O/U Point of Convergence

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duurmeehr
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O/U Point of Convergence

Post by duurmeehr » September 15th, 2020, 6:29 am

I have noticed that on my various O/U turkey guns that the point of convergence between the barrels is significant.

This is not noticeable on wing shooting but becomes VERY apparent shooting TSS loads in super tight turkey chokes.

I had originally started shooting the O/U with the plan to use a lead #7 in one barrel for in your face out to 15 yards and TSS #9.5 in the other barrel.

Turns out for me the point of convergence with a red dot sight is so different it is impossible.

I typically run the TSS in the bottom barrel because it puts the recoil more inline with your stock geometry and your shoulder and the lead load in the top barrel.

I have determined shooting the same shell in both barrels that the heaver the load the more the difference is. I think it's because the top barrels flips up more with the recoil than the bottom.

Last season I resolved to just using it as a single shot and finally this year am setting up a 28 gauge semi-auto for turkey.

Anybody have any thoughts on this?

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Spuriosity
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Re: O/U Point of Convergence

Post by Spuriosity » September 15th, 2020, 8:05 am

It is almost universally true that with heavy loads, a side by side will shoot the right barrel right of POA and left barrel left of POA. Similarly it is almost universally true that with heavy loads, an O/U will shoot the bottom barrel below POA and the top barrel above POA.

Duurmeehr is correct that one should shoot the heavier load from the bottom barrel of an O/U for the reasons he stated. So many people get this wrong and shoot their heavy, long distance load in the top barrel. Doing so will make barrel divergence worse and also have more felt recoil from the stock slap to the face. There is a reason that almost all competitive clay target shooters set up their O/Us to fire the bottom barrel first. Doing so reduces felt recoil on the all important first shot, due to the straight back recoil with less muzzle rise, which makes it easier to get on the second clay of a double. The same holds true with turkey guns in spades given the heavy loads that we shoot.

I have been shooting TSS in O/Us since 2009, and like Duurmeehr started out using TSS in the long range barrel and lead 7s through a cyl choke for the short range barrel. But I would say that my long range TSS load is optimized for 40-60 yd shooting. The lead 7s were only good to 20 yds which left a significant range gap before my long range load came into its optimal patterns. I then experimented with imp cyl (good to 25 yds), mod (good to 30 yds). Even with a turkey choke, the 7s were running out of pattern at about 35 yds.

For me, the solution was a relatively light 1.25 oz load of reclaimed TSS from my shot trap through a LM choke in the top barrel. It is effective to 40 yds (110/10") while maintaining a wide, forgiving pattern in close. I shoot a 1.625 oz load from the bottom barrel for my long range load. Set up this way, I can cover targets from 20 to 60 yds with solid patterns that still have wiggle room. I end up shooting most of my turkeys inside 40 yds with the lighter charge. That saves money (light load of reclaimed shot) and recoil, which is important to me with a light weight (6.75 lb) O/U.

It also helps with the divergence issue. Set up like that, the two barrels of my O/U shoot within a couple of inches of POA from both barrels. If you switch and shoot the lighter load in the bottom barrel and the heavier load in the top barrel, divergence increases to more than 6".

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howl
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Re: O/U Point of Convergence

Post by howl » September 16th, 2020, 9:48 am

Sight red dot for top barrel. Aim at head. If they regulated it correctly for windage, the bottom barrel should hit in the neck if you aim at the head. That's what the paper shows and how it has worked for me in practice.

My trouble is decades of aiming at the neck mean I still aim at the neck half the time. Thinking isn't my strong suit. It goes out the window entirely when the time comes to shoot. They still die the same. I just get more grief from the cook.

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poorcountrypreacher
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Re: O/U Point of Convergence

Post by poorcountrypreacher » September 19th, 2020, 10:23 pm

Spuriosity explained very well how to deal with the issue on an 0/u gun, and using 2 different loads can also solve the issue on SxS guns if the POA difference isn't too bad. I have only worked with SxS guns, and all of mine have required me to resort to a file to get both barrels to shoot to the same spot.

