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Which Lower Reciever would you be interested in seeing built this year?

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Poll for the next XCR Lower project!

3436 Views 66 Replies 8 Participants Last post by  Chowwow, 
Chowwow
New year, new start on a fresh, challenging projects!

Work on the AR-XCR lower is drawing down in terms of CAD work, though the transition to CNC machining will require it's own steps. In the mean time, I believe it is time to move forward with the lessons and tools we've gained over the last year of work and produce a new lower for the XCR family. After some thinking, I've compiled a list of possible projects that I can move forward with, and I would like to know which of these ideas have popular support so that I may focus my efforts on a specific project. Here are detailed descriptions of the projects with pros and cons to each one:

AK-XCR with XCR TriggerAn offshoot of last year's Picatinny-XCR lower using factory-standard AK magazines. This will be a CNC machined lower featuring a rear 1913 rail for stocks, the original XCR trigger group, and a low profile magwell and mag latch for the AK magazine.
  • + Low profile and light design
  • + AK magwell specifications are publicly known
  • - Requires designing proprietary mag latch; one that is longer and in a different position than the standard mag latch used in the AK. Will require trial and error.
  • - No BHO unless Yugo mags somehow work.
  • - Must purchase standard AK mag to ensure compatibility.
  • - I do not personally own 7.62x39 barrel conversion. However, I do own a 6.5 Grendel barrel conversion, which uses the same bolt and enough 6.5 Grendel rounds can be loaded into an AK mag ensure function.
AK-XCR with AR-15 TriggerA variant of the AR-XCR lower that uses AK mags. This will be a CNC machined lower featuring a rear 1913 rail for stocks, the expanded body for an AR-15 trigger group, and the AK magwell and mag latch.
  • + Uses AR-15 triggers! No longer dependent on RA for triggers
  • - No BHO
  • - Requires designing a unique mag latch that is different from the one used in the previous proposed design. It must be longer to accommodate the extra height imposed by the AR trigger group. Position of pivot pin will be different too.
Swappable Magwell XCR lower with AR-15 TriggerA variant of the AR-XCR lower that has all of its features as well as being able to swap out the magwell of the lower from a module that accepts AR mags and contains the BHO, to one that accepts AK mags and contains the mag latch.
  • + Feature rich, one and done solution
  • - Complex, and requires careful machining
  • - Development of this system basically involves developing an AK-XCR w/ AR FCG anyway, with further development on the magwell swap feature added at the end. Might be worth holding back development until other designs are proven.
AR-XCR-MEverything that I've done for the XCR-L, but with the lower for the -M. It will be a CNC machined aluminum lower fitted for the XCR-M that accepts LR-308/SR-25 magazines, a rear 1913 rail and an expanded body for the AR-10/AR-15 trigger group.
  • + Added features for the -M, mainly the option to use your own dang trigger for your -M
  • + Expected design will be similar to the AR-XCR(-L), just with the expanded magwell
  • - Not sure if expanded trigger options are necessary for the -M
  • - Might need to design a new BHO
  • - I do not own an XCR-M (yet), and I need to acquire one and go through the same process as I did on the AR-XCR to ensure the function of the design
Bren-XCR with AR-15 TriggerA variant of the AR-XCR lower that uses 7.62x39 CZ Bren 2 mags. This will be a CNC machined lower featuring a rear 1913 rail for stocks, the expanded body for an AR-15 trigger group, and a magwell accepting the Bren 2 mags.
  • + Design (potentially) will be very similar to AR-XCR and can be made relatively quickly
  • + Similar ergos and functions of AR-XCR
  • - Requires extended BHO (hopefully the same one used in the AR-XCR and AR-XCR-M)
  • - May require longer Mag catch (maybe the one on the XCR-M?)
  • - User becomes reliant on CZ to release these magazines in his country. Will be incompatible with AK and STANAG mags.


This thread will be edited to become the build log for the winner of the poll. As it was in the last thread, I expect to have major CAD work done by the summer, and something built in metal by the winter. Your opinions are welcome!
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Chowwow
Sean K. said:
On the up side....a steel one can be physically smaller and still stronger than an aluminum one.
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What's your opinion on the trigger hole dilemma? If I use the CMMG part, people can go to them for more mag releases if I disappear off the face of the Earth, but the trigger hole will be smaller. Though, looking at the pictures of the MK47, it doesn't look that bad. If I make a custom part, you'd have to rely on me to get these parts out to people, and I may end up with a small inventory of exclusive parts stashed away in my shop but the trigger hole will be unaffected.

