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Accessories Benjamin Marauder PCP .177-caliber air rifle: Part 5

Benjamin Marauder PCP .177-caliber air rifle: Part 5

by Tom Gaylord, a.k.a. B.B. Pelletier

Part 1
Part 2
Secrets of loading the Benjamin Marauder magazine
Part 3
Part 4

Benjamin Marauder
Benjamin Marauder

Before I begin today’s report, I have some news about Leapers’ scopes for blog reader Kevin. He wondered what the status was on the new Bug Buster scopes with the thinner reticle lines, so I asked Leapers for an update on that plus a couple other scopes that will be coming out soon. The new Bug Buster is apparently coming to market very soon. It’s impossible to say for sure exactly when, but the next 60 days sounds about right. Leapers will be sending me a sample to test for you, so I’ll do a report on it. But I also learned that they have several full-sized scopes that have parallax correction down to 5 yards. That’s almost in the Bug Buster range. They’re sending me some samples right now, and I’ll report on them for you.

The scout scope with the 11-inch eye relief is due to hit the market some time in September. This is a scope for your pneumatics, like the Benjamin 392, but it’ll also be ideal for Mosin Nagants and some lever-action centerfire rifles.

The bubble level scope is expected out around the Christmas holiday timeframe. This is the one I’ve been waiting for because it should be a long-range shooter’s dream. I’ll have more as I test the scopes they’re sending. Now, to today’s report.

This will be especially important to those who are new to precharged airguns and are trying to understand how to adjust their rifles for optimum performance. It should clear up some things for you about velocity, accuracy and tuning a PCP.

In the third report, I shot the Benjamin Marauder for accuracy at 25 yards. I shot 8 different premium pellets to see if 1 or 2 of them stood out. One did — the Crosman Premier 7.9-grain dome — also known as the Premier Lite. In case you aren’t aware, I link the names of evey pellet (the first time it appears) in the report to the specific pellet used. So, when I say Crosman Premier Lite, I’m referring only to the Premiers that come packed in cardboard boxes. Premiers that come in tins may work well, too, but I didn’t test them.

The Premier Lite stood apart from all the other pellets by making a 5-shot group that measured 0.139 inches between centers at 25 yards. And 10 Premiers went into 0.285 inches. The next closest pellet grouped 5 into 0.316 inches, which is more than twice as large as the 5-shot Premier target. So, today I shot only Premier Lites. After filling the rifle to 3,000 psi, I fired six shots to wake the valve up and exhaust some air to get on the power curve (the gun needed 2 shots before the velocity climbed up to the optimum range in the last test following power adjustment), then I shot 3 10-shot groups. The results were very informative!

Group 1
The first group measures 0.452 inches between centers. There are 2 shots that aren’t in the main group. The third shot I fired strayed over to the left, where it stands apart from the main group. And the sixth shot fired went high. You can see it above the main group. All the other 8 shots went into a group measuring 0.183 inches between centers. There’s a strong temptation to call these 2 shots as fliers, and they may well be fliers — but let’s wait to see the other groups.

Menjamin Marauder Premier Lite Group 1 25 yards
Ten Premiers at 25 yards went into 0.452 inches. Shot 3 went wide to the left, and shot 6 went high. The other 8 shots made a nice round group.

After this group, I adjusted the scope 2 clicks to the right and fired a second group. This one has no obvious stray shots, but the groups measure 0.397 inches between centers. When the power was set higher the best 10-shot group of Premiers measured 0.285 inches That’s a big difference. Incidentally, in case you’re wondering, the Centerpoint 8-32X56 AO scope I’m using does not stick after reticle adjustments. So, there’s no need to bump the scope or shoot several shots before the adjustments take affect.

Menjamin Marauder Premier Lite Group 2 25 yards
Ten Premier Lites in 0.397 inches at 25 yards. No obvious wide shots, but a group that’s larger than what was shot on higher power. This is the best group of this test.

I then adjusted the scope 3 more clicks to the right, for a total of 5 since starting the session. Now, I fired 10 more shots. This time, the group measured 0.480 inches between centers — the largest group of this session. You can see 2 shots at the upper left of the group that are obviously not with the remaining 8 shots. The 8 shots that stayed together measure 0.181 inches between centers and are in a very round group.

Menjamin Marauder Premier Lite Group 3 25 yards
Ten Premiers in 0.480 inches at 25 yards. Again, there are two wide shots to the upper left. The main group is nice and round — and small!