I let the tight barrel shoot wherever it wants, and take the file to the open barrel. It's a lot of trouble and most folks would probably be happier with a gun with one barrel, but I prefer turkey hunting with a break action gun, and I just like a SxS. It's nice to have a 5 lb 6 oz turkey gun.

decoykrvr
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Re: O/U Point of Convergence

Post by decoykrvr » September 20th, 2020, 9:13 am

it amazes me to hear about folks who operate on the theory, "My gun shoots high and to the right, so I'll just shoot at the turkey, low/left." What a recipe for disaster! When I was first introduced to long range shooting w/ high power rifles, a gentleman at the range, who I later learned had been a military sniper and was a dedicated elk hunter, explained the need to write down and tape the ballistics for particular loads onto the stock, so the data was at hand for immediate reference. The older gents taped load data for his 300 Win Mag included not only the loads ballistics, but wind, temperature, and relative humidity variables on neat graphs. All of this makes sense for consistent long range hunting. A lot of game is missed, or worse, crippled by "guesstimate" shooters who just "blast" and hope for the best.

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Re: O/U Point of Convergence

Post by Limb Hanger » September 20th, 2020, 12:15 pm

poorcountrypreacher wrote:
September 19th, 2020, 10:23 pm
Spuriosity explained very well how to deal with the issue on an 0/u gun, and using 2 different loads can also solve the issue on SxS guns if the POA difference isn't too bad. I have only worked with SxS guns, and all of mine have required me to resort to a file to get both barrels to shoot to the same spot.

I let the tight barrel shoot wherever it wants, and take the file to the open barrel. It's a lot of trouble and most folks would probably be happier with a gun with one barrel, but I prefer turkey hunting with a break action gun, and I just like a SxS. It's nice to have a 5 lb 6 oz turkey gun.
Very interested to learn how the file method works. I'm trying to get a SxS shooting for next season and would love to hear where and what to file.

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poorcountrypreacher
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Re: O/U Point of Convergence

Post by poorcountrypreacher » September 24th, 2020, 10:40 am

Limb Hanger wrote:
September 20th, 2020, 12:15 pm
poorcountrypreacher wrote:
September 19th, 2020, 10:23 pm
Spuriosity explained very well how to deal with the issue on an 0/u gun, and using 2 different loads can also solve the issue on SxS guns if the POA difference isn't too bad. I have only worked with SxS guns, and all of mine have required me to resort to a file to get both barrels to shoot to the same spot.

I let the tight barrel shoot wherever it wants, and take the file to the open barrel. It's a lot of trouble and most folks would probably be happier with a gun with one barrel, but I prefer turkey hunting with a break action gun, and I just like a SxS. It's nice to have a 5 lb 6 oz turkey gun.
Very interested to learn how the file method works. I'm trying to get a SxS shooting for next season and would love to hear where and what to file.
Here is a post I put on another forum several years ago in response to a guy who had a new SxS gun that was shooting way off. He filed the choke and got it centered. Good luck if you try.

It is usually not that hard to move the pattern 8" at 40 yds, but moving it 8" at 16 yds will be a challenge. Since it looks like you are stuck with the gun, I would sure give it a try. I have successfully moved the POI on several sxs guns, so I know it can be done. I had Brileys make eccentric chokes for one gun, and they definitely moved the pattern, but they moved it way too far. A guy on another forum told me how to file it to move the pattern, and I would rather do that than to buy eccentric chokes.

Filing the choke utilizes the same principle as eccentric chokes. The idea is that a change at the very end of the barrel can cause the wad to go in a slightly different direction. It's the same idea as damage to the muzzle of a rifle can change where it shoots. In a shotgun, this will only work if you use shells with a plastic wad, but most of us do that anyway.

Fwiw, here is an explanation of how to file a choke and move the POI:

Put your barrels in a vice and face the muzzle end. Your left barrel is shooting to the left, so you want to move the POI to the right. You do that by filing the inside of the barrel right at the muzzle.

