We probably need to start a separate thread and pull the 500 AccRel discussion out of Terminals and get it focused on its own issues.

The design of the 500 Accurate Reloading is the epitome of elegance. Basically, it is a 416 Rigby case that has been exapanded to accept a .510" bullet and shortened to 2.65" inches in order to fit in standard length actions. There is no belt and enough shoulder for headspacing. Bolt action rifles are able to outperform the 500NE, which already has a great reputation as a dangerous game rifle. The 500 AccR has sufficient capacity (124-130 grains water, depending on who is counting) to safely handle loads of more than 7000 foot-pounds. That puts it well into the stopper class of dangerous game cartridge and can easily match and exceed the factory loads of the 500 Jeffery and 505 Gibbs. Not too shabby.

However, questions have arisen on the throat length of many of the 500 AccR's that have been built. Jeffeoso's reamer from Dave Manson has a 1.25" freebore in order to accomodote the longest imaginable bullet in .510". It now appears that brass bullets do not engage the rifling properly with that freebore, but shear down to .500" when hitting the lands at sufficient velocity.

Here are Hatting's pictures of Ulrik's 500AccR:

quote:

Originally posted by hatting:


I have been out test shooting the 500Acc-Rel with Ulrik. We used milkcartons filled with water and wet phonebooks as targets.
1.bullet Hornady DGS 2 m straight
2.bullet Barnes 1,5 m straight 2200 feet/sec. (no rifling)
3. bullet CEB - BBW#13 1,5 m straiht 2000 feet/sec.
4. bullet CEB - BBW#13 1,5 m straight 2320 feet/sec. (no rifling)

I think the throat is too long and too big. The throat is .511 and I would like it to be .510(.5102 ) and .510 long.

Best regards
Hatting

Hatting has confirmed that bullets #2 and #4 have sheared down to .500" on the bands.

So where do we go from here?

I have made Hatting put in a new order for a new 510 barrel with 1-10" twist and have a new reamer made with a .5102" dia throat. Throatlength we will diskuss - thought that a .510" length was ok, but as you mentioned on the Terminal thread Tanzan - why not go for a shorter .25 or .3" throat - RIP shows excellent results reg both accuracy and velocity with his 500 rifle

quote:

Originally posted by buffalo:
I have made Hatting put in a new order for a new 510 barrel with 1-10" twist and have a new reamer made with a .5102" dia throat. Throatlength we will diskuss - thought that a .510" length was ok, but as you mentioned on the Terminal thread Tanzan - why not go for a shorter .25 or .3" throat - RIP shows excellent results reg both accuracy and velocity with his 500 rifle

So your reamer will not come with the freebore already included?

If someone wants a shorter throat the reamer cannot have a .510" throat extension. A gunsmith can add freebore to a basic reamer but we cannot subtract freebore if the reamer has already cut off the riflings.

Very good idea Tanz regarding the shorter freebore reamer discussion.

The 0.252" freebore works very well with the 12.7 x 68mm MT due to the bore riding style of the CEB and North Fork bullets. I recommend that some of you measure the maximum bearing surface of the non-bore riding bullets that you may be using and take that non-seated length information into your computations when determining your new freebore specification.

Buffalo, if your reamer is a European receipt reamer - not being returned to the USA - why not have the reamer freebore/throat section recut for the shorter freebore specification. I know Dave Manson will alter his reamers, I would think someone in Europe would do the same.

Also, nice pull on the Lothar Walter barrel - I found the specs and they tag it as for the 50 Sharps.

opdate:

have ordert a uni throat reamer in .510/.5102
and a lothar walther barrel twist 1/10
will send the 500 acc-rel reamer bag to mansonreamers and have the throat removed

then ulrik and I vil make som test with the throat from near zero to 1,25"

and get some pressuregauges on the barrel to se what vil happen

best regards
Hatting

I'm not sure what a 'uni-throat' reamer is, but I greatly appreciate the work and preparations that you guys are doing.

I only have a few windows of time in a year to play with these things. You will probably find load levels, velocity, weight, similar to 49-10 will work.

blessings on your adventures. We will be following the results.

