Scopes – Part 5 Zeroing your scope

by B.B. Pelletier

Part 1
Part 2
Part 3
Part 4

It’s been more than a month since the last installment, so it’s time to hit scopes, again. I’m starting a discussion about zeroing, which can be a large topic, so I’ll try to simplify it. If there are things I’m not addressing, please ask questions.

What range to zero?
Zero means the distance at which the intersection of the crosshairs coincides with the pellet in flight. Put simply, it’s where the pellet will strike the aimpoint.

Is that a new idea to you? Maybe you thought the pellet always strikes the place where the crosshairs rest. That’s not how it works. From the moment the pellet exits the muzzle, it starts dropping. To get the crosshair intersection to point to the spot where the pellet will be, we have to angle the scope to look downward. Most of the time this is done by using the scope’s internal erector tube.


The pellet starts to drop the moment it leaves the muzzle, as this simple drawing shows. The scale has been compressed.


The scope looks straight ahead. The line of sight is a straight line.


To get the scope to look where the pellet is going, internal scope adjustments must be used. Inside the scope tube, there’s an erector tube, which must be slanted down to get the line of sight to slant down like this.

I hope these three illustrations help you understand how the scope aligns to look at the place where the pellet is going. The scale of the drawings is compressed tremendously. A pellet may drop only 6″ to 10″ from the muzzle out to 50 yards. How far it drops depends on its muzzle velocity and its ballistic coefficient. Regardless of the BC, it isn’t very good, because all diabolo pellets are made to slow down rapidly.

Sometimes, the scope’s internal adjustments aren’t enough, and you have to shim the scope at the rear or use an adjustable scope mount to get it to look far enough down to align with the pellet. I’ll cover that kind of correction in a later report – for now, let’s assume the scope adjustments are all you need to do.

QUESTION: At what distance do you want the scope to coincide with the pellet?

That’s the biggest question in this game, and the most-discussed. I’ll try to simplify it for you. If you’re a general shooter or a hunter, you want the scope to be as usable as possible over the longest distance possible. That stands to reason, so you sight it in at the distance at which you get the most usable distance from the sight setting.

At what distances do you usually shoot? Most hunters and average airgunners shoot up to 50 yards most of the time. A 50-yard shot is a challenge, as is one closer than about 20 feet. Sighting-in at too close a distance makes no sense, because you won’t be zeroed for the greater part of your useful range. On the other hand, sighting-in for 50 yards also makes no sense, because at closer ranges you won’t be near the aimpoint! So, we have to find a compromise.

The compromise
Modern airguns can shoot very fast, but shooters who are serious don’t allow them to go as fast as they can. The most accurate velocity for a diabolo pellet is somewhere around 900 f.p.s. It may be 800 or it might even be 1,000 f.p.s. It all depends on the gun and its best accuracy with a given pellet. But, it certainly isn’t 1,200 f.p.s., and it isn’t 600 f.p.s. So we say 900 f.p.s., because we can work with that number.

For a pellet going 900 f.p.s., there’s a flat spot in the trajectory around 20 to 30+ yards. The line of sight has caught up with the dropping pellet, and the pellet isn’t dropping so fast that it’s a problem. Did you notice that the line of sight actually passes through the arc of the trajectory and then continues on below it? To the shooters the pellet appears to be rising. That first point of intersection is located about 20 yards from the muzzle, if you’re following my recommendations.

Why not 10 yards?
This question comes up a lot. Or, why not 15 yards? Because of what that does to the line of sight. If you sight in at 10 yards, at 20 yards your pellet will be an inch to an inch-and-a-half ABOVE the line of sight, assuming a 900 f.p.s. pellet. If you don’t care that it is so far above the point of aim, fine. Sight-in at 10 yards.

If you sight-in at 20 yards, your pellet will rise only a pellet’s diameter between 20 and 30+ yards. Where the far point actually is depends on the pellet’s actual velocity and BC. After it drops back to the line of sight, it’ll still be close to the aimpoint for several more yards. Twenty yards works out to be the ideal zero distance for the average airgunner, assuming a 900 f.p.s. rifle. Of course, 900 is just a convenient number; I’m really talking about anything between about 800 and 1,000 f.p.s.

Got it?

