Chairgun and Strelok off

I have never had luck with chairgun working for my marauder, so I purchased Strelok. It seems to be as far off as chairgun and it upsets me greatly because I spent money on the app. My problem is that I have my rifle zero set at 30 yards. At 50 yards, the POI is 1/2 mil low with my scope set at 20X. I have input my pellet speed as to what my chrony says it is, input my scope height from center of the scope to the center of the barrel, input barrel length, and everything else that is required. Both apps say I should be shooting 1 3/4 mil low at 50 yards. It's only 1/2 mil low. Anybody else have issues with these apps?
 
I do not think it is my chrony because my pellet would have to be traveling at 1200 fps to get the trajectory that I am getting according to chairgun. My chrony is only 4 months old and I have never shot it (this one anyway). I am shooting 18 grain JSB pellets and they are not breaking the sound barrier. My Marauder is stock except for a Marmot Militia hammer forged barrel. I doubt I could get an 18 grain pellet that fast. I have a UTG 6-24X56 10X half mil dot scope and I use the Hawke 10X half mil reticle for both programs. It is very clear that I am on 20x magnification with my scope. To get my scope height, I measured the distance between the top of my shroud and the bottom of my objective on the scope. I then measured the diameter of my objective, divided it by 2, measured the diameter of my shroud, divided it by two, and added those two numbers to the distance between the shroud and objective. As far as BC, I'm using what the programs say it is for the 18 grain JSB's. Strelok asks for twist rate of the barrel, so I contacted Marmot Militia for that number. The new barrel is the same length as the factory barrel, so that shouldn't be my issue. I guess I'll try to figure out my own BC. Might have to take a math class for it though. 
 
A 1/4 mil difference between the two programs at 50 yards isn't that much, but they are both over a mil dot difference from what I'm actually getting. I was able to go to my indoor "range" today where I can shoot at 60 yards. I started at 20 yards and went in 5 yard increments to 60 yards. I wrote down where I was hitting. I'm home now and I've been playing around with the numbers on Strelok and I've matched my trajectory pretty well. It's spot on from 20 to 60 yards now. I had to increase my pellet velocity from 908 to 925 and fiddle with my scope height. I wanted to get this working because my dad wants me to come over and take out some of the crows that have flocked to his property in mass numbers. The closest shot I'll be taking is 75 yards and I'll be shooting to 120 yards. Hopefully Strelok will stay true out to those distances now. 
 
I have a .25 marauder with a hawke scope. Chairgun was on the money for me at 50, 75, and 100 yards. My zero was at 30 yards. I was also shooting JSB pellets. So something is definitely not set up right either with your scope or the software. Sorry to overstate the obvious.....have you worked thru all the settings in the software to make sure you have everything set up properly on the software side of the equation? Worst case reload the charigun software and start from scratch? good luck let us know what you find.

2nd thought, you do have a hawke scope? Maybe remount the scope and check for offset due to the rings (scope tilt)? Maybe the rings are not seated on the rail?
 
All this scope magnification and mil dot spacing is confusing. If you are using a first focal plane scope changing power does not change anything but the power. Second focal plane scopes are different and everything changes when you change power. If you target your gun at the power you hunt with then you don't need Chairgun. Does not matter what the pellet bc is or velocity or scope height. You just know where your gun hits from actually shooting a target. This way you also find out how many shots you get on a fill and when your point of impact drops too far from your point of aim. It's also great to get out and shoot your gun. Hope this is helpful. I am not negative on Chairgun or Strelok. I use them on my pb varmint rifles. Have fun, Scott