Tanzan

this is a uni-throater


The Uni-Throating reamer appears the same as any other—a removable pilot up front followed by a 6-flute cutter at the desired throat angle. Rearward of here, things get a little different. On the straight portion of the cutter body a heat treated steel bushing (just under ‘06 diameter in this case) with a tapered nose is fitted to microscopically tight tolerances: it will both rotate and slide freely fore and aft, but exhibits zero lateral movement. Underneath this bushing, the flutes come to an end and the threaded shank begins, at 40 TPI. Rear of the bushing a pair of brass lock nuts is fitted: the forward one of these is graduated with 5 equidistant marks around its circumference, each equivalent to .005” and readily readable to .001”. The rear nut is knurled. [/I]

An interesting concept. What happens on recovered "regular" bullets? Do those sheer off to .500 as well?

I am very interested in seeing the differences. Especially if I have made a design flaw

I don't see it a a design flaw because you designed it to feed 50 BMG bullets. It does not like minimal bearing surface brass or cast lead bullets it seems. I think people can can have a choice between reamers of normal throat dimensions or one that can benefit from shooting BMG bullets.

I think the throat is to long and to big. The throat is .511 and I would like it to be .510(.5102 ) and .510 long.

Best regards
Hatting[/QUOTE]



The usual "modern" parallel-sided freebore is .0006" to .0010" greater than bullet diameter.
If Hatting is planning this for .509" diameter bullets, .5102" freebore diameter is fine.
However, it is a bit tight for .510" diameter bullets.
Some soot or grit in the throat under field use might interfere.
Also concentricity issues with hunting ammo and DG situations might make for stickiness or hesitation on loading.
Some slop in a DGR throat is desirable.

I would recommend a freebore diameter of .5110", just one thousandth of an inch over nominal (most common) bullet diameter.

I have had excellent results with the 500 A-Square using freebore of .5110" diameter,
and about caliber length throat, .588" length,
which handles the longest possible 50 BMG bullet, milsurp or civilian target bullet.
I have shot a sub 0.2" three-shot group with that, at 100 yards, a 705-grain "Harlow" by AAA, monometal copper with moly coating, passe.
There is absolutely no need for a 1.25" long freebore.

Indeed, henceforth, I always go no more than caliber length for freebore, for optimum balance of accuracy, velocity, pressure, and long-nose-bullet handling.

My 500 Mbogo with .510-caliber bullet:
freebore length: .5000"
freebore diameter: .5110"

My 12.7x68 M/49-10 with .500-caliber bullet:
freebore length: .2520"
freebore diameter: .5020"
Yes: an extra thou of freebore diameter here, for possible handling of .501"-diameter cast lead bullets.
It did no harm, maybe compensated for by only a half-caliber freebore length.
It put three shots into 1.069" at 300 yards.
The CEB bullets do help with accuracy also.

Barrel twist: for the slow velocity of these 50-cals compared to 50 BMG with same 700-800-grain bullets,
for accuracy the 1:12" is better at long range,
gives closer to same bullet revolutions per second as the 1:15" of BMG with the long and heavy bullets,
but I see no downside to 1:10" for the usual hunting weight or lighter bullets at closer range.
Indeed, penetration, or stability on transition from air to game animal, can only be helped by going with the 1:10" twist.

I have one 500 A-Square rifle, and one 500 Mbogo with 1:10" twist.
One 500 Mbogo with a 1:9" twist.
Two 12.7x68 M/49-10 rifles with 1:12" twist.

Jim,
Give up the "T" for Tornado as Waffen Jung has copyright and trademark on "Tornado" as applied to weapons.
IIRC, even the German Air Force had to pay them to use the name applied to one of their recent weapon systems.
That goes back to the 9.5x70 Tornado, aka .375 Tornado. 2RECON knows more about this.
From now on it is no longer the "12.7x68mm Magnum Tornado/49-10" but rather more simply:

"12.7x68mm Magnum" aka "49-bore/.500-Caliber/.338 Lapua Magnum Improved of 2010"

12.7x68M or 49-10 for short.

10-4.

