Some time ago I read an article on the Lilja website about the strength of actions needed for big bore conversions. And African Hunter ran an article by Chris Bekker about the strength of the M98 action.

So I am wondering if the M98 action (assume FN commercial 1950's) has bolt lugs strong enough to handle the thrust of the .585 nyati. Assume the .585 nyati has a rim diameter of .640", and fires a 750 grain bullet at 2300 fps.

By "strong enough" I mean strong enough to safely shoot a few thousand rounds (for argument's sake), not just strong enough to survive 20 shots at the range to sight in.

Didn't Ross Seyfried build the first 585 Nyati on a German World War II military Mauser ?

Hammer

Dan,

In order to do a calculation of bolt-thrust we need to know the chamber pressure for your load. It seems like a hot load to me, but I do not have practical experience at all with this cartridge - 8,812 Ft-lbs from 750 gr @ 2,300 fps. Quite a load for a shoulder gun and not for the recoil-shy. (I read somewhere that it could be loaded to about 10,000 ft-lbs with some powders). Pressure spikes will depend very much on the choice and type of powder being used.

All I know is that Ross Seyfried modified a 577 Nitro case which is very big for bolt guns and therefore one will have to use a Magnum length action such as Granite Mountain in my opinion. A standard length action, such as the FN, is going to be too short.

I one ventures into a costly project like this I think it would be wise to buy a modern premium grade action made from the best steels and the locking luck should be thick. I have mentioned in my article that Hartmann & Weiss have deemed it necessary that the lugs be made thicker. Going the opposite direction to cut metal away is not advisable.

It would be interesting to hear if anybody has used a Standard Length action with modifications, but it seems to me we want to fit a V8 engine into a VW. FN actions of the 50's are actually good actions. Standard K98/FN actions were used successfully on 500 Jefferies.

Sorry Dan, my answer is not conclusive, but this is my current thinking. What makes the question more interesting is the metalurgical aspect of what safety margin is desired and needed (and they may differ) - 50% up on your load or 100%.

Take care
Chris

Wasn't the whole idea behind the 585 Nyati to be a cheap (any PH could afford it) stopping rifle ?

If we must start with a $3,000+ action, write-off the average starting PH.


Hammer

I'd personally be far less concerned about the bolt lugs as I would the action strength. Will it resist the setback under the force of the larger amount of square inches of cartridge.....the bullet weight and velocity are irrevelant.....only the cartridge pressure and the diameter of the base of the cartridge.

Gut feeling is that if one don't remove the metal on the front of the action, the post war FNs would support it.....but as previously mentioned.....you don't have enough data to know that.

Any properly heat treated commercial
mauser will handle the
thrust of a Nyati case.There were only a few
made military ones during war that weren't hardened right. The shear rating on Mauser lugs are about 30,000 lbs and the thrust from a
Nyati case for example, at 50,000 psi is
11,500 lbs, close to a three to one safety
margin..Ed.

.

Alf,

Agreed,

The recoil of a 416 Rigby is already more than most can handle. That is why Harry Manners used his 375 H&H throughout his career as an ivory hunter. Shotplacement, bullet performance and quickness of follow-up shots are more important than caliber.

Chris

Dan,

you had a .585 Nyati on a win m70 I still have your pic with you and your elephant and the M70 .585.

Seyfried firstly built in ona Brno 602 .375 H&H (the basis for which I did mine).

He also built one a M98 with a special schuler mag. set up for feeding.

I want to do a second .585 Nyati one day in a full African Clobber.


It is a handful I fired mine without the break recently and did some three shot shooting (woodleigh 650 gr @2 400-2500 fps)and managed to hit minute of deer/roo targets off hand at 70 yards three times...............but I need to concentrate to do it, and my gun weigh's 14 pounds and has three mercury reducers in the butt. I want to get used to using it minus the break as it is shocking with the noise.

Here is mine below; Brno 602 action, 3 down Tobler 25"barrel removeable break, leupold 2.5x compact scope in Talley QD's. Custom Kevlar reinforced stock, three mercury reducers in butt.

Dan
the 585 and mauser is fait accompli. though when I went to build one on a 98, i gave up and did a jeffe on the enfield.

these parameters are what neal and I did the 550 express on.. with ONE more criterion...

that is be useful as a stopping rifle without a brake.

So, like ross, I built the first 550 express on a vz24, with a single stack. A PH could afford build a 550 working gun...

Chris,
the nyati is made from, but not the same size as, the 577 case.. it'll fit in a cheap action.