Air gun Trigger Gun barrel Gun accessory


I believe the AK-XCR w/ XCR FCG is small enough for a regular AK mag release, but it would only work on that design and AK mag releases can come in all sorts designs and tolerances; I'd never be able to verify that all of them would work. If someone has another idea on the mag release, I'm all ears.
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Sean K.
Chowwow said:
What's your opinion on the trigger hole dilemma? If I use the CMMG part, people can go to them for more mag releases if I disappear off the face of the Earth, but the trigger hole will be smaller. Though, looking at the pictures of the MK47, it doesn't look that bad. If I make a custom part, you'd have to rely on me to get these parts out to people, and I may end up with a small inventory of exclusive parts stashed away in my shop but the trigger hole will be unaffected.

View attachment 16176

I believe the AK-XCR w/ XCR FCG is small enough for a regular AK mag release, but it would only work on that design and AK mag releases can come in all sorts designs and tolerances; I'd never be able to verify that all of them would work. If someone has another idea on the mag release, I'm all ears.
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Meh, there's no guarantee CMMG will continue to make the AK mag releases, so I'm not sure anyone can bank on that.
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Chowwow
Sean K. said:
Meh, there's no guarantee CMMG will continue to make the AK mag releases, so I'm not sure anyone can bank on that.
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It looks like I'm building my own mag release either way, since the CMMG release is unsuited for steel mags long term anyway. I was hoping that making a steel version of the CMMG release would also appeal to MK47 users who were interested in using steel mags in their rifles, albeit with lack of steel inserts. I may just use the CMMG design as a reference for a thinner release specific for the AK-XCR; it may be the only option unless there is no opposition to reducing the trigger guard size.

In other news, initial observations with the -M have showed me that the design of the lower is significantly different from the -L; pretty much only the area between the pistol grip to the end of the BHO arm are the same; everything else is stretched to house the longer upper and magazine. In terms of CAD; there is some carry over but I have to go back to my reverse-engineering process to fill in the new dimensions of the -M lower; much more involved than the AK-XCR. Which means concentrating on the -M lower project is going to take place on the later half of this year to beginning of the next, depending on how soon I can get the AK-XCR working.
Product Engineering Machine Gun barrel Trigger



Speaking of which, I'm probably going to split off the build log of the AK-XCR into its own thread, because I need to set up a new poll concerning preferences for the mag release for it. I'll convert this thread back into a general XCR lower project announcement thread, as the poll is still relevant to gauging interest in what needs to be done for the next cycle.

Here is the mag release poll on Reddit. Vote there if you can!
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Chowwow
While I'm waiting for things to happen, I thought why not do some research?

Reap Weaponries released a lower that turns an AR-15 upper into a bullpup. The result is hideous, but that's one idea that I once considered and shot down that has come to fruition somewhere else.
Air gun Wood Trigger Machine gun Gun barrel


I wanted to know what everyone thought about making the XCR into a bullpup rifle? Because it's a bufferless, piston rifle, I believe the upper was a great candidate for being made into a bullpup rifle. Below are mockups made by mr_staypuft on the Bullpup Forum before it went down:


Air gun Machine gun Trigger Line Gun barrel


Something like this would be something to be realized some other year, but it was something that I was excited about getting into once I got a few things done. What's the enthusiasm for a project like this?
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Sean K.
That doesn't look horrible (though you wouldn't be milling the top rail off for a cheek weld. At best, you'd put a rubbery rail cover over those slots).....I bet the 16" will be the hot seller. I wouldn't pay to SBR the shorter ones personally. Well....and now that I look closer....that's not simply an upper swap to a bullpup lower. The ejection port is moved substantially back from the handguard....but I get that it's just a visual representation and photochop of what it would sort of look like.
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T
.....I don't hate it....
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Chowwow
Sean K. said:
That doesn't look horrible (though you wouldn't be milling the top rail off for a cheek weld. At best, you'd put a rubbery rail cover over those slots).....I bet the 16" will be the hot seller. I wouldn't pay to SBR the shorter ones personally. Well....and now that I look closer....that's not simply an upper swap to a bullpup lower. The ejection port is moved substantially back from the handguard....but I get that it's just a visual representation and photochop of what it would sort of look like.
Click to expand...
Yeah, there are certain design considerations to be made, such as making a cheek weld over a significant section of the top rail, and making sure there is clearance for the charging handle and ejection port. My primary concern so far has been the trigger system, I've been doing research off and on regarding the best designs that would work for the XCR. Because the rifle wasn't initially designed to be a bullpup, it's going to look a bit like how the CZ Scorpion bullpup looks like.



Again, this is a distant project but something worth looking into from time to time.
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