doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Impact testing

Would someone be so kind to describe or provide a link to a website or an on-line article that describes in detail how to properly do some impact testing to determine gun fit?

What I'm specifically seeking is the description of impact testing that I had read or heard about several years ago where you quick mount and snap shoot several times at a bullseye exactly 16 yards away. It seems to me that I recall that for every inch of deviation from the center of your patterned shots to the bullseye equated to 1/16" on the stock. I'm not 100% sure of what I recall is correct and thus my reason for the inquiry.

TIA,
bamboozler

You have decribed the process exactly as it is performed.
16 yards, light loads, Move, mount shoot. Average the patterns, adjust the try gun. Repeat.

Here's the hitch.
I found I could not do it myself.
There were too many deficiencies in my mount due to years of adaptive shooting. Ie, neck craning, head tilting, hand sliding, face jamming, etc. 100 different shotguns I adapted to, rather than their stock to me.
Once we worked out an adequate mount, we could then adjust the try gun to more consistently place the pattern where I was looking.
It was money well spent. Every stock I have that is equal, or close to, the measured dimensions is consistent, and pleasant to shoot.

I say this because I know of no way to observe all the little deficiencies without a trained, experienced observer watching you shoot.

Ultimately, my least consistent element has been cheek pressure. It's been very difficult to feel the right cheek weld during the mount on a wild bird's flush.

The process is not difficult, the observation skills are.

Just my two cents.

Oh, and the process doesn't really apply well to people that shoot alot of skeet targets premounted, whether registered or fun. They look at the bead, and measure, which is exactly opposite what is being preached in a fitting. It's a very tough habit to break. Going from sustained lead to an instinctive mount.

or "generally speaking," the method you describe is correct and reasonably accurate. The exact method is to have someone measure in inches the distance from your sighting eye to the front bead, multiply the distance by 16, and divide by 36 to get the gun muzzle to target distance in yards. Then each inch on the pattern plate will be corrected by 1/16 inch on the stock. The distance from muzzle to target must be 16 times the distance from eye to muzzle.

shotgunreport.com used to have a wealth of articles on just that thing. Maybe Mr. Buck will get all those back to being visible again soon as he def had a fine method that was detailed enough for anyone to DIY.
He comes here now and then and has his own new site too and the above link will get your there.

He d' Man!

Dr.WtS

Yeah WtS, I seem to remember now that it was shotgunreport.com where I had read about this impact testing--thank you and thank you to the other respondants also.

One thing I'm not clear on...is the one inch variation from center of patterned shots to bullseye equivalent to 1/16" at comb, face or heel?

It is at your eye. That would be closest to the comb. But, error caused by measuring to butt is easily calculated.

Say you measure 36" muzzle to eye on a 48" over all length gun. On a 16 yard target, the ratio of 1"/16 yards = 1/16" / 1 yard. Lets now do it in inches to make the 48" OAL easier to deal with. 16 yards = 48 feet = 576 inches. 1"/576" = (1/16")/36" [1/16 X 1/36 = 1/576]. 1"/576" = (1"/12")/48" [1/12 X 1/48 = 1/576].

So, if muzzle to eye was 36", the gun was 48" muzzle to butt, and the pattern was shot at 16 yards, you would adjust 1/12" at butt for every inch the point of impact (POI) was displaced from point of aim (POA). Keep in mind that adjustments at butt are intended to make adjustments at eye.

Hope that helps. Questions?

If the bend point is just in front of the pistol grip and the distance from your eye to the bend point is 6" (arbitrary number I picked) and the distance from your eye to the butt is 12" (another arbitrary number I picked for convenience) and you want to move your eye 1/4" cast off would you not have to bend the butt 1/2"?

I originally posted this info some years back, but its too much effort to go & try & find it, so ...

