Sherman wildcat cartridges and my 338
- Thread starter ruby76
- Start date
Hand Skills
CGN Regular
- Location
- In the 'heartland', southern SK
There is no heat like wood heat! Thank you for sharing your experience with brass dynamics. The idea of a case as a gasket is a gift in itself. The relatively low tensile strength of brass renders it elastic, and of insignificant structural value. I was also assuming that the conical nature of a vessel would contribute to more back pressure when compared to a cylinder. Under further consideration, The 'improved' designs differ in body taper a few thousandths per inch compared to their parents - the effects of varying taper on the on the order of 10^-3 is going to be pretty hard to measure.
Not only have I learned some things here, I feel a better understanding of the dynamics at play. It would seem the only way to reduce bolt thrust through case shape is to reduce the diameter!
Are there any benefits to reducing body taper beyond increasing capacity?
I think it's generally understood that case shape does not affect velocity, and capacity rules.
To consider case shape has no effect on brass life (shoulder angle excepted) is a new one for me. Very interesting!
Not only have I learned some things here, I feel a better understanding of the dynamics at play. It would seem the only way to reduce bolt thrust through case shape is to reduce the diameter!
Are there any benefits to reducing body taper beyond increasing capacity?
I think it's generally understood that case shape does not affect velocity, and capacity rules.
To consider case shape has no effect on brass life (shoulder angle excepted) is a new one for me. Very interesting!
The other question is just what effect the case shape, body taper, shoulder angle, etc., will have on primer pockets. The quick and easy answer is absolutely no effect whatsoever. Why not? It will have no effect because the only thing which causes primer pockets to expand is pressure. There are a couple of things which may influence the effects of the pressure. Brass hardness, brass thickness, chamber dimension, protrusion outside the barrel, are all things which influence the effects of pressure on the brass. You will note that none of these attributes are influenced in any way by the body taper or shoulder angle on the case.
I have often thought that rimmed cases will handle a little more pressure than rimless but this is more a feeling than a fact.
The thing is, once we accept that the case is simply a container for the powder charge and a gasket to seal the breech, we have come close to realizing the real truth. Sharp shoulders can make a case which will not lengthen as much when fl sized but they won't changed the ability of the case to handle pressure and certainly won't make the case produce more velocity at the same pressure if all else is equal. Larger case capacity will allow an increase at the same pressure primarily because the pressure curve is extended since more powder must be used to keep the pressure at the same level. The velocity increase is seldom all that significant, however. I've done a bunch of testing with regard to this and related subjects over the last fifty years (since before I started gunsmithing) and mostly I've learned most things don't matter nearly as much as we've been told.
I have often thought that rimmed cases will handle a little more pressure than rimless but this is more a feeling than a fact.
The thing is, once we accept that the case is simply a container for the powder charge and a gasket to seal the breech, we have come close to realizing the real truth. Sharp shoulders can make a case which will not lengthen as much when fl sized but they won't changed the ability of the case to handle pressure and certainly won't make the case produce more velocity at the same pressure if all else is equal. Larger case capacity will allow an increase at the same pressure primarily because the pressure curve is extended since more powder must be used to keep the pressure at the same level. The velocity increase is seldom all that significant, however. I've done a bunch of testing with regard to this and related subjects over the last fifty years (since before I started gunsmithing) and mostly I've learned most things don't matter nearly as much as we've been told.
Great conversation guys, I like learning different perspectives and experiences. I am in no way claiming to fully know the in's and out's of this design, I am relying on my own research and knowledge of far more experienced people than me. After considering options for my end goal of a "different" 338 cal without the case capacity of a rum or lapua, this one screamed out at me. Many different people, related to the case design, have claimed efficiency, long case life (when using quality brass), less throat erosion, etc etc. There are quite a few people out there testing and proving these cases, they are constantly meeting or exceeding their belted magnum case cousins.
Hand Skills
CGN Regular
- Location
- In the 'heartland', southern SK
Most interesting. Very much appreciate your insight into this matter, Leeper!
I follow you on the 'rimmed cartridge' supposition. All things equal, yes they would handle pressure better due to increased diameter (hoop strength - primer pocket), and increased surface area (reduction of pressure on the exterior of the case head). With variations in brass thickness and composition it would take some work to test.
As far as primer pockets are concerned, it appears my efforts will be best spent sourcing brass with higher yield strength, and keeping the primer pockets free of residue.
