Colt Police Positive


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Old 07-01-2011, 05:42 PM   #1
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Default Colt Police Positive

I am replacing the barrel on an old small frame colt revolver . Unfortunately the colt threads are tapered. The old barrel threads are 32 tpi and the thread OD ranges from 0.438" to 0.445" over 1/2" The new replacement barrel is also 32 tpi and the threads range from 0.444" to 0.450" OD over 1/2" length. So the new barrel screws in all the way but for about 1/4", by hand. It is much tighter than the original barrel which is loose up to the last 1/4 turn. Forcing the new barrel in isn't an option, it's brand new, old stock, and nickel plated. Does anyone have any ideas about how to chase the threads on the new barrel? I haven't found a die (or a tap) this size so far. It's a bit bigger than 7/16X32 and tapered!
thanks
Alex



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Old 07-01-2011, 06:48 PM   #2
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It sounds like you might have to chase the threads by hand with a file CAREFULLY until you get them the correct size. I wouldn't go very far and remember that you will have to apply some force when screwing it in.



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Old 07-01-2011, 07:03 PM   #3
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Default Over size thread.......

Place some blueing on the thread to make sure that the two tapers match and it will also show if you have a defect in the starter thread. Clean the threads on the barrel and inspect with a magnifier to make sure that you have a good profile and not something that was threaded with a burnt or chip incert..Good luck, this is one time that I wish I still worked in a machine shop.

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Old 07-05-2011, 02:10 AM   #4
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Thanks for the replies guys.
Tried the layout blue idea, these 32 tpi threads are so fine couldn't see much problem even with a magnifier. Since I was concerned about the tapered threads ( and my ability to not screw it up in my chinese lathe) I went with 400 grit valve grinding compound and lapped the threads in. Took a while but worked pretty well. At this point I have the crush relief cut and the barrel is hand tight at 45 degrees from sights lined up. The remaining gap measures out to 46 degrees, serendipity.
So far so good.
Alex

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