Q: I’ve been thinking about having my Winchester Model 70 rebarrelled for a 7mm magnum and am trying to decide which one to get.
What would be your choice between the 7mm Rem Mag and the 7mm STW? Why?
Bob Barrett
A: I have had quite a bit of experience with both of the magnums you are considering. A few years ago I took them to the Gulf and used them both on game.
To be honest, I couldn’t see a bit of difference between the way they performed on everything from pigs and deer to scrub bulls.
The criterion of what any 7mm magnum will do is with a properly constructed, ballistically efficient 160gn bullet. The 7mm Rem Mag drives this weight at 3050fps and the 7mm STW requires roughly 10gn more powder to shade it by a mere 100fps, which hardly makes a noticeable difference to performance.
During the time I spent handloading for the 7mm STW I found that it reached maximum pressures before even the slowest powders filled the case, which reduces its efficiency.
Some might label the 7mm STW “over-bore capacity” — a meaningless term since expansion ratio is what most shooters mean when they claim a cartridge is over-bore capacity.
Expansion ratio is a number showing the relationship of case volume to bore volume (or bore diameter; but diameter doesn’t vary with barrel length, and volume does). A high expansion ratio means a big bore relative to the case capacity. A low expansion ratio means the case is big relative to the bore size.
The most efficient cartridge is one that gets the most velocity from the least powder.
Which of them is the most efficient: the 7mm Rem Mag or the 7mm STW? You can push a 160gn AccuBond from the STW at 3080fps with 78gn of AR2217, but the 7mm Rem Mag gets 3053fps using 66gn.
Burning that much extra powder erodes the throat more quickly and cuts barrel life in half, so the STW is hardly worthwhile.
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