Point of Impact Adjustment on Target Shotgun

There seems to be quite a lot of confusion about the effect of adjustable ribs and combs on target shotguns. I submit the following explanation of how this works.

A vertical adjustment at the front of the rib will change the POI as follows:
— Raising the front of rib will lower the POI.
— Lowering the front of the rib will raise the POI.
A vertical adjustment of the stock “comb” will change the POI as follows:
:— Raising the comb will raise the POI.
— Lowering the comb will lower the POI.
A horizontal adjustment of the comb will change the POI as follows:
— Moving the comb to the right (as viewed from the rear of the gun) will move the POI to the right.
— Moving the comb to the left will move the POI to the left.

Rib and comb elevation changes are additive. Therefore, if you lower the front of the rib and then raise the comb (to maintain your original sight picture) the net change to the POI is the amount of the two changes added together.

Now the obvious question, “How Much”?

The amount of change by moving the front of the rib or the comb depends on how you shoulder the gun. If you’re like me, when I mount the gun my sighting eye is approximately 4.5” behind the rear face of my 34” barrel.
— If so, a vertical change to the front of the rib by .026” will change the POI 1” at 40 yards.
— A vertical change of the stock “comb” by .0267” (26.7 thousand of an inch) will change the POI 1” at 40 yards.
Therefore, if you lower the front of the rib .026” and then raise the comb .0267” you will raise the POI 2” at 40 yards. (1” + 1”= 2”)

As an example, on a Perazzi with a 34” adjustable rib barrel if you lower the front of the rib one notch, approximately .045”, the POI will rise 1.73” at 40 yards. (.045”/ .026” = 1.73”)
If you add 2MM (1MM = .03937”) spacers to the comb to maintain you original sight picture (as Perazzi suggests) the POI will rise 2.95” at 40 yards. (.03937”x 2 = .0787” then, .0787” / .0267” = 2.95”)
The total rise to the POI created by these two adjustments is 4.68” at 40 yards. (1.73” + 2.95” = 4.68”) Or approximately 4 3/4”.

Different length barrels will change these calculations only slightly.

Hope this clarifies rather than confuses this issue!

 

Yes, lowering the rib will raise the impact. I find it difficult to believe moving the comb to maintain an identical sight picture after a rib adjustment will change impact. Where's Sir Neil for an opinion?

 

Raising the comb is what elevates your pattern.
Adjusting the rib to give you a stacked bead sight picture is
only a reference and a comfort feature. LDS

 

Let's look at this a bit differently. The original K-80 (not a Trap Special) adjusts vertically with that funny little wheel. The barrel actually bends (flexes) while the sight picture remains the same. Obviously, moving the rib only on others will not provide vertical adjustment without also raising the comb to maintain your preferred sight picture. Therefore, vertical adjustments require a twofold application.

 

By changing front bead diameter you can also change POI

 

I have been told by some shooters that they never see the bead and don't need them. I don't know why these same shooters have adjustable rib guns, or even ribs on them at all.

 

The late Frank Little always spoke of a bird/bead relationship.

 

I agree, not of a bird/plus 30 some inches of adjustable rib that starts a few inches from your eye, then bead relationship.
Since I've completely given up on all full length ribs including those 12'' bump ribs and just shoot off end of barrel.
Which only has a short 4.5'' high extension so I can tell where end of barrel is since I can not even see barrel when focused on target.
I'm learning real quick that all this sighting down a long rib may not be as crucial as some gun manufactures would have you believe.
Main thing is to mount gun so comb is in EXACT place from first shot to last.

Going to go out on a limb now...I predict that some day, some gun company will come out with next to no rib barrel except for a front adjustable height bead.
Not for every one but I think a few who can mount a gun the same each time and focus solely on the target may just kick some ass with it.

Then again I may just be a little bias

 

This has been going on forever. You adjust your comb for desired impact height and adjust the rib after that for desired bead line up.

 

I once discussed Little's constant referencing of "Bird/Bead Relationship" with Phil Kiner and he said something harsh and HILARIOUS. I'd love to share it but I doubt he'd want me to.

-Roy

 

Kiner never had Little eyes.

 

Phil's eyes were good enough to accomplish a couple 400x400 High-All-Arounds.

Roy

 

Maybe that's why he refused to shoot any more targets at the Silver Dollar because he kept getting bank 6 or was it Little eyes? Frank never ducked a shoot.

 

16 straight years of 99+ Singles averages gives Frank's eyes the edge.

 

All the HOFers had great eyes and knew how to use them, whether natural or via corrective lenses. The point is that Little was an odd duck in some ways, one of which is that he paid WAY more attention to bird/bead relationship than other great shooters. Many of the best will tell you they have no idea where their bead is, and don't care. Their brain knows. They just see the target and it breaks.

Roy

 

Frank always claimed he had average or below average vision. I think he lied.

 

Ollie, maybe Frank just lied to you???

Dave Berlet

 

Perhaps the perennial (65 year) crackshot Mr. Berlet will share with us the number of minutes per day he spends pondering his ever-important "Bird/Bead Relationship." He likely delegated that geometry problem to his cranial computer back around 1960, so I'm going to take a wild guess and predict right around ZERO minutes. Maybe that's partly why he still breaks amazing scores.

Roy

 

Just a hunch, I think the average shooter who worries about the dreaded ''B/BR'' will find himself stopping his/her swing and shooting behind target.

 

There is a difference between conscious bird-bead relationship and subconscious bird-bead relationship. I do not think a conscious bird/bead relationship (aiming) is a sustainable method in American trap. And unfortunately a subconsious bird/bead relationship isn't really measurable so it's hard to analyze.

It's sort of like texting while driving; if your focused on looking at the phone telling you where to go, whose watching the road ahead?

I'm a piss poor shot. But when I see the bead, I'm not looking at the target and it usually results in a chipped or lost bird.

 

OK, so I'm unique. I'm sure Frank told others his eyesight wasn't that good. Then again, only us oldsters were around when Little was alive while the rest are all Johnny Come Latelys..

 

Not to Hi Jack thread, but I remember at some western shoot back in the 70s Frank L and I were discussing should we start wearing cowboy boots since it seemed everyone else had them on. This conversation was totally tongue in cheek and very funny.
OK, now back to your OP.

 

wasn't the space gun along the lines that rookie shooter describes "going out on a limb"

 

I shot 15" in high POI for years, ask anybody who shot my guns. And I shot 14 inch LOP and 3/8ths+ RH castoff,
always shot targets on the rise, never floated targets, over 50 years of shooting trap, 35 + years on the 27yd line,
Just completed putting Bondo on my Model 12 Milled Rib trap gun to get my sight picture and painted all wood Bright Ass Red.'I have Release and Pull Triggers I only shoot the release triggers.

GB.................................DLS

 

I wore Cowboy Boots after a Large Money Win, it keeps you on the Ball of your feet, for better balance and Movement, I still have my boots that haved been Re-Soled numerous times, they are on the shelf of my closet, and I still have my Stetson Hat I bought at the same time, from the Western Clothing store that used to be on Route 161. Stetson is Valued at over Hundreds of Dollars$, I would wear the boots if I could get them on my Prosthetic left foot..

GB........................................DLS

 

Keeping the same sight picture is critical for the sight picture POI Change. When I want to raise my POI, I raise my comb or lower the front rib adjustment then I reset my sight picture for uniformity. Keeping POI stable for perfection. Stock fit is critical, I have kept my stocks at zero pitch, and 14"in.LOP, that is why 1st thing I cut is the stock for uniformity, for excellent scores and perfection.

GB...................................DLS