Picked up the first piece of a M240B at a gunshow today.  You never know what you might find in a pile of parts.

For comparison to MG42 (MG3) topcover


Notice how much smaller and shorter it is--much narrower receiver.

However, the internals of the bell feeding mechanism are very, very similar.  As a matter of fact, they are nearly identical except for the bolt feed track.   The MG42 has a front pivot so that when the track moves right the feed moves left, while the M240 is direct acting.  Notice with the feed palls in the same position the bolt feed track lays on opposite sides of the topcover.   This makes it more compact.


Close up of internals.  Another difference is that the cartridge hold down on the MG42 has a "nose" that pushes down on  the bullet and the M240 lacks this.

Next time you see this thing it will be more interesting.  I won't be building a clone M240, it will be a one-off.  The parts are simply so dang expensive.  I think a barrel assembly is over $1000.   I will be deciding on the rest of it after I get in the shop and start digging in my "goodie" boxes.




Edited by gundoctor

Gundoctor,

To bad on NO M240b clone. I was just eyeing them in Shotgun News. Sweet machines. However, I agree on the $$ pretty scary. Collecting is geting expensive.

Thanks for the pics, I like!

I look forward to your "one off". This will be a fun build!

how does it compare to the RPD top cover?

I have noticed that a lot of the newer AK belt Feds are using RPD top covers. I'm sure the M240 would work just as good

teasing you.   Decided to turn a 10lb block (drop) of aerospace alloy into some chips and ?    That experience inletting locks on muzzleloaders and double shotguns comes in handy when you start with no print.

About 2.5 hours to inlet the feedtray and topcover.







This one has us fired up.   Looking at the best the Stoner and MK 48 have to offer, maybe more, in a 7.62 package. The bolt design is the heart of the system.

If anyone has a Mk 48 ammo box or nutsack I could sure use it--to buy or to measure. Would love to insure some backwards compatability.

now that has my attention!

Checked and I can get a new Mk 48 LE dealer sample for $17,000 from FN USA. Guess I'll just order one......On second thought, I think I'll keep making chips.   

A little progress. The design is done, really proud of the gas setup, bolt group, trunnion........I really believe the design is solid.   The M240 would be hard to improve upon, given its life expectancy and reliability, but I am going to try.

Going with a short stroke piston gas system and rotating bolt of my own design.

whittled the receiver down to about 5 lbs. I think it will lose about 1.5 more lbs when I'm done.   I am going to put a rail (COP) on the topcover and the forward receiver. Would have milled it in the receiver but easier on the prototype to decide at the end how I want the rail systems to work.


My 3 lug rotating bolt design. Uses AR type ejector and extractor. Comparison bolt is Armalite AR-10


Here is a shot showing the simple setup using a dividing head on the mill drill to machine the bolt lugs and drill the ejector plunger hole (shown). I still find myself using the little mill drill /DRO setup to prototype on. End up with the coordinates to put in the CNC if I want to make more.



I work with my CAD program some but to be honest I am working nearly everything out on graph paper for this prototype.

Gundoc,

Now that is going to be simply incredible!!!

Got a few hours in tonight. Got a stock mounted, worked on the gasblock / tube. Went with HK lower--might be interesting with a registered sear.    This is all I am going to post until it is done.

Was able to redesign the Minimi stock to incorporate a buffer and the gas system is really taking shape. The VZ58 provided some inspiration for the gas system. I'll post some detailed pix of my original gas system design in its own thread later.



Need to name it.

Here is the MK 48, which most people are not familiar with.



The Mk.48 mod. 0 7.62mm LWMG (Lightweight Machine gun) is being developed by the FN Manufacturing Inc. (an US-based outfit of famous Belgian company FN Herstal). The request for new weapon came in 2001, and the first units in the US Special Operations Forces are scheduled to receive this machine guns in august, 2003. The Mk.48 mod. 0 is due to replace infamous 7.62mm Mk.43 mod.0 (M60E4) machine guns, which are quoted as insufficiently reliable. US SOCOM plans are to acquire several hundreds of Mk.48 mod. 0 LWMGs.It also probably will be offered for export by FN Mfg when the initial US Govt contract will be completed.

The Mk.48 mod. 0 is a "big brother", or a scaled-up version of the 5.56mm Mk.46mod. 0 LMG, a derivative of the famous FN Minimi / M249SAW LMG. Both 5.56mm Mk.46 mod. 0 and 7.62mm Mk.48 mod. 0 were developed for US Special Forces, led by the US Navy, hence the Mk. (Mark) designation.

