This article was originally posted on Thefirearmblog.com
This is a guest post from Finnaccuracy.com. Considering the Finnish people’s expert skills with sniper rifles and rifle shooting, in general, it is best to read carefully and take note.
This article can save you a lot of money and increase your shooting skills.
“22LR rifles have always been very popular. Most of us have one sitting in safety. Some of us have also spent quite a bit hard-earned money to make their small rimfire feel and look similar to favorite big center-fire. All in the sake of realistic low-budget training. It is also not too uncommon to see very expensive optics on top of a 22LR rifle. But how to get very best out ol’ faithful plinker? This has again kept our R&D department wake during nights and especially days.
Disclaimer – as usually, we do apologize following article typos and even errors in advance. This too is written in rush between thousand other things going on, and English is not our native language. Bear with us, please.
In many ways, 22LR is a perfect trainer. Ranges needed for challenging shooting are relatively short. Wind reading and firing solutions must be precise as with any rifle – only difference is smaller scale and shorter ranges. 22LR noise level is low, and ammunition cost is next to nothing, at least compared to most expensive full-size precision cartridges. In many times, good 22LR accuracy doesn’t require using high-end precision ammo which can be rather expensive – especially with a large shot amount. 22LR is also one of the most underestimated rifles.
It can be a really efficient tool for MIL/LEO use too. Russian OMON, for instance, found out during 1999-2000 in Grozny/Chechenia. Even titanium plate vests do not really help against precise bullets – coming in completely silent. Typical 40gr RN lead bullet can penetrate over 30cm/12″ ballistic gelatin. Presumably, it is not fun at all to catch one with an unprotected neck, for instance.
22LR practical accuracy
Many golden rules learned from center-fire world are equally valid with smaller ones. Bedding effects, mounts should be solid etc. Smooth, even bore with minimal dimension variations is desired and almost always takes accuracy to wanted direction. The biggest practical difference is that cartridge cannot be tuned at all by self-loading, so usual way trying different primer/powder/case/bullet/COAL combinations is not available. All tuning has only to be made with the rifle itself. Gunsmiths who REALLY know 22LR tricks are rare, and sometimes grouping can behave very mysterious ways with no obvious reason. In short, accurizing a 22LR rifle seem sometimes like black magic, ask me how I know. We are concentrating in a small portion of ballistics only in this, relatively, short article – plenty of information is online as long as Google is available.
Pic: one of many range trips with new Krieger Match barrel – finding out best fit ammunition.
Ballistics and practice
22LR bullet pushes trough exactly the same air as larger caliber bullets. But there is a trick: Typical rimfire muzzle velocities are almost always close to the speed of sound, Mach 1 (M1). Mach unit is used in this article instead of feet or meters for clarity. Mach velocity includes compensation for air temperature, pressure, and humidity.
Around M1, unusual things start to happen when velocity goes into the transonic area and towards pure supersonic flight: bullet is in very high and also steeply raising drag. Because of huge drag change in small velocity window, practical wind deflection may vary very much between shots, depending on even small muzzle velocity changes.
As visible in the graph below, if muzzle velocity raises from M0.9 to M1.15, bullet drag increases in very beginning of flight to approximately 5x higher level. This mach speed would equal muzzle velocity raise from about 310m/s to 390m/s (1017fps to 1280fps).
In more practical 22LR MV variation area (depending about ammunition and barrel), drag may still double to triple causing surprisingly big horizontal POI differences target- being more sensitive to gusts and MV deviation. As muzzle velocity drops slightly under M1 and toward pure subsonic area, horizontal windage shift decrease following decreasing drag down to certain muzzle velocity point- and then starts to increase again where drag change eases up and longer flight time becomes dominant factor.
If ballistics are calculated with standard RA4 bullet drag curve (ballistic coefficient of 0.125). As extreme comparison example, M0.6 and M1.35 muzzle velocity (205m/s and 465m/s, 673fps and 1526fps) 250meter windage shifts are identical in same true sidewind! This may seem very odd, but wind drift is not directly proportional with flight time.
As side note, many online sources -almost all in fact- mention that RA4 drag curve is identical with G1 drag curve below 1400fps/M1.23 velocity. They are not even close, at least if comparing QTU library RA4 drag curve to McCoy book G1 drag curve.