10-4 on the 10-4.

That most accurate 500 A-square of mine with the .588"-long throat of .511" diameter,
was chambered using a standard 500 A-Square reamer from JGS of the 1990s,
then a separate Dave Manson throat reamer was used to extend the freebore length.
It worked very well.

IIRC, the standard 500 A-Square freebore is about 0.400" long and is .511" diameter.
I do have the reamer drawing somewhere, but not at hand.
I did find that the standard 500 A-Square throat would handle the milsurp ball and blacktip AP bullets just fine.
No throat lengthening is required for that.
The .588" freebore length was only to allow Hornady A-Max bullets (750-grainers) to be seated to 4.75" Cartridge Overall Length,
with minimum bullet shank length inside the case, about "neck length" of bearing shank inside the cartridge case,
with only the boat tail hanging down into the powder.

as i said, it'll be interesting to see how this turns out ..

i reckon i could load up some CEB in mine and shoot it into wet sand, for recovery testing.

if brass is being sheared off, it has to go somewhere...

jeffeosso,
Wet sand might scour/abrade the brass bullets too much to allow a good "reading."
Water, wet print, or even a stack of plywood or any combination of these three would be better.

I am guessing the brass is shearing off in chips and following the bullet out the barrel.

This has been a great learning experience for me.
Who would have thunk it?
Amazing how much the harder brass is acting like soft lead, as Hatting suggested.

Brass is slippery, yet brittle.
Over an inch of run at the rifling gets the velocity up enough to make it skid and shear instead of engage and spin ... I would never have thought it possible.
Learned something.

I would second RIP's suggestion. I would design for a .500 free bore length and a .5110 freebore diameter. My 500a2 uses these dimensions and works just fine.-Rob

Rob,
Thanks, this Kentuckian appreciates the endorsement of a genius entrepreneur from Sin City, Nevada.

I will put my money where my mouth is also.

To build the second 12.7x68M/49-10 I took the barrel off of 500 A-Square No.2.
That one also had a .588" long freebore of .511" diameter.

Now I have a chance to correct that barrel,
to shorter throat: .500" long and .511" diameter freebore
Will have Rusty McGee cut the BRNO ZKK 602 threads off of that barrel, it has plenty of shank,
and re-thread it for a Weatherby Mark V.
I already have the "Plus-One" floorplate, ordered from the Weatherby Custom Shop.
Alas, that part is made of aluminum alloy, but what does that matter?
After all, it is for a Weatherby Mark V.

Do a .500 Jeffery with proper throat (instead of the leade-only funnel of the original specs for 500 Jeffery),
or another 500 A-Square?
Or another 500 Mbogo?
Weatherby Mark V

I will also be leaving all my reamers with Rusty McGee--Gunsmith for use and safekeeping.
He can get Dave Manson or Dave Kiff to sharpen them if ever needed: See new thread for list.

Rip- I totally agree. An inch of freebore will indeed cause a std bullet to skid and probably engage the rifling off- center and at least initially, strip brass as it engages the rifling. Fine for a 750 -Amax or bore rider but way too much for any std length bullet. -Rob

Rob,
Yes, 1.25" of freebore is excessive for any bullet of 50 BMG persuasion at high or low velocity.
Might get by with copper which is stickier and less brittle than brass, and does not chip or shear off,
has enough friction to grab the rifling after initial skidding at lower velocity ... if the bullet's bearing surface is great enough ...

... I could have Rusty McGee--Gunsmith use the 500 Mbogo 3" reamer to make a "500 Mbogo Short."

Roy Vincent does the same thing with his "450 Vincent Long" (about 2.75") and "450 Vincent Short" (about 2.5").
Same reamer is used for both.

Just ream for 500 Mbogo 2.65", or 2.5" length instead of 3".
It would have a throat with freebore .500" long and .511" wide.

Ron,
For ease and quick practicality I like the idea of considering a short 500Mbogo as a substitute for 500AccR. Most anything on a Rigby case is great.

However, the question of standardization arises, something that is a lot easier to deal with in the day of the internet and open forums.

