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Perazzi Backboring Question

Discussion in 'Shooting Related Threads' started by k80guy, Feb 22, 2010.

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  1. k80guy

    k80guy Member

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    Just wanted to ask the folks who have some knowledge with Perazzi barrels and back boring a couple questions. I have a Perazzi 18.4 bore current type IV barrel with factory choke tubes. Is it possible to have that barrel bored out to 18.7 and the use the choke tubes for an 18.7 bore barrel? Did Perazzi change treads or choke design wheen they went to the bigger bore? I have not heard of backboring a factory choked gun, so I was wondering if this is something that can be done. I am looking for a little weight and recoil reduction.
     
  2. rick979

    rick979 Active Member

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    Backboring will not change your ability to use the original choke tubes as they do not bore the threaded area. In theory when you backbore from 18.4 to 18.7 the pattern will be somewhat tighter as the effective constriction at the choke will now be increased. Lower recoil and lighter weight? I doubt that you will notice any difference at all other than a perhaps a tighter pattern. Rick ~~Texas
     
  3. Steve W

    Steve W Well-Known Member

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    Before my opinions on back boring, I'll answer your question first.

    The factory choke tubes has the the same threads.

    The tubes for 18.4 & 18.7 can interchange after you calculate the differences in numbers. In your case, +3 if you want to use your old choke tubes.

    Here're the two kinds of factory tubes, same thread, for different bore sizes.



    [​IMG]


    Now, you're going to hear it from me. :)

    Removing metals from your factory barrel is a questionable act, people who does this for living don't like to hear this, but thinning the barrel will not only take your barrel out of proof, it weakens it. Why increase the chance of putting yourself in danger while the gain is doubtful.
     
  4. checker

    checker Member

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    Do the math...18.7 to 18.4 = .30mm increase in bore size.....the chokes will be .16" tighter....you'll have Turkey Chokes! I bought a used P-gun UnSingle bbl that had been backbored, orginally .724 nominal bore opened to .740.....fullset of Wright's choke tubes came with the barrel 0 Cyl thur 8 full. So in reality each choke tube is .16 tighter than marking. I finally realized what was going on....when I patterened it and then talked to Stu Wright.
     
  5. Guy

    Guy Member

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    Checker: Bore stampings are in millimeters....your calculations are incorrect.
     
  6. Steve W

    Steve W Well-Known Member

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    In Perazzi choke size, +3 means your #6 choke from 18.4 bore will become #9 in 18.7 bore.

    In the bloody inch system, it went from 0.024" constriction to 0.036" or commonly understood as from IM to F.
     
  7. k80guy

    k80guy Member

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    Checker: It was a two part question. Could I backbore to 18.7 (Approx. .736) from 18.4 (approx. .724) and then could I use the factory 18.7 chokes if they were the same thread pattern. Steve W. confirmed above that the chokes are the same. This was just sort of a hypothetical question. The reason that I brought it up was because I just purchased a TM1 with a Wilkenson backbore to .740 and was amazed at how soft shooting it is. I was just wondering really if it was an option to open up the bore on a factory choke tubed gun and get it to work with the new style chokes. The guys on this site are a wealth of knowledge and I figured someone had already thought of this and would tell me if I was out to lunch or not.
     
  8. TOOLMAKER 251

    TOOLMAKER 251 Active Member

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    I agree with Steve W. 100% with not taking any metal off the barrel. Your removing .012 of a inch not .30 but still, your only weakening the barrel to accomplish what?
     
  9. k80guy

    k80guy Member

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    Just got off the phone with Briley on this. I asked what my options were for backboring my .724 barrel choke tubed barrel for weight and recoil reduction and have it perform as normal and have the ability to use regular chokes. Their suggestion was exactly what I was asking. They would backbore out to .736 and have me use factory or their aftermarket 18.7 choke tubes. Weight savings of 3 to 4 ounces on a 29.5 inch barrel and should help with recoil. Also mentioned going to titanium chokes for additional weight savings. Not saying I am going to do it, but I was curious what the answer would be.
     