So, ballistics are the same but also very different in some interesting ways. If muzzle velocity and therefore beginning of trajectory are close to supersonic area, steeply increasing drag can offer dirty tricks. Luckily, typical centerfire LR shooter do not need to worry about this at all. Subsonic transition is extremely short relatively to whole bullet flight and happens far away. Supersonic-Subsonic shift can still cause many kind of troubles with full size rifles, but this is not related to pure drag curve itself. It is more about radical and quick change on bullet center of air pressure location. Good dynamic stability is needed from bullet to penetrate trough transition smoothly and repeatably, and to make calculations match within subsonic shooting distances too.
But if MV is around Mach1 as with almost all 22LR cartridges, unusual things may appear in ballistics solver screen. So it is good to know reason to get hold of it. Training is most beneficial if drop/wind charts are absolutely correct or at least as close as possible. Only then “bullet feedback” about successful wind-reading and distance measurements can be correct.
Graph below: Red, gray and blue are drags vs velocity. Blue and gray are drags based on Lapuas doppler measurements, multiplied by 200x to get graph in same scale with 250m range wind drift graphs.
Solid red is RA4 standard bullet. Sweetspot MV clearly visible, equaling velocity aligned with bottom of parabola-like graph. Spot is on Mach1 if calculated with Lapua doppler measurement drags and 6DOF calculator, Mach 0.92 if calculated with RA4 0.125 ballistic coefficient. Note also 100mm/3.9″ difference calculated in wind drift- drops are still almost perfect match in same MV, weather and wind. In both cases, smallest wind drift is equaling MV on first fifth in its steeply raising drag curve. Lapua measurement end on M1, but it is rather safe to assume that curve shape, angle and height resembles closely to RA4 curve. Lapuas curve is also measured down to zero velocitity. From ballistics calculation point of view it should be doing better job predicting actual drifts and drops on extended 22LR distances.
Drop match at 250m between Lapua’s 6DOF/Cd and RA4 function is with BC 0.122. Exact drop match on M0.93 (320m/s / 1050fps) muzzle velocity.
Various bullets compared to simulated RA4 standard bullet. Not all are this similar – close to same look selected for photo. Close to same shape SHOULD mean good results if calculations are done with RA4 standard drag function.
Scaled long range training
Basic idea of scaling came long time ago from the Finnish Sniper Instructor P. Salo. He used the same principle in various courses where 22LR was used for long range training. The old idea is still so interesting that we decided to play with it and to see how far it could be refined.
Trajectory shapes between various calibers look same. Even a pea-shooter and a 155mm howitzer grenade have the same basic shape, but in different size. As an outcome, it is theoretically possible to downscale/upscale any caliber trajectory to match relatively close each other. Never exactly the same, but close and good enough for the intention. Identical in best case.
If the typical 22LR drop is compared to typical 308Win dop, ratio is roughly 25%.
22LR rifle bullet drop is same 10mrad 25% of distance where bigger caliber drop is same 10mrad. This is valid with 25m and 100m zero ranges.
Header pic and pic below: Finnish Ostrobothnia Sniper Association’s (PohTa) tactical 22LR course in 100m range. 100m drops/wind corrections approximate 500m distance with 308 Win.
Scaling drops and winds for beneficial training is one thing – but to get same “feel” compared to larger rifles, target sizes must be scaled as well.
But it can actually be even better than just feel: If 22LR drop + wind scale ratio can be solved AND target size is scaled down correspondingly, then 22LR shooting is actually near perfect simulation of full size rifle – with fraction of cost and misery. And on top of everything, correctly scaled target trough scope look exactly same compared to large rifle targets in longer ranges.
If perfect fit scale factor turns out to be, say, 25% to match both drop and wind, target is scaled to one quarter too. 22LR shooting is then done 25% of actual distances: Large caliber charts will match to scaled 22LR drops with 25% ratio. Also – angular dimensions to scaled targets are identical trough scope, drop is same, wind same click amount in same actual/true measured sidewind. AND bullet hits exactly as it would hit in longer actual range with centerfire rifle. In perfect match situation, target sizes could even be milled as they actually were true full size- and then shoot them with 22LR using large rifle dope + wind charts. Bullet would hit or miss just as with large rifle shooting. Same click amount for drop, same clicks for windage, same wind measurement procedure, same everything.
