7mmSTW Be Careful With Barnes Load Data

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stubblejumper

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I am now reloading for my fourth 7mmSTW rifle, and until yesterday, I had always used the Nosler or Hodgdons data, and worked up from there. I usually ended up with my maximum load closely matching the Hodgdons data. I haven't done any load development for the 7mmstw since I purchased my Barnes manual until yesterday, but I was actually shocked to see the data in the Barnes manual. The Barnes data is more conservative than Nosler or the other manuals for every cartridge that I have previously loaded for , but for the 7mmSTW the opposite is true. The data in the Barnes manual starts at 78gr for 140gr bullets, with imr7828SSC, which is actually greater than the maximum load in the Nosler manual with 7828. The maximum load in the Barnes manual is 82 grains, which is 4.5 grains more than in the Nosler manual, and 2 grains more than the Hodgdons manual. I have never been able to load above 80gr in any of my 7mmstw rifles without pressure signs. I checked a few other powders,including R-22, and the maximum powder charges are much greater in the Barnes manual. Oddly enough, the velocities listed, are not that unusual for a 24" barrel.

I am posting this as a warning to be extra cautious with the 7mmSTW data in the Barnes manual, because I believe that the loads listed could cause issues in some rifles.
 
Update

I did some chronograph testing today, and discovered that my new 7mmstw rifle is producing considerably less velocity than my other 7mmstw rifles with the same load. At 80gr of IMR7828 behind the 140gr TTSX, I was seeing about 100fps less than with my other rifles,using the same load. Some of that could be due to the cooler temperature today, but my other rifles had much less freebore than this rifle, which I suspect is the largest factor.

Based on that information, I decided to do some more testing with both R-22, and with IMR7828. 80gr of R-22 was getting warm, and at 81gr, the web expansion was a little more than I like. I fired one round at 82gr, but an extrusion mark appeared, so I didn't fire any more. There is no way that I would use 82gr or R-22 in this rifle, and I would likely not exceed 80gr. As a comparison, I topped out at around 79gr in my other 7mmstw rifles.

Then I moved on to IMR7828,80gr and 81gr were still okay, and 82 was right at my comfort limit. I topped out at 80gr with my other rifles.

I should repeat that today's testing was done at 10 degrees C, so warm weather will very likely ad a little more pressure as well.

Overall, while you might get away with the IMR7828 loads in some rifles, I have yet to come across a 7mmstw rifle that would be safe with the R-22 loads listed in the Barnes manual. As such, I still suggest extra caution caution when using the Barnes load data.
 
Someone should give them a heads up! I load for my Voere Titan II with a Douglass barrel (30") and have found it will take more than my Win Mod70 before showing any signs of over pressure. But that data seems odd, I wonder what that was tested in?
 
stubblejumper said:
Update

I did some chronograph testing today, and discovered that my new 7mmstw rifle is producing considerably less velocity than my other 7mmstw rifles with the same load. At 80gr of IMR7828 behind the 140gr TTSX, I was seeing about 100fps less than with my other rifles,using the same load. Some of that could be due to the cooler temperature today, but my other rifles had much less freebore than this rifle, which I suspect is the largest factor.

Based on that information, I decided to do some more testing with both R-22, and with IMR7828. 80gr of R-22 was getting warm, and at 81gr, the web expansion was a little more than I like. I fired one round at 82gr, but an extrusion mark appeared, so I didn't fire any more. There is no way that I would use 82gr or R-22 in this rifle, and I would likely not exceed 80gr. As a comparison, I topped out at around 79gr in my other 7mmstw rifles.

Then I moved on to IMR7828,80gr and 81gr were still okay, and 82 was right at my comfort limit. I topped out at 80gr with my other rifles.

I should repeat that today's testing was done at 10 degrees C, so warm weather will very likely ad a little more pressure as well.

Overall, while you might get away with the IMR7828 loads in some rifles, I have yet to come across a 7mmstw rifle that would be safe with the R-22 loads listed in the Barnes manual. As such, I still suggest extra caution caution when using the Barnes load data.
Click to expand...

Thanks - these kinds of thoughtful analyses are helpful.

Barnes claims that their TTSX with its "driving bands" lowers pressure. Perhaps there's something to that?

Freebore equates to extra case capacity (easily 3-4 grs in some cases I've seen) - that's certainly a factor.

Are recent batches of IMR7828 a tad slower?

All of this rules out the possibility that Barnes messed up. I have observed that they list true max loads with all of their bullets (look at "Deep Curl" loads for the 7X57). Perhaps they're smart enough to know that most shooters want max velocity (more than accuracy!), and if their bullets seem to go faster, it'll sell bullets. They're certainly smart enough to know that no shooter has ever successfully sued a vendor for an over-pressure situation, i.e. the "Lawyer-Proof" load myth.
 
Barnes has also had some issues with misprints in their manuals before. As Andy mentions, the three driving bands is supposed to lower the pressures, but I thought that was a response to the slower velocities/higher pressures that they had found with the original X bullets. Having said that, I only see load data in a manual as a guide line, and always start low and work up to what that gun in that cartridge with certain components give me. Each one is different, with different results. Thanks for the heads up Stubble. - dan
 
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