Just musing, here. Not sure if this has been done before:
Take the 408 C-T, neck up to .510", cut at (4"-(bullet length)+(.5" neck)), COL as close to 4" as will feed, and you've got a shoulder-fired mini-BMG round for your P14 or MRC PH.
The case should hold around 156g of water, at 2.5" length.
Anyone care to run a Quickload check for some of the smaller bullets, say 650g or so, out of a 32" bbl?

Wouldn't that be reverse engineering, or engineering in reverse, as the 408 CT is the 505 Gibbs necked down?.
That said, I ran a 408CT case into my 510 Phalanx dies, makes for a 2.00" case length .510" caliber round that fits most big actions.

Reverse enigneering, perhaps, but I figured the brass would be easier/cheaper/stronger, and besides, I think the only thing in common with it and the Gibbs would be the base dia.
What I'm thinking is something along the lines of SSK's Whisper, but with a bigger case. Something that will stay supersonic for 1000 yds.

SSK's peacekeeper is essentially the same as what you're talking about. A 460 Wby case necked up to hold 50 BMG bullets.

Said "whisper," meant "peacekeeper."

Sorry for the confusion.

As to this being like that, take a look at the Weatherby and Gibbs cases side-by-side.

BIG difference.



And...

The jeffery is smaller as well. Why not is that I'm talking about fitting 50-cal match bulelts in a 4" action, so a case longer than described (4" - bullet + .5") is just wasted space.

Haven't seen the two side by side, but the capicities appear to be the same, or very similar anyway, as all the load data I've seen for the Gibbs shows maximum charges of 120 gr. which would be on par with the Wby? Also, velocities for the same bullet weights appear to be nearly the same. Just asking... honestly.

Regards,
Tom

Well, I suspect that it has a lot to do with shooters' shoulders than case capacity.
Send a 600g out at 2300 and see if you want more powder....
But the Weatherby is about .582" at the base, and the Gibbs is .640" or so. (!) That's a 10% bigger case. Zoinks.

Noticed some erroneous case volumes.

The following volumes are measured and expressed in grains of water.

416 Rigby: 126 - 128
460 Weatherby: 134 - 136
500 A Square: 138 - 140
500 Jeffery: 148 - 151
500 AHR: 156 - 158
505 Gibbs: 169 - 176
585 AHR: 184 (per AHR)

You can get 2700 fps out of a 505 Gibbs with a 600 gr bullet easily, barrel length 27". I know I have done it. You can get 2700 fps with a 570 gr bullet in a 500 AHR easily, barrel length 26". Again I have done it. Never pushed a 500 Jeffery over 2500 fps with a 570, though. Ditto that for the 500 A Square.
I would however state that all of the above hotrodded loads were maximums and for safeties sake should not really be duplicated.

You should also realize that when you are working with mauser type actions ie twin opposed lugs with bolt diameters between .7" and .75", and shooting 60,000+ psi loads in the 500 Jeffery and/or 505 Gibbs case heads the primary failure mode is no longer the case. The thrust forces generated by these large diameter cases, at those high chamber pressures, can actually lead to catastrophic shear failure of the locking lugs on your Mauser type bolt action before the case blows a primer or the bolt gets real sticky. Therefore, I caution you both to be very careful if you actually go forward with a scheme like this 510 C-T. Would hate to see anyone get hurt when all they had to do was buy a 50 BMG bolt action to begin with.

Might I suggest a 50 BMG ultra short magnum instead. Take a 50 BMG case shorten down to 2.75", 25 deg shoulder, 0.5" neck. Get the idea?

Scott

Thanks for the response, Scott.
As for capacities, note that the Gibbs case has over .016/1" taper, and that can be improved pretty radically. My design has .005/1" taper, and that should account for about 9g in the full-length case. Also, not that much of that case volume comes from unuseable neck space, and that a proportionate neck on my case would make it 2.65" long instead of 2.5". I could be wrong, sure, but I don't think 155g or whatever I said is beyond possibility.

Not sure who mentioned a Mauser, but your point is well taken. My idea was to use a big Enfield-type or MRC PH, both of which it seems will handle this casehead plenty well.

My long-range interests are much stronger in the 30-cal arena, but if I do get around to building this one, I bet it will be a hoot.

Bwana-Be,

The Enfields, I assume you are referring to the M1917 or Patern 14, are essentially Mauser type rifles. I do not know anything about the PH model you refer to. So my comments are only valid for the Enfield. I would get a stronger action if I were you, but I have been wrong in the past. I know for a fact, that weakest link in an Enfield, from a catastrophic failure point of view, is bolt lug shear. The Enfield action is not really any stronger than a M70 Classic and may actually be weaker. Do you know what allow the M1917 or Pattern 14 was made of?