Dan,
if you've got a reamer, i'll build on next year

jeffe

Gentlemen,

Of course .585 Nyatis have been built on M98's numerous times before.

But the question is whether the bolt lugs of a standard M98 will stand up to this level of thrust repeatedly.

Chris, if you are able to calculate the thrust, please assume the load generates 50,000 p.s.i. of pressure.

As to cartridge length, max OAL is 3.600, but with Woodleighs it ends up being shorter than that.

Hi,

For what this is worth. The Mauser magnum action has the same locking lucks as a standard 98 action. A magnum Mauser action bold will fit into a standard actions receiver but will be to long.

I spoke to Kevin Healy from Bloemfontein Custom Rifles. He has built me the following rifles on modified standard 98 actions. 300 H&H, 375H&H and a 425 Rhino.
Kevin used two standard actions to build a longer and wider action to accommodate the 425 Rhino.
I have hunted with these rifles for a number of years with no problems.

Kevin did his Gunsmith trade at Musgrave factor. I suggest you contact Kevin and talk to him, as there is more than one-way to lengthen an widen an action. Kevin told me that in the past 20 years since he started Bloemfontein Custom Rifles he has lengthen and shortened about a 100 actions. Kevin has not had one return to date.

Kevin feels the action will handle the pressure of the Nyati. But stressed that only good quality actions must be used. Kevin’s cell number is +27 823776103

Kobus

Is a Charles Daley Mauser suitable for building a 585 Nyati ?

See where the 30/06 version is available in left-hand. Don't know of any other 98 Mauser available in left-hand since P. O. Ackley's imports.

Hammer

I wouldn't build a boat anchor out of a CD action.

If I needed a lefty I'd probably opt for a MRC 1999 Action. Close enough to a Mauser for me.

Hi Dan,

To calculate breech pressure, take the chamber pressure in relation to the internal area of the case that puts pressure on the bolt which is transfered to the 2 locking lugs, which must bear the strain. The distribution of back thrust is shared by the case and chamber walls depending on its grip on the chamber walls as it varies between tapered cases and a more parallel type cases. The balance of the thrust, plus the full thrust of the primer goes onto the bolt. If there is oil in the chamber or on the cartridge case, the back thrust will be increased tremendously and may even approach that of full chamber pressure. If we ignore chamber-wall friction, but assume a 'dry' chamber, we can compute back thrust as follows:-

Cartridge -------------------- 500Jeff ----- 585 Nyati
A) Max inside Case dia. ---- .564" ------- xx
B) Area in Sq inches -------- .250" ------- yy
C) Chamber Pressure ------ 46,412 psi-- 50,000 psi
D) Bolt Thrust in pounds --- 11,603 lbs-- oo

Just slot the numbers in for the Nyati as I do not have the measurement of the inside case daimeter. (D = B x C)

From a safety standpoint, the bolt lugs is of prime concern ... the factors are ... the strength of the metal, its dimensions as well as its ability to flex. In general then, the bigger the caliber, the greater the area that is affected ... this area is then multiplied with the actual pressure which is dependant on the actual load, comprising the bullet weight, the type of powder and the charge to yield a specific velocity. It is thus clear that a hotter load will increase the back thrust.

Daniel Lilja gives the following formula to calculate the lug shear strength:-

LS = length of Arc Segment x axial length of Lugs x No. of Lugs x Yield Strength of Material/2
= (.366 x .433 x 2 x 90,000)/2
= 14,263 pounds (original Mauser)

In the formula, we divide by 2 to get a safety margin of two. The length of the arc segment again is calculated as follows:-

L = .01745 x Radius of Bolt Body x Arccosine of the angle of the segment

The yield strength is the maximum amount of pressure the steel can take without becoming permanently deformed ... up to this point the steel will return to its original condition. The most common type of steel used in bolts today is 4140 chrome-molly steel as opposed to 1040 steel of the original Mauser which had a tensile strength of 80,000 - 90,000 pounds, whilst the Dakota bolt, made from 4140 steel, runs between 120,000 to 140,000 pounds.

The Ruger company did a comparative test with their M77 action against Mauser ... they tested the strength of the locking lugs on a Olsen tensile machine and the Mauser lugs sheared off at roughly 29,000 pounds compared to 40,000 pounds for the Ruger. If we look at Daniel Lilja's formula above, applied to a Mauser action made from 1040 steel, we find that it is basically spot on ... 14,263 x2 = 28,526 pounds. Based on this empirical test and calculation, I feel that the Mauser locking lugs are strong enough. I consulted various gunmakers and they assured me that they have never seen the lugs breaking off, save for one gunsmith that said he had seen one bolt with a cracked locking lug. Could this be due to subjecting the bolt to much higher pressures that are typically encountered at a Proof House? Incidentally, Hartmann und Weiss is the only gunmaker that decided to make their locking lugs thicker despite the use of the best modern steels.

