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Discussion Starter · #1 ·
I have a friend who has a demilled knee mortar. I may try and pick it up but if so would be more interested in rewatting it.

Who can properly and legally do this? Any ideas of costs?

Does the demilled piece need any paperwork to make a rewatt legal?
 

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Can be done by filing a form one. Paying 200 bucks, fingerprints, picture, then wait a year. Unless you e-file. Now, how was the deactivation done? That will be the big hurdle to get over. Pictures?
 

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Discussion Starter · #3 ·
Can be done by filing a form one. Paying 200 bucks, fingerprints, picture, then wait a year. Unless you e-file. Now, how was the deactivation done? That will be the big hurdle to get over. Pictures?
Hole cut in the side of the tube to the same, or roughly same size as mouth of mortar.

Buddy is out of country for a while so no pics till he gets back
 

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If he has the plug that was cut. It can be carefully reinstalled and welded. A tricky time-consuming job. If there is no plug, you have a dilemma. Not only is the plug portion rifled it is contoured to the curvature of the tube. And what most don't realize is the thickness of the tube is thinnest at the top and increases as it goes down. So, it would be very difficult to replicate all the dimensions. It may be wise just to look for one that is already papered. In reality they don't command a huge price at auctions, most going in the 3K and under range depending on completeness and condition.
 

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Discussion Starter · #5 ·
If he has the plug that was cut. It can be carefully reinstalled and welded. A tricky time-consuming job. If there is no plug, you have a dilemma. Not only is the plug portion rifled it is contoured to the curvature of the tube. And what most don't realize is the thickness of the tube is thinnest at the top and increases as it goes down. So, it would be very difficult to replicate all the dimensions. It may be wise just to look for one that is already papered. In reality they don't command a huge price at auctions, most going in the 3K and under range depending on completeness and condition.
Thank you most kindly for the info. I certainly never realized it was rifled.

Can one put a sleeve in, yes I know the caliber then changes?

I was hoping to get it from him for a couple of hundred and a few steaks on the BBQ ( assuming that was fair) and then another K in stamps and work to rewatt. Suppose that is a forlorn hope now.

Anyway thank you.
 

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besides the hole, the firing pin was removed and the firing pin hold also welded shut, so if you are going to "reactivate" you will also need a firing pin, where you get one of those, have no clue. also there is a steel rod going through the tube as well that will have to be removed.

I'm going by how my RPG-7 was deactivated, so I'm pretty sure that is how all DD are deactivated
 

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I did mine after receiving an approved form one. I worked on it a few hours a month and after two years I finally fired it. I made my own Delrin projectiles on my lathe. They replicate the style of the knee mortar round. But I need to wrap some masking tape on the base, so they engage the rifling and spin. Right now, it's like a 50mm musket. But it was a satisfying experience knowing last time it was fired was probably 75 years ago. If I can I'll post some pictures.
 

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I did mine after receiving an approved form one. I worked on it a few hours a month and after two years I finally fired it. I made my own Delrin projectiles on my lathe. They replicate the style of the knee mortar round. But I need to wrap some masking tape on the base, so they engage the rifling and spin. Right now, it's like a 50mm musket. But it was a satisfying experience knowing last time it was fired was probably 75 years ago. If I can I'll post some pictures.

You should do a separate post on your KM and the rounds you made/fire. Would love to see them.
 

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I just don't get why?

My buddy wants me to weld up an RPG he bought, smooth wall so no big issue, but with no real ammo, why bother?

I mean even if ammo was available would you trust using it in a welded tube?

With rifling, you will never get a good repair, unless it was sleeved in its entirely, rebored and recut.

I remember watching those morons on "Sons of Guns" attempting to weld an artillery barrel back together with a weld in the middle, now way to align the rifling.

If its just to launch plastic projectiles just make a non DD and use black powder.
 

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You should do a separate post on your KM and the rounds you made/fire. Would love to see them.
Send me your email I'll send pictures and video. I never made a thread because I didn't want to hear the crap I'm already hearing. It won't work, you'll never align the rifling etc,etc,etc, Blah Blah Blah. I did it and it works for what I want to do with it. I never planned on launching 80-year-old explosive projectiles. I'm sure the originals made significant tube pressure. At least I own a functioning fire able knee mortar. And have fired it. How many get to say that?
 

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I made my own Delrin projectiles on my lathe.
Have you considered 3d printing the shells? It shouldn't be too difficult to recreate them to look realistic, possibly hollow so they could be filled with cornstarch or talcum powder so you could easily see the impact. Printing them would be a lot faster than hand turning. It sounds like a fun project.
 

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Send me your email I'll send pictures and video. I never made a thread because I didn't want to hear the crap I'm already hearing. It won't work, you'll never align the rifling etc,etc,etc, Blah Blah Blah. I did it and it works for what I want to do with it. I never planned on launching 80-year-old explosive projectiles. I'm sure the originals made significant tube pressure. At least I own a functioning fire able knee mortar. And have fired it. How many get to say that?
Japanese KMs worked off gas pressure of course....The length of the firing pin in the barrel could be adjusted so as to change the volume of gas in the barrel, thus determining its firing distance....Bodes

 

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With rifling, you will never get a good repair, unless it was sleeved in its entirely, rebored and recut.
It could be done, with access to a CNC lathe preferably with live tooling, if you know the dimensions of the rifling. You could turn a brass plug, threaded reverse of the rifling to accept a bar for removing it, and use that to align the cut piece for welding. Not really efficient for a one off job but it'd make it pretty easy, if you were going to reactivate a pile of them it'd be well worth it.
 

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Here in Michigan we have Camp Graying. Which is a US Army military base. They have a firing range for various toys that the public can use.
Do they allow this type of thing at Knob Creek?....It's interesting you mention CG....I know somebody who used to shoot black powder there and lost their privileges....I'm not sure why though...Bodes
 

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In reality its pretty simple to make a new Knee mortar from a deactivated unit. On the other hand the terms Rewat and Reactivate have specific meanings in the US firearms regs and you can neither reactivate nor rewat a non registered gun. Rewat refers to a program the US Govt created for machineguns way back in the late 40s or early 50s. It lasted until the early 60s. This was the DeWaT program which allowed the import and sale of Deactivated War Trophies which were machineguns that had been permanently made non functional through welding chambers, bolts or other methods that were acceptable to the treasury dept at that time. Destructive devices were not a thing back then and until the Gun control Act of 1968 the catagory did not exist. You could buy, sell, trade, own ship via US Post and otherwise play with cannons, mortars and other stuff now considered NFA. Since the DeWaT program died long before there was such a thing as a DD there aren't really any DeWaT mortars. For that reason you cannot actually rewat one.

As for Reactivation this is a term used by the BATF for returning a deactivated firearm that is registered as NFA but non functional to a functional state. In olden times like the 80s and maybe a little later, you could reactivate a registered firearm without being required to mark your own manufacturer information on it. It would retain its C&R status and be considered as having been manufactured by the original manufacturer. This can be a big deal for buyers and at one time there were at least two or three states that only permitted NFA if it was C&R.....

As for the knee mortar, I'd be leery of shooting a gun with a plug welded into the barrel. The barrel in these guns is not very thick and it is allow so welding on it will change its hardness and strength. I'd be inclined more toward making a smooth bore barrel for it which could be done on a simple manual lathe. I'm sure its also possible to make up some sort of rifling cutter to rifle it if you're so inclined. The rifling isn't deep or terribly complex. It has a pretty slow twist rate as well so it shouldn't require a very complex tool to do.

Just my thoughts

Frank
 
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