(500 Van Horn Express article by Sam Fadala in GUNS-1991 ANNUAL added near bottom of this page.)

Jim (member capoward) did the preliminary drawing, after hearing my suggestion of necking up the 49-10 to .510-caliber and extending the case length from 2.657" to 2.700".
Why?
So as to use some Duane Wiebe 500 Jeffery bottom metal on a standard Mauser, yet avoid the 500 Jeffery cartridge, again.



Here are two 500 Mbogo-3" dummies,
(far left has fire formed shoulder, second from left is unfired from Quality Cartridge, Hornady basic)
and three of the 500 Mbogo Short dummies,
one made with 500 Mbogo brass shortened to 2.700" (extreme right below)
two made from 49-10 brass simply necked up came out at 2.650":



The 500 Mbogo brass shortened, shoulder pushed back, gave a neck diameter of .535", and nicely uniform throughout.
The 49-10/.338LM brass gave a Neck-2 near case mouth of .533", but 0.540" at Neck-1 near shoulder.
Dreaded donut was not a problem with the 49-10.
I shall declare the 500 Mbogo Short (2.7") to have a brass neck diameter of .535" at neck-1 and neck-2.
Reamer neck diameter will be .539" at neck-1 and neck-2.
Inside reaming or outside turning of 49-10 brass will be used if necessary.
Shortened 500 Mbogo brass will be easy,
proper head stamp already,
for both the 500 Mbogo 3" (Long) and 500 Mbogo 2.7" (Short).
No confusion.
Length difference is obvious at a glance.
Shoulder difference requires a closer look to discern:
500 Mbogo 3" has 35-degree shoulder.
500 Mbogo 2.7" has 20-degree shoulder.

Just to avoid doing a 500 Jeffery.
500 Jeffery case length is 2.750".

This is an FN Mauser currently barreled as a .375/.338WinMag, originally meant to become a 49-10, then changed plan to a .375/404 Jeffery Saeed of 2012,
when the bolt face was still of H&H belted case size,
it is now destined to be a 500 Mbogo Short.
The bolt face has now been opened up to accept the .416 Rigby/.338LM rim.
No going back now.



500 Mbogo Short dummies above measure from 3.380" to 3.465" in length.
The Duane Wiebe bottom metal above has an inside-box length of 3.501",
and a massively thick front wall of box.
The opening in the bottom of the receiver must next be enlarged to be flush with the side width inside the box.
This will be a better fit for the 500 Mbogo Short than it is for the 500 Jeffery.
Closer to perfection in many ways, for cartridge and rifle.
Of course the current stock will need some improvement, but that will be mainly cosmetic.
I like the way the box hangs below the stock.
Looks sort of like one of Saeed's .375/404 Jeffery rifles.
That feature might be retained by using a B&C Medalist stock for standard M98 Mauser.

Hater! Proud owner of a pain in the ass but perfectly functioning 500 Jeffery lol

Yes,
I am a proud hater of the 500 Jeffery.
Condolences to all 500 Jeffery owners, an ugly duckling cartridge only its mother duck could love.

Sure like mine.

Brad,
That First Generation RSM rebore is pretty.
Barrel looks pretty slim too.
I like the looks of that.
Bigger bore certainly improved the balance I reckon.

Was it a .375 H&H with .750" muzzle diameter at 24" length?
Or was it a .416 Rigby with .810" muzzle diameter at 24" length?
I guess the former from the taper of the barrel.

What is the dry weight of the rifle now that it has the .510-caliber rebore?
Might have lost 3/4 pound in rebore?

I am thinking a Number 6 sporter contour would be very similar to your barrel contour, and would be to my liking for the 500 Mbogo short.
Stainless and 1:12" twist is what I am thinking,
since that worked so well with the 49-10 of .500-caliber, which is the basis for neck-up to .510 caliber.
I might go barrel length of 23", or 600mm (23.6"), or 24" at longest.

McGowen seems to be the only barrel offerred standard to suit me: 1:12" twist (as well as the 1:10" of my youth ... guess I am slowing down in old age)
.500" bore/land, .510" groove, 6-groove.

Seems McGowen has had trouble delivering on time lately.
I used to get them in 6 weeks occasionally.
Lately they have been taking 6 or 7 months to deliver?

I have been waiting nearly 6 months for a Pac-Nor .375 barrel. They offer a 1:9" twist but not 1:12" in .510-caliber.
Dan Lilja delivered a .375 barrel in 3 months recently ... but 1:15" twist is as fast as they will go on twist in standard offerings for .510-cal.
Shilen, Douglas, Krieger, Lothar Walther: Nope, nope, nope, nope, none suitable in .510-caliber.