Hope it gives an indication of how far you will be off the critcal level of 29,000 pounds. Even if the thrust goes to 18,000 pounds (liberal guess), then there is still a safety margin of 11,000 pounds or 61%. Important though is that the lugs must make flat contact with no play at all - aim for a 100% bearing surface. For insurance you could also subject old actions, that may have been subjected to abuse, to x-ray examination for internal cracks that are not visible to the naked eye. Sadly Proofhouses do not do this (with older generation actions) in an attempt to save a few bucks - silly in my opinion as what would $50 be in the context of the cost of a custom rifle. Also avoid war-time K98 actions that were made after 1939 - case hardening problems have been observed, which results in lug setback as the working area is soft, and the same goes for when your gunsmith shim off too much to 'true' the lugs.

Chris

quote:

Originally posted by Hammer:
Is a Charles Daley Mauser suitable for building a 585 Nyati ?

See where the 30/06 version is available in left-hand.

Hammer

Hammer,
Since you want both a mauser and a lefty, the Daly is the only way to go. Get it IN THE WHITE, and all the rubbish about CD actions is circumvented.. of course, a $50 surface grind . a surface grind makes the dalys look exactly like... oh, Interarms, MarkX, Parker hales, and whitworths ... why? because they ARE those same actions

best of luck, and too bad the daly's aren't available with the magnum actions and lefty

jeffe

quote:

Daniel Lilja gives the following formula to calculate the lug shear strength:-

LS = length of Arc Segment x axial length of Lugs x No. of Lugs x Yield Strength of Material/2
= (.366 x .433 x 2 x 90,000)/2
= 14,263 pounds (original Mauser)

I have never got Mauser bolt lugs to fail in shear.

I just got 30 Oberndorf surplus Mausers, and two had lug set back to the reciever race. That would be a compression calculation.

quote:

Also avoid war-time K98 actions that were made after 1939 - case hardening problems have been observed, which results in lug setback as the working area is soft, and the same goes for when your gunsmith shim off too much to 'true' the lugs.

Tnekkcc,

The compression bit that you refer to is addressed in my last sentence and it is related to surface hardening that takes the brunt of the work where the metal makes contract with metal. I stated further ... " Important though is that the lugs must make flat contact with no play at all - aim for a 100% bearing surface."

Chris

Hello Dan,

Have you had a chance to plug the numbers into the formula for a result, If so what is the backthrust?

What do you plan for this custom rifle - exclusively for elephant hunting? That is why I love the 404 Jeff so much - it only yields a bolt thrust of 8,060 pounds; the 458 Lott yields 11,077 pounds, the 460 Weatherby yields 14191 pounds, whereas my guess would be 18,000 pounds for the 585 Nyati.

With the modern/premium bullets we have today, The 404 Jeff povides the best ballistic ballance in my opinion - enough momentum, low recoil, low chamber pressure, low back thrust, sufficient penetration with solids, and on top of all that, it is a classic with a good reputation.

Chris
Take care.

Chris,

When I get a moment I plan to put a .585 nyati case in a vise, cut it in half, measure the inside of the case head to get the figure you referred to above, then do the calculation. Unfortunately it was -18 degrees C. in my garage this a.m., so not a good time to do the sawing.

I have my 2nd .585 in the process of being built, but progress is very slow. It uses an Ultramag action, which has a 0.720 bolt body diameter but basically just M98 lugs. However it is made from modern steel, and I was curious what the figures would shot. My M70 .585 held up just great, but I did not shoot it a lot - definitely under 200 rounds although I did not keep records to tell me exactly how many shots.

The rifle, once completed, will kill at least one elephant at close range. Is there any other purpose of a rifle?

Thanks for laying the groundwork!

quote:

Originally posted by 500grains:

...The rifle, once completed, will kill at least one elephant at close range. Is there any other purpose of a rifle?

Prairie dogs when they go under.

Becareful Dan. Use that .585 too much and your .500 NE might get lonely...

