Home Forums Hunting & Shooting Long Range Hunting 7mm Wby and LRAB results...........

I don't know shcid about rifles but I know enough to know that the difference between a Mashburn and a 7 Weatherby ain't enough to get mad about.

MadMooner,

"Chamber capacity" is one way to put it. I've used "functional powder capacity" too.

It all boils down to being able to use more powder, for more velocity, in a case with a certain amount of powder capacity for the caliber.

Someone, what are the SAAMI pressure standards for the 7 RM and the 7 Wby?

May as well go to the horses mouth...

http://www.saami.org/specifications_and_information/specifications/Velocity_Pressure_CfR.pdf

Yeah, SAAMI information has been on-line for a while now. It's not any big secret.

Absolutely.

Would also say my favorite source for loading data is Hodgdon because they give pressure data for loads. I really wish all manuals printed pressure data... in this day and age of chronographs, it strikes me as a smart thing to do. I extrapolate pressure from velocity without pressure testing gear.

Also, I understand the desire for something a little different (7 Mashburn)... my dear friend Mark Dobrenski loves the round. But realistically that may have more to do with his relationship with Bob Hagel than any illusion about what the Mashburn does or doesn't do differently than other 7 Mags (at least that's my take and I wouldn't presume to speak for him).

Mark's a smart fella and knows 100 fps either way amounts to nada. I've shot his Mashburn and watched it work on game. It's a fine round and I get a kick that he loves the round so much.

Me, if I wanted a 7 Mag I'd go with a 7 WSM.

But I have no need for anything Magnum...

I hate to say it, but anyone who handloads without proper pressure testing equipment is guessing.

The "Bee" was my brothers. With it he took much of what North America has to offer in his 20's DIY.

Baloney.

If you have access to pressure tested data you can extrapolate pressure via velocity.

This isn't rocket science... or maybe it is

Brad, I've been handloading for a long time. Using a chronograph and any other "conventional" pressure indicators I have yet to KNOW the pressure of any cartridge I've loaded for. There are far too many variables. Extrapolating data for the MSM is the same darn thing.

Exactly.

The people I have spoken with off-line about this thread,and who have experience with the 7mm Weatherby,say the velocity claims for the 175 load made here are malarkey.

The SAAMI table indicates that as well....even if a 3/8" freebore allows a bit more speed, it isn't enough to jump velocties up to the levels of an STW or RUM.

Got it.

4 to 6 more grains of powder in the Mash urn ain't much velocity gain without higher pressures

Higher pressure than "what"? The Weatherby? I doubt it.

It's common knowledge that the cartridge has always gotten the velocities Weatherby claims for it with a trick barrel and high pressures.

Take a look at the case dimensions of a 7 Rem Mag and a 7mm Rem Mag....the 7 Rem Mag case body is bigger....not by much but the two are so close that what one will do the other will do.Where it gets the additional capacity I do not know but suspect it is thinner brass....and I can tell you for sure you are not going to operate a 7 Rem Mag and 175 gr bullet anywhere near 3100-3150 with a 175 gr bullet.....not at sane pressures anyway.

Any time I want I can make a 7 Rem Mag that goes just as fast as a 7mm Weatherby and have done it and actually gone right to 7mm Weatherby data with some powders. It's the barrel/throat "trick moves" that do it.Plus 26" barrels. There is a reason most Weatherby rifles come with 26" tubes.

With "normal" throats, the 7mm Weatherby is no faster than a 7 Rem Mag.

The next step up in capacity above these two are the Dakota,the Mashburn, and the STW. I've had them all..the Mashburn is not much greater in capacity but it's certainly enough more that, based on its capacity,it gives more velocity,safely.All three have more capacity than a 7 Rem or Weatherby.

If I want a cartridge that reliably gives more velocity with heavy bullets than a 7 Rem Mag, the Weatherby is not the next stop.It's one of the other three.And even they are hard pressed to move a 175 gr bullet at 3100 fps or better....we can look it up and see it.

I may be "interpolating data", but I have been around enough to know how much velocity each is capable of without opening primer pockets and getting short case life.The differences may not be huge but they are there...just like going from a 300 WS to a 300 Win Mag....the Win Mag is capable of higher velocity...not by much; but it's there.

The notion that a 7mm Weatherby is "safe" with a 175 gr bullet at 3100 or more is ridiculous...especially considering the willy-nilly swapping of data that has gone on to establish the point. Personally I don't find any of the "evidence" in this thread remotely credible. It's nothing but swapping data and guessing with a wink and a nod by people who should know better.

I don't for every 10 percent increase in case capacity there is a 2.5 increase in velocity at the same pressure. That is in escapable

For grins let's assume a powder capacity of 80 grains an 8% increase in case capacity would increase to 86.4 rains less than a 2.5% increase in velocity at the same pressure

So let me get this straight...

