I spend some time on the Lathe today and made a few belted .600 Overkill cases out of 7/8 brass roundstock to do some dimensioning work. The case was made from 7/8 brass roundstock and is 3.00 inches long and .671 at the belt. COL is 3.600 same as a .375 H&H. The rim is the standard .640 Nyati/Gibbs rim. The bullet is a 900 gr Woodleigh. It should do 2400fps at 11,000 ft lbs of energy and no it is well within the design criteria of a CZ550 mag action. Here are some pictures of the .600 overkill along side a 500A2 and a .470 MBOGO. This thing will romp !. You could build a Ruger number 1 for it, but only Overkill himself will be allowed to shoot it,-Rob
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[ 08-02-2002, 07:36: Message edited by: Robgunbuilder ]

[ 08-02-2002, 07:31: Message edited by: goneballistic ]

Sick, sick, sick

I love it

Yes, but can you fit it into a lever action?

I want to hunt cape buff...


Now that is one big assed damn round!

Wow Rob, I never thought that my .600 JDJ post would turn into this. I guess that I should have known better than to even mention a .600 anything around here. Also how close dimentionally is this cartridge to the .620 Rimless that Seyfried came up with? Do you know what I'm talking about? I think I got that info right.

Robgunbuilder - please stop teasing, I have not yet completed my 500A2 and you come up with something like this; for us fellow recoil junkies, this cartridge would be the "ultimate drug" - any idea what this cartridge will have for felt recoil? - another greyhound bus killer on the loose, thanks for the inspiration KMule

Nice cartridge Rob. But if it is only posibble to make a one shoot rifle of the Brno CZ 550 Magnum action, That is the only problem...

Will the .600 NE have higer velocity than this .600 Overkill with the same barrel lenght...???

Cool!!

It's Alive

Thanks guys, I should make it clear that as far as I can tell, at least two, maybe three .600 Overkills will fit in the magazine of a CZ550, Zkk-602, 1917 Enfield, Granite Mountain, Prarie gunworks or Mcmillan action. You also get one in the pipe! It's so big the magazines involuntarily become single stacks so it looks like feeding will be just fine. A Ruger number 1 will take one round and a lever action might fire one once! This is designed as kind of a 577 NYATI on steroids. It uses most of the good features of the NYATI and none of the bad and is designed to fit the same boltface as the Nyati or Gibbs. It's really just a scaled-up .458 Win Mag.. My buddies here in Kalifornia are also amazed at the difference in quality of a Lathe turned case versus the Bertram NYATI stuff. The wall thickness is also much greater than the Bertram stuff. FWIW this work was all done on a Hardinge toolroom Lathe with DRO. This is the cat's Meow of manual Lathes in my opinion and worth every penny it costs. The precision is astonishing.
Recoil Energy will vary with the powder used assuming you stay with a 900 gr bullet. It should be flexible enough for a velocity range from 1500 fps with XMP5744 to 2400-2500 fps with H414 according to my calculations. Thus, you could expect recoil from under 100 ft-lbs to over 300. I'd sure want as much gun weight, muzzel break, butt pad and recoil pad as possible when you touch off the latter. Just to be fair to the Ruger Number 1 crowd, there is no reason you could not use cast bullets and XMP5744 and actually have a shootable gun with this cartridge.
Now the question is, do I make or buy a chamber Reamer?
JR I don't know what Seyfrieds .620 Rimless was- If you have the info I'd be interested. I hope it wasn't one of those headspace off the casemouth abominations that show up from time to time.-Rob

Rob-
Way cool. If I didn't already have a .577 T-Rex to slap my brain around in this thick head of mine, I'd be on the 'list' for one.

I really like the design of the round and due to the size it will single stack in the popular CZ 550 mag magazine. Also, barrels & smithing from PAC-NOR would be reasonably priced. Bravo my good man!

For brass, you could also try Rockey Mountain Cartridge (RMC http://www.rockymountaincartridge.com/ ). They made some .577 Snider brass (lathe turned) for me this spring and can do almost anything. They specialize in old/obsolite calibers however I asked them about T-Rex brass and they said 'sure, just get me the dimensions' (I also asked about .600NE and they said 'sure'). Horneber would be best, but if it doesn't pan out RMC could be a viable second choice with the correct headstamp.

