22lr - velocities and exceeding stated m/s

[Farmer rick]

Hi all,

Been doing some ammo testing with standard velocity target grade ammo, but found all the brands to be extremely loud, with a distinct crack of super sonic speed - rifle is cz 457 mtr 20" barrel + ask moderator.

SK rifle match: 327m/s - Quietest but still a decent crack
Lapua Centre X: 327m/s - 2nd
Eley Match 331m/s ( mean quoted as 317-331m/s) - really loud, supersonic crack every time.

So my question is, are these going supersonic and if so why, based on the following:
Speed of sound at:
0deg = 331 m/s
2 deg = 332 m/s
5 deg = 334 m/s

Todays temp was around 4deg, so should be above the 331 limit, but I would say they were all much nosier that the RWS (315 m/s) & CCI (320 m/s) subs I normally shoot, and consistently cracking, rather than just being the odd occasional one.

So many people say that 16" barrel is the max for burn / velocity in 22lr, so theoretically the 20" barrel should be slowing it down... it appears SK test their ammo in a 660mm barrel - that's around 26"...

Any thoughts or insights are more than welcome.

[brown dog]

As you say speed of sound at 4 degC is  c333m/s 

So the avg vels you quote aren't far off that...    ie you're  teetering on the edge of supersonic 'as is' ... 

then, taking an average as meaning, by definition, 50% shots above and 50% below that value, you could expect half your eley shots to crack, and (depending on SD) a fair chunk of the SK and Lapua to crack.

If all are cracking, my first thought would be that that's probably within tolerance, as you're right on the edge and the ammo avg estimate is just that, an estimate, and maybe your rifle routinely shoots a couple of m/s fast, for whatever reason..

But, if not, my second thought would be charge temp.. was the ammo warm? 

[Farmer rick]

Interestingly I think eley state their average speed to be 319 - 331, so therefore percentages should be well under sonic speeds... every round was over. Tested again today and every round was cracking again (4 degs again)

I went and tested subs today:

rws sun hp - 315m/s - all reminded sub sonic.

cci sub hp - 320m/s would say around 20% sub sonic and very obviously sub with significantly low poi...