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Discussion Starter · #1 · (Edited)
**** SOLD OUT ****

All adapter spoken for, 2 pending payments.

I'm having a local machine shop design and produce a run of adapters to interface a Bushmaster ACR stock with the USC upper and UMP lower. This will reduce the LoP by design and the ACR stock is adjustable to clear the trigger area when folded.

Price is ***UPDATE*** $155 including retaining pin and shipping, they will be hard coat annodized, 6065 aluminum construction, 4-axis CNC produced. Designing is complete, 3-D prototyping finished, and the aluminum prototype will be here by Feb 8th, production to start the Monday after Valentine's Day, done by the end of the 3rd week of February, shipping by the end of the month.

Since the Stock block B is $160+Shipping plus the $100 to have Tom do a fuse conversion plus a $125 donor HK stock, this is less than that by a good amount INCLUDING buying the Bushmaster ACR stock ($156.95 from Bushmaster), and you don't feel bad about chopping a perfectly good HK stock.









Now accepting discreet gift Paypal payments to [email protected] or you can PM me for my address to send a check.

Please post here and send me a PM. Thanks

Edit: List of everyone who wants one:

1. Myself
2. Phaedrus - PAID IN FULL
3. jsbsmarine - PAID IN FULL
4. Mr.Maim - PAID IN FULL
5. kobra - PAID IN FULL
6. BLFuller - DESIGNER - Cannot thank you enough for helping us do this!
7. Sigma05 - PAID IN FULL
8. Plinker72 - PAID IN FULL
9. MichaelHK - PAID IN FULL
10. Warpdrv - PAID IN FULL
11. M198Gunner - PAID IN FULL
12. Shockwave - PAID IN FULL
13. USMC-F4 - PAID IN FULL
14. SP3 - PAID IN FULL
15, 16. JT15550 (for 2) - PAID IN FULL
17. diezel - PAID IN FULL
18. Lohe - PAID IN FULL
19. Chuckanut - PAID IN FULL
20. Corbin Dallas (in for 2, see below) - BOTH PAID IN FULL
21. Thompsoz, in for 2 now - BOTH PAID IN FULL
22. MS1210 - PAID IN FULL
23. Rudedog - PAID IN FULL
24. Mine4 - PAID IN FULL
25. rtse4me - PAID IN FULL
26. 713HoustonTX - Withdrawn
27. Renegade - PAID IN FULL
28. unrequited - PAID IN FULL
29. LaTex - PAID IN FULL
30. Ruckus43082 - PAID IN FULL
31. Victorr - PAID IN FULL
32. Outta_bubblegum - PAID IN FULL *** Added a 2nd Adapter, also PAID IN FULL ***
33. Benthell - PAID IN FULL
34. kxf327 - PAID IN FULL
35. dashpilot79 - PAID IN FULL
36, 37. FlyByNt ** (Reduced to one adapter) -1 from total at bottom. - PAID IN FULL
38. Frogman342 - PAID IN FULL
39. Doug_262 - PAID IN FULL
40. Corbin Dallas in for a 2nd one. - PAID IN FULL
41. JohnnyCat - PAID IN FULL
42. Lowrybuc - PAID IN FULL
43. Jdyer - PAID IN FULL
44. JohnGA - PAID IN FULL
45. demondiver - PAID IN FULL
46. ptoguy - PAID IN FULL
47. Tommeh - PAID IN FULL
48, 49. DeepSnow (2) - PAID IN FULL
50. 65FSVBK - PAID IN FULL
51, 52. OneQBall66 (2) - PAID IN FULL
53. LCPL4ever - PAID IN FULL
54. Barrett - PAID IN FULL
55. Anklebiter - in for 2 - PAID IN FULL
56. LCSO264 - PAID IN FUL
57. DUMA13 - PAID IN FULL
58. Tat2Vinnie - PAID IN FULL

UPDATE 02-17-2015 @ 2300 CDT

60 total adapters committed to, 59 paid for, 1 payments pending (note to cross-check with screen names), 60 will be ordered.