Kudo's on the idea & follow through, great design.

BMG

This is getting so close it's scary. And to answer you question Rob, HELL YES you should get a reamer made up. We have come this far right ? You know as well as I that the sickness has set in and it's too late to turn back now!!!!

Why not a .700 belted rimless?

Rob,

Now I'm starting to get curious...

If a guy was to send you a new CZ 550 in say, 416 rigby, (or would another chambering be better, like 458 WM??) what kind of money would we be talking to get it shipped back as a 600 OK? Time is not an issue. I'm thinking open sights only, say like a ghost ring or aperature type rear sight. Could the stock be saved with say double cross bolts and an extra recoil lug, or are we talking synthetic stock time (yuck!)? I'm thinking a 12-14 (or should it be heavier?) pound rifle with say a 25-26 inch barrel may be shootable? Would such a rig require the "mercury reducer" route? Do you think the mercury reducers would eliminate the need for a muzzle break, (I hate muzzle breaks!)?

Who could you trust to do the dies if you sent them the reamer dimensions?

I would think that a 900gr woodleigh at 2200-2400 fps would be more than enough from either end of the rifle!!

fla,

You'd have to exceed the rim/belt dimensions of the case Rob has designed. Unless it had a rebated rim, it would exceed the boltface dimensions of the 585 Nyati/505 Gibbs, but even then the girth of the case alone would not likely fit in a CZ550 action.

Canuck

[ 08-02-2002, 23:41: Message edited by: Canuck ]

CH Tool & Die could make the dies for about $140. They didn't make T-Rex dies until I talked to Dave (owner & gun nut). I sent him a fired case and he said 'no problem, it'll be about 3 months'. He could easily make dies for the .600 Overkill from the reamer dimensions.

CH does great work and at a VERY fair price. RCBS wanted $400 for a set of dies .

ps. Mel at Acrabond stocks will be making drop-in stocks for the CZ 550 sometime this winter. http://acrabondlaminates.com/index.htm

[ 08-03-2002, 00:45: Message edited by: BMG ]

The .600 Overkill case capacity is about max for reliable ignition with Large rifle primers. A Belted .700 would not work in a CZ550 as the amount of metal left in the barrel after reaming would be so small as to make it unsafe IMHO. It would work fine in a Mcmillan action, but why bother when a .700 BMG Improved would totally outperform it.
Yes Dave at CH4D could easily make dies for it and would probably give us a discount if enough people wanted to go in on having some made. I also see no reason why a properly reinforced CZ stock could not be made to work. Again, the recoil level can be tailored from mild to horrendous.-Rob

I want one.

Rob,

Me and my sick mate would most likely be interested in getting a set of dies if they can be had at a discount if a few of us put in.

If I can get dies and cases in my greedy hands first then I would be on the hunt for a second 602 or 550 action. This one will definitely be opened sighted

I have not even fired my .585 Nyatti yet and I am already looking for something bigger

I am just pissed this was not invented before I went ahead with the .585

I seem to have misplaced my info on the .620 Rimless round. Can anybody help Rob out by providing any info.? I'd appreciate it. Not at all to steal your thunder Rob it's just that I know that I've heard of a round kinda like this before. Maybe I'm delusional.

I seem to have misplaced my info on the .620 Rimless round. Can anybody help Rob out by providing any info.? I'd appreciate it. Not at all to steal your thunder Rob it's just that I know that I've heard of a round kinda like this before. Maybe I'm delusional.

Sorry, double post.

Rob,

If I sent you a .620 bore barrel would you be willing to chamber ream it for me, or at least rent me the chamber reamer? Naturally, I would pay you for your trouble. I am thinking of loading it to 600 NE performance levels.

Let me know.

Robgunbuilder...!

You have to send photos of the gun when it is clear on this site...!

So the .600 Overkill is max powder charge with large rifle primers. The next stepp is a .700 BMG IMPROVED if you want any thing bigger than a .600 Overkill or a .600 NE

Since you are starting from scratch why couldnt you design in the use of .50BMG primers to ensure reliable ignition?

