Lyman GPR nipple thread question

[ThreeCedars]

First time poster, but I’ve learned a lot here. I have searched for an answer to my question without any luck.

I have a 2013 Lyman Great Plains Rifle, and ordered some replacement Hot Shot nipples in 6mm x .75 from TOW, which came in today. The factory nipple came out without any trouble, but the new nipple starts to feel tight within 1/8 of a turn so I backed off to avoid cross threading.

My question is if Investarms ever used a different thread pitch? All information I can find suggests that 6x.75 is it.

Possible other factors could be that the nipples I got weren’t labeled properly and have a different thread pattern (which I doubt), or that the sharp new threads on the Hot Shot nipples are too tall for the tapped threads in the barrel.

The diameter across the peaks of the original nipple threads measure at 0.226” and the Hot Shot measures 0.335 so there is a difference there.

Any information or advice would be great. Thanks guys!

 

[ThreeCedars]

 

[Boomerang]

6mm is .236. So your new nipple should still fit as long as the pitch is the same. Put both nipple threads against each other and see if they interlock with each other the same. If they do then you might have a little residue in your bolster making your new nipple tight.

 

[Indy Durtdigger]

The threads on that Hot Shot nipple look rough and jagged, the die they cut those with must be slap worn out. If the two nipples to mesh properly indicating a matching thread the new one may just need cleaned up. 6x.75 is a common metric thread so a die or thread chaser to clean them up with should be an easy find.

It's an absolute shame everything is getting like this. I've got a job at work with the third cylinder head on order for it trying to get a new one that's not in worse shape than the bad one I'm trying to replace.

 

[64Springer]

Chuck your nipple up in a drill chuck.

Run your drill in reverse on slow while holding a triangular file in the threads.

This will chase your gnarly threads in no time.

 

[ThreeCedars]

Thanks guys! I ended up running to the hardware store, and threaded both of them into a new 6x.75 nut and they went in smoothly. I like the idea of taking the sharp edges off - I’ll definitely give that a try. I also have a tap on the way, so feeling very confident that I’ll have a solution soon.

And sorry the original measurement of the Hot Shot threads was .235, not .335. That was a typo.

I appreciate the help!

 

[ThreeCedars]

Quick update - I ended up chasing the threads with a bottom tap, and the Hot Shot nipple threaded right in without having to clean the nipple threads up first. Nice and solid. I made sure to use a small amount of antiseize and it seems to be perfect. Thanks again for the ideas!