HKPRO Forums banner

1 - 14 of 14 Posts

·
Registered
Joined
·
65 Posts
Discussion Starter · #1 ·
So I've finally decided to convert my USC to a UMP clone. I will be doing the SBR at the same time. I've sent a few emails to Ed at HDPS, but have only recieved one quick short response back from him.

I'm debating if this is something I can do myself, or is this something that I should send in to HDPS? I'm pretty handy and would prefer to do the work myself, but I don't want to screw it up and have it cost me more than it would if I would have just had someone else do it.

My biggest concern is the lower reciever. Can I buy an FBI lower, and swap the parts myself (meaning is this tough to do)? I also know that there is some milling on the front hooks of the FBI reciever to fit my USC upper, is this something a normal person can do if they take there time?

I think I'd have the upper vents milled when I have the SBR engraving done, so some parts will need to be shipped out anyway.

Any personal experience is appreciated. Thanks!
 

·
Registered
Joined
·
360 Posts
I think it is something you COULD do, but the question is do you want to.
I had Ed do mine and the fit was so perfect, I couldn't believe it. I know I couldn't have done nearly as good of a job.

By contrast I am trying to do my own G36 conversion and that seems simpler to me.

So I've finally decided to convert my USC to a UMP clone. I will be doing the SBR at the same time. I've sent a few emails to Ed at HDPS, but have only recieved one quick short response back from him.

I'm debating if this is something I can do myself, or is this something that I should send in to HDPS? I'm pretty handy and would prefer to do the work myself, but I don't want to screw it up and have it cost me more than it would if I would have just had someone else do it.

My biggest concern is the lower reciever. Can I buy an FBI lower, and swap the parts myself (meaning is this tough to do)? I also know that there is some milling on the front hooks of the FBI reciever to fit my USC upper, is this something a normal person can do if they take there time?

I think I'd have the upper vents milled when I have the SBR engraving done, so some parts will need to be shipped out anyway.

Any personal experience is appreciated. Thanks!
 

·
Registered
Joined
·
626 Posts
I did my own conversion.

the trigger swap is kind of a pain, but pay attention to how you take it apart and it goes back together pretty easy. if you have a way to prevent springs from flying across the room, use it. make sure you fill the front 'sear' cavity with something that will not let the auto sear be reinstalled. I used jb weld.

I think the trigger group for the g36/sl8 is the same and there are links as to how those go together.

as far as the front hooks of the lower, I used a dremel and went VERY slow. you cant grow back the plastic if you take off too much. there appears to be a seam mark right about as deep as you will need to go. kind of where the bevel ends.

when I opened up my mag well I had a ump mag and tested the fit as I went, again, there is seam marks on the outsides of the mag wells. I probably cut my mag well a little tight, but I have had zero failures and the mags fit nice and tight. the usc mags do fit after opening up the mag well, but if you are going to be using them for a while, i'd hold off on opening up the mag well. the fit is much better.

as far as the dyeing, and vent cuts, I will be sending the rifle out to get that done. im pretty good with a dremel, but I think a mill and a fixture to hold it will be much smoother than I can do. while its out, I will probably have my info engraved as well.

if I can be any more help, let me know.
 

·
Registered
Joined
·
65 Posts
Discussion Starter · #4 ·
Well, I'm in the process of picking up an FBI lower. And I'm thinking I'm going to try to fit the lower myself, as well as swap the parts, fill the cavity, etc....

I need to find a stock and an HDPS stock block.

Then I'm sure I'll just send the upper off to get milled and engraved. I'm too much of a perfectionist to mill the vents in the upper myself, plus I'll need to get it engraved for the SBR anyway.
 

·
Registered
Joined
·
52 Posts
Well, I'm in the process of picking up an FBI lower. And I'm thinking I'm going to try to fit the lower myself, as well as swap the parts, fill the cavity, etc....
fit it myself with a file, shop around to find a file that closely matches the pins, piece of cake. beware of flying springs!
 

·
Premium Member
Joined
·
8,629 Posts
Well, I'm in the process of picking up an FBI lower. And I'm thinking I'm going to try to fit the lower myself, as well as swap the parts, fill the cavity, etc....

I need to find a stock and an HDPS stock block.

Then I'm sure I'll just send the upper off to get milled and engraved. I'm too much of a perfectionist to mill the vents in the upper myself, plus I'll need to get it engraved for the SBR anyway.
Just remember - filling the cavity is really mostly a CYA mod by the pros doing it. That is because even if you were to take a full-auto lower and machined the hooks, bought a stock block, etc., it still would not go together. It will not fit onto the receiver with the full-auto parts in place without cutting the receiver to expose the full-auto trip pin area.