You don't rely on a manual for pressure data and you don't rely on a chronograph to extrapolate pressure from velocity, even though pressure = velocity, and the velocities in the manuals come from pressure tested data.

You have your own pressure testing gear?

If not, what you're saying is you guess.

Which, of course, is why most wildcat rounds "out-perform" conventional rounds so dramatically...

Bob.
True story for you Bob.
Local gunsmith I know,not the guy building my current stuff.Built a 7mm Weatherby for one of his customers.
Customer insisted on a custom chamber without the standard free bore.
Gunsmith agrees to do the work but be cautious about only usuing hand loads for the 7.
Customer says he only shoots handloads.

Several years later. Gunsmith gets a call from Customer.
Big time problem with his Weatherby and he needs to get it fixed.
Turns out the guy had gone on an elk hunt and some how during the trip out, had forgot his ammo.
He picked up a box of Weatherby ammo and used it sight his rifle in before the hunt.

The rifle was built on a M98.Turns out the M98 really can handle gas leaks without blowing up and killing the shooter pretty well.Big time case head leak.Bolt stuck in the rifle.
case head,after they finally got it out, pretty much incinerated.Just looking at,I actually saw the after math.
The guy was lucky he didnt eat it.
Thats what happens when you run Weatherby factory ammo is a chamber set up without free bore.
Weatherby factory ammo is some of the hottest loaded stuff you will ever run across.

I had a 7mm Weatherby in a Mark IV back in the early 80s before I did my Alberta hunts.
I could not equal factory ammo for speed with my handloads.
When I got close.I blew primers.
I know what they say about an example of one.
But for me, one was enough.
The Weatherby accuracy guarantee is 3 shots into a 1.5 inch group at 100 yards.
And thats exactly what I got.
The hotter I loaded it the bigger the groups got.
I found over time the only way it would go sub MOA was to down load it to 7-08 speed and then it was dandy accurate.
But thats not why I bought it.

My last factory built rifle the 7mm Weatherby.
After messing around with the thing for as long as I did and not getting anywhere.I finally got fed up and sold it.
My next rifle was built by Walt Bergers brother Nelson Berger.A M700 in Mr. Ackleys fine shooting 280.
I carried the 280 AI all over NA and Canada and never looked back.Didnt own a Magnum of any kind untill I finally built a 300 WM in 2000.

I have built a few more mags over the last 10 years or so.
Took awhile for the Weatherby magnum scar to wear off.


dave

I see this thread has wandered even further into the theoretical since last evening.

Yes, you can extrapolate pretty closely on pressures if you know what you're doing, and a chronograph is the #1 way to do it. I've done it a bunch of times, and been able to test my loads with either strain-gauge equipment, or have a piezo-electronic laboratory test them.

I see Bob still insisting the 7mm Weatherby Magnum gets it's results with too-high pressures, despite all the pressure-tested data to the contrary. I just happened to do an article on the 7mm Weatherby recently, and have the Nosler and Norma maximum-velocity 160-grain handloads for it and some other 7mm magnums at hand:

7mm Wby. Magnum Norma 26 inches 3199
7mm Wby. Magnum Nosler 24 inches 3197

7mm Rem. Magnum Norma 26 inches 3084
7mm Rem. Magnum Nosler 24 inches 3077

7mm STW Norma 26 inches 3176
7mm STW Nosler 26 inches 3229

7mm RUM Norma 26 inches 3186
7mm RUM Nosler 26 inches 3261

Somebody will no doubt point out that Norma is a European company, and the SAAMI equivalent over there is the Commission Internationale Permanente (C.I.P.), which uses a slightly different piezo-electronic set-up to measure pressures. But Norma is also a member of SAAMI, so adheres to their guidelines.

Also, Western Powders runs one of the larger pressure labs in the country, which does a lot of testing for other companies as well. They've done some experimenting with C.I.P. piezo barrels to see what the actual difference was, rather than speculate about it, and found there was around 1000 psi difference.

The reason most companies don't publish pressure data (though Western also does, for Accurate and Ramshot powders) is that reloaders are very much likely to extrapolate what they can do, and possibly get into trouble. For one thing, the pressures listed by Hodgdon and Western are Maximum Average Pressures (MAP). There are a couple of other pressure standards that cartridges have to meet, one being how much pressure varies from average on the HIGH side, since individual rounds can vary considerably. This also affects the MAP either SAAMI or C.I.P. select for a certain round.

Also, you can be assured that any load found in any current source of SAAMI-member data does not exceed the MAP of that cartridge, so that limit in pressure is implicit in any data.

Uh-oh.

Step back from the ledge, Bob.

Now John, don't start injecting facts into this thread... what fun is that?