46 Responses to “Scopes – Part 5 Zeroing your scope”

  • Anonymous Says:

    So, lets get specific…..22 cal. 24″ barrel A.F. Condor shooting Crosman premiers over a chrony at 900-950, Air force 4-16x50A.O. scope. Sight in at twenty yards and where is the pellet going to drop back into line of sight? 40-50 yards? From SavageSam

  • Dr. G. Says:

    B.B.,
    Diabolo pellets are generally most accurate around 900fps and wadcutters are most accurate around 550fps (for 10 meter shooting)? – Dr. G.

  • B.B. Pelletier Says:

    SavageSam,

    Forget the 24-inch barrel, forget the Condor, forget the caliber, even. It doesn’t make any difference.

    The velocity, alone, coupled with the diabolo pellet means the pellet will drop back to the point of intersection at about 33-37 yards, depending on whether it is 900 or 950.

    B.B.

  • B.B. Pelletier Says:

    Dr. G.,

    Yes, with reservations. The 550 f.p.s. is a little slow. You can bump it up to 800 and they are still accurate. But the flat nose does limit their high end just a bit, and the transonic region is where the bad things start to happen. A wadcutter simply drops the velocity at which badness begins, because it pushes the air more violently.

    B.B.

  • JP Says:

    Big problem BB: a lot of rifles advertise 800 FPS, but reality and testing show them only making around 600 FPS. What is it about the low velocity that is inaccurate? Is it the Pellet’s dropping in speed too quickly to be accurate at distance? JP

  • B.B. Pelletier Says:

    JP,

    I said accurate AT LONG RANGE. Or, if that wasn’t clear, why aren’t you reading my mind?

    There is no difference in accuracy out to 20-25 yards, but after that, it takes some velocity to keep the group tight. That’s only because of air movement, but when is the air really still?

    B.B.

  • pestbgone Says:

    B.B.,
    I don’t think you’ve mentioned scope height too much, and I have a vauge question(s). I always thought that having the scope as close to the barrel as possible gave the “best” results, whatever that means. But after trying several different setups at different distances, I don’t think that’s necessarily true. I know that with a high-mounted scope, the hold-under height at short distances can be pretty extreme and takes some concious estimating.
    But it seems that a slightly higher mounted scope might help to move the two POI cross-over points down range a little. But when I look at the pictures, I’m not sure.
    So I guess my questions are, does scope height really affect more than aiming distances inside that first POI cross-over point? Are there situations where a tall scope mount works better?
    Thanks,
    Pestbgone
    PS. The big bore project is going very well. Lots of empirical data, prototypes, and experimentation.

  • B.B. Pelletier Says:

    Pestbgone,

    I came to the same conclusion about scope height. At close range it does affect things a lot, but past 15 yards the effect starts to become minimal. There are too many other things that really do matter for me to worry about scope height.

    The only thing a tall mount does better is clear the action for loading.

    When you have enough data, we’d love to hear what you’ve learned in a guest blog.

    B.B.

  • Anonymous Says:

    B.B.

    So, what happens when the field target shooter encounters a target at some unknown distance? Using the adjustable objective will tell pretty precisely what the distance is, but then how does the shooter modify the sight picture for that quarter inch target? Does he use holdover or re-zero? I guess it is not possible to preregister every single distance in the course, but a few reference points would help in the estimation. Is that what the enormous sidewheel is for?

    I read somewhere that the lower-mounted scope gives generally better results since you can use more of your face as a rest for the stock. Don’t know if that’s true.

    Matt61

  • pestbgone Says:

    B.B.,
    OK, I’ll stop fretting about scope height except for the very close range stuff.

    Thanks for the guest blog offer. Your previous guests have kept up with your standards and set the bar pretty high. I’m flattered.

    Back to Friday and the Condor. What does the power wheel actually adjust?

    Thanks,
    Pestbgone

  • Sweet Home Aaron Says:

    BB,

    Glad I caught you back on scopes. Just a reminder I have a Beeman SS1000H that I intend to hunt with from distances of 20-25 yards. You already recommended a Leapers Scope and I think I’ve narrowed it down to two good ones.

    1. Leapers 3-9×40 AO Mil-Dot Scope with R/G, 1″ Tube – I like the features on this scope and think it would work well both on my pellet gun and my .22 rimfire if I wanted to use it on there. This is the one I’m leaning towards right now.

    2. Leapers 6x32AO Bug Buster Compact Scope Combo, Gen 2, Illuminated Mil-Dot Reticle, 1/4 MOA, 1″ Tube, See-Thru Weaver Rings – I love the look of this scope!! And I think the short range capability could be a lot of fun on my pellet gun. I worry though that I won’t be able to get it to mount back far enough on my gun to get a comfortable look through it (since it is so short) and I wonder about the longer range accuracy if I wanted to put it on my .22.