Like I said before, have fun but be safe.

Scott

Enfields are fine. Lots of room. A-Square blasters are built on them.Mine in 458HE puts out 9000 ft lbs.Just
don't crack the reciever taking out the square threaded barrels that set up in action after many years...IE, machine away shoulder on old barrel and it turns out easier.
If recievers are not cracked from putting in and taking out barrels they work.And they can be re-heat-treated also.Some were not heat treated properly, and those show the cracks.

As mine was a wildcat test rifle I made a third lug
on the root of bolt handle, that contacted back of the bolt handle recess, at same time as bolt lugs.Thus I had 3 lugs
bearing when chamber loaded.Ed.

Ed, that's a damn fine idea.
I was lookign at some Remington 30's the other day, wondering how I could get a third lug into the bolt. The handle is where it goes, though. And with all the expense of getting one into shape, this can't rreally add anythign to overall cost.

Yes the bolt handle is already a safety lug(a very big and strong one, that sets about .030 inch away from back of
the bolt cutout recess,So when I straightened and welded bolt longer I added round spot of metal to close up the
.030 gap.Actually made it thicker and ground it off using
dye on bolt lugs until they all touched.Then I chambered and headspaced.My first test rifle for my blaster, my Ruger
77, I did same process to it.If I was using a third lug rifle(like a Mauser)for my hairy wildcats I would do the same on third lug.And grab that Model 30, as it is a super
nice bolt action for big cases, like Enfield.The Enfield has
such a long rear bridge, that when shortened up it allows opening for long cases.Have a friend with Model 30 in 300
Weatherby, and heavy barrel and he can stick a bullet in
a deers ear at 400 yds.Never could get it away from him to
make big bores.Ed.

Thanks for the info, Ed. How much clearance did you leave?
Does the handle literally cam down onto the receiver?

Bwana-The camming action is done by the time the bolt
with the contact spot goes into the reciever bolt handle
cutout.And it contacts tight at the same time as forward
bolt lugs.Done that way,as my Enfield and Ruger77 is, you couldn't blow the bolt out with a 150k load..Ed.

Ed,

If I understand Bwanabe correctly, he wants to modify a 505 Gibbs case to improved standing. He then wants to load 50 BMG 647 gr ball bullets and load them up to get a muzzle velocity of ~ 2700 fps.

In order to achieve this he will have a chamber pressure of ~ 70,000 psi.

In an Enfield rifle with the front lugs bearing 100% (which is impossible even with lapped lugs) here is the deal:

Lug shear stress is greater than 180,000 psi. That equates to bolt in forehead!!! Your third lug idea may keep the bolt from hitting your forehead, but it will not stop the front lugs from shearing on the first or second shot! Sorry.


150,000 psi loads?? What kinda case are you using? Or was that a little bit of an exaggeration?

Scott

With shortened case he wants to make he doesn't plan
on getting that velocity..And he isn't planning on that
pressure.50-55k is what I think he wants.As far as Enfield,
the blue pill they test them with are much more than 70k,
and only two lugs.And getting those lugs to bear even can be done as I have.With a 55k load the thrust against the bolt with Chey-tac base is about 20k minus what the
case helps to hold when it grips the chamber on firing.
Bolt thrust will be about half of that I think.
And 50k loads in my wildcats extract easy in the Enfields,
one is 458HE and other was 510HE(soon to be a 55OHE)..
The 510 got a 600gr soft jacket bullet to 3000 fps.Ed.

Perhaps I misunderstood his intentions.

For the record, a Enfield that was proof tested at 70,000 psi would have been proofed with either a 30-06 or a 303 British. A 30-06 producing 70,000 psi of chamber pressure would generate ~ 85,000 psi of shear stress on the lugs of an Enfield rifle if both lugs are bearing 100%. Considerably less than the same pressure in the MUCH larger 505 Gibbs case!

What is you 510 HE? I have ran several different lengths of 500 NE basic brass through a program and with a 600 gr pill loaded to 58000 psi these are the predicted muzzle velocities:

500 3 1/4" - 2440 fps (30" tube)
500 3 1/2" - 2617 fps (30" tube)
500 4" - 2814 fps (30" tube loaded to 60000 psi)

Please tell me more about this wildcat of yours. Will it fit a Ruger No1?

Scott

Ed, for the record, you've got me right.
Something like 2450 from 30", 50-55k.
As a single shot, with less restrictions on COL, I fantasize that the right powder could get it to 2500. Definitely plenty for 1mi supersonic at any rate.

My 510, soon to be 550HE(Barrel goes for reboring after holidays), is a 3.7 in case, with a base
of .580. Straight like all my wildcats. Loaded with 185gr
compressed load of W-760 it gets 600gr soft jacket to
3000 fps. Barrel is 32 in. Gun weighs 16 lbs.