For example, comparing the the front part of the Mbogo and AccR from the body-shoulder pivot angle to the mouth of the case, there is .529" length in the Mbogo and .525" length in AccR. That wouldn't be so bad, but the neck and shoulder positions are in different places.

The AccR neck is only .466" long,
using a gentler 20* degree and longer (.059" x-axis) shoulder, which means that an AccR case will hit the chamber wall and stop .034" early
because the Mbogo has a .500" neck
(with a short .029" x-axis shoulder and sharper 35* angle). Headspacing cannot tolerate 0.030" of slop as far as I know, with 0.006" more likely.

So it looks like the short Mbogo and AccR would not be interchangeable, even though they would be ballistically identical. I can live with a .466" neck length, and would recommend that the basic 500 AccR dimensions remain the same in order for there to be interchangability between long throat and short throat versions of the 500 AccR.

Max-max loads would be different between the short and long throat versions of AccR, but that probably would not affect many people. I haven't heard of anyone running a long-throated 500AccR at a point where they start to get pressure signs. Please sign in and let us know, if so. I would imagine that all of the Ammoguide loads for AccR would work for short-throated versions, too, if prudently developed with 2 grain lower loads. The loads will probably reach closer to the max limits and maybe getting an extra 50-100 fps for the steeper pressure curves at various stages along the load development with similar powder levels.

As someone who likes the idea of longer range capability with a rifle I often carry on foot (I learned to hunt with O'Connor's favorite), I would wish that a 500 AccR reamer be designed with 0.250" freebore and .511" parallel diameter. We need to work off of the .510" bullet standard and cannot worry if one run of Barnes bullets is only .508". The standard is .510" and that is what people will be finding in 2020. With a .25" freebore, someone would be able to add an extra .25" or more of freebore should they have a hankering for BMG plinking bullets. The extra freebore could also be added at .5102" diameter to further tighten things up.

PS question:

I notice that the outside neck reaming for the 500 Mbogo and 500AccR is .535", which only provides .25 for case neck thickness.

However, the 49-10 has a .531" outside neck reaming, which allows .031" for neck thickness.

I would think that .030" is a safer brass neck thickness than .025", especially with DG rifles.
Why are the current Mbogo and AccR so tight, instead of, say, .538-.540 like the 500AHR and 510/505Gibbs?

quote:

Originally posted by 416Tanzan:
PS question:

I notice that the outside neck reaming for the 500 Mbogo and 500AccR is .535", which only provides .25 for case neck thickness.

However, the 49-10 has a .531" outside neck reaming, which allows .031" for neck thickness.

I would think that .030" is a safer brass neck thickness than .025", especially with DG rifles.
Why are the current Mbogo and AccR so tight, instead of, say, .538-.540 like the 500AHR and 510/505Gibbs?

416Tanzan,
The 49-10 requires such a chamber neck diameter because the brass neck wall thickness requires it.
.338 Lapua Magnum brass blown out and shortened is still thicker in neck wall than the long Rigby.
I always measure bullet-seated dummies before specifying the neck on a reamer.
Neck of reamer allows the usual .004" expansion for release of bullet and springback after firing ...

... (continued from above) ... The .025" for the 500 AccRel and 500 Mbogo allows .021" for 2 x neck wall thickness: allowable neck wall thickness of .0105" is more than enough.
Actual brass is not that thick.

Likewise for the 49-10, .031" corresponds to brass neck wall thickness allowable of .0135", but actual brass neck wall thickness may or may not be that much.
The loaded (with .500" diameter bullet) cartridge neck diameter is .527" max, and it fits into a .531" minimum chamber neck diameter. There is that .004".

All this is working within max brass specs and minimum chamber specs.
Actual brass may be smaller than max specs, actual chambers may be larger than minimum specs.
Hopefully not by much.

It is indeed gratifying when everything works out as well as the 49-10.
I have lost only one case to minor case mouth split for 150 cases fire formed from virgin Lapua brass.

I am on the road and posting on the fly.
Any imprecision in the numbers could be corrected by reference to specs and actual brass measurements,
but that is the basic drift of the brass and chamber specs.