    Any advise would be appreciated.

    Thank you,
    Sweet Home Aaron

  • B.B. Pelletier Says:

    Matt61,

    It IS possible to pre-register for every single shot in a field target match. It involves a LOT OF ZEROING!

    No FT winner holds over. They all adjust for every shot.

    What you have read about lower-mounted scopes is untrue. Just look at what FT champions use.

    B.B.

  • Anonymous Says:

    B.B.

    Wow, that is meticulous. I’ve wondered about the format of FT. How do they limit the number of shots you can take? Surely, you can’t blast away until you hit the target because everyone could do that eventually. Having one shot only seems a bit severe. Is there a limit to the number of shots or is the number of shots factored into your final score or is there a time limit?

    Whatever the format, I’m sure it is not as strenuous as what is described in the novel about ancient Egypt called Warlock by Wilbur Smith. The rite of passage to become an elite warrior was to “Run the Red Road.” This involved driving a chariot through a course of tests of warrior skills such as archery and wrestling all the while knowing that a group of men were racing after you to wipe you out. Their start signal is the resolution of a cock fight that starts when the candidates begin the course(!) So, the challenge is to be as quick as you can without rushing because if you miss a target on the archery course, for instance, you have to shoot all the targets over again. I read somewhere on the internet, perhaps apocryphal, that your favorite book is Clan of the Cave Bear, so I thought I would mention this fantasy of the ancient world.

    Anything interesting at the gun show?

  • nate in mass Says:

    BB,
    A few months ago you did a post on buying used 10 meter air rifles. I was hopeing you could do one on used air pistols. Thanks

    Nate in Mass

  • Anonymous Says:

    I thought I would report on my attempt at conversion to airguns with my visiting parents. The results were somewhat mixed. They were kind of bemused at my set-up. And once I caught them comparing the sound of airguns firing to other noises and giggling!? At least, I think their fear of guns is diminished. But then at the shooting range, while wandering over the top half of a target with the Winchester .30-30, my Dad planted a shot right in the bullseye. Instant pandemonium! Then there were long conversations about holdover, the direction in which the gun kicks, trigger squeeze as well as numbers of pictures of him smiling with his finger pointed at the bullethole…. I guess I’m starting to hold my own here.

    Matt61

  • B.B. Pelletier Says:

    Pestbgone,

    The power wheel adjusts the tension on the hammer that opens the valve.

    B.B.

  • B.B. Pelletier Says:

    Sweet Home,

    How are you going to attach Weaver rings to an airgun?

    I think the 3-9 will work best for you.

    B.B.

  • B.B. Pelletier Says:

    Whoever asked about the gun show,

    What keeps FT competitors honest is they shoot in squads with their competition. It’s like golf. Nobody cheats because everybody watches.

    B.B.

  • B.B. Pelletier Says:

    Nate,

    I start a 10-meter pistol blog this week.

    B.B.

  • Henry Says:

    DONT FORGET SCOPE HIGHT! It makes the gap between the two zeroes larger.

  • Mario J. Says:

    Hi, from Puerto Rico:
    Couple of months ago you mentioned a new mount from leapers that will work with the diana/rws dovetails, have you tried it. I beleieve it is rearward offset base i saw at leapers website mounted on diana. I bought a panther 34 and want to mount a scope on it, but first I need to find a good base for it, and if possibe one that does not have to be mounted with the pin over the front of the dovetails.

    Also I own a FWB 601 and 100 pistol, but are leaking through the valve, as if the valve were stuck in the open position, very strange as both were bought at about the same time, close to 20 years ago, if you know is there any solution to this problem other than sending them to beeman.
    Any help will be appreciated.

  • Anonymous Says:

    how do you convert meters/second, to FPS?

  • Anonymous Says:

    what weight would a pellet need to be in a super streak to keep them from breaking the sound barrier? did the pellets you use break it?

  • .22 multi-shot Says:

    mps to fps,

    Go to the Google search engine and type something like “convert 300 meters/second to feet/second” in the search box.

    .22 multi-shot

  • nate in mass Says:

    meter/second to fps
    go here

    http://www.onlineconversion.com/speed_common.htm

    Nate in MAss

  • Henry Says:

    Ok heres my table! It is extremely accurate. Sighted for 50 / airwolf / beeman kodiak (BC is .036) / 41 foot pounds / still more energy than a non FAC gun at 160 yards (12 fp). THis is just the drop. As you can see, 50 yards is a good place to sight in with this gun.

