I just finished modifying my Granite Mountain action for the .600 OK1. It will now hold three down and feed/ eject flawlessly. The action is interesting. It is a direct copy of a Brevex magnum Mauser but with 12 TPI threads. To feed the 600 OK with 900 gr round nose bullets it took quite a bit of ramp work as well as milling out of the rails. The rear action ring had to have a large port machined into it and some metal removed from under the rear bridge to gain adequate clearance. Interestingly,the bolt ejector raceway had to be both deepened and elongated to allow the ejector to move foreward enough to pop into place. Apparantly Granite mountain copied a mauser bolt with the WWII ejector flaw built in! I'm told this was a trick done by the concentration camp people laboring for the Nazi's making mausers in order to screw-up the guns by causing them to fail to eject reliably. A few minutes with a Dremel tool and cut-off wheel fixed that problem. It's definately a good action in my opinion for really big cartridges like the 585 NYATI, T-Rex ,505 Gibbs, 600 OK1. Given the capacity, it's worth the hefty pricetag! Perhaps when the Montanna Rifleman PH is available and shown to work reliably,there will be a less expensive alternative.-Rob

Rob,
Have you seen this action?

http://www.adcosales.com/whatsnew.html

It's Euro distributor is Manfred Alberts but I'm not sure of the manufacturer yet. It's under $2,000 Dealer. I received what appears to be a fairly detailed brochure on it but it's all in German.

[ 05-24-2003, 07:03: Message edited by: Nickudu ]

Nickudu- No I've never seen one! looks like a Vektor though! Darn things are Pricey! If we ever get the Schuler Mag thing worked out for the CZ550,I think that's still the ticket!-Rob

Rob - The action is made in Germany, according to "ADCO".

I have it that R.S.A. - "Vektor" has ceased production of their action.

[ 05-24-2003, 16:23: Message edited by: Nickudu ]

Robgunbuilder what happened to this 600 OK?
Rob's CZ550 action 600 OK

I would be interested in obtaining this one if you replaced it with the Granite Mountain Arms action. Also, what is up with American Hunting Rifles? I noticed that they are no longer advertising the 600 OK on their website. Does this mean they are no longer barrelling actions and performing the feeding modifications?

Axel

According to the picture, it looks similar to the action distributed by NECG. However, at that price, there will probably be only few hardcore buyers. I think the PH action from MRC is the way to go to build a big bore. Thanks.

No- AHR will still be happy to build you a 600 OK on the CZ550. I think ED is updating the website with more pictures! The only problem with the CZ550 is the mag capacity limit of two in the box/one in the chamber. Frankly the conversion is about the same for the Granite Mountain action and the Cz550. The Granite mountain action is quite a bit nicer looking with the double square bridges, comes with a large enough box( made by blackburn) for a 600 OK-2 ( 3.2 inch case) and a large bolt diameter .750) which makes it suitable for the non-rebatted rim .688 of the 600-OK-2. I originally bought this action for the pupose of proofing the .600-OK-2 but have deceided to do a test run on the 600 OK-1 first. I can always open the bolt face up more later. Another disadvantage is that the Granite Mountain action has to be milled for Tally mounts or drilled and tapped for a weaver style mount.
To date I've worked on CZ550's,602's a Bauska BBK-02, Johansen Magnum, original Brevex Mausers and the Granite Mountain action. I still think that a CZ550 with a Sculer Mag is the best bang for the buck for a big bore. With the 500 a2 conversion of a Cz550 being the all time easiest to do!
The Montanna Rifleman action sounds good, but until we actually get one and do a successful conversion, I'm a bit skeptical. My major worries are in the mag box dimensions and the ramp/rail area. In general, you do get what you pay for and the Montanna PH just sounds too good to be true. I have two on order and if they come through on sked and it works, I'll be a pretty happy camper. However, I really don't expect the Montanna PH to be plug and Play. To date none of the above actions have been.-Rob

RGB, when is the projected launch date of the 600? I'm anxious just reading about this beast of a cartridge; isn't someone here in Alaska building a 600? No offense intended but one in the pipe and two down should take out anything on Earth, probably to include a Greyhound bus Good luck and take care - KMule

Rob!