What we have here are 3 groups — all shot on the power curve of the rifle that now averages about 886 f.p.s., rather than the former 1,015 f.p.s. I told you earlier that I thought a velocity of around 900 f.p.s., give or take, would be ideal for my purposes; and I thought it would give several more shots per fill. We did see those extra shots in Part 4. There were 45 good shots at the lower velocity compared to 31 good shots at the higher velocity.

If I’d been right about the lower velocity not making any difference in performance, everything would be fine. But from what I see here, everything is not fine. The 3 groups fired at the lower velocity were all much larger than the one 10-shot group shot at the higher velocity. And 2 of the 3 groups have 2 stray shots in them. They’re not called fliers in the sense that I did anything to make them go astray. They just went where they went.

My thoughts are that the rifle doesn’t shoot Crosman Premier Lites as well at 886 f.p.s. as it did at 1,015 f.p.s. I think I need to increase the velocity and see if I can get the groups to shrink again. I’m thinking 950 f.p.s., give or take. That way, I’ll still get a few more shots than I was getting when the average was over 1,000 f.p.s., and hopefully the groups will shrink back to the 0.300-inch region for 10 shots.

Sanity check
Before you start commenting, take another look at that dime against these 3 groups. They aren’t that bad! But we’re now down in the minutia, looking for perfection. That’s what I meant when I said this day was especially important to those who are trying to understand and tune their PCPs.

20 thoughts on “Benjamin Marauder PCP .177-caliber air rifle: Part 5”

  1. Maybe I should of posted this in part 4 as it seemed you were talking more about the mechanics of adjusting fill pressure in relation to the striker and hammer adjustment.

    This is something I see though now that I have my Talon SS and Crosman/Benjamin pcp guns. The tuning works a little bit different between the 2 types of brands.
    And please correct me if I’m wrong. And remember this. I totally like all of the brand guns I just listed.

    But it seems to me if I look at the way a Crosman 2300S is adjusted It is similar to some body modding a Disco so the spring pressure is adjustable The hammer stroke is not. I will use one of BB’s recent sayings. If I compare the spring adjustment of the 2300S to the hammer and spring adjustment of my Crosman 1720T it is like apples to oranges. I know one is CO2 Cartridges compared to pcp. But the modded Disco is similar to the 2300S in the way they are adjusted. You (cant) adjust the stroke of the hammer.
    Now take the 1720T, Marauder rifle and Marauder pistol with the spring and hammer stroke adjustment and you start getting into a different world of tuning.

    I look at the AirForce guns power wheel adjustment to be something of a combination of the Marauders and the 2300S and modded Disco in the way they work.

    Any way. BB you got your work cut out for you on the Marauder tuning. But knowing you the way you explain something there will be nothing to it.

    And also I see where you are going with the shooting test. The higher pressure gave more consistent shots when you fired your 10 shot group. ( a tighter group )

    But here is something to think about. Maybe lets say on my gun I was shooting 10 shot groups at targets or I was hunting and wanted at least 10 consistent shots available. And I was topping off the fill each time to 3000 psi before each 10 shots. And I didn’t care if I got 30 or 40 shots per fill. With the Marauder spring and hammer stroke adjustment you have a way more tunable gun than if you only have the spring adjustment.

    I been wanting to say this for a while but didn’t know how to fit it in. But I hope I didn’t make it sound more complicated than it really is. And if I’m looking at this the wrong way let me know ok.

    • GF1..

      You might not always want to top off to a max fill if you are going to shoot outside. I went outside yesterday for a bit of plinking and testing with one rifle. My fill was indoors, but the outside temp (20 degrees warmer) will quickly give me a 10 BAR overfill (in the shade). NOT desirable with that rifle.
      Also NOT desirable with my Talons.
      With the Talons, I have been cranking the power wheel up a half turn when shooting outdoors in weather warmer than indoors where I do my fills. I don’t know if it’s exactly right , but seems to work.
      In cooler weather outdoors, it does not matter. The pressure will drop below the indoor fill and will be on the curve for sure.

      As long as I will have more than enough shots for hunting, I won’t bother topping off. It’s up to you.
      You want to plink, burn up targets, or do some testing, then go ahead and fill it up.


      • TT
        I know you said you were going to look at the fill pressure. Inside cooler than outside temperature.

