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Vent liner size?

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jtmattison

70 Cal.
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Mar 17, 2004
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Hey Gents,
I'm refinishing an old CVA for a buddy of mine and the vent liner is rusted in place. I've gone through all the standard removal attempts to no avail. I have to drill it out. Assuming it's the usual 6x1mm metric that CVA uses, what is the correct thread to drill it out and thread it for? Maybe a White Lightening?

Thanks,
HD
 
I've only done the 1/4 inch ones that Jim sells, but I know he makes a 5/16 and a 3/8. If you buy the kit they come with taps and a drill. I just buggered up a 1/4 inch one so I'm going to be learning about the 5/16 version this week. :surrender: They're all 32 threads. 1/4 X 32, 5/16 X 32 etc.

One thing I've learned using the white lightnin's is to use a slightly smaller bit than is supplied with it. My 1/4 inch liner came with a 7/32 inch bit and that's a tiny bit too big, at least on my drill press. I don't know if I've got a little wobble in my press or what, but the hole ends up being too easy to tap for my comfort. Luckily, I've got an old barrel that I practice on so I figured this out without damaging a good barrel. I use a number 4 drill now and it seems just right. Also, make sure you clamp stuff down real tight.
 
If the liner is a M6-1 thread the tap drill for it is a 5mm. (.1969").

If I were drilling it out I think I would use a 3/16 inch (.1875) drill bit.

That would leave about .005 per side in the hole which could easily be picked out with a sharp awl without damaging the original threads.
 
First off, a shim is taped to the swamped bbl so the WL liner is perpendicular to the bore and hand held on a reinforced, 3/4" plywood. A 3/32" dia. pilot hole is drilled followed by the recommended letter"I" drill. A .020-.025 deep ctsk ensures enough shutoff for the WL's angled head and also is deep enough for a TH land length of .04. The hole is then tapped by starting the spindle and shutting off and while the spindle is coasting, the tap is lowered into the hole. After the 4-5 threads stop the spindle, the tap is unchucked and the remainder of the tapping is done in the bench vise. I use machine oil on the tap and of course all this work is done w/ the breechplug removed. Drills that have been improperly sharpened have different length cutting lips and don't cut w/ the spindle axis and the result is an oversized hole. Also if the "heel" of the drill isn't relieved enough a lot of force has to be applied and again an oversized hole. I hand hold so the pilot drill can pickup the center punch and the larger drill is free to follow the pilot hole. The tap easily centers in the hole and is perpendicular to the bore......Fred
 
If you do want to go with a White Lightning liner and the existing liner is a M6-1 you will have to use a 5/16-32 thread sized liner (or larger).

Retapping a M6-1 thread using a 1/4-32 tap will not produce good threads as there is not enough material in a M6-1 hole to provide full threads in the slightly larger size.
 
I ended up tapping it for 5/16 - 24. I had a tap on hand and TOTW had the liners. It's good to go now.

I forgot how relaxing it is to build a rifle. This is actually an old Investarms Hawken kit. I don't know how old it is but it has a long rectangular patch box.

Whoever "built" it the first time chopped at it with what appears to be a Dremmel because it was covered end to end with deep divots. It took me four hours of sanding just to get rid of the divots. Luckily there was a ton of wood on it and it needed a LOT of shaping.

I think it will turn out to be a nice rifle. I'll post pictures when it's done.

HD
 
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