Sterling HR-81 .177 underlever air rifle: Part 2
by B.B. Pelletier
Today, we’ll look at the velocity this Sterling HR-81 underlever air rifle produces. You’ll recall that this airgun started out as a UK rifle, so the power was limited to 12 foot-pounds. Benjamin-Sheridan didn’t change that when they took over manufacture in 1994. The U.S. production ended in 1994 when Crosman bought the Benjamin company. So, an American Sterling rifle is probably a pretty rare airgun.
I finally had the opportunity to test and evaluate the Sterling trigger. It’s single-stage with lots of creep before the release. The trigger-pull measured 40 oz.; because of the creep, it felt like more. The safety is manual, which I really like. When it’s applied, it just blocks the trigger from moving.
The rifle fires with a solid thunk and no vibration to speak of. That’s probably due to the tune that Jim Grossman put on this particular gun, because all the online reviews I read about Sterlings criticized the vibration a lot. This one is solid.
The underlever releases by pulling back on a knurled handle located at the end of the underlever. Unfortunately, the handle must also be manually pulled back to return the underlever to the stowed position. This slows the cocking process just a little. The rifle cocks with 25 lbs. of force; and because there’s no anti-beartrap device (nor is one needed, because of the bolt-action loading), it’s possible to uncock the rifle.
The lever catch has to be pulled back to both extract the lever for cocking and to put it back.
Now, I’ll go through the velocity test. I did warm up the powerplant with two shots before starting the first string.
The first pellets I tested were Falcon pellets from Air Arms. At 7.33 grains, they’re a very lightweight domed pellet, yet they’ve also been among the more accurate pellets in a number of other rifles. In the Sterling, they averaged 626 f.p.s., but the range went from 506 all the way to 653 f.p.s. That’s a spread of 147 f.p.s. That one slow shot was not an anomaly, either, because there was another shot that registered only 614 f.p.s. The bulk of the shots went in the 630s and 640s, but there was another slower shot, so the 506, while surprising, was not a complete fluke. At the average velocity, the rifle generated 6.38 foot-pounds.
JSB Exact 8.4-grain pellets
The JSB 8.4-grain dome pellets averaged 597 f.p.s. in the Sterling, but, again, the spread was pretty large. It ranged from 564 to 625, with half the shots in the 600s. The spread was 61 f.p.s. At the average velocity, the muzzle energy generated was 6.65 foot-pounds. It’s interesting that this pellet, which is heavier than the Falcon, also generated slightly more energy. Usually a heavier pellet will make less energy in a spring gun.
Crosman 7.9-grain Premiers
The next pellet I tested was the Crosman Premier lite 7.9-grain dome. It averaged 580 f.p.s. in the Sterling and once more the spread was huge. It ranged from a low of 467 f.p.s. to a high of 611 f.p.s., which is a total of 144 f.p.s. At the average velocity the energy was 5.90 foot-pounds.
A little less energy than I expected from this rifle. And, the wild velocity variance is anybody’s guess. However, I had a theory that it could be pellet skirts that weren’t sealing well. So, I conducted a little experiment. I used a ball-end pellet seating tool to enlarge the skirts on 10 of the lightweight Falcon pellets and chronographed them again.
Second test after enlarging the skirts
Well, I was wrong. I enlarged the skirts to the point that the pellets had to be pressed down into the loading trough. Even with that, the average velocity was 584 f.p.s. The spread went from 496 to 648 f.p.s., a range of 152 f.p.s. The average muzzle energy was just 5.55 foot-pounds. Obviously, something else is at work here. Tight pellets are not the answer to tighter velocity spreads.
I’m hoping I’ll find the rifle accurate — though, with 100 foot-second spreads, I can’t hope for much past about 20 yards. The rifle has a Lothar Walther barrel, so maybe it’s a tackdriver in spite of the numbers. We shall see.