How many 500 AccRel reamers are in circulation in the US?

Do any of the reamers have a shorter throat or are they all 1.25" design?

Does anyone have a reamer that they might want to have 1" 'sanded off' the throat-leade sections? (That might be tricky to get the leade right. Again, an area where I have no knowledge.)

PacNor listed 500AccRel on their wildcat list, but haven't answered my enquiry yet about throat length.

There are a couple likely less than 12 worldwide. Can we wait and see the results before branching the design? changing the throat will change allowable pressure profiles

quote:

Originally posted by jeffeosso:
There are a couple, likely less than 12 worldwide.
Can we wait and see the results before branching the design? changing the throat will change allowable pressure profiles

Amen. More testing.

While preliminary tests seem to show copper bullets as gripping the rifling, it would be nice to see some of the lighter copper bullets pushed to velocities in the 2500-3000 fps range.

Anyone ready to test GSCustom's .510" 450 gn? I think it's copper and should do 2600+ fps in AccR. Woodleigh plinkers could provide a first test, as an approximation, though they will have more bearing surface than the GSC.

PS:

quote:

changing the throat will change allowable pressure profiles

Yes, certainly, pressures will be different.

On the other hand, current loadings have gone over 7200 ftlbs without seeming hot. I would imagine that short-throats would stay within 500 ftlbs of the longthroats, probably closer.

Has anyone loaded long throat versions to pressure limits?

I loaded the 570 grs CEB tp 2376 fps and got absolutely no pressure signs at all... But thats not a guarantee that pressure is not high... Could be... According to QL it must be a bit hot, but I guess QL do not take the 1,25" freebore into consideration.....

quote:

Originally posted by buffalo:
I loaded the 570 grs CEB tp 2376 fps and got absolutely no pressure signs at all... But thats not a guarantee that pressure is not high... Could be... According to QL it must be a bit hot, but I guess QL do not take the 1,25" freebore into consideration.....

Thanks. that's about 7150 ftlbs. I could do a lot of hunting with a 570 TSX at 2300-2350fps.

On AmmoGuide 'ShortandFat' listed a 535gn at 2468 fps for 7238 ftlb and called it 'heavy' but not max.
I'm guessing that with long throats this cartridge will go 7500+ ftlb.

(Even our little 416Rigbys have done 2900+fps, 350 gn = 6550 ftlb with no pressure signs [but for how long?], though we aim to run them in the 2800's. and consider 6200 a better ceiling for Africa.)

little opdate

just ordert 2 barrels 1 in stainles and 1 in steel
cal 510/499 twist 1/10
2 uni throat reamers one in .51015 and one in .511

will send my reamer to manson reamers to have removed the throat

next projekt building a bullet trap/collector

regards
Hatting

Let us know how the Manson repair works out.

In the meantime, it would be helpful to know what happens with LIGHT (under 500 grain), COPPER (or non-brass jacket material) bullets work in the old barrel.
Do you get rifling at 2600 fps with copper/jacketed bullets in the old barrel?

From the .49"-.500 calibre thread:

quote:

So there we go for whatever it’s worth.
Rifle No. 1 with 430gr .500 CEB MTH copper HP spitzer
Necos – QuickLOAD/QuickTARGET for Win7 – G7 bullet drag profile = 0.426 BC
JBM – Ballistic for iPad – G-1 bullet drag profile = 0.623 BC
JBM – Ballistic for iPad – G-5 bullet drag profile = 0.396 BC
JBM – Ballistic for iPad – G-7 bullet drag profile = 0.301 BC
And,
Rifle No. 2 with 360gr .500 Talon Tipped CEB ESP Raptor brass bullet (350gr W350 bullet + 10gr W Talon tip)
Necos – QuickLOAD/QuickTARGET for Win7 – G7 bullet drag profile = 0.296 BC
JBM – Ballistic for iPad – G-1 bullet drag profile = 0.775 BC
JBM – Ballistic for iPad – G-5 bullet drag profile = 0.483 BC
JBM – Ballistic for iPad – G-7 bullet drag profile = 0.390 BC

So there you go...right, wrong, or otherwise.