What is the different between the .600 OK-1 and the .600 OK-2 ???

Is the .600 OK-2 more powerfull? what veloicty with 900 grainer?

Thanks!

The 600 OK-1 is a 3 inch case desined to be 3.600 inches with a 900 gr woodleigh. It has a .682 belt and a rim of .640. The 600 OK-1 was designed for 2500 fps out of a 26 inch barrel and specifically designed to work through a CZ550 action. Thus, the need for the rebatted rim( something I'm really not fond of). The 600 OK-2 actually came first and has the full .682 rim, ( same as the belt) and is 3.2 inches long and will have a COL of 3.8 inches. It will not work through a CZ550 but will work on a Granite Moutain action, a Prarie gunworks action or perhaps a Montanna Rifleman PH Magnum. The 600 OK-2 should hit 2700 fps with the same bullet weight. Assuming of course we can find someone stupid enough to fire it at this level of performance. In a 14 lb rifle, at some point recoil tolerance limits the power level of the round!
Remember at 1900 fps, this cartridge duplicates the performance of a 600 NE in a bolt action rifle that will hold 3-4 rounds. -Rob

Rob!
It most have a very good muzzle brake. I think I am stupid enough to fire a max loaded .600 OK-2 when i wear a fat jacket
2700 FPS with a 26 inch barrel. Isnt 14 ib to light for that power?
Is any one going to use a scope on it?

Hmm lets see.. it will have a muzzel energy of 19744 joule My .460 have a muzzel energy of 9400 joule.

Rob-
How is the GM actions made - drilled from bar stock or what??
Isn�t 2500f/s for OK1 and 2700f/s for OK2 a bit optimistic...? As far as I see it, the OK1 will have quite a bit less casecapacity than the 577 T-Rex and the OK2 vil have about the same at best...

Ulrik, you bring up good points. According to my calculations the case capacities of the cartridges are as follow:

585 Nyati 2.85" ~ 182 grains of water
577 T-Rex ~ 212 grains of water
600/3" OK ~ 195 grains of water
600/3.25" OK ~ 212 grains of water

Maximum velcities achievable with 64,000 psi chamber pressure and 26" barrel:

585 Nyati 2.85" ~ 2490 fps with Woodleigh 750 gr
577 T-Rex ~ 2600 fps with Woodleigh 750 gr
600/3" OK ~ 2320 fps with Woodleigh 900 gr
600/3.25" OK ~ 2420 fps with Woodleigh 900 gr

Since the same assumptions have been made for all the above, those of you with 585 Nyati and 577 T-Rex rifles should be able to correlate the calculations to reality. With this correlatio data we can then correlate the 600 OK model to reality!

My reality, is that I DO NOT want to shoot any of these rounds at MAX velcity unless the rifle is muzzle braked and weighing 30+ pounds!

Axel

Nickudu at a Shot Show New Orleans a few years backs I saw the ADCO Mauser action & fondled it.(touch lovingly according to Danial Webster). I went beyond that i think It is a real piece metal working of art! Absolutely fabulous.

[ 05-26-2003, 18:14: Message edited by: D Humbarger ]

Axel,
I agree. The OK1 has about the same casecapacity as the 600 NE. Saeed acheived a max of almost 2300f/s in his Heym Express.
Case capacity of the Horneber cases in 577 T-rex are 225 grs.So I really doubt that 2700 f / s is realistic with safe pressures in the 600 OK2..

Your calculations are close to mine, however, with H414 and a Three groove, 26 inch barrel I believe the barrel will add about another 150fps. I have a three groove barrel on a .416 Rigby and have definately observed a significant increase in speed and lower pressures. We will find out for sure very soon!~-Rob

With a full load of ball powder THE Formula
shows 2600fps in the 3.25 case, at 52 to 55,000
psi.Takes more peak pressure with stick powder to
get same velocity.Ed.

