Benjamin Marauder PCP .177-caliber air rifle: Part 6
by Tom Gaylord, a.k.a. B.B. Pelletier
Today, I’m going to attempt to correct the accuracy problem I created in the last report, where I reduced the average velocity from 1015 f.p.s. to 886 f.p.s. in the Benjamin Marauder while testing with Crosman Premier 7.9-grain pellets. The best group at the higher speed was 10 shots in 0.285 inches, center to center, at 25 yards; but at the new lower velocity, the best group was only 0.397 inches between centers. I was hoping to get approximately the same group size — around 10 shots into 0.30 inches at 25 yards at the lower velocity. When that didn’t happen, I had a decision to make. Should I continue with the other things I wanted to do, or should I fix this one first? I decided to do what I would have done had I not been testing the rifle for a blog, but just for myself. I decided to get the accuracy back on line.
Once again, I removed the barreled action from the stock and got access to the power adjustment screw on the right side of the receiver. To see where this is, read Part 4 of this report.
I turned the power screw another 1/3 turn counterclockwise, bringing the total adjustment to 2 full turns out from all the way in. Remember that when we began this test, I discovered that the power screw was adjusted 2-1/3 turns out, so we are now 1/3 turn shy of that.
Then, I fired 10 Crosman Premier lites. I was concerned that the first shots might not be up on the power curve because we found in Part 4 that the first 2 shots were below the desired speed when the rifle was filled to 3,000 psi. Here are the shots as they occurred:
Average velocity 955 f.p.s.
It seems like I hit the desired velocity on the first try. I locked the power screw and put the action back into the stock. I had now fired 10 shots on this fill; and from all the previous testing, I knew there were at least 20 more good shots available — and probably several more. I decided to shoot 2 groups of 10 shots each at 25 yards.
The first group from 25 yards put 10 pellets into 0.268 inches. That’s slightly smaller than the best group at the highest velocity. Of course, I didn’t know that while I was shooting, so I continued to shoot group 2.
Group 2 is larger than group 1. It measures 0.327 inches between centers. In light of group 1, however, I feel this is not so bad. I had larger groups at the higher power, too.
After shooting the second group, I thought about the reader comments I might get when I published this report. Comments like, “Why did you stop after group 2? Are you sure the rifle wouldn’t continue to shoot good groups, even though after 30 shots it will probably fall off the power curve at some point?” So, I shot a third group just to see what would happen. Those 10 shots went into 0.416 inches.
At no time during this shooting were any shots called pulls. All shots went off with the crosshairs on the 10-ring (dot) of the target as they should have been. All pellets were straight from the box with no sorting of any kind. So this test was conducted exactly as I would shoot the rifle at any given time.
I now feel the gun is shooting as I want it to. The next step will be to adjust the fill pressure level so the rifle can be filled to a lower pressure and still operate at this velocity. I’ll probably have to adjust the power screw again as I adjust the rest of the firing mechanism to keep the gun shooting at this velocity. The purpose of that exercise will be to see how many good shots are in a string at a lower fill pressure and to see if it’s worthwhile to lower the fill pressure.
One last thing before I end this report. I haven’t yet commented on the shot counter that’s built into the Marauder magazine, but it’s there and it really works well. I haven’t ever used shot counters like this in the past because I’ve always found them clunky and difficult to see.
The shot counter is a circular window on the right side of the magazine — the side that sticks out away from the rifle. The number in the circle indicates the number of pellets that have been moved from the magazine into the breech of the barrel. It doesn’t tell you if that shot has been fired yet, but you should know that.