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

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Discussion Starter · #1 · (Edited)
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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What? No AK-XCR lower with ALG (the BEST AK trigger)? 😂 JFYI...I'm joking.
 
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Discussion Starter · #5 ·
I'm out of the 762 game but a 545 ak lower with AR fcg and 1913 would be sweet.
I'm terribly unfamiliar with 5.45x39 but as far as I understand, it uses the same bolt as 7.62x39 but a different magazine? A difference in mag shape would definitely warrant a new lower. It seems relatively niche even for us. I'll see after I refine the process for the AK-XCR, since the design will be similar.

I'm also very interested in an XCR-M lower but figured anything on the L platform would probably happen sooner since you started with the L-1913 lower.
Yeah, I'm attempting to acquire an -M this year but it will have to appear as a target of opportunity; those rifles don't just fall on your lap, frankly. On the other hand, I'm not sure how popular using after market triggers on .308/AR-10 style rifles are. I see some utility but considering the recoil and pressures involved, I figured the default trigger on the -M would be enough. How popular of an idea would this be anyway?

I'm surprised no one is interested in the lower that uses the XCR low-profile trigger, I figured that combo would appeal to the lean rifle crowd. Then again, waiting on RA for parts is a drag and using AR triggers offers the most utility. What brand of AK mag would be most reliable that I can use as the standard template to test off of?
 

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I'm terribly unfamiliar with 5.45x39 but as far as I understand, it uses the same bolt as 7.62x39 but a different magazine? A difference in mag shape would definitely warrant a new lower. It seems relatively niche even for us. I'll see after I refine the process for the AK-XCR, since the design will be similar.



Yeah, I'm attempting to acquire an -M this year but it will have to appear as a target of opportunity; those rifles don't just fall on your lap, frankly. On the other hand, I'm not sure how popular using after market triggers on .308/AR-10 style rifles are. I see some utility but considering the recoil and pressures involved, I figured the default trigger on the -M would be enough. How popular of an idea would this be anyway?

I'm surprised no one is interested in the lower that uses the XCR low-profile trigger, I figured that combo would appeal to the lean rifle crowd. Then again, waiting on RA for parts is a drag and using AR triggers offers the most utility. What brand of AK mag would be most reliable that I can use as the standard template to test off of?
Different bolt too.

AR10s almost all use normal AR triggers.

I'm fine with the XCR trigger...it's not great, not horrible. I think the thought on my end is to try to keep your process as simple as possible. The more changes one makes, the more complexities (and potential for reliability issues) arise.
 
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^^ what he just said, once accuracy is to a point (mine is 2.5 moaish) reliability and ergos are all the matters, we got the ergos for sure.....make sure reliability doesn't take a hit.
 

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I'm terribly unfamiliar with 5.45x39 but as far as I understand, it uses the same bolt as 7.62x39 but a different magazine? A difference in mag shape would definitely warrant a new lower. It seems relatively niche even for us. I'll see after I refine the process for the AK-XCR, since the design will be similar.



Yeah, I'm attempting to acquire an -M this year but it will have to appear as a target of opportunity; those rifles don't just fall on your lap, frankly. On the other hand, I'm not sure how popular using after market triggers on .308/AR-10 style rifles are. I see some utility but considering the recoil and pressures involved, I figured the default trigger on the -M would be enough. How popular of an idea would this be anyway?

I'm surprised no one is interested in the lower that uses the XCR low-profile trigger, I figured that combo would appeal to the lean rifle crowd. Then again, waiting on RA for parts is a drag and using AR triggers offers the most utility. What brand of AK mag would be most reliable that I can use as the standard template to test off of?
5.45 is a different bolt
 

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something else to consider - bren 7.62x39 mags have lrbho, it just needs a slightly larger magwell (about 0.1" in each dimension).
Vz58 mags also have lrbho and rock-and lock. Worth looking at the cmmg mutant latch mechanism. Bolt catch would need to be modified to work with vz mags since the catch is offset
 

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Discussion Starter · #13 ·
No it's a stanag+ size so the mag doesn't have as aggressive of a curve. Should work with the stock lrbho mechanism
I was under the impression that the CZ Bren mags were like AK mags but I see that they have a hole for a mag catch. It looks to me that the lower compatible with Bren mags is gonna be completely different from the lower compatible with AK mags.

