20mm brass alloy for wildcat. Anyone know?

[nelsonted1]

I was hanging out at a friend's shop and we started talking about the trouble they are having forming 20mm brass into a 50 cal/20mm wildcat cartridge. They are really working the brass and have an overwhelming number of case splits. I told them about annealing the brass with tempilstik markers that are smeared on the brass turning color when the brass reaches the rated temp. The question I have is does anyone know what the alloy of 20mm brass is? The alloy may require a different temp rated marker.

This is still sort of super secret type stuff so I can't get into the actual rifle yet. The prototype works well but the brass is the hangup.

Please help!

[beagle]

I'm thinking back. As well as I recall the brass for the M61 20mm was brass plated steel. I might be wrong as I've been out 21 years now. That could account for the brittle cases.

I know he'll have a heck of a time with primers as that stuff is electrically primed and takes a 320 VDC shot +/- 10 volts to set it off./beagle

[Lee W]

Wow. I hope pictures are forthcoming..

I use deep drawn stainless steel shells often and they are formed with a 16 step process. Perhaps you need to do that many steps and anneal between each step or two..

Now to search for the alloy type....


Looks like you will need to get a copy of drawing number d11075813. It should have the alloy type on it. Google did not turn anything up.

[nelsonted1]

They have four great big CNC mills lined up in a row like dragons panting for release.

THey showed me one of the machines milling out the pockets for the primers they are using. THey had a box of sleeves for the primer pockets. The original case bases were slightly deformed by the cannon extractors so the bases were milled flat in one of the stages. They are brass for sure.

I was absolutely dumbfounded by what I saw. My nephew works for these guys. He talks of almost 4,000 ft per second. I heard right but I can't cope with the blast and noise. He said the bullet disintegrate on impact. He may have been trying to rile me up with the numbers but I'd already hit my max so I just let everything fly on by.

Can you imagine this man-gun going off?

[Johnch]

Have them ask SSK
I remember at one time SSK was making a big boomer based on the 20 MM case
Not sure if they still do

John

[Shiloh]

Is your prototype fired electrically?? Or are you going to modify the primer pockets for .50 cal??
Are .50 cal primers hot enough to ignite all that powder??

Shiloh

[HammerMTB]

Does someone??? (not ME!!!) hold this thing up to their shoulder?
Is it recoilless?
Or maybe got a set of wheels and drawbar, so you can haul it to the range, then set it up and shoot it?
What might it be aimed at? paper? :rolleyes:
Maybe small trees for harvest....
Or old cars to be demolished....
4000 FPS and a .50 slug of 650gr or so, should be good to a couple miles anyway:holysheep
Where do y'all find a range with that kind of downrange distance? An ocean?
That's where we useta make the most of the 5" guns on the ol' gray boat....

[Greg5278]

I don'tknow thje brass alloy you are referring to, but annealing should be the same. Heat the area to a dull red in low light and water quench the heated area. I am not certain, but perhaps an induction furnace could be used for better temp control. I know induction works for Steel, but the process may not heat brass. Maybe Molten salt like a salt pot used for heat treating would work also. How many cases do you need to process?
Greg

[pluto]

I can clear a couple of things up for ya. It is shoulder fired. Prone obviously, although a very brave man could try it standing. The prototype weighs about 60lbs but for the final draft we are hoping to have that down to about 45lbs. We are using .50 primers. We're expecting to have 2 rounds for sale with it, a 3200fps and a 3600fps and if I remember the numbers right it will still be supersonic at over 3000 yards. Any how we could still use some info on the neck issue if you have any suggestions. Also it is legal in all states and it transfers on a 44-73. Appreciate any input.

[edsmith]

at what range are you going to sight it in for? 4 miles?:)

[Cap'n Morgan]

Like someone suggested, size the cases in multiple steps. When sized the case neck will stretch and the friction increase, so make sure the dies are counter bored/relieved, leaving only a narrow belt to do the actual sizing.

[SlowLeadBullets]

According to Cartridges of the World, Gale McMillan did a similar thing. The 50 McMillan FatMac. I scanned the article.

http://i217.photobucket.com/albums/cc207/SlowLeadBullets/FatMac.jpg

[jhalcott]

I asked Rock about the barrel life being so short, A gun rag reporter claimed Rock said as few as 12 rounds would ruin one, Rock said "That is a rumor and the guy has NEVER talked to me(Rock)!" I would have LOVED to shoot that LITTLE round,but at my age and health now, I'm not so sure! I could set up in one field and pick off groundhogs in the next zip code with it though!

[JeffinNZ]

..........it will still be supersonic at over 3000 yards........

That's FANTASTIC. How many loads to the pound though? :bigsmyl2:

[462]

Talk about a project...

20 mm on the left, .50 cal. on the right.

[rob45]

They are really working the brass and have an overwhelming number of case splits. I told them about annealing the brass with tempilstik markers that are smeared on the brass turning color when the brass reaches the rated temp. The question I have is does anyone know what the alloy of 20mm brass is? The alloy may require a different temp rated marker.

I have never seen a 20mm case (50 BMG is biggest I've worked with), so can't really help you there. But it would be very difficult to imagine it being anything other than 70/30 cartridge brass (unless steel as mentioned by beagle). Cartridge alloy is one of the most popular brass alloys, and the desired strength characteristics (for cartridge cases) are usually attained with both varying degrees of thickness and varying degrees of hardness, rather than changing to a different alloy.