The key advantages of the Mk.48 mod. 0 over the 7.62mm M240 /FN MAG are the light weight (essential for SpecOps, 17% lighter than M240B),parts compatibility with M240 and Mk.46 mod. 0, and a rail mounting system, that can be fitted with various sights and SOPMOD kit accessories.The Mk.48 mod. 0 will provide several firepower advantages (in both terminal effectiveness and range) over the Mk.46 mod. 0 and M249 SAW,being much lighter than M240 and much reliable than Mk.43 mod. 0 (M60E4).

Technical description.
The Mk.48 mod. 0 is a gas operated, air cooled, belt fed machine gun. Its action is very similar to one of M249 / Minimi, being a gas operated, with underbarrel gas system and a rotating bolt locking. Gun is fed using standard disintegrating 7.62mm belts (no magazine feed is available, as on the smaller Mk.46 mod.0). Belt can be fed from separate boxes or clip-on combat pouches for 100 rounds. Barrel is quick-detachable and has a carrying handle to assist replacement of the hot barrels. Mk.48 mod. 0 is fitted with open sights, and has 5 Picatinny rails (one on the top of the receiver, 4 on the for end), that can accept wide variety of sights and accessories.Mk.48 mod. 0 is fitted with solid, non-folding plastic butt, folding integral bipod, and a carrying sling. It seems that it also can be mounted on vehicles and infantry tripods for sustained or long range fire missions.

Soliciting input.

How much should it weight? I have a lot of leeway yet, especially in the barrel.

Here is a table of known weights I accumulated

Minimi/ SAW M249 5.56mm
     Standard model: 6.85 kg (15.1 lb)
     Minimi Para: 6.56 kg (14.5 lb)
7.62mm Minimi versions
     Minimi 7.62: 8.17 kg (18.0 lb) fixed stock
     Minimi 7.62: 8.4 kg (19 lb) telescopic metal stock

Mk 48 7.62mm   18.26 lbs

M240 7.62mm 26.0 lbs

BAR M1918 30.06   21 lb

HK21   7.62mm   17.5 - 21.5 lbs

MG3 7.62mm   23.35lb

M14 Rifle 7.62mm   11.5lb
     USMC M39 M14-based DMR 16.5 pounds

G3   7.62mm 10lb


I believe I can bring this thing in at as little as 15lb, maybe less. The question is should I.

I used to carry the M60, and it was HEAVY.  typically weight helps recoil, but these days a muzzle brake works better.

I would say 16 lbs would be the goal.  if you can make it weigh less, than that's even better

Yeah, shoot for RPD weight...

I can't wait to see the finished product

Jealousy and awe are words that come to mind.

wish i had your skills

Here is a great article on the MK 48 and the quest to shave weight off the M240 so it also includes references to the new M240L

mk48_article.pdf

My project weighs exactly 7 lbs right now (receiver, bolt, buttstock, topcover, feedtray, complete lower.)   Does not include bolt carrier, recoil assembly, trunnion, barrel assembly, bipod, or gas system.

weaponeer wrote: I used to carry the M60, and it was HEAVY.  typically weight helps recoil, but these days a muzzle brake works better. I would say 16 lbs would be the goal.  if you can make it weigh less, than that's even better

30 lbs heavy.

i carried the SAW and it was not near as heavy as the 60. if he can keep this under 16 lbs, that will be cool, but recoil is going to be a pain with the bolt slapping back and forth.

im eagerly watching this build.

The lug width on your bolt looks too wide to push a round through a link. Hard to tell without one in the picture and I'm sure you have probably thought of this already. Great work so far, looking forward to the final product.

Mongo, thanks for looking things over.   I made one mistake already that made me redesign on this one (that I won't have in version 1.1). I double checked the lug width--0.310" fine with U.S. links and fine going forward thru a loaded MG42/MG3 type belt but too wide to come back thru an empty MG43/MG3 belt. I have topcovers for both belt types and will need to thin that lug a little to work with the German belts.

The bolt head minor diameter is 0.646", giving a minor circumference of 1.938". To get maximum lug contact on a three lug bolt: 1.938 / 2 / 3 = 0.323" per lug. I took off 13 thou for clearance. I considered a triangular bolt like Ronnie Barrett uses but decided it wasn't needed.

That said, a three lug bolt has a lot going for it. The 3 lug design is so simple and strong. The 4 lug bolt could have assymetrically spaced lugs with the 4th lug as a safety lug only.   Will likely have to change the lug number and geometry to accomodate my final magazine, extractor, and ejector placements.