*** SOLD OUT ***

This run was done at cost plus $7-ish bucks including shipping and tracking just to cover my time to organize and ship everything. I'm not in this for a business, so the next batch will take 30 people minimum to make another run and will be priced at $195 shipped to make it worth doing, plus I'll need to become a vendor/sponsor for HKPro, etc. Those of you who got in on this, congratulations! They're going to be awesome!
 

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What would the time frame be? I like the ACR stock a lot! Right now I only have the USC, haven't done the UMP conversion, but I'm interested. Do you know by chance if the ACR stock is US made? Would it matter for 922r?

It does sound like a robust way to attach a better stock!
 

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Need picture to imagine this. I'm highly interested but my imagination needs inspiration. Is it folding left or right?
That's what I'm thinking. It would be cool to see a tech drawing, even a sketch on a cocktail napkin! But I'm still really interested.
 

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Tom Bostic does this type of conversion to USC's that have already had a UMP rear fuse/weld job done or use a HDPS block B as the op noted. Tom's ACR stock conversion itself is also a plastic fuse/weld job requiring and ACR stock and a donor UMP stock that is used as donor for its front button assembly, hinge, and pin. There are pics of this on Tom's page here: UMP conversions

It sounds to me like the op is saying is that the adapter he is proposing is another option for USC owners that want to use a stock block with and ACR stock so that there is no need for a donor UMP stock and that the ACR stock can be used and will attach to the stock block as is without modification .
 

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I believe Tom Bostic does this type of conversion to USC's that have have a UMP rear fuse/weld job done. The stock conversion itself is also a plastic fuse/weld job requiring and ACR stock and a donor UMP stock that is used as donor for its front button assembly, hinge, and pin. There are pics of this on Tom's page here: UMP conversions

It sounds to me like the op is saying is that the adapter he is proposing is another option for USC owners that want to use a stock block with and ACR stock so that there is no need for a donor UMP stock and that the ACR stock can be used and will attach to the stock block as is without modification .
That's what I got from this. It looks like it will basically be a Stock Block B but with a receptor for the ACR stock instead of the standard UMP stock.
 

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It sounds to me like the op is saying is that the adapter he is proposing is another option for USC owners that want to use a stock block with and ACR stock so that there is no need for a donor UMP stock and that the ACR stock can be used and will attach to the stock block as is without modification .
That's what I took it to mean, too. The more I think about it the more excited I am. Less surgery on my USC, a smidge less expensive and a much better result. I realize Mr. Bostic does amazing work but I'd rather have an ACR stock than use the HDPS block and wind up with the real UMP stock. It would look more "correct" but I only care how it handles and shoots.
 

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I may be in for something like this.

Especially if I can just unbolt my current block and bolt this in.

It may give me a reason to build another UMP. Gotta watch out for those spare parts growing into another spare rifle.
 

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Discussion Starter · #10 ·
It sounds to me like the op is saying is that the adapter he is proposing is another option for USC owners that want to use a stock block with and ACR stock so that there is no need for a donor UMP stock and that the ACR stock can be used and will attach to the stock block as is without modification .
Yes, that's it exactly.

Here's a picture of what it looks like when Tom Bostic does his plastic weld job with the ACR stock on the UMP.



You can see that the original HK UMP folding stock has been cut just behind the hinge and locking mechanism, then a section of fused plastic is added to meld the ACR stock to that HK hinge assembly. Tommy's work is excellent, there's NO doubt about that, but I was looking at the whole thing with the added Length of Pull necessary in melding those two parts together, plus the destruction of a perfectly good UMP stock to do it, and was thinking "I hate ruining good parts, there's got to be a better way to do it".

Hera put together a similar setup for the original USC here:

Hera Arms

The downside to that is that they were $600 bucks or so and didn't include the stock, and you can't ever find them, plus it's not for the UMP, just for the USC.

