7mm STW--any thoughts/experience with?

[stagpanther]

7mm is one of my favorites--but I see very little talk of this cartridge.

[Tallest]

I have no personal experience with it, but it must be something. I once saw two men nearly come to blows over dibs on used one at the DE Cabela's. It was a "custom" stainless model, felt like it was about 6 lbs. It had a green Bells and Carlson stock, Mauser type action, and loooonnng fluted barrel. Price tag was $2799. They started there with a bidding war over who would walk out with it. I think the (very patient) old gent running the gun library that day was considering using it to paddle them both.

But if I ever wanted a 7mm/.284 faster than my 280AI, I would probably go STW. It has a certain, vintage authority over all other 7mms.

[stagpanther]

But if I ever wanted a 7mm/.284 faster than my 280AI, I would probably go STW. It has a certain, vintage authority over all other 7mms.

What I like is that gets way up there in velocity but apparently is not the barrel burner that similar high-power 7's are--plus the parent case is the 8mm Rem Mag but can apparently also be sized from 300 Weatherby (otherwise the cases, if you can find them, are outrageously expensive!!).

[Bart B.]

Originally Posted by stagpanther

What I like is that gets way up there in velocity but apparently is not the barrel burner that similar high-power 7's !!).

The 7mm STW burns more powder than any other 28 caliber cartridge so it wears out barrels faster. 700 rounds is about all it'll give best accuracy.

[HiBC]

I am interested in in hearing the argument why it would not be a barrel burner.

I personally notice few 7mm Rem Mag loads exceed 85% load density.

IMO,cases larger than 7mm Rem offer diminishing returns. 7 MM rem does not gain much over 280 AI.

Greater overbore = less expansion ratio. Which means margin of error is more necessary .Pressure events will be more sudden and dramatic.

The mag box limitations of most rifles make bullets much over 140 gr less practical,especially those of more VLD ogive,

Many(myself included) prefer the higher BC's and wind bucking of the 160 gr + 7mm projectiles.

At long ranges,screaming whiffle bullets with the BC of a Cheeto are surpassed by the javelins that start at an initially lower velocity.

IMO,the 7x61 Sharpes and Hart was a better design than the 7mm Rem.

Bigger is not always better. There is a balance to achieve.

[Billygoat109]

Don’t shoot a 7mm STW, but do shoot a 7mm Weatherby Magnum. Also load a 175 gr Sierra SBT with 78gr of Hod-US869 using Lee Data. I like it!


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[Billygoat109]

Oh, that load travels at 2751 FPS!


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[old roper]

Are you thinking about 1/8 twist barrel?

[Billygoat109]

7mm Weatherby Magnum 1 in 9 1/2"


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[Bart B.]

Originally Posted by HiBC

Greater overbore = less expansion ratio. Which means margin of error is more necessary .Pressure events will be more sudden and dramatic.
.

Do all 7mm barrels have the same bore capacity?

If so, what is it?

[Double K]

7mm RUM is bigger if you must own the big kahana of 7mm's.
Here's a new one. 28 Nosler is nearly identical in case capacity but the guns chambered in the RUM tend to be less expensive.

https://www.gunbroker.com/item/890567124

[stagpanther]

Are you thinking about 1/8 twist barrel?

Yes. Berger has a new high BC 190 gr 7mm uberbullet but I don't have any idea what additional throat I would need to seat it effectively.

7mm RUM is bigger if you must own the big kahana of 7mm's.
Here's a new one. 28 Nosler is nearly identical in case capacity but the guns chambered in the RUM tend to be less expensive.

I've used the 7mm RUM but it's a blast furnace after not many shots, so I'm not interested in it--and I suspect the 28 Nosler is similar (perfectly good for one-and-done hunting, assuming your projectile doesn't vaporize or laser right through the game without expanding). The 7mm STW and 7mm-300 wby, which is similar, seem to be a bit less likely to quickly self-imolate, but IDK.

[Jim Watson]

Amusing story here.
Guy fell in love with the STW and rebarrelled or rechambered several rifles.
Problem was, his best accuracy was the fireforming shots. He never could get a full power load in fireformed brass to do as well.

[stagpanther]

Problem was, his best accuracy was the fireforming shots. He never could get a full power load in fireformed brass to do as well.

That is funny--what parent cartridge did he use? I wonder how important it is to adjust the freebore to get optimal results.

[Txhillbilly]

The 7mm STW was all the craze back in the early 1980's. I don't think it has much of a fan base anymore.
Some Long Range Hunter's still shoot it, but in today's current offerings most shooter's consider it an obsolete cartridge.