I just love when things are simple and make sense
Either way, I'm curious to try some ADK brass (the guys manufacturing Sherman brass) and it has got me thinking a 7x65R might be fun to experiment with...
I follow you on the 'rimmed cartridge' supposition. All things equal, yes they would handle pressure better due to increased diameter (hoop strength - primer pocket), and increased surface area (reduction of pressure on the exterior of the case head). With variations in brass thickness and composition it would take some work to test.
As far as primer pockets are concerned, it appears my efforts will be best spent sourcing brass with higher yield strength, and keeping the primer pockets free of residue.
I just love when things are simple and make sense
Either way, I'm curious to try some ADK brass (the guys manufacturing Sherman brass) and it has got me thinking a 7x65R might be fun to experiment with...
As I stated I don’t know what my pressure is running. But going by bolt lift and extractor marks I’m good. Also running loads other Sherman shooters are. My velocity of 3339 fps is not a claimed chronograph speed. Drops are confirmed out to 910 yds. Far as my property allows me to shoot.
I still cannot get my head around these claims.
Less powder and exceeding other 6.5s or 7mm s velocities?
It is the first wildcat in history to accomplish this?
I just am NOT buying it....
Less powder and exceeding other 6.5s or 7mm s velocities?
It is the first wildcat in history to accomplish this?
I just am NOT buying it....
It's wildcat magic. - dan
And pixie dust. It makes anything possible...
Case capacity and pressure are what are important for speed. If they're going faster with a smaller case, pressures are higher. They didn't repeal the laws of physics for us wildcatters. - dan
https://www.longrangehunting.com/threads/sherman-wildcats-pressure-limits.212253/page-6
Great debate here .......
Great debate here .......
But quite a mix of fact and nonsense. The very first two posts I read (#72 and #73) by well-regarded posters are good examples of nonsense.
The choice of most "Optimal Powder" (the powder that produces the highest MV at max pressure) has nothing to do with case shape (e.g. straight-walled or sharp-shouldered), but has everything to do with "Expansion Ratio" - the ratio of cartridge volume to bore volume.
For example, the 223 and 308 have Expansion Ratios that are very close (and the 308 has approximately twice the case volume and twice the bore volume as the 223). That's why they thrive on the same set of powders, with Burn Rates roughly in the H4198 to Varget range. A cartridge such as the 300 RUM, has a much higher lower Expansion Ratio, almost twice that of the 223 and 308 and thrives on much slower powders, e.g. H1000-US869. The 30 Carbine has an Expansion ratio of about half that of the 223 and 308, and works best with powders no slower than H110.
As well, as said, the 308 has approximately twice the powder capacity as the 223, and if you look at loads for a 150 gr bullet in the 308, for the same powder, the load will be very close to twice that for a 75 gr bullet (of the same shape and hence length) in the 223. The same applies for other bullet weights, e.g. 90 in the 223, and 180 in the 308.
As an aside, as it has nothing to do with powder, The 2X Rule even applies to Twist Rate - a 1:14 twist in the 308 with a 180 gr bullet has an almost identical "Stability Factor" as a 1:7 twist in the 223 with a 90 gr bullet (of the same shape and length).
The 223 is essentially half of a 308 in many regards!
These conversations are great, but I have learned that these myths never seem to die:
1. you need long barrels to burn slow powders;
2. case shape impacts bolt thrust; and
3. case shape affects "efficiency".
#1 has been disproven with several tests over the past 50 years that confirm the theory;2. case shape impacts bolt thrust; and
3. case shape affects "efficiency".
#2 goes back to a "test" done years ago by P.O. Ackley (may his name be praised) in a 30-30 and it is considered sacrilege to dismiss his incorrect conclusion; and
#3 is Wildcatter BS used to explain how their vanity wildcat exceeds its base cartridge by so much: "It's not higher pressure, it's the angle of the shoulder!"
Last edited:
You are right but what the people on the LRH Forum are trying to point out has more to do with Cartridge Design than Shape. It is well documented that smaller cartridges like the 6 BR are much more efficient than bigger cartridges like the 6 CM in that they get more velocity / grain of powder. Case design include things like the Bullet Bearing Surface being ahead of the Case Neck Shoulder Junction when bullet is seated near the Lands or properly throated. Case capacity and barrel length just right so that a near 100 % case fill, of an appropriate powder, will get a 100 % burn at near maximum Saami Pressures. This in turn will deliver a pressure curve that gets maximum velocity from the bullet. Cartridges with Bullet Bearing Surface seated down in the neck with excessive jump to the lands, especially with excessive case capacity loose a lot of their initial pressure before the bullet hits the lands and the pressure cure is not optimal to get maximum velocity even if the maximum pressure is the same.