I should add that ED is correct and that the peak pressures I'm aiming at are in the 55,000 range. I'll try and post some photos of the Granite mountain action and particularily the barrel! The three groove rifling is not very obtrusive, It kinda looks almost like a smoothbore!
Just modified the GMA ejector some more as I had poor ejection with some cases. I had to deepen the ejector slot in the bolt a little and now it works very nicely even ejecting those nasty blunt 900's from Bridger. I just soldered on the second recoil lug and the whole thing is cooling down.-Rob

Robgunbuilder, since I used 64ksi instead of your desired 55ksi for chamber pressure the velocity calculations would be even lower. I find it hard to believe that you will get 150 to 250 fps increase with a simple rifling variation. Pressure is what pushes the bullet out of the barrel! If you reduce the pressure you WILL reduce the velocity! Sorry just the facts. Your rifling may reduce PEAK pressures, but the AVERAGE pressure must remain close to achieve the same or higher muzzle velcity!

To get technical it is actually the area under the pressure versus time curve, which must remain a near constant! If you are using powders of the same general burn rate the peak and average pressures must remain practically identical to achieve the same muzzle velocity. It is when you go from a small charge of fast powder to a large charge of slow powder that large peak pressure differences are experienced while obtaining the same muzzle velocity.

Finally, I find that the calculations are almost always optimistic! That is why I said the gentlemen with the 585 Nyatis and 577 T Rex rifles should compare their actual results with the calculations! I suspect that the calculated velocities may be 10% - 15% HIGH!

Ed, I have looked at your "formula" and the pressure must be in CUP not PSI! Your "formula" does not correlate to any pressure data I have on record unless I use CUP in place of PSI! CUP and PSI are NOT interchangeable!!! The relationship between the two is different for almost every single case design. Also, I have not experienced significant differences in operating pressures between extruded double base and extruded single base powders. You state that the pressure will be lower for the double base in your thread concerning the "formula". Is this truly what you mean, or are you speaking of extruded versus spherical? In your post above I am lead to believe it is between extruded and spherical powders. I have seen significant pressure drops for a given muzzle velocity between extruded and spherical propellants. This is due to the burn characteristics of the spherical powder, which create an equivalent area under the pressure versus time curve as the comparable extruded propellant, but at a lower maximum pressure. In other words, the spherical powder as a "FLATTER" pressure versus time curve than the extruded powder does.

Ulrik, I believe that the 600 NE has a larger case capacity than the 600 / 3.25" OK. I can model it up, but I think the 600 NE is around 220 grains of water. Saeed's results seem to be VERY realistic to me.

Axel

Axel--I was referring to double base ball powders
with a full case.With over a 100 % loading.All of these are denser than
extruded, even double base extruded, so larger
charges can be loaded.With the right double-base powder it is easier to get the increases in velocity over extruded, because peak pressure
is down so that cases don't stick, but total energy is higher. The area under the pressure curve is much greater.IE, pressure remains higher further down the barrel.Thats why for power, I don't use stick powders. And for case longevity,
the lower peak pressures from DB Ball slows case stretching; even though more energy was put downrange.Most reloading calculation setups forget
to iinclude ball powder at full to over 100% loads.Like most on here talk
about use of RL-15 & 3031 for big bores.They
are the worst
there is, and I tested thousands of rounds, in comparison.Ed.

Axel- Pressure vs Time curves are what they are, but bullet resistance will be much less in a three groove barrel vs an eight groove barrel. VELOCITY will be a function of the area under the pressure-time curve as well as bullet resistance. To date I've seen about a 150 fps increase in velocity with three groove barrels as compared to eight groove barrels in the larger calibers when the cases are loaded to equal pressures( as determined using a strain guage).
As you will remember the design characteristics were 2400 fps with a 900 gr woodleigh at 55Kpsi using a three groove. I will be extremely happy if this is confirmed. I suspect ED is also correct and DB ball powders will result in the highest velocities.
I just have to find someone local stupid enough to shoot this thing at this power level -Rob

[ 05-27-2003, 05:05: Message edited by: Robgunbuilder ]

Rob-- For chrono work you need a heavy tripod
to lock onto barrel, like I use.I set it on an old
adjustable up and down heavy camera stand, with
a 2 ft wide by 4 ft long top.This is a heavy wooden one and I can stand up and shoot over
the chronograph.Your right about the velocity gains from the right ball powder.That belted
straight case will love those powders, like mine does.
Axel-That formula I use is based on psi.I helped to refine it while researching case shape as it pertains to internal ballistics,45 years ago
for a research paper.I refined it for ball powders and straight cases,about 10 years ago
after a couple thousand rounds through a 458WIN,
and I then started wildcat developement 8 years ago.I can take any load thats been chronographed,
at a certain psi and be within 4%. As good as
those run it through computer formulas.Now if you don't have psi, but the rest of info, by backtracking through formula I can tell the pressure..Ed.

