Summer Ammo Velocity

[VFL1911]

I started actively getting into NRL22 and PRS Rimfire competitions last fall, so this is my first summer competing in the south.

I’ve been reading a lot lately on most recommend finding lots of 22 ammo that stay between 1060-1100 fps for optimal accuracy. Staying within this FPS range was quite easy in the fall/winter/spring, but I’ve been watching my FPS really creep up with the rising temperatures now with 90+ degrees and ammo chrono’ing at 1100+

Do you all change your ammo selection just for warmer weather? Such as switching down from the hotter lots/types to slower to stay within a certain FPS range due to environmentals. Looking to focus on consistent accuracy at range, as my club shoots a ton of option 2 for NRL22 and most regional PRS I’ve been to have had multiple 200+ yard stages.

I’m shooting a 21” Lilja with SK Long Range Match or Lapua Long Range (based on availability).

I had great luck with RWS R50 in the winter, but that was chrono’d with avg fps of 1090 in 35-45 degrees + haven’t found R50 in months anywhere. Can’t imagine what that FPS is in warmer weather.

 

[grauhanen]

One reason many longer distance .22LR shooters may prefer slower rather than faster average MVs is because a slower .22LR round will drift less in the wind than a faster one.

Another reason is based on the mistaken assumption that .22LR bullets that exceed the speed of sound will suffer from transonic instability and as a result be less accurate. Any inaccuracy experienced with faster .22LR match ammo is because of its quality, not its muzzle velocity. Poor quality standard velocity .22LR ammo can be as inaccurate as poor quality higher velocity .22LR ammo.

Why does supersonic .22LR ammo not suffer from transonic turbulence? It's simple. Supersonic ammo may experience accuracy-robbing transonic turbulence when it slows down into the transonic zone of speeds, which is from about 890 - 1340 fps. The majority of high velocity .22LR ammo never exceeds the transonic zone. In fact, like HV ammo, most SV match .22LR ammo spends much of its entire useful flight time within transonic zone of speeds before falling below it beyond 150 yards.

It was confirmed in 1990 by Robert McCoy that .22LR ammo with transonic zone velocities (from about 1340 fps to 890 fps) doesn't suffer from the increased pitching and yawing that causes the flight instability associated with bullets slowing down into the transonic zone from considerably greater velocities. See conclusion #5, p.11 in Robert McCoy "AERODYANMIC CHARACTERISTICS OF CALIBER .22 LONG RIFLE MATCH AMMUNITION" https://apps.dtic.mil/dtic/tr/fulltext/u2/a229713.pdf

Shoot the ammo that gives best performance. If you're concerned about excessive wind drift, look for slower ammo.

 

[usafa77]

Hard enough to find a good lot. Never mind good lots by temperature.