PWS
Silver $$ Contributor
I'm mostly a lurker on this site since I've got a lot more to learn than to offer but this was an interesting recent project. Unfortunately, my evidence is mostly anecdotal and I'm sure a lot of you already know what I'm about to write but thought it worthwhile to share some details. This is the first instance of a direct, same barrel comparison of the WM vs WSM that I know of.
I shoot long range recreationally and in 2017, cobbled together M70/Krieger Palma contour 300WM that shot everything well and some great (almost always under 0.75moa and often 0.5). Accuracy went south fast at about 1750 rounds so last spring, Bugholes had a #5 Bartlein available and I tried to fit and chamber it after work one evening. In my haste, I did a total hack job. The setup never shot much better than 1.25moa and most often in the 1.50moa range. After setting the barrel back and rechambering, recrowning the muzzle twice, trying another stock, two different scopes - and about 750rounds of various loads- I finally had to admit that the project was just an exasperating waste of time and money.
In the meantime, my SA M70 6.5Screedoor was also getting a bit long in the throat. I found a mag faced bolt and after lurking on all the 300WSM threads, bought another 30cal barrel to fit to my SA M70, and chambered it with Elk Ridge's .300WSM "match" reamer. The interesting part is that I also refit the above Bartlein to the SA M70 but also chambered in WSM "match".
In exactly the same barrel, same length, same crown, same throat location (within 0.1"), etc, but chambered in WSM, the WSM unquestionably does not get as warm during firing sequences as did the WM. It was never the plan but now I wish I'd taken the time to take actual measurements.
The barrel now has 1500 rounds through it and although the lands fit a .3008 bushing at the rechamber (750rounds of WM), the throat has not moved forward appreciably as a WSM. Again, I wish was paying closer attention but there's no question in my mind that the WM is much harder on barrels than the WSM.
Accuracy has been also been cut by ~40%. Sub 1.0moa groups are much more common and the barrel will now reliably shoot under 0.75moa with loads that it likes. This will surprise no one but right around 61.0gr H4350 and 2830fps is the spot with 208gr ELD-Ms, 208gr AMAXs, and 200gr ELD-Xs. However, I have not gotten good results from 212ELD-Xs or 215Begers.
Maximum velocity in the WSM appears to be around 150fps less than the WM but I have no way of comparing pressures. Sweet spots were difficult to identify in the WM (it just wasn't consistent enough) but both chambers do seem to produce best accuracy just over 2800fps and if I were asked if the chamber made a difference in what the barrel likes, I'd say no. I am positive that, in this barrel, the WSM is much more "user-friendly".
Lastly, as an aside, be careful with IMR4955 data! The charges listed on the Hodgdon website for 208gr AMAXes were WAY TOO HOT in my rifle! Instead of behaving similar to the 4831s, 4955 was much more like the 4350s without producing quite as much speed. It may just be my instance but approach with caution!
I shoot long range recreationally and in 2017, cobbled together M70/Krieger Palma contour 300WM that shot everything well and some great (almost always under 0.75moa and often 0.5). Accuracy went south fast at about 1750 rounds so last spring, Bugholes had a #5 Bartlein available and I tried to fit and chamber it after work one evening. In my haste, I did a total hack job. The setup never shot much better than 1.25moa and most often in the 1.50moa range. After setting the barrel back and rechambering, recrowning the muzzle twice, trying another stock, two different scopes - and about 750rounds of various loads- I finally had to admit that the project was just an exasperating waste of time and money.
In the meantime, my SA M70 6.5Screedoor was also getting a bit long in the throat. I found a mag faced bolt and after lurking on all the 300WSM threads, bought another 30cal barrel to fit to my SA M70, and chambered it with Elk Ridge's .300WSM "match" reamer. The interesting part is that I also refit the above Bartlein to the SA M70 but also chambered in WSM "match".
In exactly the same barrel, same length, same crown, same throat location (within 0.1"), etc, but chambered in WSM, the WSM unquestionably does not get as warm during firing sequences as did the WM. It was never the plan but now I wish I'd taken the time to take actual measurements.
The barrel now has 1500 rounds through it and although the lands fit a .3008 bushing at the rechamber (750rounds of WM), the throat has not moved forward appreciably as a WSM. Again, I wish was paying closer attention but there's no question in my mind that the WM is much harder on barrels than the WSM.
Accuracy has been also been cut by ~40%. Sub 1.0moa groups are much more common and the barrel will now reliably shoot under 0.75moa with loads that it likes. This will surprise no one but right around 61.0gr H4350 and 2830fps is the spot with 208gr ELD-Ms, 208gr AMAXs, and 200gr ELD-Xs. However, I have not gotten good results from 212ELD-Xs or 215Begers.
Maximum velocity in the WSM appears to be around 150fps less than the WM but I have no way of comparing pressures. Sweet spots were difficult to identify in the WM (it just wasn't consistent enough) but both chambers do seem to produce best accuracy just over 2800fps and if I were asked if the chamber made a difference in what the barrel likes, I'd say no. I am positive that, in this barrel, the WSM is much more "user-friendly".
Lastly, as an aside, be careful with IMR4955 data! The charges listed on the Hodgdon website for 208gr AMAXes were WAY TOO HOT in my rifle! Instead of behaving similar to the 4831s, 4955 was much more like the 4350s without producing quite as much speed. It may just be my instance but approach with caution!