McGowen it will be for the 500 Mbogo Short.

Ah so now we have more exact measurements for the neck area. So that has some related changes for the reamer…here’s an updated copy:

Wunnerful, wunnerful, thanks Jim.

Well if you really want to do in the 500 Jeffery why not go with a 2.75” case length and just open up the box? Here’s what you’d have with the same 35º shoulder of the original 500 Mbogo 3” case – the new 500 Mbogo Short v2…

quote:

Originally posted by RIP:

Shilen, Douglas, Krieger, Lothar Walther: Nope, nope, nope, nope, none suitable in .510-caliber.

Well RIP - I just received my .510 barrel from LW. 1-10" twist. Sure looks good ... This is my first LW barrel ever and it sure looks good

quote:

Originally posted by buffalo:

quote:

Originally posted by RIP:

Shilen, Douglas, Krieger, Lothar Walther: Nope, nope, nope, nope, none suitable in .510-caliber.

Well RIP - I just received my .510 barrel from LW. 1-10" twist. Sure looks good ... This is my first LW barrel ever and it sure looks good

Ulrik,
I am very happy for you. Excellent choice.
I have two rifles with Lothar Walther barrels,
and they are superb.
If I could find a stainless 1:12" LW .510-caliber barrel on this side of the pond, I would be very happy for me.

I have three McGowen 1:10"/.510 barrels,
one Pac-Nor 1:9"/.510 barrel,
two Pac-Nor 1:12"/.500 barrels.
It is about time for me to try a McGowen 1:12"/.510-caliber barrel.
Hopefully they will take less than 7 months to deliver.

I'm hoping that my McGowen 1 in 12" .510" will be done by Nov., chambered 500 AccR Nyati, and installed.

RIP-
Why the 1-12" preference over the 1-10"??

quote:

Originally posted by buffalo:
RIP-
Why the 1-12" preference over the 1-10"??

I like it when bullet fps (feet per second) at the muzzle equals bullet rps (revolutions per second).
That numerical singularity only occurs with 1:12" twist.
And I am an equal opportunity barrel buyer, want to try a 1:12" to go with the 1:9" and 1:10" .510-caliber barrels I already have.
And I doubt I will be using 50 BMG bullets much in this one, though most milsurps will work well in this short throat and 1:12" twist.
In fact, it might be the most accurate combination of throat and twist for 1000-yard target shooting with black-tip AP bullets.

A long and heavy target barrel from McGowen of 1:12" twist with a muzzle brake, on a Weatherby Mark V,
chambered for 500 Mbogo Short,
could be extended to 500 Mbogo 3" after accuracy testing of the Short.
And I do have a separate throat reamer from my 500A2/.510 JAB days ... if needed to seat 750-grain Hornady A-Max bullets out to 4.500" COL in the 500 Mbogo Short ...

Better order two barrels from McGowen.
One short and light for FN Mauser with QualCart brass.
One long and heavy, for Weatherby Mark V with Lapua brass.

More than one way to skin a wildcat, and avoid a 500 Jeffery.
Then I will look for the local Wildcatter's Anonymous chapter and try to swear off this nonsense before I go blind!!!

When .338 Lapua Magnum brass is fire formed to 49-10 brass it goes from 2.724" to 2.707", shortening as the neck expands.

It has been very tedious to trim this stuff down to 2.657" maximum/2.647" minimum trim-to length for the 49-10.

Now I will have minimal trimming to 2.700" maximum/2.690" minimum trim-to length, for the 50-12, 500 Mbogo Short.
Merely a touch of trimming to uniform the case mouths and the length to 2.690" minimum length, 2.700" maximum.

However, inside reaming or outside turning may be required, with the Lapua brass.
Not so with the 500 Mbogo Quality Cartridge brass for 500 Mbogo 3".
But that will require trimming from 3" to 2.7":
@#$%^&*!!!

quote:

Originally posted by RIP:
Then I will look for the local Wildcatter's Anonymous chapter and try to swear off this nonsense before I go blind!!!

Ulrik,

Thanks for the empathy. I know you are doing some "two-barrel" exercises too.

I have slept on the idea and still like it.

.255" PS-free-bore (that is the length of the parallel-sided portion of the chamber throat) for a Mauser with 3.5" box and light, short barrel.

