The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Rifles Big Bores Difference in 600OK actionsGo | New | Find | Notify | Tools | Reply | |
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What is the difference or advantage in the different actions that are used for the 600 overkill. What is the advantage of of the GMA action over the CZ550? Will the CZ550 not do what the GMA action will in terms of power? or is it an accuracy issue? also the MRC PH? | ||
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The MRC action is a giant blown up Winchester M70. It is a huge and nice action but MRC seems to be having trouble keeping up with their orders. I was fortunate to get my PH action through a trade and it is what I am planning on building my .600 Overkill on. It is a massive action with a huge magazine box / bolt throw / travel. I also plan on my barrel coming close to matching the receiver at 1.3" (a big barrel). I don't have mine handy to measure but I think its bolt face is ~.800(?), however its M70 style slanted bolt face does offer some large rim limitations. Weight is not an issue for me as while I want a .600 OK I can't imagine me taking it to Africa. It is an awsome round but just too much for me in the field. The GMA acion from what I have been told or read as I don't own one is a wonderful action with a .750" bolt face. This is a good thing but not necessarily needed for the ~.640" bolt face of the Overkill / Gibbs (same rim). It is a very big Mauser type action. But, while worth it, it costs a bunch. The .600 Overkill (from my readings) was designed by our own "Robgunbuilder" to be the largest round that would fit into a CZ550 action. He would be the best historian here. The CZ action has a .700 bolt face and while minimal for the .640 rim of the OK / Gibbs it has proven none the less completely adequate. The PH or GMA action gives the option of loading to 2400 fps with the Overkill. To what end I can not imagine, but if you want to go there you can. The CZ action allows you to duplicate or exceed the .600 Nitro Express in ballistics maybe to 2100+fps and if that is not enough I give up. So the over simplification of it all from someone that has a CZ .505 and a PH action slated for a an overkill build is the same as the .500AR / .500 A-Square/ .500 Jeffery / .505 Gibbs argument. In all comes down to cost and a personal choice. | |||
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thank you. I was wondering if the cz was "weaker" and couldn't get to the 2400 fps range. | |||
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Jim, As a fellow newbie, I welcome you to the site. I agree with Viperidae, the most qualified person to speak with about the 600 OK is the creator, Rob Garnick (Robgunbuilder). You can also talk with Wayne Jacobson at AHR, as he has built quite a few for many of the guys on this site, and is one of the finest in the business. Wayne is building me a 600 OK and a 700 AHR, both built on the GMA African Express action (in fact, I pick up my transfers tomorrow!) There is no finer M98 action anywhere, though you do pay for the quality ($2500.00 per unit through AHR). They are worth every penny. The CZ550 is a fine piece of steel, and as this is the action that the 600 OK was designed around, I cannot see anyone being displeased with the results of a build based on that action. As far as the threshold for FPS, I am not aware of a limit using the CZ550 as opposed to the GMA AE or the MRC PH. The 1999 MRC PH action is truly a monster in size; however, the specs for the bolt face are actually available in three (3) dimensions: .543", .604", and .648" (the bolt diameter is .805"). This is also a great action, whether you choose SS or CRMoly. If there is an updated version that I am unaware of, please feel free to correct me. Respects, Phill | |||
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If I did not have a PH action available to me I would have built my OK on a CZ action and never looked back. The CZ 550 action dollar for dollar is the best magnum action available right now. Anything above 2200 fps can be down right painful in these monster rifles. | |||
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In an email from Wayne Jacobson he states "The CZ 550 is the strongest action on the market as far as I’m concerned." So I guess there shouldn't be any fear in shooting up to 2400. Well at least any fear that the action can handle it anyway.  | |||
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The CZ550 will handle max loads in the .600ok with no issues as will the others. I own all three actions and would pick the CZ 550 with a AHR single stack magazine as the most cost effective followed by the MRC And then the GMA. Each has advantages and disadvantages but none offer any discernible difference in Accuracy. you won't go wrong with any of them. I've seen .600 oks built on 1917 enfields, BBK02's, M70s and even a M98( two shot). None ever failed.-Rob Never underestimate the power of stupid people in large numbers to do incredibly stupid things- AH (1941)- Harry Reid (aka Smeagle) 2012 Nothing Up my sleeves but never without a plan and never ever without a surprise! | |||
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what makes the GMA action sp expensive? i'm getting a 600 Ok built for myself as well. i'm sure the GMA action is top quality and i'm thinking of getting my 600 built on that action but i'd like to know why it is so expensive before i pay that much for it. if it doesn't have anything about it that really appeals to me to make me feel it really is worth the extra money i am going for the CZ action. | |||
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The GMA is a interesting and big action which can hold 3 .600Ok rounds down in the cavernous mag box and can reliably feed the rounds double stacked. Its basically a modernized version of the double square bridge magnum Mauser action made from modern steel. It comes std with the 505 Gibbs boltface. I think its made from 8620 steel( dont know for sure) and is heat treated to be pretty darn hard. Requires Carbide for all machine work. It offers a double square bridge that can be elegantly machined for Talley scope rings. The action and threads are square right out of the box and looks great with engraving. Its nicely made and blues beautifully. However, it does require extensive machining i.e the ejection port and back bridge need to be opened up considerably for the .600Ok to work properly and the feed ramp needs to be re-shaped and de-horned. I have to say that having to do extensive machining on a $2500 ( 10 years ago) dollar action kinda bothered me at