CZ/NIKON (exceptionally long!)

[5-Shot]

I love a good puzzle. Always have. This one was about as good as it gets.

After several years spending way too much on the Rimfirecentral forum I finally found myself on the loose in Buds Lexington store with a little extra balance in the checking account. To my delight they had a nice CZ 452 Trainer on display and were more than willing to part with it. One of the CZ's many appeals to me was a graduated rear sight similar to those found on old military Mausers. Once sighted in at a specific range one could, theoretically, move to another distance a scoot the sight slider to that range and be dead on. Naturally, I bought it.

The first thing I did on arriving home was to perform the simple trigger adjustments described on the above mentioned forum (which worked perfectly) and then head to the back yard. I sighted my new rifle in at 50 yards and was rewarded with nice round 3/4 inch groups, perfectly located (iron sights). Then it was time to back up and try that nifty rear sight at longer ranges. Unanticipated problem! For years I have battled advancing age with carefully chosen Walmart reading glasses and a Merit eye disc. The reading glasses were selected to bring the front sight into focus and the disc cleared up the distant target. It was a rude shock to discover that I could no longer pull it off. Glasses strong enough to snap the front sight into view were too strong to be offset by the disc. Scope time!

I gave up hunting several years ago (see advancing age, above) so I have a good supply of quality high-power rifle scopes, mounts and rings lying around the house. Finding workable combination for the CZ wasn't too hard. That allowed me to move on to ammo testing. As you know, 22's can be pretty picky. For example, this rifle just loves Eley Target (who doesn't) but can't tolerate Federal Auto Match. Surprisingly, it thanks CCI AR Tactical is pretty dandy stuff, and you'll no doubt agree it is economically superior to Eley. CCI's what I used in the shooting described below.

During all this testing one nagging point kept rattling around in the back of my mind. "This fine Leupold scope is parallax adjusted for 100 yards and I'm shooting at 50. That can't be right." I really needed a 22 scope or something with an adjustable objective. As luck would have it I attended the grand opening of one of those big box sporting goods stores in my community and they had a killer deal on Nikon 3x9 Prostaff Rimfire BDC scopes. I couldn't let that slip by. I bought it and it worked great. The combination is shown in the first picture.

There's an added bonus feature in this scope call the BDC…bullet drop compensator. Sort of an optical version of my sliding rear sight. Look to the right side of the second picture (sorry about the size, it was a screen shot) and you'll get an idea of what it looks like in the scope, absent all the numbers of course. Here's how it works: go to Nikon's Spoton web site and open the page you see in the second picture, choose your scope, choose your ammo and choose your sight in distance. That allows you to generate all sorts of interesting tables and graphs or you can go to the picture on the right and see at what ranges those circles will put you dead on.

There's only one problem. IT DOESN'T WORK! Thinking that, as usual, the problem was yours truly, I checked around the WWW. Their conclusions seem to match mine. Fine scope, especially for the money but the BCD is simply wrong.

My first hunch was that their ballistic model was in error. Fortunately, the Generate Ballistics Reports button allows you to print up some pretty detailed trajectory tables. To see if they were the problem, I went to JBM Ballistics' fine site and used the same muzzle velocity and ballistics coefficients that Nikon had employed. Surprise! Nikon and JBM figures were nearly perfect matches. Keep looking!

Next on the agenda was to determine where, exactly, those circles in my scope were located. That's where the third photo comes in. Assuming the center of that gap between the two dark lines is "zero", those colorful dots are the designated minutes of angle below "zero". I performed my examination at 50 yards so dot 4, for example, is four minutes, or two inches below the "zero" gap. I hung that sheet up fifty yards, placed the horizontal crosshair in the gap and looked for where the circles were. The first circle was down two minutes of angle, the second circle was at -4.5 minutes, circle 3 at - 7.0 minutes, circle 4 at -11.0 minutes and the post is down 15.0 minutes. In addition, the circles are three minutes of angle in diameter. All very useful information.

Armed with the knowledge of the circle locations it was possible to run the JBM ballistic program again and determine at what range each of the circles should be dead on. I chose to begin my testing with circle three. That circle is down 7 minutes of angle and according to JBM the CCI bullet should drop that far below the 50 yard zero at around 107 yards. Disappointingly, shooting showed it was a little lower. After some intense head scratching I plugged in several different muzzle velocity values into JBM and found that 1150 feet/second worked far better than the published 1200 I had been using. Assuming 1150 ft/sec had the bullet landing exactly where it should land.

After some reflection that made perfect sense. Twenty two rifles produce their maximum velocity with barrels around 16 or 17 inches long. I presume CCI publishes the best (fastest) velocities they can. Longer barrels are slower. My CZ barrel is a bit over 24 inches long.