Ed, thank you for the points of clarification.

Robgunbuilder, good luck on obtaining your velocity numbers. My only experience with this type of thing involved 12 ga shotguns. Three different makes of shotgun were invovled firing slugs in both smoothbore slug barrels and rifled slug barrels. There was NO STATISTICALLY SIGNIFICANT difference in muzzle velocity. Also evaluated an old Springfield rifle with the two groove barrel and then again with a 4 groove "match" barrel by Douglas. Same loads in the rifle and NO STATISTICALLY SIGNIFICANT difference in muzzle velocity. This is my experience, and is the reason I doubted you. I have no experience with rifling you are using though, it must be less resistant than rifling at all.

Axel

Mickey-They're the worst for getting the most power, before the pressure is a problem.Most ball
powders allow you to get more at a relatively lower and later pressure spike on the pressure curve.Ed.

Ed, I agree with you about the IMR3031 and Rel15 powders. IMR 3031 is nothing more than a single base extruded version of CORDITE. It has almost the exact same mass and burn rate characteristics of Cordite. I find it to be a dirty and pressure to peak too quickly to achieve good muzzle velocities in big bores. Rel 15 has the same problem with regard to lower than achievable muzzle velocity. In short both powders are too fast for big bore / large capacity cases! It is that simple. Use a full case of slower powder, just like you said.

This experience is why I thought your equation was based upon "CUP" and not "PSI". According to your equation I should be able to get ~ 3050 fps from my 416 Rigby with 350 grain bullets! This is loaded to 63500 psi with extruded powder, which is the specification for the Weatherby Magnum. I have used some W760 in the Rigby to get ~ 2800 fps with what was supposed to be a 63,500 psi load and a 350gr Magtip. I was able to get the same velocity using IMR4350 and there was no discernible difference between the cases. The case stretch was identical to 2.5 microns, that = 0.0001". Realizing that "CUP" is lower than "PSI" for almost all cartridges in existence I assumed that this was the cause of the error. The "CUP" data for the 416 Weatherby, and therefore the 416 Rigby, of ~ 55000 is roughly equivalent to 64000 psi. This assumes that my pressure estimates based upon case head measurement are accurate enough. That was my problem. It could be nothing more than I was not measuring the cases well enough. An error of 2.5 microns would explain the entire discrepancy!

Axel

Robgunbuilder said in the initial post-

quote:

---

Interestingly,the bolt ejector raceway had to be both deepened and elongated to allow the ejector to move foreward enough to pop into place. Apparantly Granite mountain copied a mauser bolt with the WWII ejector flaw built in!

---

All you had to do was bevel the inboard front corner of the ejector. What you removed was a gas seal.

'Granite Mountain action' and 'Dremel tool' used in the same sentence sets my teeth on edge.

What velocity is possible with a 750 grain bridger bullet in the .600 OK-2???

Overkill, try out Ed's formula!!!

Axel

Overkill--With 750 gr Bridger bullets grooved
radially to work at same pressure, as copper
jacketed, for velocity; they will get
2800 with full load of right ball powder.And
With slower twist and 3 groove barrel it should be little more.This with longer barrel.Now if he does Col Jeff on the barrel, it will be less.Ed.

Rob - pardon my poor memory but what do you use to solder your second recoil lug ? Do you dovetail the lug fit, then solder and utilize small machine screws ? Thanks - KMule

Kmuleinak- I machine my second recoil lug to exactly match the radius of the barrel. I use 1X1 bar stock. This is done in a milling machine with a flycutter set up to exactly cut the radius of the barrel into the lug. I then drill , tap and countersink the lug for a 8-32 cap screw . The barrel is drilled and tapped for the cap screw and I then use Hi Force 44 solder and the cap screw to locate everything and a turbo torch to solder it all together. These things never come off! works on Chromemoly or SS barrels.-Rob