SMc Cartridge Developement.

[MAX]

Now I'm on the spot! Well, I'm no engineer, and not bashful....

The essence of what they are doing is the use of a hemispherical shoulder on a short wide case, which apparently gives them a velocity boost for a given charge(efficient) due to a myriad of engineering priciples I cannot accurately represent here, though they are in the two articles published to date.

One of the guys is a retired engineer from Morton Thiokol. Their thrust seems to be that of ignition efficiency, as relates to primer shock waves, shoulder design, and burn thru the shear zones of dynamic powder charge. Whew!

Tyey're working with Norma for pressure validation and brass, and the data published to date indcates a gain similar to moly coat except the magnitude is greater. Same charge=greater velocity & less pressure w/ their design. Or option 'B' Equal the pressure and go like hell... Their data suggests that there lies a threshold on the low end below which little gain is found, and possibly on the top end as well except the pressure will still remain less per equal load. It is a helluva load to digest.

The powders they've been working with are very slow

and some of the calibers relatively small(6mm), but as I recall up to .308 or maybe bigger. Sidebar: Their analysis of case shape found the 45 degree shoulder the most efficient other than their own design. Their additional consideration being VERY fat case design due to the above mentioned shear issue. I don't know if this will become useful application or just theoetical research. Interesting nonetheless, particularly in regards the subject of this site.

Regards

 

[Darryl Cassel]

Hello Max

Some of this was tried 30 Years ago in Williamsport by a fellow named Drummond who I spoke with not to long ago at the 1000 yd club.
He expermented with the miniumim tapors and up to 60 degree shoulders which he designed and called the 7mm drummond and the 30 Drummond.

If they could ever design a case like the 6PPC only on a much larger scale, that may be the answer. I'm not sure if they can improve to many cases above the size of the 308 Win though.

We shall have to wait and see what they end up with as their final test results and applications of such.
In some of my bigger mag cases, I really don't need any improvement for the applications I use.

Thanks for the follow up on that and keep us informed.

DC

 

[MAX]

Roger Red Leader.
FWIW, these fellows analyed the 60 degree shoulder as well and found it wanting in comparison to the 45 angle. The cases they have designed are...odd in appearance, to say the least. The shoulder is a true hemisphere with a neck sticking out the top. I found the 22 PPC odd as well, first time I saw that one. Should have seen my first wife; You'd know my eyes aren't exactly perfect.
The thing they seem to have accomplished is to focus the shock waves of the primer burst at one point below the bullet base, rather than promoting random scattering thoughout the shoulder region.

Their names are By Smalley(MT), and M.L. Mcpherson. Time will tell, but I'm guessing we'll hear more about this concept.

Take care.

 

[MAX]

Darryl,

You're probably aware of the SMc design developement as reported in the last few issues of Varmint Hunter Magazine. What's your take on this? I'm thinkin' these guys may be on to something...

 

[Darryl Cassel]

Hello Max

I have been so busy, have not had a chance to check it all out yet.

What's your take on it?

Later
DC

 

[PrimeTime]

Precision shooting has had a few articles following the development of these cartridges. As mentioned, they are working with Norma to build cases and a 6.5 is definitely in the works. Their whole premise seems to be based on consistant ignition. Who knows, the project may die tomorrow or become the next PPC. If they do come out with a 6.5 and have brass available, I just may have to get one.

 

[Mysticplayer]

Maybe a bit simplified but isn't a Weatherby shoulder basically the same thing as a hemispherical shoulder?

These cases aren't short and wide granted, but the benefits of the venturi shoulder (as Wby calls it) is not a big deal. In fact, I have found more case stretching with this type of shoulder then with a straight sharp (35deg) shoulder.

Am I off base with what these hemi cases look like?

Are the cases wider then a conventional magnum ie wider then .560"?

Appreciate your feedback...

Jerry

 

[Lee Owens]

Jerry-
The Wby cases have a "double venturi"; neck/shoulder and shoulder/body. The SMc cases have no "venturi" at the neck/shoulder junction.

There was a PS article on this concept about 2 years ago. Look up one called "Carbide toothed beavers" (the only way case forming could be more difficult is to breed carbide......) This article was about M.L. McPherson's idea for the perfect 6mm bullet launcher. He called it the 6mm Thermos. As far as I know, there has not been a follow-up article.

 

[Mysticplayer]

Anyway to post a picture or drawing of this case. Having a hard time picturing what this looks like.

good new tech is always a good thing...assuming it works.

Jerry

 

[MAX]

Cut an orange in half, jam a soda straw in the top...there's your shoulder and neck. The design calls for very fat cartridges but I don't have the numbers available. Fatter than the PPC things.