Lengthened PS-free-bore for a Wby MkV with 3.8" box and long, heavy barrel.
PS-free-bore will not exceed whatever is needed to give effective free-bore of +0.050" with the Hornady A-Max 750-grainer loaded long.
I don't know how long, just yet.
Making it too long with the Hornady parallel-sided bullet shank hanging out too far beyond the case mouth:
That will make it inaccurate with the vast majority of target bullets and milsurp bullets.
It might even turn out that 0.255" of PS-free-bore length is the accuracy optimum for all!!!
Just have to seat to fit that throat,
which I am sure will work well with the light weight hunting bullets.

Maybe my goal is this for the 500 Mbogo Short:
Accuracy, and supersonic velocity to 1000 yards with BC of 1.050 for 750-grain Hornady A-Max.
Throat as needed to do that.
Slower velocity, seat deeper, keep throat as short as possible, close as possible to .255" PS-free-bore.
Guess: 1750 fps MV will give 1150 fps at 1000 yards with BC = 1.050? Need 'puter calculation ...
Anything over 1800 fps MV will be gravy for the 500 Mbogo short with 750-grain Hornady A-Max.

This is where the "effective free-bore" comes into play, incorporating all components of transition to and length of throat:

Plus chamber length tolerance to case neck mouth diameter, neck-2.
Neck chamfer of 45 degrees for "step-down" from chamber neck-2 diameter transition to throat at PS-free-bore diameter.
Parallel-sided free-bore length.
Leade.

Effective free-bore for a specific bullet ogive and Cartridge Overall Length (COL) is adjusted by adjusting the length of PS-free-bore,
with a throat reamer.
Throat-only reamer: Incorporates a diameter of PS-free-bore and a fixed leade angle, leading the way, with a pilot of bore diameter.
PS-free-bore is lengthened by pushing it in further.
Not a neck-and-throat reamer. Chamber neck is left untouched.

Captain Obvious:
"No need for any confusion in throat terminology, it is just obvious, plain English."

Assume 2700 fps with 750-grainer in 50BMG accuracy load in 1:15" twist rate barrel: RPS = 2700 x 12/15 = 2160 rev. per sec.

Slower plinkers:

2150 fps with same bullet in a 1:12" twist: RPS = 2150 x 12/12 = 2150 rps

1800 fps with same bullet in a 1:10" twist: RPS = 1800 x 12/10 = 2160 rps

I think a long-barreled 500 Mbogo Short will do closer to 2150 fps with 750-grainer.
Especially if using Lapua brass to 65,000 psi.
Just keep throat as short as possible over .255" PS-free-bore length and all else will be good.

A preliminary cartridge drawing, shoulder is tiny, neck diameters will not exceed .535" on the brass, will make it fit as necessary.
Smaller shoulders than this have worked on some famous cartridges. This obscure one will do:

Cartridge brass Maximums:



Chamber Minimums:



750-grain Hornady A-Max BC 1.050, MV vs 1000-yd retained velocity in fps:

2700 ... 1914
2150 ... 1478
1950 ... 1333
1750 ... 1205

All still supersonic at 1000 yards, all worthy velocities for plinking.

I have overcome my fears of necking up .338 Lapua Magnum brass to .510-caliber.
The intermediate step to .500-caliber was very reassuring along the way.

This Old Thread is from 2-19-2006:

http://forums.accuratereloadin...1043/m/830108924/p/1

In this old thread jeffeosso was thinking of making use of the name "500 Mbogo Short" as a cartridge name,
and initially thinking about a 3.1" COL and a shoulder other than 20-degree.
500 AccRel cartridge drawing was changed to current final in this thread.

Everything old is new again.

I also bit the bullet and ordered the all-in-one 500 Mbogo 3-Inch reamer, noted in this thread,
instead of fussing with separate neck and throat reamer to use with a 470 Mbogo reamer with .510 pilot.

Next order:
All-in-one 500 Mbogo Short reamer, aka 50-12.
The time is now right, 2012, for the Fifty-of-Twelve.