Bren magazine, noting mag catch hole and lack of latch on the back:
Sleeve Rectangle Fashion accessory Font Electric blue

Dimensions from AK-47 stamped receiver, specifically the mag well.
Slope Rectangle Line Parallel Font


Am I getting the right magazine you're talking about?
 

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I was under the impression that the CZ Bren mags were like AK mags but I see that they have a hole for a mag catch. It looks to me that the lower compatible with Bren mags is gonna be completely different from the lower compatible with AK mags.

Bren magazine, noting mag catch hole and lack of latch on the back:
View attachment 16039
Dimensions from AK-47 stamped receiver, specifically the mag well.
View attachment 16038

Am I getting the right magazine you're talking about?
Yeah, it would be a COMPLETELY different magwell for an AK mag vs. a Bren.

Yugo/Serbian AK Mags have BHO followers and just about any metal AK mag can take the Weapontech BHO followers. On an AK, they just lock the bolt back on the last round....which just tells you the gun is dry. The minute you remove the mag, the bolt slams forward, so you have to insert the mag and rack the bolt to chamber a round; not as fast for most folks as putting in a fresh mag and hitting the bolt release.
 

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Yeah, it would be a COMPLETELY different magwell for an AK mag vs. a Bren.

Yugo/Serbian AK Mags have BHO followers and just about any metal AK mag can take the Weapontech BHO followers. On an AK, they just lock the bolt back on the last round....which just tells you the gun is dry. The minute you remove the mag, the bolt slams forward, so you have to insert the mag and rack the bolt to chamber a round; not as fast for most folks as putting in a fresh mag and hitting the bolt release.
I wonder if the spring pressure is enough to actuate a modified bolt catch with a nub extended slightly to grab the follower
 

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Discussion Starter · #17 · (Edited)
Yeah, it would be a COMPLETELY different magwell for an AK mag vs. a Bren.

Yugo/Serbian AK Mags have BHO followers and just about any metal AK mag can take the Weapontech BHO followers. On an AK, they just lock the bolt back on the last round....which just tells you the gun is dry. The minute you remove the mag, the bolt slams forward, so you have to insert the mag and rack the bolt to chamber a round; not as fast for most folks as putting in a fresh mag and hitting the bolt release.
I better update the poll then. The Bren 2 7.62 mag is interesting because I have most of the design data anyway and the Bren 2 mag allows for the presence of the XCR BHO and mag release. The issue that I see for the community is would customers be able to obtain those Bren mags to feed this platform? What would most people rather use, the Bren 2 mag or AK mags?

Worth looking at the cmmg mutant latch mechanism. Bolt catch would need to be modified to work with vz mags since the catch is offset


I'm glad you brought up the CMMG Mutant/Resolute. That lower is basically what I plan to do with the AK-XCR; in fact I might be able to buy and use that mag latch that CMMG uses. That would really simplify things and would feel really comfortable!
 

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Just my 2 cents, the bren mags would be a lateral move and not offer any distinct advantage over the existing stanag x39 magazines, I'm doubling down on my ak mag vote, for the mass availability. Also I like the price point of ak mags much more. $30 mags was a lot of what I didnt like about the existing Robinson x39, I don't think another expensive and hard to find magazine is the right solution (atleast for me), unless one already has a bren2 and is already invested into their magazines.
 

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Just my 2 cents, the bren mags would be a lateral move and not offer any distinct advantage over the existing stanag x39 magazines, I'm doubling down on my ak mag vote, for the mass availability. Also I like the price point of ak mags much more. $30 mags was a lot of what I didnt like about the existing Robinson x39, I don't think another expensive and hard to find magazine is the right solution (atleast for me), unless one already has a bren2 and is already invested into their magazines.
Agreed. An AK mag is the draw. It's a completely reliable, inexpensive and ubiquitous solution to the problem of feeding tapered Russian ammo.
 
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