I have a RDIAS in NFA Jail and I'm looking at getting my host ready.  I have several ARs and plan to just set up one dedicated host for the DIAS and leave it in there.

The Windham MCS Rifle caught my attention due to the modular magazine well and quick change barrel system.  With this setup I would only have to set up one receiver for the DIAS and have multiple configuration/caliber options.  The problem is I have only seen the MCS online and have not actually handled one.  I have no idea if it has a high shelf or low shelf etc.

Has anyone tried to install a DIAS in the MCS Rifle?  If so what problems did you run into?

Is there another modular mag well lower receiver out there that would work better?

MGI has a modular system.. maybe it’s the same as the MCS..

The colt 901 is a bit modular as well.. not as much as the MCS but you can switch between 308 & 556 and similar caliber like 300blk etc.

mgi sold the rights to wihndam as they don't make them anymore

OP as a dias owner I would pass on the modular lower and just get dedicated lowers since they are so cheap right now.

I would also pass on the 762x39 with ak mags. you will have to mod the mags/and or chamber area. that only leaves you with a 9mm or 45 setup. Not worth the cost IMO

The MGI Hydra and Windham MCS appear to be the same rifle.  MGI however, has more caliber options and actually sells the barrel assemblies separately.

OP, what TaylorWSO said, keep a dedicated lower. Just make dedicated uppers for your different caliber/ length barrels, I don't shoot 9mm FA and cannot imagine anyone would be shooting 300 BO FA, $$$$. Presently, I am shooting 2 5.56 uppers, 14.5" mid length gas and 20" A2 clone rifle length. I have have used 4 different brand lowers over 29 years, my present one an Aero Precision (SP1 spec low shelf) with carbine receiver extension, Tubb spring and tune with H1,2,3 buffers depending on ammo. Not all low shelf lowers are milled to the Colt SP1 configuration which the DIAS was designed for, although it may work in non SP1 spec' low shelves.  See Armory>M16 forum for DIAS compatible lowers, the "*" marked ones are ones that I have used. Presently building a Colt 14.5" SOCOM upper to replace my BCM Gov' upper. Also start with an "other" stripped lower to build as a pistol 1st.

Get a high quality lower and call it a day.  I wouldn't mess with any of that other junk.

Can't you mill out any high-shelf lower to a low-shelf w/ a jig & a router?

The MGI system is fascinating, but you can build complete ARs for the price of parts.

Topic Moved

Of course - or with a mill and just using the verniers or eyeballing it. The RDIAS indexes off the takedown pin post, so just needs clearance for it to physically fit - the shape and exact dimensions of the pocket in the lower are not particularly important to its function.

I've been running the MGI modular lower setup since they first came out around 2003 or 2004 or so.
I have a circle of friends over the years with RDIAS' or RLL's that all use the MGI lowers.
Below are some of my setups:


I leave a Geissele SSF trigger in the lower and rarely move it.
I've never been a fan of the quick change upper though.  I don't think it holds zero and there are no windage adjustable front sights when switching  barrels.

The issue is that I don't think MGI makes anything and availability is spotty.  A lot of potential though. I would agree that today for just having the AK and 556 magwells available, it isn't worth it.
I would like to get some magwells 3D printed.

I also know the Windham magwells work with the MGI back half.

Damn. I'd really like to have an AK upper for my RLL but I've been advised against lol. Maybe down the line or something...or I'll just get an AK

Why not?...I would advise to do it.  
I think the AR platform is smoother and more controllable than an AK is in 7.62x39
75 round 7.62x39 AK drum and RDIAS

so whats the lower I'd need? MGI or MCS? I was skimming the above...still multitasking at work. Looks like MCS only comes with full rifle option?

As mentioned before since I'm a RDIAS owner, I don't like moving my fire control all over the place and pretty much leave a Geissele SSF in my MGI modular lower.
Since you have a LL, maybe you just want FA only and don't care about select fire?  If that is the case and you want to go cheap then maybe go for the PSA KS47.
They are out of stock now but PSA announced that they are coming back next month: https://www.ar15.com/forums/Industry/KS47-update/301-288527/
You can get a complete setup from them or just get the KS47 upper from them.  Note that they also sell 'AR47' parts which do NOT take unmodified AK drums/mags, you need to make sure you get the KS47 'Hybrid' upper and BCG since both are clearanced to take unmodified AK mags/drums.  
Of course you would need to get the carrier clearanced for your LL.

If you want to go the modular route, I'd get just the MGI lower back half for $99 direct: https://www.mgi-military.com/store/index.php?product_id=80&type=&category=20
Doesn't look like you can add to cart or anything and I have no idea about availability.  It's been a long time since I've bought anything from them.


Then just get the AK magwell from Windham for $125: https://shop.windhamweaponry.com/collections/mcs-multi-caliber-system


The Windham AK magwell has more clearance than the MGI AK magwell.  I had to grind on my MGI magwell to work with Bulgarian AK waffle mags.  Doubt you'd have to do that on the Windham.

Thanks! I have a burst kit for select fire in the lower it is currently being tuned to. I'd probably go with modular just to have all the options. Price on that isn't bad if I can find it available. Thanks!!