Jim

So you are saying that the talon tips in 50 calibre are running over .450 BC?

That would be a great reason for setting up my 500AccRel to use brass-banded bullets.

His heavier 430 grain MTH bullet had the higher BC.
The 350 raptor had a .296 BC by his calculations.

Tan& Boomie,

If you look at RIP's specific trajectories for each bullet...then yes, the new numbers are correct as each G1-G7 BC exactly matches each bullet's trajectory at 100yds and again at 300yds. Long way of saying that, "Yes the ESP Raptor indicates a higher BC than the MTH."

I would think the difference in these chambers deserves a designator in the caliber marking to identify them. Like the 6.8 SPC and the 6.8 SPC II. Or the 223 Winchester and 223 Wylde. Otherwise we're setting someone up for a problem. With the volume of powder involved, it's a much more serious issue than the calibers just mentioned.

quote:

Originally posted by tiggertate:
I would think the difference in these chambers deserves a designator in the caliber marking to identify them. Like the 6.8 SPC and the 6.8 SPC II. Or the 223 Winchester and 223 Wylde. Otherwise we're setting someone up for a problem. With the volume of powder involved, it's a much more serious issue than the calibers just mentioned.

The throats should be mentioned in load information, however, I don't think that we have an issue YET.

All of the published load data that I have seen is relatively conservative. For example, I don't think that 500AccRel loads in the range of 7000-7200 foot-pounds will produce excessive pressures in short-throated guns. Why not? Well, the capacity of the 500AccRel is approximately equivalent to the 416Rigby and is only a smidgin (little bit) below a 460Weatherby. AmmoGuide lists the 500AccRel at 124 grain H2O and the 460 Weatherby at 128.5 grains. When you consider that the narrow-mouthed 460 Weatherby has been loaded up to 8000 ft-lb. loads, and that wider-mouthed cartridges can always generate more energy while keeping pressures under 65000 psi, then it should be pretty obvious that 7200 foot-pound loads in the 500AccRel will not be a problem whether "short-throat" or extremely long-throat.

From another angle, one can also compare the 49-10. Quite obviously, a 500AccRel (.510", "equal case") will be able to equal or better the 49-10 (.500"). If the 49-10 can go over 7000 ft-lbs. without pressure issues, then so will the 500AccRel.

Now, the above does not mean that throats can be ignored when considering pressures and velocities. They need to be specified. However, we don't know where the long-throat pressure limits will be. They have not yet been researched, developed, and published. Using the 460Weatherby as a guide, I think that we can say that the pressure limit for the 500AccRel LONG-THROAT will be around 8000ft-lb. or slightly over. The short-throat 500AccRel will probably have a limit that is somewhere between 7200-8000 ft-lbs., and for the moment that is greater than any published load.

One extra caveat (warning): it is possible that a cool 7200 ftlb. load in the long-throated 500AccRel will become a max load or slightly over-pressure in a short-throated version. A short-throated version may be able to duplicate a long-throated load by reducing powder 2-5%.

I don't own one, but I think for future users/owners that having the additional designation would be very smart. It won't make a difference to the bozos but to the normal reloaded it will be a good indicator of a difference between chambers. Might use 'ST' rather than 'II' though as recently all of the 'IIs' have had a longer throat than the original chamber.

I think when you make such a drastic change you have to err to the side of caution. I like to load in the 58,000 60,000 range because I shoot the 50 BMG blue tips at pretty long ranges from my 500 AccRel MRC PH. If my load data were to fall into the hands of a short thoat owner who didn't know the difference and he were able to close the bolt on a jammed bullet, I think a blown primer would the least result. And a blown primer behind 100 grains of powder is a very serious issue.

quote:

Originally posted by tiggertate:
I think when you make such a drastic change you have to err to the side of caution. I like to load in the 58,000 60,000 range because I shoot the 50 BMG blue tips at pretty long ranges from my 500 AccRel MRC PH. If my load data were to fall into the hands of a short thoat owner who didn't know the difference and he were able to close the bolt on a jammed bullet, I think a blown primer would the least result. And a blown primer behind 100 grains of powder is a very serious issue.