Observations and questions
The 500 Jeffery no matter how you feel about it good or bad has less than .35" neck.
If you necked up 416 Rigby brass to .510", trimmed to 2.7" and started the shoulder at the same place as the 416 Rigby position you would have about the same length neck as the 500 Jeffery but possibly less neck/shoulder forming and neck reaming issues?
Fire form, trim and maybe some neck reaming. Not a purist approach to design but maybe slightly more practical? I like longer necks too but this idea might be easier to make brass. Just some musings.

quote:

Originally posted by boom stick:
Observations and questions
The 500 Jeffery no matter how you feel about it good or bad has less than .35" neck.
If you necked up 416 Rigby brass to .510", trimmed to 2.7" and started the shoulder at the same place as the 416 Rigby position you would have about the same length neck as the 500 Jeffery but possibly less neck/shoulder forming and neck reaming issues?
Fire form, trim and maybe some neck reaming. Not a purist approach to design but maybe slightly more practical? I like longer necks too but this idea might be easier to make brass. Just some musings.

Egad! Who would want such a short neck?
Also you will note from the old thread that I suggested (to jeffeosso) using the 20-degree shoulder on the 500 AccRel,
which he did in final design.
I am in love with that shoulder angle.
Same as on the .338 Lapua Magnum.
Same as on the .395 Tatanka.
Same as on the 404 RIP.
Same as on the .375 Tornado.
Same as on the 49-10.
Same as on all my .338 Lapua wildcats.

The shoulder on the current 50-12 (500 Mbogo Short) under construction is located at the same base-to-shoulder distance as the .338 Lapua Magnum shoulder, same shoulder angle,
but shoulder diameter had to be blown out for both the 49-10 and 50-12.

If you neck up a .416 Rigby with all its case body taper and narrower shoulder, there is no shoulder left, irons it flat with a .510-caliber bullet.
Gotta blow the shoulder out to have any shoulder at all. So, why not change it to the better 20-degree angle instead of the horrid 45-degree angle of the Rigby,
and use the same shoulder diameter and headspace gage as used for the 49-10?

The case body taper is already minimized there to about 0.0085"-taper per inch of case length.
IIRC the .416 Rigby taper is over 0.0200"/Inch.
That is way-no-good as is for a simple neck-up and neck trim, won't work.

When I have a rifle properly chambered and the .338 Lapua Magnum brass is fireformed in it, there may be zero neck issues.
Will have to see.
Neck uniforming will easily correct if any problems.

Using .416 Basic or 500 Mbogo-3" brass trimmed down and sized in 49-10 dies, then necked up to .510 instead of .500 bullets,
will be an easy start on ammo ready to shoot, maybe even ready to hunt with.


If you change the .416 Rigby shoulder angle from 45 degrees to 20 degrees, leave base-to-shoulder distance and shoulder diameter same,
then you will shorten the over-long .416 Rigby neck a little, and increase the case capacity a little.
That would be a beautiful .416 Rigby Improved.
That is similar to what they did as a birthday gift for Bill Ruger once upon a time.
That was the "FIRST" .416 Ruger, back in 1991:





They made the rifle for Mr. Ruger's birthday in 1991.
His birth year was 1916.
They finally made 200 pieces of brass for the rifle in 1997, 6 years after the rifle was presented as a birthday present.
Hence the funny headstamp numbers.

Wait a minute!
Is that a double-radiused Weatherby shoulder on the .416 Ruger of 1991?
Was it also the the first .416 Weatherby-Beltless?

http://www.ammo-one.com/416Ruger.html

No. 6 sporter and medium target contour barrels ordered from McGowen.

Emailed the above drawings to Dave Manson to see what he thinks of them, see if he can make the reamer.

Gil Van Horn was prolific. The 1980's forerunner "500 Van Horn Express" occurred just before the easy availability of .416 Rigby brass.
He turned belts off of 460Wby brass:

From Dr. Ken Howell's book:
Designing and Forming CUSTOM CARTRIDGES for Rifles and Handguns:




And GUNS-1991 ANNUAL article by Sam Fadala about Gil Van Horns's favorite big bore wildcat, back by popular demand:

According to Dr. Ken Howell, the 500 Van Horn Express required inside neck reaming.

It was still Gil Van Horn's favorite.

Great article Ron, thanks for posting...

Hi Jim,
Those have been posted here before. Resurrected.
Can you imagine what Gil Van Horn would have done with easy availability of .416 Rigby and .338 Lapua Magnum brass?

The 49-10, with .500-caliber bullet, has a little more case body taper, thicker neck wall, longer neck, and sexier shoulder angle,
yet similar shoulder width as the 500 Van Horn Express with .510-caliber bullet.

The 50-12, aka 500 Mbogo Short, does all that too, except for having smaller shoulder width,
but it will do.

Anyone wanting an "Egad!-short neck" could trim 0.100" off the 50-12 neck, reduce max brass length to 2.600", and still have more neck than a 500 Jeffery.
Call that the 500 Mbogo Short-Shorted, "500 MSS."