the time. When I bought mine, I gave M.Roden a sample .600Ok cartridge and he assured me his gunsmiths would send me a tweaked action that would feed it. Will that didn't happen and I had to figure out how to make it all work on my own. Fortunately, I was successful and passed that info on to others. Dont know if any of that got incorporated back into the design. I do know AHR has built many GMA actioned .600Oks and Wayne knows what he's doing! Nevertheless,for those who want the very best, the GMA action fits the bill, but the cost is way up there. Not necessary IMHO, but confers major bragging rights and envy on others. Finally a little history lesson! When, I designed the .600Ok it was actually around the CZ550 action. The concept was that the CZ550 was very affordable( although the 505 Gibbs boltface didnt yet exist) and extremely strong and most importantly, big enough to take the .600OK-1 case. It still required alot of machine work to make things fit but we knew it could take the bolt thrust of the .600Ok at full tilt. I had a second cartridge the .600Ok-2 that was based on a 3.25 inch case and even a .600-OK-3 on a 3.5 inch case that I needed a bigger action for. Thats where the GMA came in. The .600Ok1 proved to be so powerful that I never built the .600 Ok-2 or .600-0K-3 although I still have cases. I built the second .600Ok rifle around the GMA action and it works fine, I'd just not do it again personally. AHR developed the single stack .600 OK mag Box just about this time and in my view solved the feeding issues associated with the first CZ550. BTW, a std CZ550 mag box can in fact be made to work, it just isn't easy.-Rob Never underestimate the power of stupid people in large numbers to do incredibly stupid things- AH (1941)- Harry Reid (aka Smeagle) 2012 Nothing Up my sleeves but never without a plan and never ever without a surprise! | |||
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thanks for the very helpful info on the GMA action. what you said just may make me put back the extra money for one if i'm able to. also want to tell you that i think you designed a killer, killer cartridge in the .600 Overkill. the 600 OK and the 577 Tyrannosaur are my absolute 2 favorite extreme power big bore cartridges. the 600 OK just fascinates the heck out of me and between the .577 T-rex and the .600 OK i think the .600 OK may actually be the more useful one. i keep hearing the recoil is not as bad as the .577 T-Rex and it looks that way in the videos i've seen of both of the 2 being shot. i want something that is extremely powerful but practical as it can be for that power level also. | |||
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I only own one CZ 375, a lefty. But judging from the quality of this action it is a fantastic buy. If the CZ action would sell for triple the current price shooters would be all over it. My biggest fear is when I die my wife will sell my guns for what I told her they cost. | |||
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The .600Ok exceeds the T-Rex at full power by a considereable margin. A advantage of the .600Ok is that with 750 gr bullets ( T-Rex bullet weight) you can easily hit 2700 fps. I was never able to do anywhere near that with my T-rex without hammering the bolt open afterwards. I owned a T-Rex and frankly recently sold it as it never actually impressed me and I only took it out to let potential .600Ok owners see the difference. I had issues with sticking brass and even finding brass for my T-Rex and hated the stock design and execution on the hannibel. The tar on the stock did give me a good cheek weld though! The T-rex has a sexy name and great PR. That coupled with the fact they they are nearly unobtainium has created a legendary status surrounding them. The realitity at least for me was a disappointment. .You probably have never seen video's of the .600Ok at full power. It becomes a real hand full at that point. Most enjoy shooting it at 1950- 2150FPS or just duplicating the old .600NE loads where the gun is extremely easy to shoot well and recoil is like a maidens kiss!-Rob Never underestimate the power of stupid people in large numbers to do incredibly stupid things- AH (1941)- Harry Reid (aka Smeagle) 2012 Nothing Up my sleeves but never without a plan and never ever without a surprise! | |||
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man, that info has me liking the .600 OK more than ever. it seems the more i learn about the .600 Ok the more i like it. | |||
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Pez- Get AHR to build you one. Its just a check away! No One has ever been disappointed. It will put a big smile on your face. That I can assure you!-Rob Never underestimate the power of stupid people in large numbers to do incredibly stupid things- AH (1941)- Harry Reid (aka Smeagle) 2012 Nothing Up my sleeves but never without a plan and never ever without a surprise! | |||
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This thread has been so helpful to my undertanding of the 600 OK. I am definitely having AHR build me one at the first of the year. I wish there were some tacked threads here for like FAQ of 600 OK and others for that matter too. I have been using the search function to read everything I can on this round. I can't imagine a 3.5 inch 600 I can't imagine the 600 the way it is. Thanks for all the info Rob. | |||
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I will also add that Wayne Jacobson at AHR www.hunting-rifles.com is great to reply to your emails and answer questions. Absolutely the best in that regard. | |||
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Gentlemen, I think AHR actually has one on a GMA action with all the bells and whistles along with brass and dies for sale on their web site. Click on "Available Now" on the AHR website. Yes, that was as shameless plug ...  NRA Lifer; DSC Lifer; SCI member; DRSS; AR member since November 9 2003 Don't Save the best for last, the smile for later or the "Thanks" for tomorow | |||
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i promise you that is exactly what i am going to do just as soon as i can! man, i wish most of my savings hadn't of had to go to a new car as i'm not really a car person anyway. i also wish i had waited to buy the last rifle i bought until a later time. i spent $2,000 on a Weatherby MkV Accumark in .30-378 Wby. i really like the rifle a whole lot but not as much as i like the 600 OK and the rifles i saw on the AHR website. i wish i had that 2 grand to go on the 600 OK now and i would get the Weatherby at a later time. | |||
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