Initial Zeroing - Acceptable Elevation and Windage Corrections ?

[stephfx]

Being new to airgunning, I'd be happy to know what acceptable elevation and windage corrections are when zeroing a quality air rifle/mounts/scope combo at, say, 25 yards.

I've got a new FX Airguns rifle, new Hawke SideWinder 30 SF, new set of fully adjustable SportsMatch ATP66 mounts, and I'm VERY concerned by the correction I had to make the first time I sighted in.

How I did it:
- CAREFULLY installed the scope by following the instructions provided by Hawke and SportsMatch (leveled the reticle, didn't over-tighten any screws, cross tightened the top ring screws, ensured adequate eye relief).
- ATP66 setup: as I didn't want to make any scope mount adjustment for the initial zeroing, I ensured that the elevation adjustment screws were not pushing the rings up, and I centered the adjustable piece on both mounts.
- First 3 shots at ~25 yards: the POI was off by 4.5" down and 3.5" left. Consequently, the corrections I had to make on the turrets to align the POI with the Point of Aim were quite significant. Once zeroed, the pellets consistently hit the point of aim.

What could be wrong that caused such a significant deviation in elevation and windage before zeroing the rifle?

Thanks to anyone who can help me out !

 

[bdzjlz]

I don’t know what everyone else will tell you, but I would have shot the rifle, then used the adjustable mounts to get within 1/4” or so, then made the final adjustments off of my turrets.

 

[skeptic]

The scope may not have been optically centered before you mounted it. This can happen if the scope was previously mounted on another gun or if someone played with the clickers while it was in the store. It has happened to me once or twice. There are several methods to optically center it. The three I have seen most frequently involve using a mirror, rotating the scope in a circle and counting clicks (the number will vary based on MOA and maximun W and E adjustments). I don't recall the exact procedures, you can search for them online or maybe someone here can provide. You can also email Hawke and they can give you the best procedure for that particular scope.

 

[L.Leon]

I don’t know what everyone else will tell you, but I would have shot the rifle, then used the adjustable mounts to get within 1/4” or so, then made the final adjustments off of my turrets.

The above reply gives you your answer....

 

[jwrabbit123]

do you still have plenty of adjustment once scope is zeroed ? . There is 2 ways to set up scopes , naturally both you level and Toqure screws to specs

If you have plenty of adjustment you ,but if you saying you almost bottomed out on windage or elevation ,then something is wrong , if so flip rings and recheck , I had alot a few bad hawkes .

I am not sure what you asking , I know there is 2 ways to set up scopes one is have it zeroed near the scopes reticle near optically centered as Hawke will tell you it gives better image quality and accuracy .

Then there is the way I adjust all of my Tier 1 German scopes , I use adjustable mounts and say I mount MY Schmidt and Bender 5x25 PM2 ,I adjust my zero with my mount so scope has entire travel to dial for shooting long distance .

another words the pm2 FFP has 26.2 mils of elevation . so I want to utilize all of it to reach out . Why would I want to lose 13 MILS of adjustment?

I my self adjust all my scopes SO I can use my elevation

 

[Tweeter]

I've had that happen on plenty of guns. I have always just zeroed and shot them. If you haven't adjusted your turrets near the end of their max travel I wouldn't worry about it. Just get out there and shoot it!

 

[nervoustrig]

X2 on what Tweeter said. The deviations you are seeing are pretty typical in my experience.

The elevation in particular is to be expected even if all the machining is perfect. It’s been a while since I ran the numbers but I think the typical airgun needs about 30 MoA of correction to zero at the trajectory apex.

The windage error can be from a variety of things, particularly on PCPs that have a fairly shallow barrel tenon or loose fit held with grub screws. The very slightest angular deviation translates to a large error at something like 25-30 yards. 

 

[bandg]

I don’t know what everyone else will tell you, but I would have shot the rifle, then used the adjustable mounts to get within 1/4” or so, then made the final adjustments off of my turrets.