Gentlemen,

For reliable ignition in such a large case, I recommend using 2 grains of Bullseye under the whatever charge you might wish to use.

We found that our .700 NE will hang fire most of the time, untill we added these two grains of Bullseye.

[ 08-09-2002, 13:56: Message edited by: Roger Rothschild ]

What number or brand are the .50 BMG primers ??. Should they also be used in the .585 Nyatti ??

Rob,

If this cartridge does become a reality and the CZ conversion works out, would you be willing to build the rifles for the members here that are serious about it? The 600 Overkill is the last thing I need, but for some reason the want factor is extreme Put me first on the list if you will do it!

Take care,
John

Edit: In my haste I didn't see BigBores post, so make me 2nd on your list!

[ 08-05-2002, 02:13: Message edited by: JKS ]

Depending on the amount of interest, I might be willing to make a number of Long Chambered barrels in .600 Overkill. These barrels would be threaded for a CZ 550 or Bruno 602 or frankly whatever action you want. You specify the contour. The barrel shank would have the correct shoulder installed and the muzzel threaded for a break( I reccomend a Vias) or an integral one installed. I would then long chamber for the .600 overkill. A gunsmith would then only have to face the barrel to set the headspace and install your open sights(assuming you want them). From a liability standpoint, I don't want to get involved in building complete guns right now. However, I could supply a complete set of directions. I'll have to figure out the cost, but it's probably $400 to $650 depending on what's involved. If I get into this, I want to do them all at the same time. I could also talk to Ed Plummer at AHR and see if they would be willing to do the action work and final fitting. Ed's gunsmiths are quite knowledgeable on the CZ550( he has a working 585 AHR which is really a modified NYATI) and I don't imagine it would be more than $250 for the action work required to make it feed. I do have to say that a functional prototype needs to be built and tested before anyone gets too excited. Ed is very interested in this project and also has the contacts for the brass. Let me know by E-mail if your interested.
As for the primer ignition problem, While I have not tried this, I am not convinced that a normal CZ firing pin spring has enough strength to reliably ignite a CCI-35 primer. I may just try this,however, with a Lathe turned case. I know ignition is a problem with the .700NE but I have not encountered it with the .600 NE myself using Fed 215's. I really dislike the idea of a bulleseye priming charge as when the cartridge is shaken on a hunt for example, the bullesye will migrate into the charge due to the differential grain size and become unreliable. There are ways around this, but I'd rather not have to go there if possible.

Sounds good to me Rob! Just get the final pricing down, pick a brand of barrel and let us know. I'm sure there are plenty of folks here that would like to take advantage of this. While I don't have a CZ550 right now I would sure like to stash away a barrel for when I do.

Rob,

Thank you. I can certaily understand why you don't want to build the complete rifles. I'm with JR that what you propose sounds great and I'm in. Oh, sorry, I'm not supposed to get_too_excited just yet
E-mail is coming your way Rob.

John

Rob,

I would be a liar to say was not interested. I will send you e-mail.

I would agree however that a working prototype be made up first to see how she all functions and to iron out any glitches.

Rob,

One more thing to add, maybe pac-nor could do a discount barrel chamber for us if we ordered a group "long chambered .600 OK" order from them ??

Might save you the work having to make them up.

Rob,

Could the case be designed to use 50 BMG primers?

That should eliminate all concern about ignition and it should not be a difficult change.

What do you think?

500grains,

Rob addressed his concerns with 50 BMG primer utilization in the 600 OK in his last post. Basically, Rob is concerned that the CZ550 striker lacks sufficient striking force to ignite the 50 BMG primer.

Now I hope you have learned something if that is you read Rob's last post.

Rob,

I agree that Mr Plummer & Co. would be a valuable asset in the feeding department. Are you at liberty to say whether or not AHR might consider chambering rifles in the 600 OK if it proves to be a viable chambering in your prototype rifle. By all means keep us all appraised of the progress. I was serious about the chamber job if for no other reason to find Pecos45 and let him fire off one hell of a big bore.