Help with Trajectory and Ballistics

[nak81783]

I purchased an RWS 34 a little over three years ago to dispatch chipmunks, red squirrels, and any other varmints that were chewing up items in my shed and garage. Once I learned how to properly shoot a springer (artillery hold), I could make consistent hits from 20-30 yards with a 25 yard zero. Most of the trees, shed, etc. were in the 20-30 yard range. I always had issue with closer shots though. Only recently did I start trying to figure out why. Here's my setup and other pertinent info.

RWS 34 .22 cal, Hawke Sport HD 4-12x50 AO Mil-Dot IR, RWS Lock Down Scope Mount, 1.65"-ish Sight Height (hard to measure)
-Scope is very repeatable. Box test at 25 yards was excellent, and it returned to zero perfectly.

H&N Field Target Trophy, 14.66 gr, 5.53mm Head, 0.029 ballistic coefficient, muzzle velocity 637 fps (8 shots, 10 fps spread, 3.1 std dev) as measured with Caldwell chronograph, 44 degrees Fahrenheit, 66% humidity, 29.91" Hg (standardized), 830 ft elevation
-25 yard zero, dime to nickel size groups
-12.5 yards, 1" high, all shots touching
-10 yards, .5" high, one ragged hole
-6.25 yards, .125" low, one ragged hole
-50 yards, 4.5" low, 2-3" groups, mostly side to side spread, as the wind was starting to pick up and vary

This made me realize why I always missed the close shots. I always aimed high, assuming the pellet was still rising to sight height until apexing at the sight line at 25 yards. This is what various ballistic softwares stated, and it is how my firearms behave. How is the above trajectory possible? I thought the pellets might be spiraling, but the groups at various ranges stay centered within .125" or so. I played around with sight height, ballistic coefficient, and muzzle velocity in ballistic software, but I cannot get the trajectory to match. I do not expect an exact match with the ballistic software, but I thought it would give the general pattern. I.e., I thought it was correct showing an apex at my sight line, instead of two ranges where the pellet crosses the sight line (one somewhere between 6.25 and 10 yards, the other at 25 yards). If the latter is the situation, I would expect a much lower point of impact at 50 yards.

I repeated the above yardages with JSB RS, 13.43 gr, .034 ballistic coefficient, muzzle velocity 703 fps (8 shots, 9 fps spread, 3.2 std dev), same environmental conditions. I did not re-zero for this pellet, but the pattern repeated itself -- not exactly the same numbers, but general trajectory confusion.

Let me know if any other information is required. Any help is greatly appreciated. Thank you.

 

[JohnL57]

From your data it looks as if your pellet crosses the line of sight first at around 7 yards, and is over your line of sight till 25 yards. Not being a techie I just set out targets at different ranges and see what happens. I do a fair bit of rabbit hunting and being able to 'thread the needle' at close range in heavy cover is often very necessary. I'm not sure if this is a factor for you but it's common for RWS/Diana rifles to have some barrel droop-that is, the barrel points slightly down in relation to the scope grooves. Many RWS/Diana specific scope mounts have some downward compensation built in to offset droop.

 

[nak81783]

John,

Thanks for the reply. The common sense side of me says to do exactly what you state: shoot the rifle at incremental distances, and just record what happens. However, the OCD and engineer side of me gets frustrated when things don't match the math.

Concerning the barrel droop, I suppose that would be a problem if the pellet never crossed sight line. Since it does (twice), it should mean that the RWS mount and Hawke scope have enough adjustment to compensate for it. Once compensated for, I would think it'd act like a normal setup.

 

[JohnL57]

Concerning the barrel droop, I suppose that would be a problem if the pellet never crossed sight line. Since it does (twice), it should mean that the RWS mount and Hawke scope have enough adjustment to compensate for it. Once compensated for, I would think it’d act like a normal setup.

I agree, it also sounds like you've got a consistent hold and repeatable POI-Congrats, that's no small thing with a springer. I was just shooting my R9 and noticed POI shifts depending on where my Left hand supported the fore part of the gun. PCPs have kind of spoiled my springer technique, guess you have to use it or lose it.

 

[Guest]

Here you go brother. You gotta love that RWS Model 34. No nonsense light hunter right there in your hands.


You are probably zeroed a bit high (5/32 inch) at 25 yards. You are just about perfectly zeroed at your optimal zero for a .84" kill zone. Ten yards and 12.5 yards do not match up with your data but 50 yards and 6 yards do and 25 yards isn't off that much.

Check your zero with this:
http://www.oldspooks.com/agstuff/Targets/zero/zero-method.pdf

If you are zeroed according to what CGP says then you'll be four or five clicks high (1/4" to 5/32") at 25 yards. Should be close anyway.

 

[nak81783]

John: I struggled a ton at first with the springer, especially with support hand placement. Luckily, the rifle is naturally balanced with my support hand directly below the front of the scope mount, so I have a good visual reference with each shot. Trouble comes when shooting in awkward positions, like hanging out my second story window to try to get a shot around the corner of the house. 

oldspook: I love the RWS 34. Just want to understand the actual trajectory vs ballistic software difference. I'm glad you're seeing generally the same thing I am. I'll give that zero method a try asap.