I've done some archive searches and there is plenty of talk about desertordinance's semi auto m249's but nothing about someone actually building one on their own.

So I have been looking into buying a parts kit, and making a receiver. I know that the M240/MAG 58 part kits come with all parts except the receiver plate, which is only one side of the receiver.
I've never actually handled one of these in real life, but aren't the receivers just stampings that are riveted together? I know the tolerances must be pretty tight, but would it be that hard? Does anyone know what the BATF says about making these things compliant? I know it can't fire from a open bolt, which would probably be the hardest part of the conversion. And I would need some US made compliance parts too.

I have looked all over the Internet and haven't found much good information. Which strikes me as odd, since there are a bunch of pages that show how to convert an SL8 to a G36, or USC to UMP...

I am leaning towards the MAG 58 since I will only need to make the receiver plate which sounds like it would be easier. I have a decent set of tools, MIG, TIG Plasma, Drill press, ban saw, etc. I don't have a milling machine or a lathe though.

I would really appreciate it if you guys could lend me some of your input and tell me if this is even feasible. Especially, since these kits are sold for at least 3500$
I am also looking at an RPD but I would rather have the FN.

Thanks in advance,
Zack

if the MAG58 is anything like a 1919 internally (which I believe it is), you will most definitely need a mill.

Especially if you're trying to make a side plate from scratch.

Ohio Ordnance has their M240 SLR which fires from a closed bolt.  They don't list a side plate available separately.  I know you can get their 1919a4 side plates, maybe it wouldn't hurt to ask them?

Yeah I know, every time I email them they just send me a price quote. I will have to call them this week. That would make this a lot easier, however I doubt they will sell their side plate cheap, cause their M240 costs 13.5K. But who knows?




That's not good to hear... I guess the internal surface of the side plates are chrome lined too.

They are open bolt weapons - the amount of modifications required to make one semi-auto is pretty significant.

Despite some of the 'appearance similarities' between the 1919 and the '58, they are two totally different beasts... NO, the 19i19 rec will NOT work on a 240/58. The 240 has a rotating bolt and fires from the open bolt position.

Significant machining will be required...



And the 249? It's a stamped-reciever gun (think AK), so good luck...

youd be better off building a semi auto m60 or one of the many varients the shorty m60e3 has always caught my eye , the semi auto parts are out there

I have a US ORD semi M60.

From what I can tell, this is what was done to it to make it compliant.

1 - Pistol grip has been moved from its original location, .5" rearward.  (even if a full auto op rod would fit, the engagement couldn't occur)

2 - a plate has been welded to the bottom of the receiver to cover the original hole location,  and also to prevent a full auto op rod from fitting.

3 - op rod has had the engagement surfaces sheared completely off.  A F/A op rod can't fit in the gun at all.

4 - The rear of the bolt has been modified into a striker assembly instead of the standard spring cap.  It's as wide as the rails and rides them.

5 - a little bar comes up alongside the pistol grip into the receiver channel, and proceeds through a slot on the rails.  This has a notch in it, which engages on the striker mechanism to trip it.   This is how the gun is fired.  The hook pulls down when the trigger is actuated, and it causes the striker to release against the firing pin.  

I don't know how adaptable this is to the 240/58, but perhaps some of the compliance measures make sense for starters.

The gun costs that much not because of the side plate or labor, but principally because of the high excise taxes they have to pay.  Almost $1500 of it.

They wouldn't have to pay very much on a side plate and semi parts though  

––Fargo007

You also have to consider the fact that it has to built so that it can't be turned back into a NFA gun.

So consider what you would have to do just to get it to fire from a closed bolt, in semi auto only.  Then figure out how to keep someone from just dropping the orginal parts back in.

Thats one reason the side plate of the 1919 is thicker, and the internals need to be modified.

You'll need a milling machine.  And some skill to go along with it.  The reason you need a mill with the 1919 kit is that the parts are hard as f**k (55+RC is I remember correctly).  You'll wear out a 1000 files before you make a mark on some of the parts.

Also remember that if you do take on the project, and when you send it off to the ATF to get their approval, and it doesn't comply for any reason, it WILL NOT be returned, as it is contraband then.

Good luck

Yeah, thanks for all the input guys. I think I bit off more than I can chew with this one. It was a fun idea, but I don't know if I have the time or energy to do all that. I can dream though. I wish someone would market a belt fed upper for the AR(Ares...). I am also a little leery about dropping that kind of coin and then having the ATF say it's not compliant and confiscating it, or throwing me in the slammer.

So now my plan is to win the lotto, and buy a real M240G
Wish me luck

Edit:spelling

Well building your own MAG-58 (M240) would be a true pain in the ass.

You need to know and understand all the processes that are involved have access to mills/cnc/ ect.. (way more then one) you need the ability to heat treat, punch rivets; have the different prints with specs/tolerances and well the list list is long.
The receiver plates have to be machined to match the front block. The side plates need to have the locking shoulders. They are matched down to the micron during assembly. Holes (lots of them) need to be drilled with the proper fixtures. The rear sight, bottom plate and the two sides are riveted, the mount bushing installed/cut and then the rear end is milled for the slot to install the stock.
The gas tube is next. It has to be measued/cut installed/pinned and then proffed.
Don't forget surface treatments and all the small stuff that gets added and that just the receiver. The op rod, bolt, trigger and all that jazz still need to be done.
Not even sure where you would find a good barrel.


Thats only a small sample of the steps involved.

I work at FN and build this beast.  A job best left to the skilled craftsmen that do this every day.
We are pushing out over 900 a month!

If you were able to build one from a kit I would bet it would not be safe to fire.

the M60 can be done semi auto..the Mag 58 is another whole story...
took OOW a while to get it right...better off just saving up and buying it...

its a beauty.