So I thought, "Why can't we do that for the UMP?" Turns out we can, just takes someone to program the CAD file for the machinist, then the machine shop to crank them out, deburr them, cerakote or anodize them, then ship them out. The initial CAD program setup isn't cheap, but if you wanted cheap you would buy an AR. I kid... sort of. :D

The ACR stock comes complete with its hinge piece, which is what we're using for specs on the rear hinge area. Here's the ACR stock, they're about 4-6 weeks back ordered at the moment (scroll down the page, 5th one down, folding/telescoping stock - $160):

ACR Accessories

So in essence, I wanted this to be a similar price as if you went with the original HK stock. HDPS charges $160 plus shipping I think currently for their stock block, I'm looking at $170 plus shipping for the UMP ACR stock block. We're probably going to thread it instead of having a pin, using your original USC screws for a secure lock up, plus the ACR stock has a built-in sling attachment piece on the left side.

Then purchase an ACR stock for $160 instead of a HK UMP original stock for $125-135 directly from Magpul.

For those who want the ACR, saves them close to $100 bucks with a closer to original UMP LoP, and gives an alternative to the original HK stock for those who might just want something different.

JSBMarine, it folds to the right. Comes like that from Magpul, can't change that.

Hopefully the images give people an idea of what it would look like, with the ACR lockup hinge and release instead of the HK shown in Tom's conversion pics.

Phaedrus, we're looking at 3 weeks to have the final CAD program, 2 weeks to do initial programming, then he'll render it on a 3D plastic printer to make sure everything bolts up and lines up properly, make any changes over the next week, then final 3D rendering prototype, then it goes to the machine shop.

The Machine shop is telling me 3-4 weeks for production and deburring. Cerakoting will take another 7-10 days. Give it another week or two fudge factor, realistically 4th of July to have the CAD program and plastic prototype, then get enough people on here to get manufacturing costs down (they're $320 a piece to run any fewer than 10, goes down dramatically when you can run 40-50 or more), then 2 months to run, deburr, cerakote, and send out.
 

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Hmm, so the ACR stock will allow adjustable LOP and adjustable cheek height correct? And at the shortest, it is smaller than the factory UMP? If so, I'll take one. I was about to pony up for the B&T short stock because the HDPS block B with a UMP stock is just too damn long. I can always dig a shorter LOP, and adjustment is always nice.

No problems with folding to the right. Just PLEASE ensure the gun can fire with the stock folded. Hate it when it blocks the ejection port. PM sent and thanks for taking up the cause on this.
 

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Sounds good! I'm in so long as we get enough people to make it affordable.
 

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Discussion Starter · #13 ·
jsbsmarine, yes, adjustable cheek height and LoP.

The gun can fire with the stock folded as long as it is in its shortest position. The amount the block sticks out is critical, because when it's in the perfect position, the stock is in the perfect position to where you can get your finger easily into the trigger guard area, and the rubber butt pad is just a CM over the REAR of the ejection port, which is still plenty of room for the spent shell casing to eject.

So we have three of us and counting.... :) I'll edit the post on Page 1 with screen names as we go so people can keep track.
 

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Sounds great. I look forward getting underway.
 

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Moving this one to group buys.
 

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Maybe you should have them machine a trigger while they're at it. ;-)
 

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I would be interested in a adjustable ACR folding stock on my HK UMP/USC. Pm Sent.
 

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Discussion Starter · #19 ·
I would be interested in one as well assuming everything goes as planned and pricing is right. Thanks.
I'll put your name on the list at the price I'm currently thinking we can get them produced for. If it goes up because we don't get our 40 people, I'll have to check with everyone anyway on pricing. If we get our 40, we're good at that price.

Thanks!
 

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Maybe things aren't "done this way", and I apologize if this is ignorant or out of line, but is there any chance that HKParts or some of the other HK-mod guys would want to get in on this? Might be worth asking. Again, if it's a stupid idea please ignore...:380:
 
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