Example: if resolved scaling is 25%, it means that 500m with larger caliber equals 125m with 22LR. Large caliber zero 100m, 22LR 25m. In this 500/125 point, both have exactly same 3.9mrad drop. In optimal case, both also require exactly same 1.5mrad wind correction in exactly same true and measured sidewind. This is valid situation with SMK 175gr and Eley Match EPS. If 48cm/19″ wide (or tall) target is used with full-size rifle, it will be scaled down to 12cm/4.75″. Then angular size is identical, and 22LR bullet drops+drifts just as with 175gr SMK.
Sounds perfect so far? It really is – almost. Differences come from true accuracy between 22LR trainer and center-fire, but even those are usually in same ballpark. 1MOA group with large rifle at 500m would mean that 22LR trainer should shoot 37.5mm/1.5″ group to 25% scale 125m distance- and this is difficult. But its not easy to shoot 1MOA at 500m with actual rifle.
Ballistically as calculated values they can still match and to be scaled. 22LR windage deflection matches and usually follows scaling ratio nice and linearly up to certain point and – but starting from around 200m (230yds) it starts to drifts relatively more than big brother in same wind. But this is very long range for 22LR, equaling over 800m distance with 308win too. Difference is still rather small relatively to actual total drift. Very close ranges with 22LR can not be perfectly matched, and usually “tail” of 22LR graph or far end of trajectory is flatter too. Shape of trajectory makes difference, it can not be identical -but is still pretty close. Tool shows differences in both mrads and cm/in, just shift reference point with “set trajectory reference range” to see it. Spindrift is another factor that can not be scaled down.
Examples and used charts must be calculated with no spin drift, and min/max ranges are locked for both calibers. 25 to 250 for 22LR, 100 to 1000 for large reference rifle. Yards work just a fine BTW if you want to use them- but all ranges must be yards instead of meters.
Comparing charts is difficult, in this case impossible. The only sensible way to find best scaling match are graphs that can be fine-tuned on fly. This is where handy tool steps in.
The tool is made with Windows Excel. Tool has active Visual Basic content, so you must “allow active content” when opening file. Depending of your Windows security settings, you may also have to right-click downloaded “LR22LR v1.1.xlsm” – file and set “unblock” from file properties in order to open it. We can assure that file is clean and safe, not including any spyware or similar. We leave that to Microsoft and NSA.
Tool functions are explained in workbook header box. Shortly said- you can copy-paste any 22LR and large rifle trajectory between “paste your data here” boxes. Then, by tweaking scaling percentage ratio, to see trajectory that matches best to ones you are using. Finally, you can select any range and see numeric error comparison for both calibers with “Set trajectory reference range” buttons. Finally, select target size you want to scale down for trainer, and it will be calculated automatically to match best fit scaling you just found out. Note that this is scaler only- it does not include any kind of ballistic calculator. It is noting but dumb, a simple scaler that tweaks your numeric charts for visually easier comparison and automatic 22LR target size scaling. Grab a coffee and play with it few minutes, its not difficult at all.”
There is a scaling tool which you can download from Finnaccuracy:
Here’s a demonstration video:
Let’s end with an example, using some of my rifles and ammunition:
Below you can see an example that Finnaccuracy helped me with. It’s my JP CTR-02 AR15 shooting 55 grains Geco vs. my JP NC22 22LR upper shooting Top Shot (CCI Standard) 40 gr bullet.
The conclusion is that I would get pretty much an identical drop match and feel if I use a 25% scale height.
The 25% scaling should give me an identical drop match from (real 223 Rem. rifle) between 160 to 575 meters. (See upper graph)
A 57 cm high full IPSC target would then be 14.25 cm (~5,6 “) tall for 22 LR. The biggest drop trajectory scale error is at 160 m, equaling 40 meters as a scaled distance. But even the difference in POI is 1.6 cm, the 22LR hits a little higher.
Shooting such a small target with a 22LR at 75 yards (25% of 300 yards) won’t be easy, I’m still only interested in the much smaller A Zone which is going to be tiny. It will be a challenge for sure and would require a bipod (preferably) and a really good shooting position. Then again, so would shooting at 300 yards.
Unfortunately, a certain level of accuracy is needed to make sense out of this scaling method, I’m not sure my NC22 LR upper has enough of it, but there should be plenty of 22 LR bolt-actions up for the task.
I also want to remind you about the Practical Rimfire Challenge. Great fun at low cost, and no Excel sheets needed.