Any Ballisticians here? (Cartridge Pressure Discussion)

[jthor]

There are some folks on Facebook preaching a wildcat called the “7mm Moses”. Claiming it can shoot at 7 Rem Mag and 7 PRC Speeds below at or below 65k PSI. It’s a 308 based case that looks to be fire-formed from a 7mm-08. Straight tapered body with a Weatherby styled shoulder.

Claim of 2921 FPS with 180 ELD-Ms out of a 28” barrel and at 3012 he blew out a primer.

I’m no ballistician, but these claims do not pass the sniff test with the pressures they claim. They have not done any testing with a pressure barrel as of yet and I don’t believe they will.

Thoughts? Over 65k PSI or not? Pic of the cartridge on the right.

 

[Murray Brook]

Hard to tell just looking at the case. Knowing the case capacity and freebore of the rifle would help.

 

[gunsandgunsmithing]

Not saying it's impossible but there's usually well over 100fps between 65k psi and blowing primers out of pockets. Several variables too. Call me skeptical. What makes it so special as to be able to make speed from case design. I don't believe it's as simple as the shoulder or short neck.

 

[Dusty Stevens]

Youd have to show me

 

[SKWERLZ]

Getting around short action magnum speeds with a 308 length cartridge sounds spicy
I’m sure a long freebore and probably a powder like R26 help.

I’ll pass on a neck length like that.

 

[CharlieNC]

You can use Quick Load or Gordon to spec a wildcat to evaluate pressure, velocity. etc to address the what ifs.

 

[Gary in MD]

That velocity seems awfully optimistic to me for the small case. The 28" barrel is surely helping but I would think the pressures are still high "if" they are getting that velocity.

 

[DaveTooley]

And what could go wrong?
A lot.
That violates rule #1

 

[LVLAaron]

And what could go wrong?
A lot.
That violates rule #1

Don't blow your face off?

 

[Laurie]

Mic McPherson wrote about this sort of thing years ago describing how every year cartridge companies get people contact them with claims of a design whose 'efficiency' is so improved that this allows their proposed design to match that of much larger case/charge existing models.

As he pointed out, the performance increases are invariably the result of a modest amount (sometimes) from an 'improved' case, changed shoulder angle etc holding a bit more powder, but 90% + comes from simply increasing the charge and pressure enough for the extra couple of hundred fps or whatever claimed. This is invariably done through a simple (ie crude) load development process in which charges are raised until the primer blows, then reducing that charge weight by a half grain (or whatever depending on case / charge size). If anybody actually bothers to test such 'wonder cartridges' it turns out pressures are such that no manufacturer would ever consider their use. Reduce the charge to that of the highest-pressure factory models and the performance increase disappears.

So far as the 'improvement' in the photo of the case shows, whilst that may increase case capacity a fair bit, remember the rule of thumb in this matter. For an X% case capacity increase, you get an X divided by 4 percentage MV improvement all other things being equal. The all other things are bullet weight, peak pressure and barrel length.

Yes, increasing case capacity may in some cases allow the cartridge to have a compressed load of a slower burning, very high energy powder to be stuffed in to allow a performance step-change. In this case, IF Re26 is the powder the 'Moses' uses, much if not most of the improvement comes from a major technological improvement in the powder itself, as this is one of the Alliant Reloder grades made for the company by Nitrochemie Wimmins ag in Switzerland incorporating the very efficient 'EI' technology that infuses the burn-deterrents into the powder kernels and allows a longer controlled early charge burn than the normal surface coating method. This is the technology used in Re17 that produced almost 200 fps MV increases in 284 Win and 6XC heavy bullet match loads, but was found to come with downsides in all year use if full advantage of heavier loads was taken. (Excellent powder if people don't tip the powder can too much though!) Use the 'search' facility in Accurate Shooter forums and the Daily Bulletin if you're unfamiliar with this propellant. There are no free lunches in internal ballistics.

 

[okie]

bovine feces

 

[jthor]

You can use Quick Load or Gordon to spec a wildcat to evaluate pressure, velocity. etc to address the what ifs.

They will report to you that QL is inaccurate and can’t be used as a reference. Sounds to me that they are covering up the pressures the software shows.

 

[CharlieNC]

They will report to you that QL is inaccurate and can’t be used as a reference. Sounds to me that they are covering up the pressures the software shows.

Maybe the updated program has been changed, as this was an option in the past.

 

[dellet]

It would be nice the see the velocity curve as the load was worked up.

I have seen more than once in load development at the high end, to have the velocity stall. Example have 50 fps increases each step of the ladder, then have the velocity remain within the margin of error for the ES/SD numbers for a couple steps.

The next velocity increase is generally is associated with some type of major/minor catastrophe.

Basically a sign of an unstable max load that could be interesting in temp swings or a hot barrel. Maybe an indication you should have stopped a few steps earlier on the ladder, or invested in a pressure test.

 

[SKWERLZ]

That velocity seems awfully optimistic to me for the small case. The 28" barrel is surely helping but I would think the pressures are still high "if" they are getting that velocity.

My 7 saum with R26 runs comfortably at 2950 with 180’s and a 28” barrel.

I agree
They have to push it hard for a SA 308 based cartridge.

Would love to know the useable case capacity of this for some investigation.

 

[dcali]

I don't know about velocity, but 65+ ksi is going to wreck your brass with a quickness.

 

[Larryh128]

The neck is a joke at best.

 

[K22]

This is simply another outstanding case of the nonsense that is going on in our sport. With the preponderance of safe, laboratory cartridges already on the market why would anyone be interested in something like this? Hard to imagine what void this cartridge is intended to fill.

 

[jackieschmidt]

I guess you can claim anything.

A question. Since the boat tail on the bullet he is using is probably longer than the remaining neck on the case, how is he going to seat a bullet without it going down into the case quite a bit, cutting capacity That he needs to achieve the touted velocity?

 

[Kurz]

Stan Ware’s Radical No-Neck Wolfpup Wildcat​

https://bulletin.accurateshooter.co...y-stan-wares-radical-no-neck-wolfpup-wildcat/