10 http://www.riflemagazine.com Rifle 305
Indents on the rims of these .17 WSM cartridges indicate misfires, which are not
terribly unusual due the case’s thick brass.
.17 Winchester Super Mag Accuracy Results
extreme
recorded velocity average
load velocity spread group
(grains) (fps) (fps) (inches)
20 Hornady Varmint Express V-MAX (3,000*) 2,960 32.
20 Federal American Eagle tipped (3,000*) 2,896 48.
20 Winchester Varmint HV tipped (3,000*) 2,992 58.
25 Winchester Varmint HE tipped (2,600*) 2,643 88.
25 Browning Performance tipped (2,600*) 2,624 52.
* stated velocity
Notes: A Ruger 77/17 .17 WSM with an 18.5-inch barrel and a Burris Signature Select 6-24x 44mm scope
was used to test all loads. Group size is the average of four, five-shot groups at 100 yards. Velocities were
recorded at 10 feet with a PACT chronograph.Table IThe Savage B.Mag was the first .17 WSM bolt-action rifle. An all-new design, it was
specifically developed for the cartridge.powder charge. For a rough size
comparison, I measured external
dimensions of Hornady .17 WSM
and .22 Winchester Magnum Rim-
fire (WMR) loaded rounds using
a dial caliper. This method is not
intended to be exact, particularly
when it comes to rim thickness,
but it provides a bit of insight.
The .17’s dimensions included
a rim thickness of .070 inch and a
case diameter just below the rim
of .265 inch. In the same order, the
.22 WMR’s dimensions were.
inch and .238 inch. Case length for
the .17 WSM was roughly .300 inch
longer. A fired WSM’s case mouth
measured .012 inch in thickness,
but there were no fired .22 WMR
cases on hand for comparison.
Here it should also be noted that
the thick rim of the .17 WSM re-
quires a stout blow in order to ig-
nite the priming compound. Both
rifles tested early on produced
several misfires. The short-barrel
Ruger showed that the same prob-
lem still exists, though it appears
to be less common. When testing
the early rifles, three or four car-
tridges out of 50 or so failed to fire.
While shooting the new batch of
ammunition, close to 300 car-
tridges were fired. Of those, four
were misfires, their rims having
been smashed no differently than
all the others.
Though case dimensions pro-
vide a clue as to why the .17 WSM
is so much faster than other rim-
fire cartridges, the true difference
can be found by a little research
on the Sporting Arms and Ammu-
nition Manufacturers’ Institute(SAAMI) website, where Maxi-
mum Average Pressure (MAP, or
standard operating pressure for
rimfire cartridges) can be found.
For instance, the .22 Short has
a MAP of 21,000 psi, and the.
Long Rifle and .17 Mach 2 have a
MAP of 24,000 psi. The .22 Win-
chester Rimfire’s MAP is 20,
psi; the .17 HMR operates at 26,
psi, and the .22 WMR, based on the
same case, has a MAP of 24,
psi. Due to its oversized thick case,
the .17 WSM has a standard oper-
ating pressure of 33,000 pounds
per square inch, quite a bit higher
than any previous small-caliber
rimfire cartridge.
The six loads available include
Winchester Varmint High Veloc-
ity, 20-grain Polymer Tip; Win-
chester High Energy, 25-grain
Polymer Tip; Hornady Varmint
Express Rimfire, 20-grain V-MAX;
Browning Performance Rimfire
Varmint Expansion, 25-grain
tipped and Federal’s American
Eagle, 20-grain Tipped Varmint.
Winchester also lists a VarmintX
Lead Free Polymer Tip Rapid Ex-
pansion load containing a 15-grain
bullet with a stated muzzle veloc-
ity of 3,300 feet per second (fps)
that was not tested due to lack of
availability.
When Hornady and Winchester
were the only companies that sold
.17 WSM ammunition, three loads
were used to test a Ruger rifle
with a 24-inch barrel in 2016, and