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Discussion Starter #1
Anyone got details of the hook modifications and the rear NIB plus any other fitting requirements for moding a UMP lower to fit a USC.

Obviously I know about the FCG swap just looking for the fitting instructions for the lower to upper.

Thanks
 

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There's sticky at the top of this forum that has a lot of good info:

http://hkpro.com/forum/showthread.php?t=66118

including this:

http://home.comcast.net/~UMPlower/

Which has a good step by step guide on what needs to be done. He adds a sear pin block and relocates the sear pin, but from what I've read recently, this doesn't need to be done if your USC upper has NOT been cut for the sear trip lever.
 

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There's sticky at the top of this forum that has a lot of good info:

http://hkpro.com/forum/showthread.php?t=66118

including this:

http://home.comcast.net/~UMPlower/

Which has a good step by step guide on what needs to be done. He adds a sear pin block and relocates the sear pin, but from what I've read recently, this doesn't need to be done if your USC upper has to been cut for the sear trip lever.
Bad Bad advice, if your USC upper is cut for the auto sear, you have just made an MG, welcome to club FED. Jeff
 

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Discussion Starter #4
Thanks for the info thats just what I needed I did and search and didnt find that stuff

Thanks Again
 

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He adds a sear pin block and relocates the sear pin, but from what I've read recently, this doesn't need to be done if your USC upper has NOT been cut for the sear trip lever.
For some reason, Top Notch doesn't show a copy of the letter he received from the ATF. I know Tactical Excellence worked with their local ATF when developing the conversion, well before anyone else did. I don't know that they told him specifically that it was necessary but Jeff goes to some length to do what he does with the sear pocket- arguably there's good reason for doing so.

My philosophy is "better safe than sorry".
 

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HDPS

Any thoughts on compliance issues/concerns about the HDPS conversion? I'm pretty sure it is fine, but would appreciate any contrary thoughts.
 

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Any thoughts on compliance issues/concerns about the HDPS conversion? I'm pretty sure it is fine, but would appreciate any contrary thoughts.
I wouldn't think you'd have an issue with how Ed fills that cavity. If there really is a letter in existence that clearly says the cavity does not have to be filled, then it's a moot point. The only difference between the TE and HDPS approach is that TE enlarges and offsets the pin hole. I don't really see a big difference between an aluminum block or a cast-in-place piece of polymer. The ATF bases alot of their opinions (and prosecutions) on the concept of "reasonable" Is it reasonable that an average individual could reverse the TE sear block? The HDPS one? That depends on whose interpretation of reasonable we're talking about.

The issue I have with any interpretation of any letter is just that- interpretation. The ATF is notorious for writing letters full of nebulous language and then later clarifying those letters with more of the same. Assuming that because something isn't addressed in their position statements makes it acceptable to proceed with a modification is a dangerous assumption. Thinking that because they didn't tell you, they won't consider it improper anyway is a bad idea.

Another thing- the ATF has written letters based on incomplete and/or misleading information as provided to them, only to reconsider and rescind their opinions and approvals at a later date. The most recent example that comes to memory was the bump-firing device that fit on AK's and browning 1919's allowing them to fire in what could be considered full auto (the device allowed the recoil to move the weapon back and forth, causing individual, manual trigger trips). The maker gave some semi-deceptive functional description and a semi-operable sample to the ATF. ATF went ahead and issued a green light. After several people wrote asking for confirmation of the approval, basically asking how it could be legal considering similar devices had been denied previously, the ATF reversed itself and issued an order for the devices to be withdrawn from the market.
 
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