Adjustable comb

I just had a conversation with Browning arms. I said I was looking at the CXT Trap with adjustable comb. what would my POI be? He said 70/30 which is standard even with a monte carlo stock. I asked if the adjustable comb would change the POI. I was told no the adjustable comb is for site picture (etc. stacked beads). He also said adjustable rib is how you change POI not the comb.
I would like your thoughts on Browning's statement about no change in POI using adjustable comb. Thx

 

If the comb is adj., you can change the poi--if its all the way down & its 70/30--thats is the lowest--each 1/16" of an inch should raise it 10%--check it out on paper

 

The guy at Browning didn't know what he was talking about.
If you have both an adjustable comb and an adjustable rib, you do use the comb for setting the sight picture
and the rib for POI. However, most guns do not have both adjustments so POI is set by raising the comb.

 

I agree the guy at Browning didn’t know what he was talking about. However, the POI is adjusted by the stock/comb and later you can adjust your view of rib/beads by its adjustability. Think about it. Your rib doesn’t change your guns POI. Your gun’s fit/stock does. Once you have that figured out, you adjust your wanted beads/rib view when you mount the gun. Good luck and good shooting, Rey

 

If the rib doesn't change anything, I guess Dennis DeVault was BS'n me when he told me the rib on my Infinity at the top notch was 70/30 and all the way down was 100%--if I needed more then I had to raise the comb, which I did to get it to 140%

 

From my archives:
Some ins and outs (or is it ‘ups and downs’?) of adjustable ribs from Phil Kiner's blog @ http://www.trapandfield.com/philkinerblog.htm



There is always confusion about how to adjust shotguns for point of impact (POI) and where the classic “figure 8” the beads-sight-picture theory fits in. The confusion is heightened by the addition of adjustable ribs to the mix.



First, a couple of points about gun adjustments and how they affect your POI. Moving the comb effectively moves the pattern in the direction you moved the comb. Up is up, down is down, left is left, and right is right. Regarding the rib, moving it up at the muzzle—making the front bead higher above the barrel—moves the POI lower. Ribs that bend the barrel work the same, but instead of moving the rib down (to make it shoot higher), the barrel is actually being pulled up. Additionally, because there is pressure on the barrel, sometimes the POI moves can be erratic; i.e., one notch could be one inch one time and six inches the next. So for the ribs, at the front, up is down and down is up. This would also be the same for changeable ribs; i.e., a 90/10 rib will be lower in the front than a 60/40 rib will be. (This assumes that the comb height remains constant.)



Next, let’s talk about the classic “you must see a figure 8” theory. I believe in this statement: “The guy who tells you that you must have a figure 8 to shoot never broke a 100 in the handicap.” This does not mean I believe that the figure 8 is bad, but that we should be worried more about getting our guns shooting where we are looking as opposed to having some preconceived sight picture that we “need” to achieve. The classic figure 8 will not give the same POI among different brands and models, or even among different guns of the same model and brand. Ope of the advantages of the adjustable/changeable ribs is that if you do have a “view” that you prefer to see, you can tune your gun to shoot where you are looking by adjusting/switching ribs and still get the view you prefer.



Where to start? Assuming you already know where your previous gun was shooting, you would look at the owner’s manual and set the rib so it would approximate your previous POI. With the rib set, then adjust your comb to get a figure 8 sight picture. Why? Because the factory predicted POI settings are based on a figure-8 view. Then you would add or subtract 1/16˝ from the comb until you get to smoking targets with a high percentage of center hits. As mentioned in a previous article, I like to set POI with the trap set to throw straightaway targets from Post 3. Start there and do some fine-tuning, then rotate to the other posts. When you are centering the fixed angles from all posts, then let the trap oscillate normally.n



This is where it gets a little tricky. If you have a setting that gives you a full figure 8 or one where you can see some gap between the beads, you are probably good to go. Ip you are not used to any gap between the beads, then at first your mind may reject this new view. Shoot the gun this way enough to see if you can get used to the new gap look. I like to have at least a full figure 8 or a little gap between the beads because with your head higher, it improves visibility over the gun barrel. If you get the comb flat enough that the beads are in line with each other, you are cutting your vision around the barrel/rib significantly. If you are used to this flat picture, the increased vision you will achieve being higher over the rib is worth converting your brain to accepting this as being normal.



If the gap is too much and your brain cannot handle that much rib between the beads, you will have to adjust the rib so that you get a sight picture your mind will accept. A quick tip for those of you with fixed ribs: have the gunsmith move your middle bead forward to get the sight picture you want, and you are good to go. Moving the middle bead forward will not impact POI; it only changes the way it looks by decreasing the gap between the beads. How to do this will depend on what type of adjustable rib your gun has. If it is one that pivots at the back and the front bead is all that rises/lowers, then first you will lower the comb 1/32˝ at a time while at the same time lowering the front bead enough to get more of the sight picture your brain needs. Lowering the comb lowers the POI, but lowering the front bead raises the POI, so what you are trying to accomplish is getting the sight picture more to what your brain wants to see while keeping the gun shooting where it was. Now you need to shoot the gun again, going through the same process for sighting-in as before. By making the moves incrementally like this, you can “circle the wagons” and get the gun where it needs to be.



