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Thread: Undersized bore, chambered with normal sized solid pilot.

  1. #1
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    Jun 2008
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    Undersized bore, chambered with normal sized solid pilot.

    I picked up an excellent used 6mm barrel with just enough tenon to cut off and re-thread. My dad has chambered his share of barrels, all of which have shot quite well, but doesn’t keep up with competition type things. Today he calls and says that he’s about .350” from finishing the chamber and taking a break, and mentions that he’s never had this issue before, but the reamer doesn’t want to pull out of the barrel and he just isn’t getting the normal amount of feel, and asks if I sent him a dull reamer. I said, “no that reamer was plenty sharp”, and didn’t think much of it. I get off work and he tells me that he’s finished up, and he found out what the issue was....”you’re pilot is oversized...” Then it dawns on me...I didn’t ask, but it’s not that unusual for guys to get a .236” lands diameter in a 6mm barrel. Sure enough, the solid pilot is .2365”(obviously normal for a standard .237” lands diameter barrel) and won’t go into the bore on the muzzle end(not re-crowned yet). Inspecting the chamber it appears to be excellent, except that forward of the through, you can see where the pilot was riding the lands.

    Is the barrel going to shoot like crap? The previous owner was competitive shooter that won a number of high power matches with it, and claims it shot in the 1’s when new, and was shooting in the .3’s when he sold it to me. I was sure hoping it would do the high .2’s to low .3’s after being rechambered. Unfortunately there isn’t enough tenon left to set the barrel back beyond where the pilot rubbed the lands.
    Last edited by ImBillT; 07-01-2020 at 04:25 AM.

  2. #2
    Join Date
    Feb 2003
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    Houston, Texas
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    Quote Originally Posted by ImBillT View Post
    I picked up an excellent used 6mm barrel with just enough tenon to cut off and re-thread. My dad has chambered his share of barrels, all of which have shot quite well, but doesn’t keep up with competition type things. Today he calls and says that he’s about .350” from finishing the chamber and taking a break, and mentions that he’s never had this issue before, but the reamer doesn’t want to pull out of the barrel and he just isn’t getting the normal amount of feel, and asks if I sent him a dull reamer. I said, “no that reamer was plenty sharp”, and didn’t think much of it. I get off work and he tells me that he’s finished up, and he found out what the issue was....”you’re pilot is oversized...” Then it dawns on me...I didn’t ask, but it’s not that unusual for guys to get a .236” lands diameter in a 6mm barrel. Sure enough, the solid pilot is .2365”(obviously normal for a standard .237” lands diameter barrel) and won’t go into the bore on the muzzle end(not re-crowned yet). Inspecting the chamber it appears to be excellent, except that forward of the through, you can see where the pilot was riding the lands.

    Is the barrel going to shoot like crap? The previous owner was competitive shooter that won a number of high power matches with it, and claims it shot in the 1’s when new, and was shooting in the .3’s when he sold it to me. I was sure hoping it would do the high .2’s to low .3’s after being rechambered. Unfortunately there isn’t enough tenon left to set the barrel back beyond where the pilot rubbed the lands.
    You were basically pressing the solid reamer pilot into the lands with about a .0005 interference fit.

    It might not hurt anything, since in theory the lands at that point just forward of the lead might be a few tenths looser.

    Heck, shoot it and see. If everything else checks out, I bet it didn’t hurt a thing.

  3. #3
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    Feb 2003
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    Poetry, Tex.
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    Quote Originally Posted by ImBillT View Post
    I picked up an excellent used 6mm barrel with just enough tenon to cut off and re-thread. My dad has chambered his share of barrels, all of which have shot quite well, but doesn’t keep up with competition type things. Today he calls and says that he’s about .350” from finishing the chamber and taking a break, and mentions that he’s never had this issue before, but the reamer doesn’t want to pull out of the barrel and he just isn’t getting the normal amount of feel, and asks if I sent him a dull reamer. I said, “no that reamer was plenty sharp”, and didn’t think much of it. I get off work and he tells me that he’s finished up, and he found out what the issue was....”you’re pilot is oversized...” Then it dawns on me...I didn’t ask, but it’s not that unusual for guys to get a .236” lands diameter in a 6mm barrel. Sure enough, the solid pilot is .2365”(obviously normal for a standard .237” lands diameter barrel) and won’t go into the bore on the muzzle end(not re-crowned yet). Inspecting the chamber it appears to be excellent, except that forward of the through, you can see where the pilot was riding the lands.

