Velocity VRS Deviation.!!

[native hunter]

G'day, Not my statement but found it on the net while looking for rimfire stuff and thought it might be interesting reading for some.


Those unfamiliar with smallbore rifle competition are often surprised to learn that target shooters almost universally use standard velocity ammunition in preference to the many varieties of high and hyper-velocity rounds available. The reason given is the low-velocity ammunitions resistance to wind deflection.

Despite what might seem at first to be the case, wind deflection is not proportional to the time of flight. Instead, it is proportional to the amount of delay in the flight caused by air resistance. The 1145 f.p.s. standard velocity .22 long rifle round takes .287 seconds to go 100 yds., but would take only .262 seconds to cover the same distance in a vacuum. The latter figure is easily found by dividing 300 ft. by the speed of the bullet (1145 f.p.s.), which would remain the same throughout its flight if it were in a vacuum. Thus the delay caused by air resistance is .025 second with the standard velocity ammunition.

The 1335 f.p.s. high velocity ammunition, which will take .259 second to cover 100 yds., would take only .225 second in a vacuum. Thus, the delay for this bullet is .035 second or 37% greater than that of the standard velocity round .22.

The high speed round, then, suffers about 37% more wind deflection than the standard velocity.

This remarkable result is due to the very rapid rate at which air resistance increases with increase in bullet speed in the region near the speed of sound. The .22 rimfires rimfires are the only important rifle cartridges that occupy this speed range, and they are the only ones that show more wind deflection as velocity is increased.

While air resistance always increases when the bullet is shot faster, the rate of this increase is less steep at supersonic velocities. Rifle bullets in general, contrary to the case of rimfires, are made less sensitive to the wind by raising their velocities.
NRA Firearms Fact Book

Regards
Native

[SnipeWench]

I think you'll find that standard velocity ammo is used because it's in the rule book that standard velocity must be used. We generally aren't allowed to use HV ammo because of the noise.

But if you were out hunting varmints, that'd be another story!

[native hunter]

G"day,
Snipe- I basically put that up there as I and a few others were/are under the impression faster ammo bucks wind better in rimfire ammo,as you can see by this theory thats not the case.!!
Ive used winny subs to bust bunnies for years and dispatch a few slightly bigger critters,they work well.
I agree nothing puts you off more than a loud shot ringing out while your plinking with your standard ammo.
Regards
native

[m12vlp]

Lets do the calculations ( BC's from here http://www.exteriorballistics.com/ebexp ... imfire.cfm )
10 mph 3 o'clock wind, Drift and drop in inches. Range in meters.

Edit: Added Vel = 1050

Code: Select all

Dist	Velocity	Drop  	Drop (MOA)	Wind 10	Wind 10 (MOA)
0   	1050    	0     	0         	0      	0
25  	1012    	3.97  	13.88     	0.35   	1.23
50  	979     	5.41  	9.45      	1.11   	1.94
75  	951     	4.14  	4.82      	2.33   	2.71
100 	925     	0     	0         	3.98   	3.48
125 	902     	-7.18 	-5.01     	6.05   	4.23
150 	882     	-17.55	-10.22    	8.49   	4.94
175 	864     	-31.26	-15.6     	11.29  	5.63
200 	846     	-48.46	-21.16    	14.43  	6.3
225 	830     	-69.28	-26.89    	17.91  	6.95
250 	814     	-93.87	-32.79    	21.74  	7.59

Vel = 1445

Code: Select all

Dist	Velocity	Drop  	Drop (MOA)	Wind 10	Wind 10 (MOA)
0   	1145    	0     	0         	0      	0
25  	1085    	3.5   	12.24     	0.44   	1.53
50  	1038    	4.8   	8.39      	1.45   	2.53
75  	1002    	3.7   	4.3       	3.01   	3.5
100 	971     	0     	0         	5.05   	4.41
125 	943     	-6.45 	-4.51     	7.53   	5.26
150 	918     	-15.83	-9.21     	10.45  	6.08
175 	896     	-28.29	-14.11    	13.78  	6.87
200 	877     	-43.98	-19.2     	17.47  	7.63
225 	859     	-63.06	-24.47    	21.5   	8.35
250 	842     	-85.66	-29.92    	25.89  	9.04

Vel = 1335

Code: Select all

Dist	Velocity	Drop  	Drop (MOA)	Wind 10	Wind 10 (MOA)
0   	1335    	0     	0         	0      	0
25  	1244    	2.75  	9.61      	0.47   	1.64
50  	1165    	3.82  	6.68      	1.66   	2.9
75  	1101    	2.98  	3.47      	3.61   	4.2
100 	1050    	0     	0         	6.23   	5.44
125 	1012    	-5.33 	-3.73     	9.44   	6.59
150 	979     	-13.2 	-7.69     	13.13  	7.64
175 	951     	-23.78	-11.87    	17.28  	8.62
200 	925     	-37.23	-16.26    	21.87  	9.55
225 	902     	-53.72	-20.85    	26.88  	10.43
250 	882     	-73.4 	-25.64    	32.26  	11.27

Edit: velocities below 905fps all fixed up.

[native hunter]

M12,maybe 1050fps compared to 1250 would be more realistic.
But that table shows more speed equals more drift.
Regards
native

[stinkitup]

I'm not so sure about wind bucking ability but from what I have read due to the transition from super sonic back to subsonic the hyper ammo doesn't fair well or it affects accuracy during this period. Also the 22lr bullet shape is designed for subsonic flight rather than the slippery pointy rounds seen in 17hmr now 22wmr and CF loads.

Another point is alot of hyper 22lr rounds the projectile is lighter than the other loads too so this will be affected by wind. Prob not a factor till between 50-100m some of the guys that shoot alot of 200m rimfire fly might have some better info on what works for them.

Ryan

[m12vlp]

M12,maybe 1050fps compared to 1250 would be more realistic.
But that table shows more speed equals more drift.
Regards
native

Added to the original post.

Ignore the velocity bottoming out at 905fps. I've never used this program to calculate low velocity rimfire trajectories before. (edit: user error. I entered the BC incorrectly for velocities below 905 )results out to 100 are perfect though.

[chris.tyne]

You can use high velocity in comp if you wish and in some rifles certain lots of R100 can be preeeeeeeeeeeeeeeety close at times,if you do decide to use high velocity in comp dont be surprised if you are the only one.................................................and there is a reason for that .



Regards Chris.