Help with 870/HP9 mag extension

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LloydM

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I'll start off by saying that I know a few things on this task have already been discussed... removing mag tube detents, using sling plates to keep things tight, etc. But I don't think my problem has been covered.

I have a custom magazine extension for an 870, made by Tactical Ordnance, that I am trying to fit on a Norinco HP9. I have two questions:

1.) A factory HP9 has a magazine spring with a follower on one end, and another part on the other end (not sure of correct terminology) - when you instal an extension do you remove that other part or keep it in the extension?

2.) Can extensions for the 870 even fit on an HP9? The threads seem to line up, but it is impossibly tight to turn on. I can't even spin it on a full thread before it is too tight to turn any farther. I am not sure if other extensions would allow for this, but with the Tac Ord extension I can unscrew the tube from its base ring and then thread it in the other end - if I do this and thread the opposite side onto the HP9 magazine tube I can get it on much further, but it still gets much to tight before making it to the barrel band.

Help would be greatly appreciated!
 
Some extensions don't work on the HP9. Vang comp does, it's what I have. Still took some minor "gunsmithing". You do not need to keep the plastic cap, the detents will be removed so it becomes useless.
 
The kind you already mentioned, detents and such. I'd consider it prep work. I have the same problem on my HP9 attaching some stocks. The threading won't allow the bolt to snug up and leaves tons of play. Odd how my DA Grizzly attaches everything just fine.
 
So is there anything a guy can do to make the threads work, or am I hooped? Catching by half a thread is not gonna cut it.

Would blasting the finish off the threads loosen things up any at all? Perhaps some sort of a caustic dip to eat away some thickness off the metal?
I could try canging out the magazine tube - can you even buy spare tubes? Actually, can you even change the tube?
 
I'd talk to tacord, if you send your shotgun into him he should be able to make you a new extension made with the same thread pitch.

Not sure why some stuff doesn't work with Norcs, its like they randomly change things throughout production just to mess with you. I have a Scattergun Tech extension and it fits my HP9 no problem.
 
I have already spoken with Tac Ord, and for the record he has been very gracious. He has offered a full refund, or to have me send it back and have him tinker with it. I was just hoping for a quick fix...

I did have another idea though. What about drilling through the factory Norinco mag cap and welding on an extension then refinishing the whole thing? Has anyone tried anything like that?
 
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