    Is the barrel going to shoot like crap? The previous owner was competitive shooter that won a number of high power matches with it, and claims it shot in the 1’s when new, and was shooting in the .3’s when he sold it to me. I was sure hoping it would do the high .2’s to low .3’s after being rechambered. Unfortunately there isn’t enough tenon left to set the barrel back beyond where the pilot rubbed the lands.

    Did you get your answer on the other forum?

  4. #4
    Join Date
    Jun 2008
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    Quote Originally Posted by Butch Lambert View Post
    Did you get your answer on the other forum?
    No one has said “yep, been there done that, doesn’t hurt anything” or “yep, made that mistake, shot like crap and had to be re-chambered correctly”. Just lots of “shoot it first, and who knows maybe this will help” type stuff. All of that is welcome, but I was definitely hoping that someone else had made a similar mistake and knew exactly what to expect.

    I intend to shoot if first either way, but if it doesn’t shoot well, I’d like to know if need to track down some other potential reason for the problem, or I could safely assume that pilot damage was the problem.

  5. #5
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    Jun 2008
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    Quote Originally Posted by jackie schmidt View Post
    You were basically pressing the solid reamer pilot into the lands with about a .0005 interference fit.

    It might not hurt anything, since in theory the lands at that point just forward of the lead might be a few tenths looser.

    Heck, shoot it and see. If everything else checks out, I bet it didn’t hurt a thing.
    Yeah. I may need to barrow a bore scope. If you get the light perfect and look closely you can see that the lands where the pilot was rubbing look different than the lands farther down. In my mind I could see it just being a bit of a burnishing, or I could also see it rolling a little bur that might or might not clean up, and I could imagine the bur messing with my jackets and causing fouling issues or bullet blowups. I shall see.

  6. #6
    Join Date
    Feb 2003
    Posts
    30
    Never cut a chamber with a solid pilot reamer much less an oversize one so no help there. The more I work on barrels the less I understand about what is truly important to accuracy and what is not. That being said I have never seen a barrel perform really well with a rough or uneven throat.

    Of course we always want things a perfect as possible but lots of barrels and work out there that is less than perfect yet it still performs superbly.

    Seeing how badly it's damaged with a borescope would be nice but shooting is the only real test.

    During the first AWB barrel blanks were hard to get. A buddies Palma rifle barrel gave out mid season. He wanted a light Palma. Only thing the maker had that they could ship in a reasonable amount of time was a heavier contour from a canceled order but they said their would recontour to the light Palma at no charge.

    The bore seemed to be straight but when spun between centers it had a huge about of runout. I believe when it was recontoured the center was way to tight and bowed the barrel a lot.

    I believed it was nothing more than a tomato stake. I was wrong. Thing is that is the only barrel I have even seen that had the mythical "hummer" qualities. That barrel shot like none before or since.

    Not my work but I have seen marginal work that has performed way better than I would have guessed. I have also done a couple that were as close to perfect as I have seen yet they were just average at best.

    The target and only the target will provide the actual answer.
    Last edited by Joel; 07-06-2020 at 12:20 AM.

  7. #7
    Join Date
    Aug 2005
    Posts
    808
    bore scope, Teslong, on amamzon ,about 60 bucks. works with computer They have other models as well - they might have the I phone stuff figured out now. got one about a year ago works great. fiber optic cable .22 on up comes with right angle mirror, very good optics way beter than any thing else short of that 700+++ unit but I do not have one of those to compare it to. Others have and reviews at that time were exceptional. software is down load from sight so you can make a video or still shots . Definitly worth the Jingle. out classes the lyman unit 1000%
    For $60 no reason not to have one. Oh and it is variable lighting as well runs off usb port.

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