If the front two lugs sheared off you would still have more to break to stick the bolt in your cheek. Remember when crunching all these numbers that the 98 Mauser has at least 3 maybe 4 lugs if someone has done a winchester style custom bolt job. Nothing like a little safety net. If something is going wrong, nothing deflects all the crap coming back in your face better than a 98 Mauser. At Trinidad we filled a 338winmag full of red dot and fired it in a 7mm barrel filled with lead. This was in a Chinese wartime 98mauser copy. The bolt still wouldn't come out!
gunmaker
gunmaker

Chris,

As the temperature in my garage rose to +8 degrees F., I went out and sawed a .585 Nyati case in half. Here are the actual measurements. This was a piece of Bertram brass. All measurements are in inches.

A - case rim: 0.636" diameter

B - extractor groove ahead of rim: 0.569" diameter

C - case head (ahead of extractor groove): 0.665" diameter

D - inside of case head, where flash hole terminates into case: 0.314" diameter (the case head wall is quite thick at this point)

E - from point "D" above the case wall thickness tapers sharply outward in a funnel shape toward the case mouth for about 0.300" along the case length. At that point, the measurement is 0.590" diameter. If it is not clear already, measurement E is taken 0.300" toward the case mouth from measurement "D".

What is next? I am still a little unclear of which measurement to use in calculating thrust. If you could guide the way, that would be great! Thank you.

Dan, I am quite surprised that the case head walls are so thick. Anyway the clever people say one must use the max inside diameter of the case head and not the outside diameter of the case rim. So let me stick to that then, and use .590"


Cartridge -------------------- 500Jeff ----- 585 Nyati
A) Max inside Case dia. ---- .564" ------- .590
B) Area in Sq inches -------- .250" ------- .348
C) Chamber Pressure ------ 46,412 psi-- 50,000 psi
D) Bolt Thrust in pounds --- 11,603 lbs-- 17,400

My guess of 18,000 pounds was thus not too far off.

That is a serious thrust. Make sure the lugs are in good condition and that they are case hardened properly again after machining. I would insitst on an X-Rays, as the few dollars will just add to your peace of mind.

Take care buddy.
Chris

Chris,

Thanks for the calculation.

Is it true that Mauser 98's are designed for 30,000 pounds of thrust? At 18,000 pounds, that still gives a fair margin of safety (unless there is a defect in the action, as you mention).

Also, it would seem that the .585 nyati cartridge may make guys age prematurely. What say you?

Dan- Forget using a M98. Unless you really know what metal alloy was used to make that action, and how it was hardened, you might be facing a very expensive fix after only a few rounds. Get a CZ550/602 action and do it right. I have a very good formula for a .585 NYATI now including the right chamber reamers and integral m uzzzel brake. I used it last year at the Texas STC hunt even making running shots on pigs with the gun. Many others here have also fired it. Give me a call and I'll give you the details.-Rob

Dan,

The Mauser action was designed for a 7x57 and a 8 x57 actually. Later on it was adapted for bigger cases. So it was not originally designed to handle a thrust of 30,000 pounds day in and day out. In fact the Ruger company did a comparative test with their M77 action against the Mauser action and found that the Mauser lugs sheared off at roughly 29,000 pounds compared to 40,000 pounds for the Ruger.

Not being a metallurgist, I am not quite sure what margin of safety one should have to avoid metal fatigue over the long haul, but I would venture to say that the margin between 17,400 and 29,000 pounds would be adequate.

What we do not know is the extent or possibility of prior abuse to the action. When a proofhouse test to a level of 50% above CIP (say 62500 psi, for 3 shots @ 1.5 = 93,750 psi), I regard that as abuse, and if the action is not subsequently subjected to an X-ray examination, I regard such a practice as positively negligent and unsafe.

Superficial examination provides me with no comfort at all. Dammit, these engineers should know better and that for the sake to save R100 (in SA), which is the equivalent of $15 in the States. Even if it was $50, then I would still insist on it.

Chris

When you are figuring thrust like in the
585 you must subtract the part of thr thrust
that the brass holds, which is about 5000 lbs.Sothat gets the thrust back down to the figure I gave above. I use a simple formula so cases don't have to be sectioned. It is the
base area ahead of rim or belt times peak pressure times 2/3...The 2/3 allows for the
difference in OD and ID of case and the amount of thrust the brass holds... Most bolt action designers try to get close to 3 to 1 safety
margins, between operating pressures and lug shear ratings. Example is Mcbros 50 cal action,
with a 75,000 lb shear rating and the 50cal
cartridge thrust being about 25,000 lbs..Ed..

The case head does not push back until the pressure is 40,000 or so. When it comes back it comes back with full force as the yeilding brass has almost no tensile strength. This is why low pressure loads will push the primers out when there is headspace.
Good luck!