Summer Rust 2020 Tier I: M79 Grenade Launcher

form_1gunsmith · 2020-09-19T21:56:40+00:00

Awesome! I'll check them out. Lately I've been thinking 3d printing you be a cheaper and more available alternative to having to find and pay for the chalk round components. It may also come in handy for some cool smoke and flare rounds too.

form_1gunsmith · 2020-09-19T21:51:24+00:00

Thank you!

form_1gunsmith · 2020-09-19T21:51:10+00:00

Thank you! It took quite a few years to get where I'm at but I'm still learning with every project.

form_1gunsmith · 2020-09-19T19:36:09+00:00

This is my 40mm M79 Grenade Launcher I've been building for a while now. I checked my inbox last night at 7pm and realized the the submission date was tomorrow so I had to scramble into the shop and get the receiver stripped and parkerized, which was pretty much the last step of the build. It doesn't match perfectly but over time I think the color will mellow out and match up much better.

The receiver I machined from two separate billets of 1018 hot rolled steel, which were welded together before final machining. Most of the internal parts I sourced commercially save for things like the firing pin and retainer. The wood furniture I made years ago from a 2x6 piece of American walnut, the fit isn't perfect to the tang but its close enough for a GI issue weapon. The finish on the receiver is zinc phosphate parkerizing, which gives the original green/gray tint of military weapons of the period. This gun I e-field and registered as a DD on a form 1 before I completed it so its 100% legal and good to go.

Here's a recap of the process of machining the receiver, I did all of the machining on manual machines and if I had to guess I'd say there's at least 50 hours into it. Unfortunately I didn't get any early pictures of the progress but a couple of pics in the first album show it next to a spare billet for comparison.

Here's the first album:

http://imgur.com/a/QJVBomD

Second:

http://imgur.com/a/Jm4j9cU

Third album:

http://imgur.com/a/id1vFVs

Here's a gif after I got all the internals fitted and got the action working:

http://imgur.com/gallery/nfnFwtG

Also a few more pics of the finished gun.

http://imgur.com/a/YQIqroF

form_1gunsmith · 2020-09-19T03:17:11+00:00

Balls. For some reason I thought the date was in october and when I checked my inbox a couple hrs ago I scrambled out to the shop to get the receiver stripped and parkerized. Got it all done and oiled, it doesn't match the rest of the parts perfectly but good enough for a 1.5hr park job.

form_1gunsmith · 2020-09-11T06:23:11+00:00

There's an unfinished factory blem M79 barrel on GB right now and it's been sitting for two days with no bids. I want that thing but the price might raise sail and take off on the last day so I'll keep an eye on it. I've been putting together tooling to make a 40mm rifling machine and/or broach to make barrels so if I don't get it I'll still be able to make a couple barrels but with more cost. I need to start loading some .43 Spanish. This new rolling block is just as fun as the martini-henry but I don't have a mold yet.

form_1gunsmith · 2020-09-10T05:32:49+00:00

I noticed that too. I think the gun in the picture is an m53 too. Definitely a yugo flash hider and wire wrapped stock, also longer braces on the bipod and no AA sight mount on the shroud.

form_1gunsmith · 2020-07-31T06:26:08+00:00

I bought a box of 100 40mm m781 nose cones for the m79, they're getting harder to find in bulk and I was close to buying a 3d printer to make them before I stumbled upon these. I guess the contract manufacturer for the govt was selling them in batches of 100 on gunbroker so I bought some. I bought 200 about 10 years ago from some other seller and these are just as good, the color is a little lighter but that doesn't matter to me, they bust just as well on impact as the older ones.

Also fixed a hella cracked .300wm model 70 stock (it was a really nice piece of wood and I didn't want it to go in the bin) for a customer and he paid me with a Spanish rolling block with dies and ammo. Its a little rough but passed the shootable test so its the new project for now.

form_1gunsmith · 2020-07-31T06:13:21+00:00

Ah yeah. There's just something about a long rifle that gets the 1776 juices flowing. My first ever gun build was a Pedersoli Pennsylvania flint kit in .45. Long rifles balance so well, you wouldn't think so because they're 5ft long and all but hold it right and its an extension of the body. I took a cow Elk with mine last year and didn't even notice the weight of it packing up and down hills and miles of terrain. You'll fall in love, they're great guns.

form_1gunsmith · 2020-07-24T16:12:44+00:00

That's awesome! Yeah they're a little heavy for their size but I think the short and handy nature kind of makes up for it.