Imagine the image of a clock placed over the muzzle. The left barrel is shooting to 3 o'clock now, so you want to file it at 9 o'clock. I use a round chainsaw file, and start by making 4 strokes at 9 o'clock. Hold the file at a 45 degree angle and you will be removing metal from only the inside edge of the barrel. Next, make 3 strokes at 10 o'clock and 3 at 8 o'clock. Then make 2 strokes at 11 and 7, and feather it to 12 and 6.

What you want to do is to create a chamfer that is deepest at the direction you want the pattern to go, which is 9 o'clock in this case, and then slopes to no chamfer at 12 and 6. After making the initial cuts, fire a test shot and see if the pattern moved. If it didn't move far enough, file again. Keep filing and keep shooting until it centers.

You will probably have to get the choke to a knife edge at 9 to move the pattern as much as you need, and even that may not be enough. It's good that your gun uses choke tubes. If you don't want to risk one of the tubes that came with the gun, you can buy a tube for about $20 and that will be all you are risking. This procedure will degrade the pattern to some extent. If you want modified performance, start with a full choke tube.

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poorcountrypreacher
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Re: O/U Point of Convergence

Post by poorcountrypreacher » September 24th, 2020, 10:41 am

I posted this on another forum:

It is usually not that hard to move the pattern 8" at 40 yds, but moving it 8" at 16 yds will be a challenge. Since it looks like you are stuck with the gun, I would sure give it a try. I have successfully moved the POI on several sxs guns, so I know it can be done. I had Brileys make eccentric chokes for one gun, and they definitely moved the pattern, but they moved it way too far. A guy on another forum told me how to file it to move the pattern, and I would rather do that than to buy eccentric chokes.

Filing the choke utilizes the same principle as eccentric chokes. The idea is that a change at the very end of the barrel can cause the wad to go in a slightly different direction. It's the same idea as damage to the muzzle of a rifle can change where it shoots. In a shotgun, this will only work if you use shells with a plastic wad, but most of us do that anyway.

Fwiw, here is an explanation of how to file a choke and move the POI:

Put your barrels in a vice and face the muzzle end. Your left barrel is shooting to the left, so you want to move the POI to the right. You do that by filing the inside of the barrel right at the muzzle.

Imagine the image of a clock placed over the muzzle. The left barrel is shooting to 3 o'clock now, so you want to file it at 9 o'clock. I use a round chainsaw file, and start by making 4 strokes at 9 o'clock. Hold the file at a 45 degree angle and you will be removing metal from only the inside edge of the barrel. Next, make 3 strokes at 10 o'clock and 3 at 8 o'clock. Then make 2 strokes at 11 and 7, and feather it to 12 and 6.

What you want to do is to create a chamfer that is deepest at the direction you want the pattern to go, which is 9 o'clock in this case, and then slopes to no chamfer at 12 and 6. After making the initial cuts, fire a test shot and see if the pattern moved. If it didn't move far enough, file again. Keep filing and keep shooting until it centers.

You will probably have to get the choke to a knife edge at 9 to move the pattern as much as you need, and even that may not be enough. It's good that your gun uses choke tubes. If you don't want to risk one of the tubes that came with the gun, you can buy a tube for about $20 and that will be all you are risking. This procedure will degrade the pattern to some extent. If you want modified performance, start with a full choke tube.

Good luck with it.

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poorcountrypreacher
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Re: O/U Point of Convergence

Post by poorcountrypreacher » September 24th, 2020, 10:48 am

Sorry for the double post. It told me my first attempt violated something, so I tried again, then found that it actually posted the first attempt. Then it told me I didn't have the authority to delete the second. Maybe a moderator can remove it?

Limb Hanger
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Re: O/U Point of Convergence

Post by Limb Hanger » September 24th, 2020, 10:14 pm

poorcountrypreacher wrote:
September 24th, 2020, 10:48 am
Sorry for the double post. It told me my first attempt violated something, so I tried again, then found that it actually posted the first attempt. Then it told me I didn't have the authority to delete the second. Maybe a moderator can remove it?
I greatly appreciate the explanation. The gun is new to me and I haven't seen how far off it is yet. I will start shooting it soon and I suppose I'll be filing from there.

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