There is a dif in finding where a gun shoots & where it shoots for you. The best method of doing the latter was described to me by a well known & charismatic 'pig' shooter named 'Billy'. His method consisted of taking an old thread bare sheet and stretching it between two pine trees, then drawing a circle aprox 6" in dia. w/red lipstick in the centre. Next he would back up the recquisite distance that he thought he would be first shooting the target from [vis a vis, visually acquiring the target & locking in on it] and then after turning partially away from the sheet he would turn back toward it and fire BOTH bbls at the red circle target as soon as it was acquired. After roughly a box of cartridges he could detect an area of overlap or darkening & that was where the gun was shooting, for him w/that particlar load. How much adjustment to make to the stock is a simple matter of doing the math from the distance involved as Rocketman advocates; of course the distance will likely be dif., but you need only change the values as necessary.

This is not the same thing as seeing if the bbls. are properly regulated. Perhaps this will help someone out. I was major bearing a conundrum when first confronted w/the issue .... how does one determine where their gun shoots? This is the best answer & method that I know of; it is both dynamic and practical, moreover it is wholey accurate and takes into account both bbls.

If the bbl. regulation is off, that's a dif. horse and one that should be broken before trying to ride this one.

Hope this does not sound pompous, its not intended that way at all, but it is a subject that cannot be underrated if one intends to absolutely know where his gun shoots w/a given load. FWIW, the method can be as easily utilized w. a single bbl. repeater.

It can also sometimes show you about 'staying in the gun' or the advantage of using a load w/less recoil, if you don't/can't stay in it. NO AIMING, just natural quick shooting, as fast as you can .. for accurate assessment.

kind regards, tw

George Bird Evans also described that method of testing for gun fit in his classic "The Upland Shooting Life". He did it with the Purdey Dr. Norris left him . . . and then made some adjustments to the stock. I might try that on a Stevens, but if someone leaves me a Purdey, I'd probably take it to a stock specialist for the modifications.

Thank you to all that took the time and effort to reply. And thank you to a special forum member that scanned and then e-mailed a 3 page article describing this method of impact testing for gun fit written by Michael McIntosh for Gun Dog Magazine.

For those interested in this sort of thing another respondant on another BBS wrote the following:

"Patterning is both, finding the guns POI (point of impact) and then setting the POI to meet your needs. Last evaluate choke/load at target distance.

Just like a rifle, you need to know where the gun/barrel(s) shoot. Most would bench the gun at 13 yards with the tightest choke available. Leaving small patterns related to small aim points and easier to measure. Place 3 to 5 rounds side by side on paper to confirm where the gun is placing shot while looking down the rib using your preference. if you know what POI setting you need and the barrel is centering horizontally, you can move on to patterning at target distance. Having an adjustable comb and or rib makes quick work out of setting the POI to your requirements. Knowing your requirement is much more difficult if you have never set up a gun to your needs or experienced a gun that shoots to where your looking. Again, making this easy if you do have a gun that shoots well for you. The easy part is to 13 yard pattern that gun and set the next one to place shot to the same place.

For example if the gun is set to place shot 2 inches high at 13 yards, you can multiply that 2" by 3 for 39 yards (= 6" high). In gun club talk thats about 70/30%. Patterning at target distance should prove the point and you will be able to see on paper what the pattern looks like in relationship to a fixed point of aim. Some shooters drop 3 or more rounds on the same pattern to get better coverage and evaluation. Many shooters find they pull the shot off to one side, hight or low offhand. Could indicate that you have changed your stock mount from the bench to offhand. If you can confirm a change in the mount during the shot, you will be able to re-set the comb to compensate.

If your at the beginning of a shooting carrer and have no idea what will work for your needs, you need to take the gun to a trap field and shoot straight-away targets to set the comb vertically to center targets. This can be done on station 7 of a skeet field also, but shoot targets and read target breaks. Average hitting the bottoms, raise the POI, tops, lower the POI. The conversion from paper to moving targets has only the difference of your movement the move to the target. Raising targets must have some vertical lead that can be set from the comb, horizontal is your responsibility and reflects timing, both trigger and speed of personal movement .

Evaluating the gun fit is an entirely different aspect of the game. Has little to do with POI setting, but has much to do with shooting well. Your form, both mount and stance is in consideration. Your physical size also part of the the process. You need to order Rollin Oswalds book to learn for yourself or go to a pro-fitter. BUT...it is the difference between shooting average and shooting well."