The other reason to fill that area, however, is because the hammer springs push against two small ribs, and you can see that they deflect. It was designed that way, so it's probably not necessary, but I filled mine with black JB weld just to increase the support for those springs.

But you really don't need to go to the trouble of some of the conversions - like drilling an off-axis oversize hole, and plugging it with a solid block and blind pin. Besides, no matter what you were to do to prevent the full-auto parts from being installed, any work could just be un-done and made to work again. Like the semi-auto pack - I could remove the ribs that block that area and drill a hole for the trip lever with nothing more than an x-acto knive and a hand drill.

So as long as you leave the upper receiver alone (except for enlarging the magazine area) it doesn't matter what you do to the lower.

Or you can send it to me. :) I'll do it for $50. I've done 2 so far already. Now if the stupid stock blocks would just come in, I could actually go shoot the thing.
 

·
Registered
Joined
·
53 Posts
Cutting the UMP vents in a USC

Here are a few pictures of the vent job I did myself. I'm a gunsmithing student and I figured it did not look too hard plus I'm pretty good with the Mill. After I deburred the vents (not shown) it cleaned up very nicely and I'm getting ready to die it black.




 

·
Premium Member
Joined
·
8,629 Posts
They do look good. I see you zero'd off the rear rail mount hole. What did you use as coordinates for the start/stop of each of the slots? I'm thinking you didn't just guesstimate, or you wouldn't have used the center finder first, right?
 

·
Registered
Joined
·
53 Posts
Well I think somebody emailed me the actual Hk dimensions. I had to convert them to standard from metric, but if I do any more I will make a trued piece that mounts to the holes just like the rail would, then clamp that in my vice and start cutting. We do have a CNC mill here so I might mess with that and cut it there. I did mine in about an hour because I wanted to go very slow and do everything perfect. I also cut the bottom vent as well and everything turned out really well. I would do anybody elses for $45 and whatever shipping is. I'm not trying to make a profit, but time is money.
 

·
Registered
Joined
·
186 Posts
fatbob,

I will have a lower up for sale in a day or two, so keep an eye out for it. it's a stripped fbi lower with the hooks enlarged already and the auto sear cavity filled and blind pinned.

Scottoe
 

·
Premium Member
Joined
·
8,629 Posts
Well I think somebody emailed me the actual Hk dimensions. I had to convert them to standard from metric, but if I do any more I will make a trued piece that mounts to the holes just like the rail would, then clamp that in my vice and start cutting. We do have a CNC mill here so I might mess with that and cut it there. I did mine in about an hour because I wanted to go very slow and do everything perfect. I also cut the bottom vent as well and everything turned out really well. I would do anybody elses for $45 and whatever shipping is. I'm not trying to make a profit, but time is money.
If you have a squared vise, and make an attachment to use to clamp the receiver in a vise (same thing I'm going to do once my mill gets here next week, BTW), and the coordinates of where the slots begin and end, that could be done very quickly.

It would take more time to set it up on a CNC than it would to finish the job on a manual mill with a DRO. Besides, with a $1500 receiver at stake and not just a block of aluminum or steel you're machining, I'd rather have the control you get with a manual mill than chance an error with a CNC. If something goes awry with a manual mill, you just stop cranking the handle. I've seen full vertical machining center CNCs inexplicably lose their mind and decide to try and plunge to 4" below the table instead of the 4" above they are programmed to do.

Oh, and BTW - you did a really nice job with your slots. As a student machinist/gunsmith, you should be really proud of your work. They look great.
 

·
Registered
Joined
·
14 Posts
Well I think somebody emailed me the actual Hk dimensions. I had to convert them to standard from metric, but if I do any more I will make a trued piece that mounts to the holes just like the rail would, then clamp that in my vice and start cutting. We do have a CNC mill here so I might mess with that and cut it there. I did mine in about an hour because I wanted to go very slow and do everything perfect. I also cut the bottom vent as well and everything turned out really well. I would do anybody elses for $45 and whatever shipping is. I'm not trying to make a profit, but time is money.
Hey were you the one who asked for the dimensions on arfcom, if so I think im the one who got them to ya. Anyways, the slots came out rather nicely. I hope to pick up a usc here soon and doin it too.
 
1 - 14 of 14 Posts
Top