CVA Nipple problems, retap?

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platypus

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Good day.

I have a .50 cal CVA Blazer. Last week at the range, the nipple blew out on me. It was a 6x1mm nipple, and I got some replacement ones from Cabela's.
Unfortunately, the new nipple screw in, but do not lock into place and spin until infinity, which means that the threads on the barrel are probably shot.
I accidentally initially bought some Thompson/Center 1/4''-28 nipples, which did not fit in the 6x1mm hole. I was wondering if retapping the hole to 1/4''-28 would be a wise idea, or if the size is too close to 6x1mm. I will initially try retapping to 6x1mm, but if that fails, 1/4''-28.
 
Either which way, I ran the 6x1mm tap into the nipple hole, and the second nipple I put in held. The first one still spins free, so the threads in the barrel must have been buggered by the blow out and buggered the first nipple. Tapping it got rid of whatever imperfection was there, and the second one seems secure. So at this time, I don't need to investigate the size difference between a metric and a standard #11 nipple.
 
Using the 6mm tap will have cleaned up the threads. Wouldn't have made them any tighter.
You have had one nipple blow, and another spin free.
This would suggest that the fit of the current nipple is marginal; I wouldn't trust it.
If it were mine, I would tap to 1/4-28. Wouldn't be perfect, but the nipple threads should really bite. There are also the oversized 1/4 inch nipples - .255, .260, .265, etc., which can be used to get a really tight fit.
 
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I would echo Tiriaq's comments; I suspect the pitch on the original thread was 26 per inch but more importantly they are no longer suitable for safely holding the nipple. Try the 1/4 x 28 tap and if the resulting threads still look questionable, go to a larger tap in .255 diameter or larger until you get good clean threads. Obviously use a matching nipple. I would expect that you will find the oversize nipples and taps at an outlet like Track of the Wolf

Worth mentioning that a friend had a cleanout screw stuck in his ear from a muzzle loader being shot several feet away to one side of him. He had to have it removed at the hospital. Same shooter blew out the replacement screw a few weeks later. dumb

cheers mooncoon
 
I successfully tapped a stripped/cross-threaded 6mm nipple hole to 14/28 a while ago and it is still working in a 54 cal. Be sure to use a bottom tap to finish the hole so you get maximum new threads. Track of the Wolf carries oversize 14/28 threaded nipples.
 
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