Here is the sister cartridge, 49-10 .500" bullet, in a virtually identical case capacity.
From Ammo Guide 12.7x68mm, and considered a "heavy load" but not listed as "max":


500 gn. bullet
H-322 powder
98.0 grains (case is full)
2561 fps
7285 ft.lb.
24.0" barrel length
3.520" COL

We can see that 7285 foot pounds was reached in a bore that is 2% smaller. Those guns have a throat around 1/2", certainly not anything like 1.25". So the 12.7x68mm becomes a general guide for capability, even though powder charges may need to be increased 2% in order to reach the same performance levels in a short-throated 500AccRel ST (short throat)and maybe up to 5% in order to reach similar performance in a 500AccRel LT (longthroat).

quote:

Originally posted by 416Tanzan:

quote:

Originally posted by tiggertate:
I think when you make such a drastic change you have to err to the side of caution. I like to load in the 58,000 60,000 range because I shoot the 50 BMG blue tips at pretty long ranges from my 500 AccRel MRC PH. If my load data were to fall into the hands of a short thoat owner who didn't know the difference and he were able to close the bolt on a jammed bullet, I think a blown primer would the least result. And a blown primer behind 100 grains of powder is a very serious issue.

Here is the sister cartridge, 49-10 .500" bullet, in a virtually identical case capacity.
From Ammo Guide 12.7x68mm, and considered a "heavy load" but not listed as "max":


500 gn. bullet
H-322 powder
98.0 grains (case is full)
2561 fps
7285 ft.lb.
24.0" barrel length
3.520" COL

We can see that 7285 foot pounds was reached in a bore that is 2% smaller. Those guns have a throat around 1/2", certainly not anything like 1.25". So the 12.7x68mm becomes a general guide for capability, even though powder charges may need to be increased 2% in order to reach the same performance levels in a short-throated 500AccRel ST (short throat)and maybe up to 5% in order to reach similar performance in a 500AccRel LT (longthroat).

not far from the truth I think... My fireformed 500 Acc Rel brass from 416 Rigby Hornady brass holds 140 grs water and the ones fireformed from 338 Lapua brass was 135-136 grs as I remember... but sure less with the Lapua brass.. To reach 7000 footpounds was no problem, for sure not a hot load, no pressure signs whatsoever and brass reloaded 5 times with that load so far and have needed no trimming and primer pockets still tight as new...

quote:

Originally posted by 416Tanzan:

quote:

Originally posted by tiggertate:
I think when you make such a drastic change you have to err to the side of caution. I like to load in the 58,000 60,000 range because I shoot the 50 BMG blue tips at pretty long ranges from my 500 AccRel MRC PH. If my load data were to fall into the hands of a short thoat owner who didn't know the difference and he were able to close the bolt on a jammed bullet, I think a blown primer would the least result. And a blown primer behind 100 grains of powder is a very serious issue.

Here is the sister cartridge, 49-10 .500" bullet, in a virtually identical case capacity.
From Ammo Guide 12.7x68mm, and considered a "heavy load" but not listed as "max":


500 gn. Bullet
H-322 powder
98.0 grains (case is full)
2561 fps
7285 ft.lb.
24.0" barrel length
3.520" COL

We can see that 7285 foot pounds was reached in a bore that is 2% smaller. Those guns have a throat around 1/2", certainly not anything like 1.25". So the 12.7x68mm becomes a general guide for capability, even though powder charges may need to be increased 2% in order to reach the same performance levels in a short-throated 500AccRel ST (short throat)and maybe up to 5% in order to reach similar performance in a 500AccRel LT (longthroat).

Hey Tan,

If I’ve feed the Manson’ finish reamer data correctly into QuickDESIGN, then here are the correct throat dimensions for the 49-10 (12.7x68mm Magnum, .500/.338 Lapua Magnum) chamber:
Length from Neck Chamfer to Bore Diameter: 0.4956”
Neck Chamfer Angle: 45º
Length of Freebore: 0.252”
Freebore Diameter: 0.502"
Throat Angle: 1.5º