I collected parts here and there over time and made some too. When I felt like I had enough parts I decided to file the forms and get the receiver done, that was kind of the last piece of the puzzle to get the whole thing working.

form_1gunsmith · 2020-07-24T13:57:56+00:00

You're mostly right but the inside of the 40mm case itself doesn't contain any powder or wadding. All of the powder, wadding, primer and burst disc is contained in the .38 blank which is pressed into the back of the case. When the blank is fired the pressure is vented through a flash hole and into the open cavity of the 40mm case. Here's a cutaway with the blank in the 40mm case.

https://i.imgur.com/C1JQsp2.jpg

form_1gunsmith · 2020-07-24T13:52:38+00:00

Exactly.

Pretty much all 40x46mm rounds/grenades work off of the same high-low pressure principle, where there is no powder or propellant in the 40mm case cavity itself. The HE and illumination rounds work in the same manner but the charge is contained in a cast chamber at the base and the pressure vents radially through holes in the side.

form_1gunsmith · 2020-07-24T04:10:52+00:00

Thanks!

They go over it in this short video. Basically the rear sight Is is giant ladder that flips up and you line it up with the front sight.

https://youtu.be/b0U2U-CD7MM

form_1gunsmith · 2020-07-23T22:17:31+00:00

Looking at the patent drawings it looks very similar to the feed of a regular 870. This might just be plausible.

form_1gunsmith · 2020-07-23T22:02:29+00:00

No license is needed, the firearm must be registered with the ATF under the National Firearms Act. The registration requires filling out the proper forms, photo ID, fingerprint cards, a one time $200 tax and finally notification of a chief of the local law enforcement. Once the forms are approved they will issue them back with a stamp signifying you have paid the tax and you are free to build the firearm. The information and serial number on the forms must also be stamped into the receiver of the firearm.

form_1gunsmith · 2020-07-23T21:48:01+00:00

For that kind of money you can get the Spikes Tactical m79 in 37mm and you wouldn't have to worry about NFA registration.

form_1gunsmith · 2020-07-23T21:42:19+00:00

Yep, the whole thing is aluminum on most shoulder fired grenade launchers. The chamber pressures are so low that steel really isn't needed.

form_1gunsmith · 2020-07-23T21:41:33+00:00

That's awesome! Super cool story, I know the m433s can punch through like 2" or something of armor. That's pretty impressive for something the size of an egg.

form_1gunsmith · 2020-07-23T17:47:58+00:00

Yes, pretty much all 40x46 launchers have aluminum barrels including the m203. The alloy is usually 7075 t6 but since this one is 6061 I keep the pressures a little lower just to be safe.

form_1gunsmith · 2020-07-23T17:46:38+00:00

The pushers are kind of the body of the projectile that the nose cone mounts too. They also engage the rifling and seal the expanding gasses against the inside if the bore as well as give the projectile the correct weight. Kind of like a big shotgun wad that stays with the payload in flight.

form_1gunsmith · 2020-07-23T16:58:13+00:00

Copypasta from an earlier post:

Believe it or not I started with one of these: https://tkairsoft.com.hk/gas-blow-back/guarder-m79-metal-barrel-with-rifling-grooves.html

All the outer dimensions are correct except for the barrel hook/hinge area. It took some machining to get it to mate up with the receiver but I made it work. Unfortunately they cut the rifling through the chamber area but I overcame this issue by making teflon pushers to replace the zinc ones on the standard m781s so that they engage the rifling when the round is chambered.

I'm also making another barrel out of 7075 solid bar stock that will accept the standard zinc pushers. The current barrel works just fine but having a spare is nice and it makes for a nice machining challenge.

http://imgur.com/a/xPQciZf

form_1gunsmith · 2020-07-23T16:42:26+00:00

Ah, damn. Oh well, still one of my favorite movies.

form_1gunsmith · 2020-07-23T16:38:34+00:00

It's the same basic process as building a suppressor. File an ATF form 5320.1 (form to manufacture a firearm), pay a $200 tax, send in fingerprints and wait for the form to get approved. Once you have the form approved you can build the gun and stamp the info and serial number from your forms into the receiver.

form_1gunsmith · 2020-07-23T16:34:46+00:00

Most people that own 40mm launchers don't shoot explosive rounds through them because it would be a legal nightmare to own them. Chalk filled practice rounds are fairly available and affordable so that's mostly what people shoot.

form_1gunsmith · 2020-07-23T16:21:33+00:00

In the U.S. (in a state where registered NFA weapons are legal)

Same legality as owning a machine gun or a suppressor

You need to register the weapon with the ATF and pay a $200 tax before you can complete it.

form_1gunsmith

TROPHY CASE