Anyone built a semi MG3? Recouperator question

[Der Alder]

I'm working on a semi-auto MG3/M53 hybrid clone. I'm using an Apex M53 kit as a base – (M53 shroud and a few small parts), combining them with as many MG3 parts as possible from RTG. Basically I'm trying to make an semi MG3 clone or as close to one as I can get being that complete MG3 kits are not available.

The MG3 rear receiver stub section that I'm using from RTG has the provisions for the longer MG3 recoup tail (I'm using a MG3 buffer as well). I'll have to cut the tab off the M53 grip hanger (the part that supports the rear of the M53 recoup).

Is it safe to assume that I will not need the rear part on the M53 grip hanger that curves up into the receiver then and can cut it off just behind tripod stud mounts? (I haven't seen a MG3 grip hanger so I'm not sure how they are set up).

I’m aware of the differences in the MG3 vs M53 recouperators; MG3 having a longer tail, extra spring and thus stiffer spring rate.

That said, does anyone know if using a MG3 recouperator in a semi build will give me problems due to the increased spring rate? I know in a full auto it would not matter, but I do know that the semi conversions with the weaker, shorter recoil springs and added drag of the semi hammer and such operate on the edge of functionality and I'm just concerned that the MG3 recoup might be an issue.

Comparing both recouperator types, pushing on each I can feel a significant difference in spring rate between the two types (MG3 is much stiffer). Is this additional spring rate going to effect a semi build? Or would I be better off sticking with the M53 recoup (something we know works)?

Thing is, being I'll have to cut the M53 grip hanger support, it would be very difficult to go back to the M53 recoup later if the need be, but on the other hand if the MG3 type works ok in a semi-auto using one might be a nice upgrade, at least for this build. Thoughts? Has anyone built a semi MG3 or used a recoup from one?

[marknct]

Just throwing it out there, I don't know. I don't think the recoup would be a problem with the semi because it's a function of the booster nozzle sizing? That is done and over by the time the semi issues pop up.
Looking at the 2 I think you have to commit to the mg3 during the build. At first I thought about replacing the 2 rivets with button heads to hold a spacer in for the m53 recoup. The problem is the swing space that the buffer needs to install leaves you with no space. Probably a no go, it gets whacked every time.
The mg3 recoup I saw from RTG had a pretty good bend in the tube. I would make sure I had a proper functioning one or two before committing. That one had less spring pressure than a new-ish m53.

[Der Alder]

Yeah I thought about that after I posted this. Going through the manual I see the bolt is unlocked and on its way back before the recuperator kicks back (recoil gases) so *hopefully* the added recup spring rate will have no impact. Thing is these semi builds can be so fussy that I have to admit I’m a bit skittish going outside the normal realm with this MG3 clone build. Fact is I just won’t know for sure till I test it. Evidently no one else has tried this in a semi build as of yet. So I’ll be the test dummy .

As far as the bend in the RTG recup, mine has a small crimp in the front window hole (looks like maybe an armorer mod?) so that the plunger does not pop out when the front threaded part that goes into the receiver is removed. Doesn’t seem to impair the function and like I mentioned it seems about 50% stiffer than my M53 recoups due to the added spring length for the .308 round. Maybe the one you tested was well worn because they should be stiffer than an 8mm recup.

So far as buffer clearance, its not an issue for me being that I cut the rear section off and welded on an MG3 stub and I’m using and MG3 buffer as well. I also cut off the rear part of the grip mount tail that goes up into the receiver as that will no longer be needed since the MG3 rear has the recuperator support build into its buffer tab.

I did the final receiver welding making it one piece finally this past weekend. *So far so good.* The specs all look good, looks straight and the recup has plenty of spring rate on the “pogo test” and the barrel door opens and closes well with a barrel installed - though it is noticeably stiffer closing than on my semi M53, course that should be expected on an MG3.

I still need to do the cuts on the bottom, mount the grip hanger and install the rails. Probably will get in done within the next month or so (I’m slow..lol). I’m doing the milling by hand with a dremel. I plan to do a detailed build write up with lots of pics here and on the Weapons Guild site being that both sites have been a great help to me.

Here’s a few pics on the MG3 recuperator and a couple build pics so far.

[roadrunner]

Right on Der Alder! You got me itching to start my really similar build. My mg3 recoup. has the same crimp in front to keep the springs from spewing out when L bolt is removed. Like the laser alignment idea. Super nice work. Wally

[Der Alder]

Thanks RoadRunner
It was guys like you, Oak, Flem and others that inspired me take on this build. Without you all I would have never attempted it.

The laser alignment was something I thought I'd try being that I already had this inexpenive magnetic laser sighting tool. I just drew a "target" tracing from around the receiver, marked the center and aligned the receiver parts this way.

i used it when setting the lenths, squaring and aligning the receiver peices hitting them a little at a time on the belt sander until i got to where a few touches with a file would "target" them. I used it on the mid section-to-shroud alignment as well:


I figure when I get to the rails maybe I can remove the FP from the bolt and point it from the buffer through to the barrels end. I figure it should be as good as string with less hassle.

[42rocker]

Der Alder
Interesting with the redo dot idea. I've seen it used before on other projects that need to be straight. Hope to see more pics on this.

Later 42rocker