[HiBC]

Bart
My understanding,which could be wrong

A relatively balanced boiler room to bore ratio,like a 7mm08,might have the total volume of cartridge case and bore double when the bullet travels 8 in down the bore (a guess)

For the STW,doubling combustion chamber volume might take 16 in of barrel travel.

At the same time,the larger powder volume is turning to gas via doubling or quadrupling rapidly.

As the bullet travels down the bore,any 7mm bullet in any 7mm bore is increasing pure bore volume at the same rate, but pressure builds in the cartridge case before the bullet moves. The large pressure volume of the STW case is "diluted" less by the addition of bore volume via bullet travel.

Another way to llustrate what I am trying to say is with the absurd.

With a balanced design like the 308,its hard to blow one up using appropriate powder. The bullet can outrun the pressure.

Now lets neck a 50 BMG down to 17 caliber. It wants to be a bomb. Big production of gas, A very tiny hole . 30 inches bullet travel will proportionally increase chamber volume very little.

The cartridge will be a bit peaky.

I'm not into the 6.5 CM mystique so much,but there are reasons why it is far more successful than the 264 Win Mag.

Given the powder tech we have, there is an efficient sweet spot for a bore and projectiles.

We can hot rod beyond that,for some price. That price may be acceptable,but there will be diminishing returns

We don't need 3700 fps any more. We have learned to use adjustable sights.

[taylorce1]

Originally Posted by stagpanther

Yes. Berger has a new high BC 190 gr 7mm uberbullet but I don't have any idea what additional throat I would need to seat it effectively.

In my limited experience shooting VLD bullets, you'll never get close to the lands in a SAAMI spec chamber. These two things can happen you seat the bullet out way too long to ever use the magazine making your rifle a single shot, the second is less likely but you dont have enough of the bulkets bearing surface in the case neck for proper neck tension. With VLD bullets the ogive is much closer to the base of the bullet than a traditional spitzer bullet, so a shallow throat is needed if you want very little jump to the lands.

Just read up on the Berger "making it shoot" seating depth test. I've had good luck with as much as .120-.130" jump for accuracy. If your rifle likes that much jump it's much easier to stay inside magazine length for reliable feeding.

[stagpanther]

In my limited experience shooting VLD bullets, you'll never get close to the lands in a SAAMI spec chamber. These two things can happen you seat the bullet out way too long to ever use the magazine making your rifle a single shot, the second is less likely but you dont have enough of the bulkets bearing surface in the case neck for proper neck tension. With VLD bullets the ogive is much closer to the base of the bullet than a traditional spitzer bullet, so a shallow throat is needed if you want very little jump to the lands.

Just read up on the Berger "making it shoot" seating depth test. I've had good luck with as much as .120-.130" jump for accuracy. If your rifle likes that much jump it's much easier to stay inside magazine length for reliable feeding.

I'm not of the jam it the lands camp--I shoot lots of Bergers and yes they sometimes prefer like the long jump over the short one. I'm not worried about the magazine length rigamarole either--in the end, everything would be dictated by the bullet and the chamber. Problem is, no way for me to know that without getting a baseline barrel made and working my way up to the ideal combo you want as far as I can tell, sorta a "chicken before the egg" kinda thing.

The 7mm STW burns more powder than any other 28 caliber cartridge so it wears out barrels faster. 700 rounds is about all it'll give best accuracy.

Good point Bart. I have a question for you--have you ever found that there is usefulness in using a treatment like moly plating on bullets to help increase barrel life and/or accuracy? I have quite a few "over bore" cartridges and was curious if the pros actually see benefits from it.

[Bart B.]

Originally Posted by HiBC

Bart
My understanding,which could be wrong

A relatively balanced boiler room to bore ratio,like a 7mm08,might have the total volume of cartridge case and bore double when the bullet travels 8 in down the bore (a guess)

For the STW,doubling combustion chamber volume might take 16 in of barrel travel.

At the same time,the larger powder volume is turning to gas via doubling or quadrupling rapidly.

As the bullet travels down the bore,any 7mm bullet in any 7mm bore is increasing pure bore volume at the same rate, but pressure builds in the cartridge case before the bullet moves. The large pressure volume of the STW case is "diluted" less by the addition of bore volume via bullet travel.

Another way to llustrate what I am trying to say is with the absurd.

With a balanced design like the 308,its hard to blow one up using appropriate powder. The bullet can outrun the pressure.

Now lets neck a 50 BMG down to 17 caliber. It wants to be a bomb. Big production of gas, A very tiny hole . 30 inches bullet travel will proportionally increase chamber volume very little.

The cartridge will be a bit peaky.

I'm not into the 6.5 CM mystique so much,but there are reasons why it is far more successful than the 264 Win Mag.

Given the powder tech we have, there is an efficient sweet spot for a bore and projectiles.

