16ga.com ~ View topic - Determining your gun's relative point of impact

*Last edited by 16gaugeguy on Thu Mar 16, 2006 12:32 pm; edited 1 time in total*

Most shotgunners never pattern their guns to determine where the barrel or barrels shoot relative to the owners focal point. Every wingshooter should know this important aspect of their gun.

This can only be done correctly after the stock has been adjusted for the correct length of pull. You must be able to mount the butt or pad comfortably in the pocket of the shoulder just below the outside end of your collar bone and not out on the point of the shoulder as some folks do. If you can only mount it out on the shoulder point, the stock is too long. Cut that stock to fit or add spacers under the pad if its too short and you are hitting your nose with your thumb. This is most important. You must be able to get your self squarely into the gun with your cheek flat down on top of the comb and your nose just behind the thumb of your grip hand by maybe 3/4 of an inch or a tad less. Your cheek should not be placed to the side of the stock as many incorrectly do. Your shooting eye should be also squarely over the comb and looking precisely down the center of the rib and seeing a sliver of that rib too. If you do not understand what I'm refering to, Go ask a very accomplished shooter. He'll be able to show you how. Now to the POI.

Either use you club's patterning board or make one out of several pieces of 48" square corregated cardboard and some light framing 1x3 framing to support it. you can tape or staple newsprint or several pieces of freezer paper as a target sheet. To the sheet, center a bright orange 2" dot and a vertically centered 3/4"" wide black stripe from the bottom of the sheet to the bottom of the dot.

Set the frame so the dot is at eye level and step back to 30 yards. place a full choke tube in the first barrel to be shot. Do the offside barrel of an SxS first and the bottom barrel of an O/U gun. Using light target ammo of small shot, load and shoot at the dot at least 6 times. 10 shots is better.

To do this properly, start with your gun mounted normally in the pocket of your shoulder with your cheek squarely on the comb while standing. Do not use a rest. Center the barrel or rib on the bottom of the vertical stripe. Now focus your eyes on the dot without moving your head up from the stock. Raise the gun up to the dot and shoot as soon as you know you are on it. It is most important to not aim the beads like a rifle at the dot. Focus on the dot like it is a flying bird or target and don't look back at your barrels when you shoot. Just let the barrels come to the dot smoothly while you focus hard at it. Your barrels will be in your secondary vision and your brain will know when the gun is lined up on the dot and will trigger the shot just like wing shooting.

After shooting, look for the densest aggregate cluster of shot from all the rounds. It should be fairly easy to recognize. The center of this cluster will tell you all you need to know. If the dot is right in the middle or a tad low of the center mass, you are good to go. your gun shoots dead on. If the dot is off center or high or low, your stock needs to be adjusted to put the center of the pattern on the dot. At least you now have reference to go by. If your gun is a double, check both barrels. Use as seperate target for each barrel. If they are both hitting tio within an inch or so of each other at 30 yards, you are fine. You can adjust the gun's stock to put the relative POI on the mean point between them.

to raise your POI, add to the stock comb a bit. to lower it, sand the comb down evenly. Left or right adjustments are actually more important than vertical. Adding or subtacting to the cheek of the stock will move the POI as needed. its important to note how far off the pattern is before trying to adjust the POI. If you obtain this info accurately, having the stock bent via the hot oil process is much easier too. Bring the sheets with you. The stock maker will know what to do frm there if he's any good at his trade.

You will be amazed at the positive affect centering your gun's POI to your personal focal point will have on your shooting. An inch or so of adjustment right or left will make a huge difference in the percentage of targets broken or birds cleanly downed. So will putting the vertical center of the POI just over the center of your focal point by an inch for skeet and field guns. Trap guns need a bit more height to their relative POI.

Your shooting will improve rapidly and your confidence will soar too. This is because you will always be able to put the sweet spot of the pattern right on the target if you execute the shot well. Your gun will mount smoother and will also shoot more comfortably for you too. 16GG.

Member Joined: 08 Nov 2005 Posts: 3438 Location: Illinois

16gg-Good advice-most folks have no clue about this Wink

I have a suggestion, to add to this very good post...You said:

"After shooting, look for the densest aggregate cluster of shot from all the rounds. It should be fairly easy to recognize. If they are both hitting tio within an inch or so of each other at 30 yards, you are fine. You can adjust the gun's stock to put the relative POI on the mean point between them."

I shoot my guns in for POI at 16 yards. I read somewhere that it was the correct distance. This works for guns with almost any choke. If I shoot in my cylinder/cyinder gun at 30 yards, I wouldn't be able to find the POI. Similarly, tighter choked guns print realatively small shot clusters at 16 yards. Using a tight choke to do this test is quite good, because the patterns print smaller and quite dense.

I use exactly this process to fit all guns. You are right, if a shooter does not take time to do this, they probably are shooting somewhere besides where they look! Cheers! Mike

Wasn't sure I wanted to wander into this one but here goes and if somebody wants to argue or call this 'BS' also, take it up with Michael McIntosh. He describes the 16 yd technique in Gun Dog Magazine April/May 93' p.98 and again in Petersen's Shotguns 1997, p. 45. It's done just as 16GG said, NOT mounting like a rifle but mount and fire like a straight-away clay or bird. The distances, vertically and horizontally from the center of the pattern to the hold point, is translated/converted as follows: 1" = 1/16" on the stock. If you need to raise your point of impact 2" then you need to add 2/16" to the comb. Need to move POI to right 1" then remove 1/16 from the face side of the comb OR add 1/16 cast off (to the right.)
Jim Greenwood in Augusta, KS (last I heard he still worked with Michael Murphy) bent the Beretta sporting clays gun stock of a buddy and he was very pleased with the results. 316-775-0161. DL Precision here in Phoenix also does excellent stock work 602-298-4635
Just adding height to the comb can be easily accomplished with the many 'stick-on' pads BUT will probably move your eye (your 'rear sight') slightly to the left (cast off and not good for a righty) I've used the 'Soft-comb Elevator pad' sold by Southwest Shooters Supply 602-943-8595 on a couple of trap guns and my Trojan (because of all the drop I finally had an adjustable comb made) with good results.
No bs guys-just facts.