In my experience, you may be better served by using the Tempilaq instead of the Tempilstik.
The sticks are best utilized for testing an already heated surface, whereas the liquid is painted onto the cold surface and becomes liquid again at the predetermined temperature.
I like to use 475 on the lower part of the case that does not get annealed, and 750-800 on the section that does. Set up your annealing process to have the higher-temp mark (on the neck) melt while the 475 on the body stays intact.

Information on suitable use of Tempil products and their purchase can be obtained through the manufacturer:
http://www.tempil.com/closeup.asp?cid=25&pid=27&theme=0

As stated in the other posts, forming may require several steps. Sometimes additional annealing may be required between the various forming operations, depending upon how much the brass is worked at each step.
All brass cases start out as a strip of brass, and go through several drawing/annealing steps before becoming finished.

[Linstrum]

From what I can tell from its mechanical properties, the current 20mm Vulcan brass is 70% copper and 30% zinc. I have seen steel 30mm and 40mm cartridges in the scrap from the Air Force Base near where I live.

When I was messing around with a .50-20mm wildcat I used CCI #35 .50 BMG primers shimmed with cotton ticking cloth like mattresses are covered with. Even though the pressure is up around 50,000 psi, in about 100 firings I never had any high pressure leakage due to failure of the cloth since it is no different than a gasket. The main problem I had was the CCI #35 primers being a bit anemic for the amount of powder, and using IMR 5010 I had one failure to ignite where the primer flash left a trail through the un-burned powder inside the cartridge that looked like a little miniature lightning strike fulgurite in sand. When I fired the CCI #35 primed cartridges they went: "pop-KABOOOOM!"

IMR 5010 is too fast and I really had to cut it down to what a plinker would be in a .30-06. I used mainly WC872, which was a little slower and worked better. Some years back Hi-Tech used to sell "Super Slow" powder in 6-pound jugs, which was 106mm recoilless rifle powder from practice shells. That stuff was great but wouldn't ignite reliably with the CCI #35 primers and I used .30 caliber carbine cartridges full of black powder. I machined a hole in the big cartridge base that was a press fit for the little .30 carbine cartridge and just pressed it in. The next problem I had was with the big firing pin mashing the base of the .30 carbine cartridge and I had to make a new firing pin. But it all worked out until Kalifornistan passed a law against owning .50 BMG rifles and even though this wasn't a .50 BMG I found a new home for it where it was welcome by exporting it out of Kalifornistan into the U.S.


rl781

[Linstrum]

JeffinNZ, I know nothing about this wildcat, but I was using between 430 and 475 grains of powder per shot, so at 7000 grains per pound, I was getting between 14 and 16 per pound with a little powder left over.


rl782

[felix]

Wildcatting at its best! More power to you guys, literally! Kinda' bends into the direction of shooting concrete core beer cans out of fox hole sized cannons. Obviously, the fun is in the pursuit. ... felix

[StarMetal]

I think I would draw the case neck and part of the shoulder rather then fully anneal it to form. Also a warm case forms better then a cold case.

[Shiloh]

That's FANTASTIC. How many loads to the pound though? :bigsmyl2:

How many rounds per barrel??

Shiloh

[HangFireW8]

20mm? 20mm?

WHICH ONE?

I have 3 (dummies of course). That only scratches the surface.

http://members.home.nl/p.geltink/pics/20mm1.jpg

http://members.home.nl/p.geltink/pics/20mm2.jpg

http://members.home.nl/p.geltink/pics/20mm3.jpg

-hf

[felix]

20x120 looks best because it appears like the standard 308, which we know is slightly below max in case capacity, and thereby making it easier to do with BOOLITS. A mid-range powder speed should be tried first with the nominal weight for the caliber. Whatever that all is. ... felix

Playing with the groove areas, it looks like a 1100 grain boolit with 327 grains of powder. Question is, will the case hold that amount of mid-speed powder, and just what would be the mid-speed powder be for the proper expansion ratio? ... fun and games.....

[Blacksmith]

This is a handy cartridge referance for military issue unfortunatly it only goes up to 15 mm.
http://www.dia.mil/publicaffairs/Foia/smcal_vol1.pdf

Blacksmith

[corvette8n]

Lets see 20mm-5.56 with a casefull of Unique = vapor wildcatting.

[EchoSixMike]

Brass availability is going to be the big issue. 20x102mm is used by US in the Vulcan guns, among others, but mostly electrically primed AFAIK. 20x110 got a little use in the USAF Hispanos and Mk 12 revolver guns but has been gone for a while. 20x82 is South African, originally German, originally 15x96mm, but necked out when high explosive was found to be more useful than high velocity in the MG151 series guns.

25x137mm is very common and percussion primed, but most cases are steel. S/F.....Ken M

[Linstrum]

The electric primers aren't a bad problem, I just shimmed .50 BMG primers to fit the slightly larger pocket. Hi-Tech and others have plenty of 20x102 Vulcan brass on hand at the moment if anyone wants some for press lever handles or paper weights. I used one for a little dust pan handle.


rl783

[Pirate69]

Bsed on what I could gleam above, I ran some calculations.

Data used:
Rifle Weight= 60 lbs
Muzzle Velocity= 3,600 fps
BC= 1.05
Powder weight= 450 grains
Bullet weight= 650 grains

Results
Muzzle Energy= 18,704 ft-lb
Free Recoil= 90.4 ft-lb (assuming no brake)
Velocity at 3,400 yards= 1,028 fps