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The Interapid 312B-15 that nearly everyone uses, has a 2.675" contact tip and is a .0005" indicator. Precision and accuracy are .0005". Pretty easy to see .0002" or less when dialing in a barrel.
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Dialing in a barrel for theading
- Thread starter COMachinist
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The idea behind dialing in a barrel that way, is to check for runout at two vastly different points. Just checking runout right at the muzzle only tells you there is zero runout at that one spot. If the runout is zero( or as minimal as possible ) 90mm down the bore, AND zero( or as minimal as possible ) at the muzzle, at the same time, then you're dialed in. I think a better option is along the lines of BSW Arms' suggestion. A tight fitting pin, commonly referred to as "range rods". But the two point measurement still applies. The runout of the rod being zero right at the muzzle means nothing, unless it is also zero at 1" or 2" out past the muzzle. Hope that makes sense.
This video shows how this is done using a range rod. Same principal as the long probed indicator. Also illustrates how important it is to never assume a bore is concentric with the OD of a barrel.
This video shows how this is done using a range rod. Same principal as the long probed indicator. Also illustrates how important it is to never assume a bore is concentric with the OD of a barrel.
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Even Gordy Gritters who was the creator of the Grizzly rods, states in his book, they are to get close. Always direct indicate in the grooves for final dial-in.
From Fred Zeglin & Gordy Gritters book "Chambering Rifles for Accuracy"
From Fred Zeglin & Gordy Gritters book "Chambering Rifles for Accuracy"
I have my own way of chambering barrels that works for me. I dont use a outboard spider and I mostly chamber through the headstock. Try several different ways and then decide which one you like best. Theres no right or wrong way to chamber a barrel. If it is accurate to your or the customers satisfaction, then its right.
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I'm glad you said that. I have two barrels on my bench right now, one is a center turned rifled 20 ga slug bbl for a neighbor that I will be single-pointing the chamber on, through the headstock, no spider. The other is a .20VT that will be chambered on the steady. I'm not fond of outboard spiders, but it's all people talk about doing anymore.
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My headstock is deep so my spider will barely grab a 24" barrel. Here in Ct brush country most of the barrels I do are 22". I usually chamber with a home made fixture with 8 brass tipped bolts. I don't have a set of rods so when I'm starting with a barrel blank I put it on centers and turn both ends for about 6 inches concentric with the bore. Then I can work in from the ends using a 4 jaw and indicate on the OD. I have some brass fribbetts I made that go in the bore to protect it from the center.
Word of the day!
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FRIBBETT- The sound made by a frog with a hairlip?
I agree, but you should see some of the books I've read or read the shooter's forums threads on the subject. They don't make it rocket science, they go full on black voodoo magick on the subject. I just roll my eyes and still somehow make small groups in spite of it.
I agree, but you should see some of the books I've read or read the shooter's forums threads on the subject. They don't make it rocket science, they go full on black voodoo magick on the subject. I just roll my eyes and still somehow make small groups in spite of it.
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