This weekend, I got a chance to bang away with my new toy, used nickel Sig 226.
For s & g's, I was shooting over my chrono with several different factory loadings.
I noticed in my strings of ten shots per ammo type, I was seeing some real interesting variations in velocities.
With Wolf 115 FMJ, UMC 115 FMJ, Fiocchi 115 HP, and Fiocchi 124 FMJ, I'd get some some shots that were within 50 fps of each other, but then I'd get rounds that would drop considerably.
I don't have my notes in front of me... so I'll use B.S. numbers... but they do represent the variation I'd see. I might get 8 shots at 1500fps, but two at 800 or 900. Also might get a way hot load up at 2000.
THe only ammo I shot that day I didn't see that kind of variation on was some old Remington green box 124 fmj.
So... is that kind of variation in factory ammo common?
FYI, the low-power shots were not first out of the barrel, or last. So I don't think I was seeing some variation of cooking the ammo.
Or, could the Sig in some way have an issue that could cause this? (I don't know...light spring that allows ejection too soon).
Or would you suspect chrony error? (I shot some three-shot strings of rifle rounds over the chrony that day...and saw no weird readings.
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May 13, 2008, 01:38 PM
Sounds to me like your crony screens were set up too close to the gun.
The only way you could possibly get 8 shots at 1500fps and one at 2000fps out of a 9mm pistol is to chrony the muzzle blast!
I just re-read your post, and now see those were BS numbers, but still, I would suspect muzzle blast if you are getting variation of BS 800 to BS 2000.
May 13, 2008, 03:07 PM
just fyi, chrony was 10 feet in front of muzzle.
I'll try to post the real numbers tonight when I get home.
May 13, 2008, 03:16 PM
I am of the belief that the variations are more due to the chrony than the ammo. Were you indoors or out? Was it sunny or cloudy?
If you were indoors the chrony could have been influenced by fluorescent lighting which often causes high readings. If outdoors, uneven lighting could cause erratic readings.
Lighting is the larges single cause of inaccurate readings on chronographs. This why most are installed in an enclosure (coffin) with separate lights in order to remove these variables when chronographing for competition.
Factory ammo is not all that consistent and can vary widely from mfr to mfr but the kind of spread(s) you indicate most likely go back to the chronograph.
May 13, 2008, 03:21 PM
Outdoors, overcastish...not direct sun, but not dark either.
chrony mounted on a heavy video tripod.
Just thinking, I'll also be putting some rifle rounds over it tomorrow... I'll see if I see any inconsistencies then.
May 13, 2008, 03:46 PM
I find the most consistent readings are when I aim low in the "v" of the screen supports. The closer the bullet passes in relation to the photo cells, the better the reading. I caution, however, that your aim has to be real good. Use soda straws instead of the wire supports and try without the screens. That way anything but a low shot won't do any damage.
May 13, 2008, 07:35 PM
I'm inputing the data for the different ammo.
Reading it, and seeing that there isn't any weird numbers in my rifle data, or in the Rem. Green box ammo... I'm wondering if there wasn't some majorly different thing happening with sun/cloud cover. I didn't get any shots, though, where the speed didn't register (which I've seen before).
For everyone's info, readings from the different ammo:
UMC 115 FMJ
Rem 115 FMJ Green Box
May 13, 2008, 09:51 PM
My vote in on a chrono issue somehow. I find it difficult to believe your 9mmx19 pistol would have extracted and ejected the fired case with a 115g @ 700 or 800 ft/sec. That's too anemic for proper function with normal springs. With that much variation the sound of firing would probably have varied a lot too.
May 14, 2008, 02:10 AM
I've found that factory ammo shoots to their listed ballistic data +/- a reasonable difference expected from using different firearms. In all those I've ran over my chrono factory ammunition has been consistent with relatively low SD values.
I've chrono'd wolf ammo from my Glock 19 along with a small variety of othe factory loads.
For Wolf the average velocity was 1,219 fps with a SD of 19.74 fps. Range was from a low of 1,191 fps to a high of 1,242 fps.
Fiocchi 115gr JHP Italian manufactured ammo ran 1,288 fps average. SD was 13.92 fps with a range from 1,272 fps to 1,310 fps. Fairly hot ammo comparable to Corbon and other +P loads.
Winchester Ranger SXT +P+ 127gr JHP's (police surplus) ran at 1,273 fps with a SD of only 8.53. Range was 1,261 to 1,285 fps. Very accurate ammo.
Some Barnual Silver Bear 145gr bi-metal nickle plated cased ammo ran at 1,054 fps average with a SD of 8.54 and a range of 1,042 to 1,067 fps. Very accurate ammo also but alas, it wasn't reliable in extraction and would seize in the chamber occasionally making the case removal difficult.
115gr FMJ S&B ammo was relatively tame at 1,142 fps average SD of 17.73 fps with a range of 1,114 to1,161 fps.
If there are any flashes of light it will throw off the chrono. I once tried to take measurement when there was a far off lighting storm and even at a great distance the readings became erratic. Occationally I've seen erratic readings from light glinting of the windshields of cars dring by. Any fluorescent lighting really throws of the readings as the lights pulsate and flicker.
May 15, 2008, 10:39 AM
I can post numbers later... but in yesterday's shooting, moved the chrony to 15'.
No errant readings.
When I have time, I'll try again at 10' and see if the issue comes back.
While setting up, realized sun was probably less over head than the first day.
btw... the fiocchi 115 HP's are some fun buggers.
May 15, 2008, 10:59 AM
Save that Fiocchi brass too ("GFL" headstamp). I've been very happy with it in 9mm Luger and .38 Special.