        I have experienced this with the Crosman/Benjamin pcp guns also.
        I have topped the gun off at 3000 psi while inside in the A/C. Then go outside in a 95 degree sun shinny day and the gage on my gun would increase a little over 200 psi.
        Its nice having a good working gage on your pcp gun for that purpose. That’s one of the reasons I asked before how people were watching their air pressure on the AirForce guns before the Spin Lock tanks came out with the gage on them.

        My Marauders would shoot about 5 good shots then I would notice the pellet hitting lower after those 5 shots. Guess what now after being in the heat and sun my gage read 3200 psi.
        And I’m sure the gun was getting partial valve lock.

        The Marauders have the degassing tool that comes with them. So I always carry that with me and its real easy to bring the gun back down to the original 3000 psi fill pressure. Take 5 more shots and the gun is back on the money again were it is hitting.

  2. BB. thanks for the heads up on the scout scope. I have the Bushnell version on one of my Sheridan C models and on a Thompson/Center Hawken barrel. It’s a great system when you need it. I have been thinking about putting one on my Winchester 94 30-30 carbine.


    • I also have a scout scope installed on a Mauser .308 rifle that I use for deer hunting and it works very well even though it took a little getting used to. Years ago , Redfield made a scout type unit for the 94 where the base replaced the rear sight with one of their scopes. Some of the folks around here thought very highly of them.

    • I’m also very interested to hear about the scout scope. For what I am interested in doing with a rifle (firearm), I’ve not seen anything that matches that design’s balance of effective binocular vision, speed, and precision out to any range I can hold effectively, and currently the only glass I have on my own rifles is the Leupold scout scope. (Mike, one of these is a Marlin 45/70, and I love the combination dearly.)

      Airgunnery seems to have at least a few different norms–based on what I’m picking up–and it may be that the scout scope’s startling speed advantage isn’t nearly as important on an airgun as it is on a firearm. (Please do educate me if I’m wrong here.) And there are certainly lots, lots more choices of conventional-eye-relief scopes than there are of intermediate- and even long-eye-relief models. I’ve been figuring that I would simply go with a conventional glass for air, but I’d love to hear about other options too. (B.B., aside from the scope itself, I’d love for you to cover a little bit about available mounting options as well.)

      • Kevin,

        I saw the scout scope at this year’s SHOT Show in January and was very impressed by what I saw. The image filled the eyepiece and seems very clear.

        As far as mounting goes, Leapers is now bundling their new quick detachable scope mounts with some of their scopes. My friend Mac reported on them in 2011:


        But for scope mounts that go forward of the receiver, which is what I think you are asking, I’m not sure what they have. Even for multi-pumps I think you’ll have to use the mounts that exist now.


  3. A velocity slower than the average of 886 may also shrink groups. It could be that premier lites at that particular velocity don’t fly well from your particular rifle. Barrel harmonics could have an effect too. Try for a velocity closer to 800 fps and see what happens. Also, I’ve read that for the marauder, leaving the hammer spring and distance adjustments to produce heavier valve strike combined with closing the metering screw to limit velocity flattens the velocity variation curve and makes much more efficient use of theair. Shot count, as you’ve already shown, goes up.

  4. Leapers has had full sized scopes that focus to 5yds for years now. I bought a few of their 5th gen scopes that go down that far somewhere around 2006-7. They’ve held up well over the years!

    Those are still nice groups out of that Marauder! You should have no trouble shooting holes in squirrel tales …


  5. The fact that this rifle may do better with a power adjustment (up or down) for this pellet leads us to common situation with probably all air-rifles, namely, pellet choice. Sure, the power can adjusted for THIS rifle, but there might be a pellet that shoots much better at this particular power setting. If this were another air-rifle, there wouldn’t be any other another option but to find a better matched pellet.

    In fact, there may be a pellet that performs better across a wider range of power levels (or possibly not).


  6. Victor
    Ain’t it amazing how many things things that little piece of lead affects.

    I have tryed way to many pellets in my guns. When you think you find the right one.
    Then try another and it just way out performs what you thought was good.
    Then try it in another gun and it just don’t perform the same. Then throw the tuning of a pcp gun into the mix and see what happens.

    Here is what I call those little pieces of lead…. Magical Flying Mystery Metal.

  7. An interesting note on the larger groups…..a few years back I was working on my wife’s Pro Target and found (repeatedly verified) that anything other than wide open on the port restrictor caused the groups to open up. Later an FX Cyclone yielded similar results. Both were quite accurate and easy to see the degradation. I’ve never seen a good explanation, but pretty much leave my restrictors wide open and adjust the velocity with stroke/striker spring changes.


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