-Mongrel- Posted July 22, 2011 Report Share Posted July 22, 2011 (edited) I have a MCT Cobra 3-9 x 40 mil-dot scope. I have been on the plinking range sorting out my hold over/under etc...and it doesn't seem logical. I seem to need a small amount of windage on the closer ranges. Odder still, I need hold over at 8 yds, then hold under at 15 and 20 then hold over as expected at range. Hold over/under as follows; 8 yds - 0.8 (of a mil) over and 0.2 right(windage) 15 yds - 0.5 under and 0.1 right 20 yds - 0.2 under and 0.2 left 25 & 30 yds - dead on 35 yds 0.2 over no windage 40 yds 0.5 over -"- 45 yds 0.8 over -"- It then continues evenly out to 1.2 dot over at 60 yds with no windage required I consider acceptable groupings to be pellet on pellet to 20 yds, within a 5p area at 20-35 and within a 10p size at 40-60, pushing it at 60 yds though and a 1.5 " group I would consider to be 'good'. While I can achieve consistent accuracy with these holds, I don't understand why I have the variation, the magnification remains constant, the only variable would be the focussing. I do tend to refocus as required. Thoughts please. Edited July 22, 2011 by -Mongrel- Quote Link to comment Share on other sites More sharing options...
ste12b Posted July 23, 2011 Report Share Posted July 23, 2011 Mongrel, try http://www.hawkeoptics.com/apps/chairgun-pro.html for hold over and under. For the windage, it could be the rifling in the barrel. Give it a good clean and check your silencer (if fitted) is on correctly and not clipping the pellet on the way out, then try again. Also try diffent pellets. I use RWS superdome .177 in my AAS400 and these work perfectly. Ste12b Quote Link to comment Share on other sites More sharing options...
Dekers Posted July 23, 2011 Report Share Posted July 23, 2011 Who knows what is happening with windage, it may be crown or pellet issues, or it may just be windy! Pellets/bullets travel in an arc from UNDER the scope, to above the scope back down to ON the crosshairs at Zero. Quote Link to comment Share on other sites More sharing options...
pabs Posted July 23, 2011 Report Share Posted July 23, 2011 Sounds like your scope is not quite lined up with the bore. And as Dekers said, the reason for hold over at really close ranges is because you are looking at the target above the line of the bore, so at close range you need to holdover to bring the bore up. Holy ****, how rubbish an explanation is that.. Quote Link to comment Share on other sites More sharing options...
FalconFN Posted July 23, 2011 Report Share Posted July 23, 2011 I'd second what ste12b suggests in getting Chairgun, it's free and very useful for estemating POI and it will clearly show you the pellet trajectory. Sometimes if you fire a pellet towards a flat grey sky (assuming it's safe to do so) you will see the pellet fly above and then below your crosshairs. Quote Link to comment Share on other sites More sharing options...
-Mongrel- Posted July 23, 2011 Author Report Share Posted July 23, 2011 Mongrel, try http://www.hawkeoptics.com/apps/chairgun-pro.html for hold over and under. For the windage, it could be the rifling in the barrel. Give it a good clean and check your silencer (if fitted) is on correctly and not clipping the pellet on the way out, then try again. Also try diffent pellets. I use RWS superdome .177 in my AAS400 and these work perfectly. Ste12b Good link, ta. Surely if the rifling or silencer was affecting the trajectory it would do so at all distances and get worse with distance ( ie require more compensation)? I also don't understand why I need hold over a 8 yds, then hold under at 15 and 20? Quote Link to comment Share on other sites More sharing options...
Gnome of the Woods Posted July 23, 2011 Report Share Posted July 23, 2011 Impossible! You sir are a magician! What mag are you on? At 9x you should need at least 1.5 mildots at 8 yds holdover. Something is not right at all. With sub 12ft/lb if you zero at 25/30yds you should never need to hold under because your zero is at the top of the pellet arc as your scope see's it! Quote Link to comment Share on other sites More sharing options...
FalconFN Posted July 23, 2011 Report Share Posted July 23, 2011 Impossible! You sir are a magician! What mag are you on? At 9x you should need at least 1.5 mildots at 8 yds holdover. Something is not right at all. With sub 12ft/lb if you zero at 25/30yds you should never need to hold under because your zero is at the top of the pellet arc as your scope see's it! If you zero at, say 15 yards, then that may be the case but as most zero distances are around 30, then the pellet has already reached it's maximum height and is in fact dropping when it strikes. You have to remember that your scope is above your barrel and that the pellet is in effect rising to meet the height of the scope's cross hairs, and as it passes that height it's arcing flight will take it OVER your line of sight and then it will dip back down under your cross hairs. In short you have TWO zero points and various hold under/over decisions to make depending on distance, that's why .177 with the flatter trajectory is more forgiving with range finding. Download Chairgun to help explain what I mean. Quote Link to comment Share on other sites More sharing options...
Dekers Posted July 24, 2011 Report Share Posted July 24, 2011 (edited) Impossible! You sir are a magician! What mag are you on? At 9x you should need at least 1.5 mildots at 8 yds holdover. Something is not right at all. With sub 12ft/lb if you zero at 25/30yds you should never need to hold under because your zero is at the top of the pellet arc as your scope see's it! An aim point is rarely, if ever at the top of the pellet arc, (except apparently in your case)! ZERO is ALWAYS on the fall, therefore over the arc and well on the way down, at the second point where the cross hairs exactly coincide with the impact point, having already passed through the line of sight of the scope (FIRST zero) on the upward part of the pellet arc! Look at some charts as already suggested! Edited July 24, 2011 by Dekers Quote Link to comment Share on other sites More sharing options...
-Mongrel- Posted July 24, 2011 Author Report Share Posted July 24, 2011 Impossible! You sir are a magician! What mag are you on? At 9x you should need at least 1.5 mildots at 8 yds holdover. Something is not right at all. With sub 12ft/lb if you zero at 25/30yds you should never need to hold under because your zero is at the top of the pellet arc as your scope see's it! LOL! Impossible it may be, but I'm no magician. It is at 9x mag, and zeroed at 32 yds... ...I may just recheck a third time becuase logic states the 8 yarder is the anomaly. FalconFN, I've downloaded it, just need to find 10 minutes now to use it! Quote Link to comment Share on other sites More sharing options...
JKD Posted July 24, 2011 Report Share Posted July 24, 2011 Here's another link which shows the basic idea of pellet trajectory etc. http://www.arld1.com/trajectory.html HTH Chris Quote Link to comment Share on other sites More sharing options...
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