or make parts for the gun. I do a lot of my own work but know my limit and have Brad Bachelder do the items I can't. It's really up to you, not some math forumla [ no offence rocketman ]. Paul

No offense taken at all, Paul. My work is about making a tool that allows handling fitting (self fitting at this time). Just as the yardstick is the tool for stock fitting, a weigh scale, balance fulcrum, and MOI machine are the tools for handling fitting. It is not my intent to make a math formula to recommend fit, either stock or handling.

The vast majority of people "experience" guns in a relative random order. If, instead, they were presented guns from their first encounter in a logical order of fit, both stock and handling, they would not develop first learnings and muscle memories that suit them poorly.

DDA

Let me put it another way:

In the 1939 Stoeger catalog, the most expensive Parker shotgun, the Model A-1 Special, sold for $890, the Premier Grade L.C. Smith was priced at $832, the SPE Grade Fox sold for $99, the Ithaca Number 7 Ejector Double sold for $379.20, and the "Trap" Grade Model 21 Winchester sold for $188.25.

On the other hand, the Powell No. 1 Best Grade with self opening action sold for $835,the Holland and Holland "Modele De Luxe" for $1150, the Woodward Best Grade for $1100, the Stephen Grant self opener for $895, the John Rigby "Regal" Grade for $940 (all sidelock ejectors), and the W.W. Greener (boxlock) Ejector Gun for $325. Stoeger also offered a Model 219 Ejector with hand detachable box-locks, which suspiciously resembles a Westley Richards, for $850 under its own name, as well as an European made Zephyr Shotgun in Royal Grade Model 410E, a side lock ejector, for $395.

Would anyone be willing to speculate which gun represented the best value for the money, taking into consideration the attributes I have listed above, assuming all stocked to the buyer's specifications?

I think I'd have to see those guns you mentioned all in a nice rack, in pretty much near mint condition & have a few hours spare to judge best value..I don't see that happening...
It would be one of the Brit's for me ,might even be the Greener depending on grade.
It sure would be fun to spend an after noon looking at that Gun rack though
franc

xausa, your introduction of inital costs seems illogical to me. I don't think for a moment cost is directly related to handling characteristics as just about any gun on the market can be adjusted to produce the handling as measured by Rocketman or any other such investigator. Most of the manufacturers you cited also provided a broad spectrum of handling characteristics with changes in barrel weights, stock lengths, forearm construction etc. Further, if value is your question the artistic content of the respective guns would have to be factored out to get to comparable values. $50,000 of the best engraving won't change performance but it sure changes value. If you want handling quantified, Rocketman can do that. For value, just observe market values of recently sold guns.

Having handled thousands of shotgun over the years, the job demands it, I wanted to figure out what makes a "lively" gun, as opposed to one that "balances" at some point, ie the cross pin.

Balancing at a certain point along the length says nothing about that live feel in good shotguns.

Take apart the (break open) shotgun to its three parts, stock and receiver, barrels, forend. Now hold each part from the point you would normally hold, ie the grip for the stock and receiver unit. In lively guns the part has a positive weight concentration towards the center of the gun. The more pronounced this tendency the livelier the gun.

It is possible to alter the feel by adding or removing weight. Adding weight to the center, or removing weight from the extremities (muzzle, under the butt pad) can alter the feel. Even a little weight, in the form of a lead sheet at the breech end of the barrels can have a dramatic effect on the feel of a shotgun.

As for fittig, like Rocketman above, I have been trying to get a rational system, and made my own trygun in which the shape of the stock is figured out separately from the line of sight. But that is for another thread.

That's pretty straightforward. It seems to me that these values would make it much easier to set up a try-gun for an initial fitting.

Another point: Thomas's apparatus measured MOI with the gun inverted on the pendulum; the rotation was around the CG in the horizontal plane. Is that value valid for all rotations, including those in the vertical plane? After all, recoil is primarily in the vertical plane.

.

Rocketman,

Do you in your database have any figures for the Alex Martin ribless SXS? Or other SXSs which were made without bottom ribs, like the Darne and Ideal. It would be interesting to see how they compare to conventionally ribbed shotguns of similar weights.

Also, has anyone experimented with those golf swing gizmos they put on golf clubs to calculate swing energey? At first glance it looks like they might be useful.

Yes, I was.

Well, that simplifies matters. Multiple MOIs would be inconvenient, would they not? So the next step, on my part, is to construct a torsional pendulum and start measuring.

Actually, I am very interested in applying this technology to rifles, to see if I can determine why some specimens seem well balanced and lively, and others feel....leaden and dead. And I really appreciate your input and insight.

Low MOI vs. High MOI: What effect does this have on perceived recoil? Assuming equal weight (mass), actual recoil energy should be equivalent (E=1/2mv^2).