  10. checker

    checker Member

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    Sure you can open up the bore to .736 INCHES, your Perazzi Choke tubes will still work, nothing will be done to the CT threads.....but as Steve W mentioned....your #6 choke from 18.4 bore will become #9 in 18.7 bore. +3 change in the tube you need to use......so a #3 tube will be used to get patteren you have with your #6 tube now. Sorry I forgot the mm in my 1st comment...30mm increase in bore size going from 18.4 mm bore to 18.7mm bore. Looks like a common mistake. New style chokes? Same thread as your barrel now? will work. HELP NOW TS gang.
    [​IMG]
     
  11. k80guy

    k80guy Member

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    The idea is you backbore from 18.4 to 18.7 and junk the old choke tubes. Buy new 18.7 bore choke tubes from Perazzi or aftermarket.
     
  12. Chango2

    Chango2 Active Member

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    Wish I knew who backbored my TM-1 barrel to .734 and left it with a 31/1000 choke. Works well, but still, I'd like to know the history. Seems very well done, Seitz style ports. It's a good looking shooter now, great shape, "but still"....I'm not a believer in that kind of tinkering unless by Wilkinson, Allor, or some other established "name", or by the factory. But...I guess .734 is safe as I was told by one Perrazi expert who posts here and very helpfully. (Jack)
     
  13. Ahab

    Ahab Well-Known Member

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    A TM1 is a very soft recoiling gun ... why would you go to the trouble of back boring it?
     
  14. PerazziBigBore

    PerazziBigBore TS Member

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    Backboring a SBT is one thing.. doing a O/U and thinking you'll keep you sideribs is a totally different story..
     
  15. wayneo

    wayneo Active Member

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    I'm just curious, how does reducing weight help with recoil? Wayne
     
  16. In plain view

    In plain view Member

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    This subject is dear to me as I'm going through this thought process now. I placed a call to Tom Wilkinson in North Caroline yesterday to discuss this and he was out so I figuered I would call back today. After reading these excellent comments maybe you can help me get untracked regarding Perazzi choke tubes and my TMX Special. I've owned this gun for about 2 years. the mic shows the bore at .726. I have tubes numbered 2, 4, 6, 8 & 10. I'm told to figure the constriction multiply the number on the tube times 4. My #6 tube should create a 24 constriction. This tube seems adequate at 16 yards and short yardage. When I go to the #8 tubes (32 constriction) I see no difference in the hits. On paper I do not have a good core. When I go to the #10 tube (40 constriction) the hits are great. Looks like what I need to do tonight is check the markings on my TMX barrell to determine what 18 number do I have and go from there. From what I think I understand from your comments is that newer Perazzi tubes are available that might solve what I think I'm trying to do without backboring. Thanks. Bob English in Los Angeles
     
  17. Steve W

    Steve W Well-Known Member

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    Bob, depend on when your TMX was made, and what kind of factory choke tubes the gun is threaded for, the factory big bore 18.7 choke tubes only available in 4th generation.

    And the big bore choke tubes has the same perspective constrictions, just different markings to match the bore size.

    It's only a matter of finding a good choke, because not all of them are true to their marking.
     
  18. rick979

    rick979 Active Member

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    K80 GUY: What makes you think backboring the barrels will make for less felt recoil? If in fact you would be removing 3-4 ounces from the gun I think the felt recoil will be more. My thought on backboring, forcing cone modification, porting....just a way to spend money to make you feel you are improving the gun.
     
  19. Chango2

    Chango2 Active Member

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    AHAB: I sure agree with you 110% about backboring a TM-1. Maybe we shoot better with a lighter wallet?

    Bob English: What are you trying to accomplish? I beieve that if you figure the "points" of constriction you need/want, then somebody like angle port or Briley can easily send out the exact Perrazi-fitting choke you want?

    David
     
  20. In plain view

    In plain view Member

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    Chango2: I'm simply trying to come up with a choke tube, with or without backboring to give me the kind of pattern that when I hit a target dead center I would like to see a little black smoke. With the crap I have now I seldom see smoke. I have Briley tubes in my backbored TM-1 Special and I'm not impressed with them. I'm not new to this game and have been doing it for some time now. I thought maybe by changing to a different Perazzi tube and constriction I might have better luck. Thats all. P.S. It's not a POI problem either. Bob English
     
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