16 yards is fine for open choked guns. Another alternative is shoot more rounds at the target. Even open choked guns will usually throw a center core of shot in their pattern. The accumulated hits from this core is what you are looking for in the aggregate center of the pattern or footprint. Just remember that at 16 yds, yards, a 1/2 inch over the center of the dot is equivelent to 1 inch at 30. The natural drop of the pattern will put it about the same height at 40yds.

The same thing does not apply to lateral adjustments. Just be sure to center the pattern dead on left to right. This is the most critical adjustment. We tend to miss more to the left or right when shooting than up or down. Theoretically, having the widest part of the pattern circle working for us across the target area is to our advantage.

We tend to look at patterns as two dimensional. The shot string is more of a flying column of shot pointed head on at the target. Not all of the shot arrives on target at the same instant. Therefore, the target tends to fly through the stream picking up hits as it does. Only a target flying directly away dead straight from our line of fire picks up the full effect of the center core of our pattern. The outer pereiphery of the shot column has less pellets arriving on target while the target is travelling through it. Use the core of the pattern to your best advantage by centering it in your line of sight through proper stock adjustment. This aspect is even more important in open choked guns.

PS: This technique of centering the gun's pattern for the shooter has been used for several centuries. I found it described in 19th century English shooting literature several times. These old timers also figured out a way to judge the relative hitting power of a shotgun. They used layered sheets of tarred paper and used pellet penetration at a known distance, usually 40 paces. Only the best barrels would send their shot in a good killing pattern clear out to 40 yards. These same barrels also tended to shoot a standard balanced charge of shot and powder at higher velocities than barrels not as well made and finished. That is because the interior surfaces of the best barrels had bores that were straighter, rounder, more uniform in diameter over their length, and of a smoother interior finish due to more straightening, lapping, and polishing of the bore. Thats why the guns that were made with these barrels were called "best guns."

I've a '51 Model 37 that I love..so far..haven't hunted with it yet...I've fired a couple of hundred rounds at 25 yard targets left to right passing, etc.

I KNOW I need a little cast off..

However, the gun is shootng 6-8" high for me at 25 yards. I'm not a quail hunter, mainly dove with fast passing shots. If I lower the comb to correct this, I would see no barrel , bead or anything. I like to see a little barrel (has no vent rib).

My options as I see are: elevated bead on ramp and/or smaller bead, rising vent rib from receiver to muzzle ($$$ @@@@) , bending the barrel.

What say ye?

Member Joined: 26 Apr 2005 Posts: 743

Good POI discussion. I'd add to the above that if you're off center when shooting for POI, there's a 2nd possibility, not mentioned above, that cannot be solved by adjusting stock fit, and that's bad barrel regulation. In other words, the gun doesn't shoot straight. (I discussed this over on the Woodcock Hill thread, General Discussion.) If you're off on the POI test, before you start tinkering with stock fit, you do indeed need to consciously AIM the gun, as you would a rifle, to make sure it's shooting where it's supposed to when properly aligned. If you're on target when aiming the gun, you can then eliminate bad barrel regulation and proceed to making stock fit adjustments.

One comment on shot string. Guy, you talk about a target "picking up hits" as it flies through the pattern. I think you made it pretty clear in your next sentence that you get more hits on a centered straightaway than on any other target, but I want to make sure readers understand that shot string is a negative, not a positive. String really isn't a very big deal at typical upland ranges and with modern loads, but per Brister's moving target tests, when string does come into play (mostly beyond 35-40 yards), it results in a net loss of pellet strikes over a stationary or straightaway target, where there is no string effect.

I think we are both on the same page but looking at different paragraphs here Larry. When I refer to the shot string, I'm using the term to indicate the flying column of shot which has both breadth and depth. Think of it as looking like a flying trash can with the wider end front. You break the target or kill the bird by trapping it inside the mouth of the can as the can flies across the target's line of flight or up the same line line of flight in the case of a dead straightaway. The shot pellets are dispersed randomly anywhere inside the can's dimensions. However, the greatest concentration of them is along the vertical axis of the can-- the so called central core every shot column or string has. So the closer you can place the center of the shot column around the target, the more pellet hits it will receive.

Stringing is the negative verb used to indictate the degredation of the shot column or string as it continues to enlongate and widen on its way out to its terminal range. Starting out with the shortest string or column a shell and gun barrel can produce with its given choke is what we are looking to do. It takes both well made barrels and well loaded ammo to do this. Crooked, curved, out of round barrels or those with improperly designed chokes or mischambered or misthroated barrels create stringing problems even with the best ammo. Barrels that are loose fitting can too. Poorly designed ammo will create problems even when shot out of the best barrels. That is why cheaply made guns and cheaply made ammo will never perform as well seperately or together as a well made shotgun with good ammo. 16GG

Member Joined: 26 Apr 2005 Posts: 743

Guy, have you read Brister's book, the section on his string tests? I still think his wife deserves a medal for bravery under fire: driving the family station wagon while Brister blazed away at the target sled she was towing.