If you have a rib that pivots (i.e., the front moves down and the back moves up at the same time, like a teeter-totter), you will go through exactly the same process as above except that the moves are more noticeable. The reason for this is that ribs that move in this manner will generally have notches that determine the amount of each change. These notches will typically equate to a pattern move of 10% or more. With these ribs, it will probably be necessary to move the comb up/down about 1/16˝ after a rib move. The ribs that pivot generally have a screw adjustment that is unlimited in how much or how little you can move it at one time. If you have a gun with changeable ribs, the process will be identical as above, with the exception that you change ribs instead of moving them.



Now for a couple of keys to tuning the variable ribs. First, make your moves relatively small, keep track of where you start, and record all the moves you make. Also, try to get the factory-predicted POI close to where your other gun was shooting; this will shorten the process. If your old gun was shooting about 10 inches high and you start with the new gun in either the highest or lowest impact setting, you are going to have to make a lot of incremental moves to get where you need to be. If you don’t know where your other gun was shooting, instead of starting with the flattest setting (which I see a lot), start with a predicted POI of between six to 10 inches high and then go through the sight-in process outlined. Many shooters have a gun that is shooting flatter than they actually need, and this is a good time to test to see if that applies to you.



The other key is to get the gun close and then go shoot it enough to get a feel for what it is doing. If you are struggling with targets that are slightly flat, you may be a little high or vice versa. Keep track of your scores so that you can actually see your trend. Listen to your brain when it talks to you as it is giving you feedback that you need for the process.

 

Browning is wrong -on two counts - #1 Why make a gun totally adjustable and start at 70/30 for the lowest point - #2 635-gG is right about 1/16 comb raise on a 34" barrel will change your POI by 10% - Browning did do One thing right - they adjust their rib from both ends ,my Kx5 only adjusts from the front.

 

Thanks to all for your in site. I've always used my comb to raise or lower the POI. I couldn't believe the Browning tech told me it was only used for bead alignment. I actually said to him the adjustable comb is used to raise/lower POI. He was adamant that it was only used to set the beads. I don't think Browning knows what there techs are telling potential customers. The CXT I was looking for only had an adjustable comb. No adjustable rib. Thanks again for your input.

 

Came back and read the updated postings on this thread and would just like to voice my opinion one more time. Not trying to start a debate, I think it will help others. If you don't agree with me, that's ok. We are all entitled to our thoughts and opinions. Again, I restate that IMHO, unless you change the bore axis of your gun/barrel, there is no way a teetering rib is going to move the POI. A simple example of changing the bore axis is Krieghoff O/U barrels. The bottom barrel POI can be adjusted or changed by the use of different height barrel hangers. Those different height barrel hangers are in fact changing the axis of the bore to where you want the barrel to shoot. Another example; If you placed your gun in a vice and fired it to find POI, and did not move the gun from that vice, you could literally raise the rib or lower the rib as much as you wanted in either direction and the gun would continue to shoot the same POI. You have removed human error in the test (please don't put your guns in a vice to attempt this theory) and yet you have not changed the barrel/bore axis in any direction. Hope my thoughts help some other members here. And remember, when all else fails, buy a fixed rib gun. Good shooting to all, Rey

 

You are referring to "Line of Flight" which is the path the pellets travel. ....This does not change with comb or rib adjustments. ....Technically, a load of pellets does not produce a POINT of impact, but a pattern which varies with every shell shot. ....The greatest concentration of the pellets is the pattern center and is described as the POI.

The POI is only changed when compared to the LINE of SIGHT. ...Raising the comb or lowering the front of the rib will force the Line of Sight to cross below the line of Flight, thus causing the gun to "shoot high." ....This common terminology actually means you are "looking lower" than where the pattern is going.

Lowering the comb or raising the front bead brings the Line of Sight closer to the Line of Flight, thus causing the gun to shoot "lower" or "flatter."

The space between the Line of Slight and the Line of Flight at a certain distance from the muzzle allows defining POI such as " 6" high at 40 yards."

 

After I raised my comb 3/8", I had a huge gap between the beads. Gun now is over 100% POI, and crushes targets when I do my job.

I messed around with a little piece of Delrin to see if I could get rid of the gap, and then have a rib installed.

I just bring the gun to my shoulder, make sure the front bead is sitting on, and in the middle of the little mini-rib, and forget it from there.

No mid bead BS to worry about, and this worked so good for me I have not replaced it with an add on rib.

 

Pure & simple!!! If you raise the comb, you raise the point of impact. Period. What about guns that don't have an adjustable rib. If you raise the comb, you still raise the point of impact. Adjustable rib allows you to raise or lower the front bead to get you figure 8 sight picture. Move the comb whatever direction you want the your impact to move. Your eye is your rear site.
If you are shooting to the right, move your comb left. You can't move your rib right or left can you?

 

Pure & simple!!! If you raise the comb, you raise the point of impact. Period. What about guns that don't have an adjustable rib. If you raise the comb, you still raise the point of impact. Adjustable rib allows you to raise or lower the front bead to get you figure 8 sight picture. Move the comb whatever direction you want the your impact to move. Your eye is your rear site.
If you are shooting to the right, move your comb left. You can't move your rib right or left can you?

 

Pure & simple!!! If you raise the comb, you raise the point of impact. Period. What about guns that don't have an adjustable rib. If you raise the comb, you still raise the point of impact. Adjustable rib allows you to raise or lower the front bead to get you figure 8 sight picture. Move the comb whatever direction you want the your impact to move. Your eye is your rear site.
If you are shooting to the right, move your comb left. You can't move your rib right or left can you?

 

Pure & simple. Move the comb whichever way you need your impact to go. If you are shooting to the right, move the comb left. You can't move your rib right or left can you?