We can hot rod beyond that,for some price. That price may be acceptable,but there will be diminishing returns

We don't need 3700 fps any more. We have learned to use adjustable sights.

HiBC, where does the force come from to push a 308 bullet ahead of the burning powder's pressure wave?

Note that 7.62 NATO service ammo needs at least 60 pounds of force to start pushing bullets forward in the case neck. That is when pressure in the case is about 800 psi

[Bart B.]

Originally Posted by stagpanther

Bart. I have a question for you--have you ever found that there is usefulness in using a treatment like moly plating on bullets to help increase barrel life and/or accuracy? I have quite a few "over bore" cartridges and was curious if the pros actually see benefits from it.

No.

[Double K]

Moly coating was the fad of the day back when I shot Hunter benchrest, I couldn't justify the extra expense at the time, the fad only lasted a few years. The theory at the time was the lubrication on the ojive helped the bullet center itself on the way into the lands.
My personal belief is the bullet ironed moly into the low spots and pores in the metal, it was nearly impossible to remove. I noticed that the zero on my rifle would change slightly as the gun was fired during the course of the day with only light cleanings between relays. When your trying to hit a .0050 dot at 100yds for an X it was maddening.
Moly adds another variable into the equation when your trying to reduce the variables in precision shooting.

[ligonierbill]

Interesting discussion. I shoot the parent, 8mm Rem Mag, and my take is it is a luxury to have all that case capacity. Which 7mm is the absolute fastest is not that meaningful; these big case rounds are all very fast, and they will all burn out barrels a lot faster than a 7x57. So, you replace the barrel more often. OK by me. I grew up thinking the whole rifle basically lasts forever, but even the 1917 Danzig Mauser I carried in the '60s was likely rebarreled in 1926 when there was a major refurbishment at Suhl. If you shoot a lot, it's a replacement part.

[HiBC]

HiBC, where does the force come from to push a 308 bullet ahead of the burning powder's pressure wave?

I never envisioned the bullet being ahead of the "pressure wave"
The pressure is on the bullet base. Using written words has its problems .
Expansion volume can mitigate pressure increase(the way I envision it)
A large case volume also plays a part in mitigating peak pressure.

But lighting up twice the powder will drastically increase gas production.

An imperfect analogy would be to take an 3 liter engine with 9.8 compression ratio that just runs without pinging on pump gas mid grade. (Like 60,000 psi chamber pressure)
Now we bore it and put in a stroker crank Its now a 3.7 liter engine. But we use the same heads,.
Compression ratio goes up to 12 .5 to 1 . It pings. We can go to higher octane (slower powder) and that will help up to the limits of the powder/fuel we can get.

A previous poster told us about his success with his 7mm Weatherby. About 2750 with a 175 gr bullet? He is happy,I am happy, Enjoy a fine rifle!!

If you go to Hogdon and look up a 280 AI,six loads with a 175 gr bullet exceed 2700 fps and one exceeds 2800 fps. No,I cannot tell you barrel length right now.

My point is,it seems a 280 AI is near an efficiency "Sweet spot" Its diminishing returns to go bigger,

I've owned 3 different 7mm Rems. Its a very good cartridge that I use less now.
Most loads,even the higher perf ones,are around 85% load density.

If I cannot use nearly all the case volume I have,why pursue more?

Its acyually rather miraculous the velocity that can be achieved with RE -15 and RE-19 in a 7-08.

I'll take a heavy for caliber,high BC bullet at 2600 to 3000 fps over a lighter,lower bc bullet at 3400 plus .

I get 2900 with a 200 gr Accubond from my 30-338. That bullet will expand/perform(over 2000 fps) at ranges much farther than I will shoot at a big game animal. Actually,I can say the same about a 30-06 AI launching a 180 gr bullet at 2900.

I'm not making rules for anyone else,but I just do not have a hunting requirement for more.

For long range plinking? I have a target elevation knob when I need it.


And if we run the numbers in ballistic software...If we are still using "Max point blank range" ...relying on velocity to xtend range,run the numbers!!

See just how much a couple hundred fps extends your MPBR. You will be disappointed.

[Double K]

Your point blank range increases 10yds per 100fps roughly a poor excuse for magnum cartridges. To me energy on the target is the real reason for the extra velocity along with bullet expansion.

[HiBC]

Fair enough.
Most folks would agree a 30-40 Krag loaded with a 200 gr bullet will give adequate performance at 100 yds for hunting any North American big game.

The 30-338 launching a 200 gr Accubond at 2900 fps gives that performance at 700 yds.

I do not shoot big game at 700 yds. I don't shoot at 600 yds.

I don't need more than my 30-338.

But I'm not telling you what to do or not do.