With all the pieces of the puzzle finally falling into place I was able to produce the the range charts depicted in photos 4 and 5. Using those I should be able to aim with confidence at anything out to about 150 yards. To see if it worked, I conducted the following test. I carried my portable bullet stop in the yard out to a convenient spot and set it down (I live out in the sticks), walked back to my bench, lasered the range, consulted my range chart and fired three rounds. I did this four different times at what turned out to be at randomly selected 113, 99, 84 and 67 yards. The results are shown in the final photo. I'm not too proud of my shooting but the target in the last picture confirms to my satisfaction that the system actually and finally works. For reference the red circle is 1.7 inches in diameter.

Due to photo limits the last photo is in a response below.

Ed

 

[5-Shot]

And here's the final photo:

 

[BB57]

/... Twenty two rifles produce their maximum velocity with barrels around 16 or 17 inches long. I presume CCI publishes the best (fastest) velocities they can. Longer barrels are slower. My CZ barrel is a bit over 24 inches long.

This point gets argued a lot, but at a minimum it's not quite that simple.

Many people refer to the "ballistics by the inch" site, but there are some problems with that data. Last time I reviewed their methodology and data base, they were using a 3 shot sample shot over 2 chronographs back to back to get a "sample" of 6 data points. But this is really still just 3 shots with some measurement errors from 2 different chronographs.

The end result in most of their data is a standard deviation in velocity that is often greater than the differences in velocity between barrel lengths. In simple terms this means the differences are not significant, and a higher or lower value average between barrel lengths cannot be attributed to anything other than random chance.

And, with .22 LR they stop at 18" in their single barrel testing, so they don't even explore velocities out beyond 18".

That's unfortunate given that their data, even with it's statistical limitations clearly suggests that the velocities are increasing past 18" for the majority of rounds tested.

Their real world data has 16", 16.25", 18.5", 22" and 23" examples, but all that really tells you, given the variation and non linearity in the data t different lengths is that there are clearly other factors involved, such as chamber dimensions, bore diameter, rifling pattern, consistency of the bore and any choke in the bore, etc.

----

I've used my chronograph extensively for the last 25 years and I've used it with all off my .22 LR rifles. What I've noted in general is:

1) 16"-17" is arguably the point where the .22 LR passes a point of diminishing returns for velocity.

However, the velocity does not stop increasing nor does the bullet slow down past that point.

The possible exception is some primer only powered gallery rounds. For a .22 LR, the distance needed before the bullet would actually start to slow down in the barrel because the pressure behind it is less than the pressure in front of it would be measured in feet or yards, not inches.

This is a common phenomenon in all calibers. 18" for example is the sweet spot in the .223 Remington. Above that point you start seeing a smaller increase in velocity per inch of barrel as barrel lengths increase to 20", 22", 24", and 26". You still see an increase, you just see a lot less increase per inch for each extra inch. Below 18" you see a much more substantial decrease in velocity per inch of barrel length and the velocity loss per inch accelerates as the barrel gets shorter.

Pick any cartridge and there will be a corresponding inflection point on the velocity versus inch graph, but the slope will still be positive as the velocity will still be increasing at least slightly at any practical barrel length.

2) Longer barrel lengths tend to produce lower standard deviations in velocities.

This means more consistent velocity from shot to that. This is one of the reasons why target rifles tend to have barrels longer than 20"-22".

There are sight radius advantages to the longer barrel, but longer barrels also are not as stiff as shorter barrels. A lower standard deviation in velocity however makes up for the greater amplitude in barrel whip due to the more consistent velocity and harmonics.

More consistent velocity also makes long range groups smaller in both windage and elevation.

3) Ballistics programs require accurate velocity data to produce accurate ballistic data.

Your best bet is to get a chronograph and a data book. You'll find your true velocity and be able to input accurate velocity data in order to get accurate ballistic data.

Over time, shooting under a wide range of temperature conditions, you'll also note the effects that are caused by changes in temperature. These effects tend to stack on one another. At colder temps, the muzzle velocity will be lower and at the same time, the colder air temperature results in denser air, which increases the elevation needed at a given range. I've found that with standard velocity match ammo, I'll have to add between 5 and 7 MOA of elevation on a 30-40 degree day in the winter compared an 85-90 degree day in the summer at the same 200 yard range.

If you don't have a chronograph, you'll have to reverse engineer the velocity by observing the actual trajectory down range and adjusting the muzzle velocity input, until you get the ballistic data to match your observed data. But even then, be sure that you consider the effects of temperature, or you'll find you're no longer on target at longer ranges in temperatures substantially warmer or colder than your zero temperature.

If you don't have an accurate BC, you can similarly reverse engineer a BC for the if you have solid velocity and target data. You just adjust the BC until the data aligns. The good news for .22 LR is that the BCs are all very low, low enough that the range of BCs in .22LR round isn't enough to make much of a difference even at long range.

Measured BCs range from .093 to .161, but most are in the .120 range, and you'll changing the BC from .100 to .140 just won't make much difference. Temperature and measured velocity are much more important factors.