Tuesday, August 26, 2008
Aguila Super Colibri VS. CCI CB Long, a velocity comparison
This coming weekend I hope to spend some range time sorting through a big box of .22 long rifle, seeking my Marlins favorite. I'd like to do the shooting past my chronograph, charting velocity variations. By doing so I should learn something about the consistency of the various rim fire products.
To that end, after work today I sorted out the parts of my Pact Model 1 chronograph and assembled it near the garden. To be sure it was working properly I needed to do some shooting through it. There were kids swimming not far away, and I preferred to make as little noise as possible. Since I'm not Frank James and don't own a 'sound reduction device', I decided to use truly quiet .22 ammunition.
A box each of Aguila Super Colibri and CCI CB Long ammunition were pulled from the safe, and a'shootin we did go.
Only a few rounds were required to test the Chrono, but I figured "Why waste the opportunity?" I shot ten rounds of each through the screens and made note of the results, as an investigation of the ammunition, while I tested my equipment.
The Aguila Super Colibri with it's 20 grain conical bullet showed considerable drop from my rifle at the range, and poor accuracy. It's possible these chronograph results reveal why. The velocity variations are sharp.
With an average muzzle speed of 565 fps, the extreme spread in velocity of 118 fps was huge. Thats almost a 20% variation in velocity. At least as significant was the standard deviation of 32 fps. It's no wonder my Marlin spit this stuff all over the landscape. On the other hand, the very low velocity helps to explain the extraordinary quietness of this ammunition. It barely goes 'Pfft' out of a long barrel.
Moving on to the CCI CB long with it's 29 grain round nose bullet (a favorite of mine for pest control) I fired another ten rounds. This ammunition was a bit louder, which was backed up by the higher velocity. It averaged 623 fps, and on the whole was much more stable in velocity variations.
There was one clinker round amongst the CCI string, and it heavily skewed the numbers. While shooting the CB longs, I had 'Pop', 'Pop', 'pfft', 'Pop'....
'Scuse me? what is this 'pfft' and where did it come from?
There was round in the bunch which came out of the barrel much slower than the others. Almost 150 fps slower... and this made a huge difference in a ten round string.
Dropping that round from the math brought the extreme spread from 184 fps down to 88 fps. This is still a very wide number accuracy wise. Velocity variations like this have to adversely effect accuracy.
I verified the chronograph works, and also verified something I suspected regarding the super quiet CB and Colibri rounds. They are not very accurate for a good reason..... the manufacturing variations in this type of ammunition seem to be rather extreme. The chrono clearly shows this.
Hmmm................... Perhaps I should take some apart and figure out why......