That is the entire purpose of the Sportsmatch rings. Why else use such an expensive but highly functional setup. Center your scope using whatever method you prefer in order to have it near the center of it's range for both windage and elevation and then use the mounts to get very near zero. A few clicks with the scope is usually all that is then needed to zero exactly. Common assumption is that a scope is most stable near the center of it's adjustment range.

But JWRabbit does make a valid point as well if you wanted to "cheat" a bit on elevation so that you have more usable range available. I would keep it as near to center as possible myself.

 

[AirSupply]

99.9 percent of barrels (that’s a guess)have a slight curve in the bore. This curve is generally not considered a defect but normal to the barrel making process. Barrel Indexing is the process of aligning the curve of the barrel to the vertical axis when mounted in the action. 

If you want to go to the trouble you can index your smooth x liner. You need to mark it and then shoot and rotate it between shots keeping the same poa. Make sure your target is large enough. You can do this at your 25y distance. Try to move the liner 60 degrees between shots and you will find you end up shooting a circle. Align your liner at 6 o’clock. The lowest point on your circle for best accuracy. 

Michael

 

[stephfx]

Thanks very much for all the answers !

@bandg - I understand the purpose of having adjustable mounts. But I first wanted to see how much deviation before making any adjustment. And what I measured worried me. Ultimately, I'll make mount adjustments, as I want to have plenty of clicks available when shooting at 100 yards.

@jwrabbit123 - Going to reset the turrets to their initial values and flip the front and rear mounts to see if I still have similar results.

@skeptic - Just found a video posted by Tominco. He explained how to find the optical zero (the easy way). I'll definitely go through that. URL: https://www.youtube.com/watch?v=SvgOKMX9Gvg

@AirSupply - Was not quite sure to understand your suggestion. So I looked for some info and found a video that explains how to. As this is a brand new rifle, still under warranty, I'm not gonna take the risk of doing that. I'd rather go to a gunsmith if it turned out that such an intrusive process was required. Right now I don't have any indication that this is the case. URL: https://www.youtube.com/watch?v=KBYsZSetODc

 

[bandg]

I've had many firearms with similar issues as well as airguns. Maybe manufacturing tolerance on most setups will have a range of error that may commonly be in the range you noted but it is quite a bit of distance as you noted.

One thing I question about JWRabbits idea. It sounds like it would work and would produce more "usable" elevation range but is it desirable? If I understand what he is saying, to use the "entire" elevation range of the scope you would have to run the elevation near the lower limit of it's range and set near zero there using the adjustable mounts. That would allow use of the "entire" range of up elevation adjustment of the scope for long distance shooting but seemingly would defeat the concept of optical (or mechanical) zero of the scope at rest and would also seemingly "load" the internals of the scope at rest. I've read that the mechanism (springs and gimbals) used in most scopes is most stable near center of both windage and elevation ranges but I certainly don't know this from experience as I've never tried that method. Maybe some scope designers will comment.

 

[stephfx]

Update:

- Moved the rear mount to the front of the dovetail rail, and front mount to the rear.
- Reset the scope to the optical zero. Both windage and elevation were slightly off (1 MRAD). Then I unscrewed the turret caps to reset them (aligned the "0" with the mark). 
- 3 shots, all were off: 4.5 MRAD low, 3 MRAD left. So quite similar to the result I had before flipping the scope mounts. I assume that I can conclude that the mounts are not faulty.
- Turned the windage turret, 10.5 MOA to the right; Turned the elevation turret, 15.5 MOA up.
- 3 more shots, all in the bullseye.

I will ask Hawke to comment on these initial windage and elevation deviations. Will see if that brings me anywhere.

That said, there seems to be a consensus amongst most of you to say that these values are not completely unusual. And 10.5 MOA and 15.5 MOA corrections still leave me with enough clicks for longer distance shooting.

As soon time permits, I'll move the scope back to its optical zero, will make the corrections with the adjustable mounts (at 50 yards), and then the final/minor adjustments with the turrets.

Thanks for all the comments and help !