I like the quality bottom metal from Duane Wiebe with 3.500" + .001" length inside the box.

Actually most bullets I would use could be loaded as short as 3.400" length even with the 500 MS-2.7", let alone the 500 MSS-2.6".
And as well documented in the 500AccRel adventures, a Ruger Hawkeye box is long enough for that.
I measured one and got 3.425" inside box length.

Dara says Dave Manson is on vacation for a couple of weeks.
He deserves it, I say!
He will get to the 500 Mbogo Short reamer drawing when he gets back, and dug out, I reckon.

The 500 MSS-2.6" has a new "stepped-free-bore" length of 0.355" length.

I gotta go fire off some .338 Lapua Magnum loads in the 49-10, then trim the brass to 2.700",
then do a little inside-neck reaming experimentation,
to get a loaded bullet neck diameter of 0.535" maximum with .510-caliber bullets.
Quality Cartridge brass with "500 Mbogo" headstamp will serve easily for these three cartridges:

500 Mbogo (3") aka 50-08
500 Mbogo Short (2.7") aka 50-12
500 Mbogo Short-Shorted (2.6") aka 50-13 (this will have to wait until next year)

Goals for 500 MS/50-12 :
2075 to 2150 fps with 750-grainers
2225 to 2300 fps with 600-grainers
2325 to 2400 fps with 570-grainer
2425 to 2500 fps with 535-grainers
2625 to 2700 fps with 450-grainers
... roughly reckoning, somewhere around that, in 23" to 26" barrel length.

Hi Ron,

I'd read the article years ago but it's always good to have a refresher resurrection.

M77 Hawkeye w/3.425" internal box length is perfect...also would be very easy to open up to 3.5" for your 500 MS without degradation of the action's strength.

Gill did very well with his cartridge designs; it would have been interesting to see what he'd have come up with if he'd had access to the shear volume of cartridge cases currently being sold.

I saw that Jamison's brass has been resurrected by the new owners. I understand - though I've personally not verified - that Jamison used the same head and wall thickness designed for the 338 Lapua Mag for his 416 Rigby brass (perhaps just thinning the neck area for the longer length of the Rigby). If so, perhaps they'll offer cylinder Lapua or Rigby brass in the near future at a decent price point.

I've heard good things about Privi mfg/brand brass and notice that Graf's has a good price for 100-piece boxes. May have to pick up some later on and put it to the neck sizing die test!

Yahoo to what I could do with some Rigby basic cylindrical brass from Jamison!

Privi is new to me. Let us know what you think if you come across any, thanks.

Quality Cartridge 500 Mbogo brass = Hornady, good stuff.

quote:

Originally posted by RIP:
Yahoo to what I could do with some Rigby basic cylindrical brass from Jamison!

Privi is new to me. Let us know what you think if you come across any, thanks.

Quality Cartridge 500 Mbogo brass = Hornady, good stuff.

Yep Hornady brass is good stuff.

There's not alot of difference in cost between Lapua mfg/brand 338 Lapua Magnum brass and Hornady/Norma/Nosler 338 Lapua Magnum brass when you compute for 100 cases; but the Privi Partizan mgs/brand 338 Lapua Magnum brass is less than 60% the cost of Lapua brass, less than 62% the cost of Norma/Nosler brass, and less than 67% the cost of Hornady brass. All around a pretty good deal...

Here's a link to Graf's website for the Privi Partizan brass:
http://www.grafs.com/retail/ca...duct/productId/12640

Ooh-la-la! Pretty picture of PRVI brass!
Less than $160/per 100 pieces.
Nicely annealed appearance.

Seyfried's Law of Wildcat Brass Forming: "Anneal before necking up and after necking down."

Corollary: "New brass direct from factory annealing is great for blowing out to larger caliber in fireforming."

PRVI annealed it after they necked the cylinder down to .338 Lapua Magnum.
How nice.
Looks as good as Lapua brand.
If it is a little thinner at neck and shoulder, then inside neck reaming might not be needed.

2.724"-long .338 brass might blow out to 2.707"-long .500-caliber brass, or 2.700"-long .510-caliber brass.
Easy trim job to 2.690", fingers crossed.

http://www.captechintl.com/products.html

Yep good news in both quarters...new annealed Privi Partisan brass at an economical price point and Jamison International back in business.

Now if either would offer 65k-68k PMap 3" cylinder brass with the Lapua/Rigby rim/case head diameter at a reasonable price point the world would be ...