As for the shear stress on bolt actions the actual bolt thrust is not like the figures you mention... On Lilja's
site they analyze a McBros 50 BMG Action.Its two lugs have
a .99 sq in cross-section, with a shear strength of 71,000
lbs.(about 71,000 per sq in).They used a 65,000 psi load
as example, which puts a thrust of 23,600 lbs on that bolt, for a safety margin of about three times.You get the thrust by the base area times psi times 2/3 as the case carries
about 1/3 at those pressures.(on BMG .8 x .8 x .8 times
65,000 psi times 2/3)....Now my Enfield with the extra bearing lug on the bolt handle base has a total lug shear
area of .75 sq in, which would have a shear 53,000 lbs.(the
rifle with two basic lugs the shear is 33,000 lbs).The bolt thrust with above formula for 65k load and a .580 base case
is .58 x .58 x .8 times 65,000 times 2/3 = about 12,000
lbs, still with plenty of safety margin for two lugs
with shear rating of 33,000 or with extra lug on bolt handle
base with shear rating of 53,000 lbs. You asked if I had a case good for 150k and no it wasn't good except to not come apart when I shot one at that pressure, on my first wildcat 458He rifle, the Ruger 77 with same extra lug surface added.
Wasn't something I planned. Bolt didn't budge and I removed barrel and case with lathe.Safety factor working...Ed.

Ed, are you a pro smith, or just work on your own stuff?

I work on my stuff only-Nothing fancy--Do own, barreling, chambering,welding, all the cartridge and load development, and building my rifles strong ehough to be test rifles.
I can inlet a stock but no checkering, and no engraving,
and mediocre finish and bluing.I have studied internal ballistics for 50 years, and that has made me into a
wildcatter.Ed.

Ed,

Thanks for the information. My reason for posting the stress data was to instill in those reading this thread that bad things can happen when doing the things we are talking about in this thread if due care is not taken. My motto, particularly in internet forums is, 'safety first'.

Scott

Scott-Safety is word.That is why I added third bearing lug
in my experimenting with huge long cases.IE the relative
quickness of powders change as the powder column gets longer
between starting and max loads.Thus if a case stuck from an overload as I incrementally added powder,( the relative quickness of half the powders changed in my big case compared to Lott size case), the extra lug kept the original
two lugs from setting back, and I could keep on testing
(without reseating lugs and re-headspacing),
throwing out the to high of psi loads.

In all of this bolt thrust engineering the most important
thing that goes along with the proper lug area is the quality and strength of the reciever.IE make sure no cracks
and heavy enough.In high pressure the reciever has to hold
more outward stress and if it blows, even though safety
lug keeps bolt out of face the front of action can do you in.It would be nice for MRC to take their .800 dia bolt PH
action and design it to a little larger dia barrel thread,
(like 1.25),and build action correspondingly thicker, as I have a wildcat little bigger than 600 NE size base.
And it would be great for Bwana's creations, 600 OK, Nyati's,JD's stuff,and T-Rexs...Ed.

If you're interested in the 408 CT case, The one I weighed with water was 164.5gr to the top. I'm not sure what the taper is on it compared to the Gibbs, but it does have quite a bit of taper, and thus room for lots of improvement.
There is a substantial difference between the Gibbs and the 500 Jeffery case too, the 460 WBY case is much smaller on top of that.

Ed,
How am I doing for bolt thrust on the Remington 700 with my 30-338 Lapua Imp? The case tapers from .585" at the base to .570" at the shoulder. My brother has a 700 in 338-378 WBY as well. No problems I've ever heard of with them to date either. I've run the 210 Berger and JLK's to 70,000 PSI (Oehler M43 and PressureTrace) with no lug setback. Mine also has a 30" 1.35" dia straight barrel on it, but is going in a barrel block soon. I'm also sizing for just .002" headspace.

Brent--Your load in the 700 is putting 15,000 lbs of force
against bolt lugs that have a shear rating of about 37,000
lbs, as best as I could figure from the size of lugs.In all of this discussion about bolt thrust, they all designed in a lot of excess rating.For example the Germans took Mausers
and made the Geha and Remo 12ga shotguns with no lugs bearing on front with the safety lug as the only bearing surface, and it was proof load tested, with no problems.They had to machine out all the lugs seats to get shell into action..Schultz & Larsen made a rear locking lug action that Weatherby used as well as their own real high pressure cases(like 308 Norma).I know for a fact that my 77 and the Enfield, could hold 35k loads with just a lug on the bolt handle, and the back of the front lugs ground away.
The Krag only had one dinky lug to hold about 35k...Ed.