    Calculated Table
    Range Drop
    (yds) (in)
    0 -1.5
    1 -1.4
    2 -1.2
    3 -1.1
    4 -1.0
    5 -0.8
    6 -0.7
    7 -0.6
    8 -0.5
    9 -0.4
    10 -0.3
    11 -0.2
    12 -0.1
    13 0.0
    14 0.1
    15 0.2
    16 0.3
    17 0.4
    18 0.4
    19 0.5
    20 0.5
    21 0.6
    22 0.7
    23 0.7
    24 0.7
    25 0.8
    26 0.8
    27 0.8
    28 0.9
    29 0.9
    30 0.9
    31 0.9
    32 0.9
    33 0.9
    34 0.9
    35 0.9
    36 0.8
    37 0.8
    38 0.8
    39 0.8
    40 0.7
    41 0.7
    42 0.6
    43 0.6
    44 0.5
    45 0.4
    46 0.4
    47 0.3
    48 0.2
    49 0.1
    50 -0.0
    51 -0.1
    52 -0.2
    53 -0.3
    54 -0.4
    55 -0.6
    56 -0.7
    57 -0.8
    58 -1.0
    59 -1.1
    60 -1.3
    61 -1.5
    62 -1.6
    63 -1.8
    64 -2.0
    65 -2.2
    66 -2.4
    67 -2.6
    68 -2.8
    69 -3.0
    70 -3.2
    71 -3.5
    72 -3.7
    73 -4.0
    74 -4.2
    75 -4.5
    76 -4.7
    77 -5.0
    78 -5.3
    79 -5.6
    80 -5.9
    81 -6.2
    82 -6.5
    83 -6.8
    84 -7.1
    85 -7.4
    86 -7.8
    87 -8.1
    88 -8.5
    89 -8.8
    90 -9.2
    91 -9.6
    92 -10.0
    93 -10.3
    94 -10.7
    95 -11.2
    96 -11.6
    97 -12.0
    98 -12.4
    99 -12.9
    100 -13.3
    101 -13.8
    102 -14.2
    103 -14.7
    104 -15.2
    105 -15.7
    106 -16.2
    107 -16.7
    108 -17.2
    109 -17.7
    110 -18.3
    111 -18.8
    112 -19.4
    113 -19.9
    114 -20.5
    115 -21.1
    116 -21.7
    117 -22.3
    118 -22.9
    119 -23.5
    120 -24.1
    121 -24.7
    122 -25.4
    123 -26.0
    124 -26.7
    125 -27.4
    126 -28.1
    127 -28.8
    128 -29.5
    129 -30.2
    130 -30.9

  • Henry Says:

    oh, and yes, my sight is exactly 1.5 inches from my barrels center.

  • Anonymous Says:

    hello bb
    there is a lot of hype about this new scope base from pyramid air. With the release of this item, pyramid air will be the monopoly. I would like to include a historic event I feel you will be familiar with, George Pullman and the town of Pullman. The prices of everything to unreasonable rates taking advantage of the people. I hope pyramid air will make the mount a reasonable price.
    thank you
    ps I’m not trying to beat or challenge you at your own game, just making a comparison.

  • Anonymous Says:

    B.B. and Sweet Home,

    Doesn’t this device convert a dovetail rail to a weaver base?

    http://www.pyramydair.com/cgi-bin/accessory.pl?accessory_id=601

    henry! How long did it take to put that table together?

    Matt61

  • NiTr0_FiSh Says:

    Here is a tragectory program for pellet rifles – it may be helpful for some in conjunction with this neat blog this week.

    http://www.chairgun.com/

  • Anonymous Says:

    BB,

    Could you do a report on the BAM B30 or the Benjamin 392/397. Ir, could you tell me which of these rifles is better? They are in the same price range, and I know the 397 is accurate, but how about the B30? Hope you can help.

  • Don in Indiana Says:

    Taller scope rings may result in cant having more effect?

    Chair gun is worth downloading, and if you do much shooting, probably worth buying/paying for.
    It’s kind of hard to figure out some of the features though.

    There are a couple of ballistics demos here: http://stevespages.com/page8b.htm

    I think that this link has been posted before, but there are some really good illustrations/demos:
    http://www.arld1.com/

    Here is a list of pellet ballistic coefficients: http://www.airgunexpo.com/airgundb/pellet.cfm

    This is a really handy-dandy converter program for windows.
    Just an exe. no install required:
    http://joshmadison.com/article/convert-for-windows

    Safe Shooting!