I will use a 204 Ruger with a 55 Grain Berger seated to Saami COAL and Varget as per Bergers Load Data which would be similar to a 6.5 Saum and my 20 EXTREME with the same bullet/powder combination to illustrate how a smaller, well designed, cartridge like the 6.5 SS can produce more velocity with less powder at similar pressures. Here are targets showing Hornady factory ammo that had 0.001" Case Web Stretch and up to 0.004" primer flow which I consider maximum in a CZ 527.
[URL=http://s920.photobucket.com/user/lclund1946/media/204%20Ruger/CZ%20527%20Var%20Tac_zpsfczz18e7.jpg.html]
[/URL]Here is Berger's load data showing a 100% load of Varget, at 23.8 grains, getting 3183fps from a 26" barreled 204 R:
The 55 Berger looks like this seated as per the Sammi 204R Specs and the 6.5 Saum would be similar with a 140+ Bullet seated.
The 6.5 SS would look more like the 20 EXTREME with 55 Berger seated.
The 20 EXTREME holds 21.6 - 22.5 grains of powder under the 55 Berger and gets more velocity with Zero Web Stretch and about the same primer flow as the 204 factory rounds. As these targets show the small difference in case capacity form the Winchester brass at 21.7 grains to the Remington brass does require a slight adjustment in powder but the Remington brass does get a bit more velocity at similar pressures. The Hornady, Lapua and Lake City fall in between the other two as far as case capacity.
- Location
- sudbury, ontario
Wow those are some fast speeds for the Sherman’s !!
Here are some of latest comments from Rich Sherman...
"People often ask what pressure we're running and the truth is, I don't know! The question I get a lot is "how can you shorten a parent case and make it shoot faster"? Glad you asked! ,
(1)There is no loss of capacity in the SS case vs the saum. Even though it is considerably shorter, with the taper blown out and the shoulder sharpened, the capacity is nearly identical. (2)Because it is far shorter, the bullet can be seated out into the neck so that useable capacity is MORE that the Saum. (3) the shorter burning column and 40 degree shoulder make the SS more efficient getting more out of the charge. (4) with low body taper, the pressure is distributed better throughout the chamber (less bolt thrust) this allows higher operating pressure without destroying brass. SS shooters will vouch that brass lasts longer at higher velocities than the Saum will reach
All these things are exactly why the SS was developed. To be the best performing cartridge available under 3" coal. You can get close to SS velocity with a saum, but you have to have a 3.1" coal to do it, and even then, you will likely come up a little short. I'm sure there are people who load hot, as with any cartridge, but the 7ss isn't running 3000' with a 180 vld by running dangerous pressure when the brass is lasting double digit loading! The skeptics should try it and see for themselves!"
"People often ask what pressure we're running and the truth is, I don't know! The question I get a lot is "how can you shorten a parent case and make it shoot faster"? Glad you asked! ,
(1)There is no loss of capacity in the SS case vs the saum. Even though it is considerably shorter, with the taper blown out and the shoulder sharpened, the capacity is nearly identical. (2)Because it is far shorter, the bullet can be seated out into the neck so that useable capacity is MORE that the Saum. (3) the shorter burning column and 40 degree shoulder make the SS more efficient getting more out of the charge. (4) with low body taper, the pressure is distributed better throughout the chamber (less bolt thrust) this allows higher operating pressure without destroying brass. SS shooters will vouch that brass lasts longer at higher velocities than the Saum will reach
All these things are exactly why the SS was developed. To be the best performing cartridge available under 3" coal. You can get close to SS velocity with a saum, but you have to have a 3.1" coal to do it, and even then, you will likely come up a little short. I'm sure there are people who load hot, as with any cartridge, but the 7ss isn't running 3000' with a 180 vld by running dangerous pressure when the brass is lasting double digit loading! The skeptics should try it and see for themselves!"
Some folks are hunters that happen to use a gun, some folks are rifle loons who happen to hunt. I fall into the latter category; I’ve lost count of all the rifles I have owned in my life. - dan
Last edited:
