Prebore and floating reamer holder

Discussion in 'Gun Project Questions & Gunsmithing' started by Shawnba67, Oct 3, 2019.

  1. Nightraider

    Nightraider

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    My shop isn't a balmy 60°, climate controlled, space. But if a .0001" indicator isn't registering, I'm okay with what runout might be there. It's more about guaranteed repetition than anything, not leaving anything to the will of the gods. As measurement .0001" is useless in my shop, but an indication it's useful.
     
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  2. Dud

    Dud

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    My wording is probably wrong but an absolute measurement like I.D. or O.D. is more susceptible to environmental error than a relative measurement like runout.

    As long as your test indicator is working properly and your lathe spindle has less than 0.00005" runout, it's pretty easy to trust a 0.0001" TIR measurement even if it's not from a temperature controlled metrology lab.
     
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  3. Tim Singleton

    Tim Singleton Silver $$ Contributor

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    Im in the pre drill/bore with a floating pusher camp
    download (1).jpg
     
    Last edited: Oct 4, 2019
  4. Stan Taylor

    Stan Taylor Gold $$ Contributor

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    I ain't LOL
     
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  5. Tim Singleton

    Tim Singleton Silver $$ Contributor

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    I’ve got a patent on my pusher!
     
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  6. Dusty Stevens

    Dusty Stevens COVFEFE- Thread Derail Crew Gold $$ Contributor

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    I sure like the pusher from steppenwolf.
     
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  7. hammerjack

    hammerjack Gold $$ Contributor

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    I have one area in my shop under climate control year round. l like to keep my beer ice cold.
     
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  8. Stan Taylor

    Stan Taylor Gold $$ Contributor

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    I got one of them also.
     
  9. HTSmith

    HTSmith Silver $$ Contributor

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    I was born to be wild but that was a long time ago.;)
     
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  10. pdhntr

    pdhntr

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    WOW! 29 replies on a discussion of whether to prebore or not.

    Butch's computer has to be broken.:)

    Jim
     
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  11. Roeder

    Roeder Silver $$ Contributor

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    Pretty much as some of the other guys said: to ensure a straight and on size chamber. There can be a fair amount of wander in the chamber length of the bore, which leads to runout and/or oversize chamber diameter.
     
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  12. Stan Taylor

    Stan Taylor Gold $$ Contributor

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    Really.
     
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  13. butchlambert

    butchlambert Site $$ Sponsor

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    Been out of town. An old high school buddy retired as State District Judge and a huge party was held at a Wichita Falls pub-way too many folks. The next night we were at his home for our class's high school reunion.
    We had a wonderful time.
     
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  14. msalm

    msalm

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    I pre-bore because I lack patience... I don't have a muzzle flush system and pulling a reamer every .100" or even .050" is excruciatingly slow....mind numbing even. I drill and bore the hole large enough in steps so the reamer enters far enough for the pilot to enter the bore (that is dialed in on the throat) and also contacts at the back end. For alignment, that give you two points of contact as far apart as possible that initially will guide that reamer straight TO WHERE YOU HAVE IT DIALED IN. If you didn't dial in properly, it'll not work out for you and a tighter pilot will try and move you back on course. If you ever have a longer chamber reamer get tight towards the end, that's the pilot binding on an off center bore trying to straighten that mis-alignment.

    I have chambered the same as Stan also and the rifles shot just as well. It works and I would likely use that method if I didn't have to pull a reamer, clean chamber, clean reamer, re-oil, and start cutting again. When doing so I tend to push things too far trying to get another .100" or so and risk picking up a chip and putting a nice ring around the danged thing that may or may not clean up depending on how far I have to go.

    This should not always delve into a p****ng contest. It all works well when done properly, it's just that some methods work better for others depending on their setup AND comfort zone.
     
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  15. jkohler

    jkohler

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    I dial in where the throat will be and dial in the muzzle end. Drill .015 smaller than the body shoulder junction to a depth of .100 shy of that depth. at that point all check the throat area again with the indicator to make sure it’s still good. Then go in with a boring bar to get the hole straight and also get the reamer started in so the body of the reamer has support as to help with any chatter. I run a loose bushing on the reamer also. Ive tried May different ways and they have all worked just fine.
     
  16. Stan Taylor

    Stan Taylor Gold $$ Contributor

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    We'll said sir.
     
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  17. Roeder

    Roeder Silver $$ Contributor

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    All things are relative. Most of the bench rest guys do something like this regardless of the method of indicating (throat and muzzle vs Gritters method.) If it doesn't sound beneficial to you, maybe it isn't. I chambered quite a few barrels for hunting rifles before I started pre-boring and they all shot very well by hunting rifle standards.
     
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  18. Papa Charlie

    Papa Charlie Gold $$ Contributor

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    Do any of you use a bore mandrel inserted into the bore to dial in the barrel before chambering? Can't imagine any other way to do it.
     
  19. Roeder

    Roeder Silver $$ Contributor

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    I use a long stem dial test indicator to indicate inside the bore. Haven't used an indicating rod or mandrel in years.
     
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  20. Jesswil61

    Jesswil61 Gold $$ Contributor

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    Seems to me that maybe counter productive for the .0001 measurement accuracy. Seems when I am indulging the "Oh hell that'll work" engages quicker!
     
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