  • B.B. Pelletier Says:

    Mario,

    The new base is supposed to be available in June.

    Have you been lubricating your single-strokes regularly? If so, they have both gotten some dirt in the seals and both need to be repaired. That’s a strange coincidence, but it seems to have happened.

    If you haven’t lubed the piston heads, the O-rings are probably torn.

    B.B.

  • B.B. Pelletier Says:

    Conversion,

    You go on Google and type “conversion velocity” into the search window. Then, when you get the converter, bookmark it.

    Or just go to

    http://www.airguninfo.com/

    and use the converters there.

    B.B.

  • B.B. Pelletier Says:

    Super Streak,

    Just read what I got directly from the report:

    http://www.pyramydair.com/blog/2007/12/benjamin-sheridan-super-streak-part-2.html

    All it takes to find reports is to enter your search term in the search window of the blog. That’s how I found this.

    A Crosman 10.5 Premier will not be supersonic in a Super Streak.

    B..B.

  • B.B. Pelletier Says:

    Pullman,

    Leapers will sell the new base to any dealer who asks. There is no monopoly, no conspiracy. Where do these rumors get started?

    B.B.

  • B.B. Pelletier Says:

    BAM B30,

    I will be testing the B30 later this year, but I know right now that it’s more accurate than a 397.

    B.B.

  • Mario J. Says:

    Thanks for the advice BB.

    to anonymus:

    to change meters per second to feet per second you multiply m/s by 3.28084 = ____ fps

  • Anonymous Says:

    Hi BB,

    I have a Gamo Viper that came with a .22 pellet adapter, for when you don’t want to use their shotshells. It’s my only .22 right now, and I was wondering about scoping it (with a Leapers scope?) for accuracy. Would this be worth it? I guess, being a smoothbore, that a domed pellet would give the best accuracy (but I really don’t know). And what would you recommend as a reasonable, minute-of-small-varmint yardage for a scoped Viper? Could you also recommend the right scope rings for it as well?

    Thanks!

    –JoeB.

  • Anonymous Says:

    BB,

    I have a damaged Crosman SSP-250 Silhouette Sport Pistol. Even after using the drop of Pelgun oil trick, it empties a new CO2 cartridge in 30 seconds of less. Years ago I contacted Crosman and they suggested a repair facility in Honolulu (I’m on Maui) but the guy was out of town and I forgot about it until the pistol rresurfaced recently. Could you recommend a good repair facility, and a possible source of extra .20 and .177 barrels for it as well?

    Thank you,

    –Joe B.

  • B.B. Pelletier Says:

    Joe B.,

    I never did a lot of testing with pellets in the Viper Express, so pretty soon you’re going to know more than me. I wouldn’t scope it just yet, though.

    The max varmint range is the distance at which you can hit a quarter 100 percent of the time.

    B.B.

  • B.B. Pelletier Says:

    Joe B.,

    I don’t know of a repair center in Hawaii. You can fix the gun yourself, if you feel so inclined. Go here for instructions and parts kits:

    http://www.crookedbarn.com/

    Guys on the Crosman forum will help you, and they may know a Crosman repair station in the islands.

    http://www.network54.com/Forum/275684/

    B.B.

  • Anonymous Says:

    I forgot to ask another question relating to my first, lets use 950 fps and 20/37 yards and .22 cal. Crosman premiers. How much will the pellet have dropped at 50 yards? From SavageSam

  • B.B. Pelletier Says:

    SavageSam,

    We are getting too far afield with suppositions here. To answer your question, which must relate to a specific pellet like the Premier, I consulted the FSI ballistics tables. They indicate that at 50 yards a Premier going 950 will drop 5.4 inches. At 30 yards it drops 1.8 inches.

    B.B.

  • Bill S. Says:

    B.B.,
    I’ve got a question concerning Centerpoint Scopes. Please forgive me if you’ve covered this else ware in this blog but is Centerpoint made by Leapers? Also, it seems like they are a little more expensive for the same options. If they are indeed made by Leapers then is there any difference in quality?

    Thanks,
    Bill S.

  • B.B. Pelletier Says:

    Bill,

    CenterPoint scopes are made by Leapers. As for the specification differences, that information is confidential to CenterPoint, and they don’t share it with me.

    B.B.

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