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Eccentric Chokes

Discussion in 'Uncategorized Threads' started by zzt, Jan 10, 2008.

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  1. zzt

    zzt Well-Known Member

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    Hooligan, why don't you explain exactly what the problem is and perhaps a solution can be found that does not involve eccentricity.

    Let's combine this with your other thread. You want to accurately determine where your barrel(s) and/or chokes shoot, not where you shoot them. You also have some doubts as to your ability accurately and repeatably aim and record POI. So either your chokes are off, or your barrels are misconverged, or both, a common occurrence with Berettas.

    Here is what I would do in your situation. You'll need lots of time, ammo, paper and patience.

    Set up on a bench with a good rest, with 15 to 20 yards between the target paper and the muzzle. Closer if you shoot open chokes, farther is OK for tighter chokes. Since you have trouble seeing the middle bead, i'd suggest you get a set of clip on turkey sights. These have a luminescent dot on the front sight and two luminescent dots on the rear sight. You simply clip them on, then sight like a rifle. When all three beads are aligned horizontally, and the front sight is on target, you are good to go. It's very repeatable.

    Next pick one barrel. Then shoot each choke tube you own in it. Record the POI of each choke. It generally takes about 5 shots through each choke tube (at a new target section every time) to really determine where the POI is for that choke. If in doubt, shoot 5 more. Now do exactly the same thing in your other barrel(s).

    Let's say that choke A shot 1" high and 1" left from the first barrel. Let's say that was an under barrel. So you put choke A into the top barrel and find it shoots 2" high and 2" right. That by itself doesn't tell you anything. So you do all your chokes in the top barrel, record the POIs, then compare. What you are looking for are the chokes that have the same POI in each barrel. Save them and discard the rest. Now if those "good" tubes shot to the same POI in both barrels, you know that everything is good, the chokes and barrels are concentric and the barrels are converged.

    Here are some other possibilities. All of the chokes shoot to the same POI in the U barrel but all hit the same different spot in the T barrel. Either the choke section and the bores are not concentric, or the barrels are misconverged. That's a clear indication.


    This takes a lot of work. I have a lot of respect for Briley tubes, and have many for my choke tubed barrels. They do occasionally make one wrong, but that is infrequent. If you have some buddies that already shoot Briley tubes, borrow some from them and use them for a test. You will save yourself a whole lot of work. When I went through the drill I just described with my Beretta combo, I found that only two of the six choke tubes supplied shot to the same POI. A third was only a little off. I subsequently ordered 3 standard Briley tubes and they all shot to the same POI.

    Anyway, when you are trying to find out where your barrels shoot and if they are properly converged, you have to eliminate all the variables. With fixed chokes it is much easier. Just set up as I described above and shoot enough shots at paper targets so that you are confident you can accurately determine POI. If POIs are substantially the same, your barrels are converged. If you have choke tubes, you have to eliminate them as variables first, because an eccentric tube (common with Beretta) or a non concentric choke tube "housing" in the bore (not as common) will skew the results.

    Here is what you will find in order of probability. Many of the choke tubes you have are not machined correctly and don't shoot straight. Second, the barrels are not properly converged. Third, the axis of the barrel and the axis of the "cylinder" the choke tube sits in are not concentric.
     
  2. gun fitter

    gun fitter TS Member

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    If your barrels are printing more than 6" appart @ 30 yards get them back to berreta they should be able to recut the choke seat and move the impact 4-6inches I've had them do it for me on several beretta guns here in the USA
    Joe Goldberg
     
  3. g7777777

    g7777777 TS Supporters TS Supporters

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    "recut the choke seat" ?????????? what the heck is that-- I am trying to imagine how you could recut and change anything on the choke end

    In answer about Briley-- call them-- I think you will find they want the barrel but I have shot those chokes and they will do whatever you want them to do within what range they say they will

    Gene
     
  4. kiwiG

    kiwiG Member

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    Hi Barry, The previous owner of my Perazzi Mirage had eccentric briley thinwalls done by Myalls(?) in Oz, they needed the barrels sent from NZ then did the biz. The guy who owned the gun b4 me is quite fastidious and was happy with the job...me personally...wondering whether the tubes are tightened properly (therefore patterning correctly) is just one more thing to worry about...so I don't use them, nor would I bother. Your mileage may vary. Cheers-Graham.
     
  5. zzt

    zzt Well-Known Member

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    Hooligan, I'd dump the gun. My 682 Optima barrels went the opposite way. The bottom shot higher, by more than the tad I'll accept. I never got used to it and sold it. By the way, how high is considerably higher?
     
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