SK S+ deviation / Rimfire

Btrain

Btrain

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Dec 3, 2013
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#1
Good evening
Picked up a Gamnin chrono and took it out today.

First time I have chronoed my 457/ Proof CF. Very surprised with the deviation out of it on SK S+… 65 Rnds / Avg 980 / SD25 / range 913 - 1006

Thoughts?

New to chronos and not sure if that is typical - want expecting a 93fps variance

Thanks for the input
 
#3
Those velocity numbers are very low, ES/SD very high. Did the ammunition get cooled to extremely low temps - like teens into 20s F.?

SK Std+ as a label should have a velocity somewhere around 1070fps - UNLESS the ammo is extremely cold and/or it's fired from a long, "slow" barrel (I had a 26" Shilen barrel which gave velocities 40-50fps slower than the same ammo fired in ACE or Bartlein barrels, so a "slow" lot of Standard+ I had was down in the 985-1025fps range).

I Have no hands-on experience with a Garmin chronograph, but I can say with confidence that significantly off-angle shots picked up by my LabRadar can read VERY low. I haven't heard of this sort of thing being an issue with Garmin.
 
#4
Every once in a while my Garmin will pick up a shot that is in obvious error. It won't usually indicate the FPS for that shot but includes it in the summary calculations. I am looking at a 20 shot string of SKLRM right now that shows an SD of 248. Average velocity of 1108.8. Good SK ammo is going to have an SD in the single digits - less than 10.
If you look in the Shot List for that Session you will be able to see the errors and you can delete them out of the string if you so choose to correct the data.
 
#5
SK is always slow for me close freezing and at high humidity. Your velocities are probably correct. I pay much more attention to SD than ES. ES is usually a function of ammo cost, which is actually ammo consistency. 80 shot SD 8-ish I have only seen with Eley Match. SK is not top tier ammo in my experience.
 
#6
SK is not top tier ammo, that is true, but there are some very good Lots out there. I normally shoot 50 shot strings for testing and it has to be +10 Celsius or greater. In the past 2 years I have only had one lot of SKLRM that had an SD greater than 10 and a few approaching half that. My Bartlein barrel just likes that particular ammo.
 
#7
Yes - Very cold today +\- 15 F, but the ammo was at room inside until fired

I would t call SK S + top tier ammo either but would have expected much closer

Do we think it’s that simple - Really cold? Could it be a barrel issue that would cause what I was seeing?
 
#9
Try to track shots that may be from a cold clean barrel, first shot after the barrel cools, etc. I find that the first shot from a barrel after changing a target may show a higher velocity from average. I was trying a different cleaning method and didn't have lower velocity after cleaning but I'm starting to question my accuracy from the cleaning.
My current sessions with Center X show SD's from 7 to 10, 50-80 or so shots same lot. I'm getting ready to try out the Cortina V2 tuner and may check the SK S+. Even with CX I will get a low and high shot from time to time, to date 1063-1115, avg is usually 1080-1090, mostly 1085/6/7.
I really don't know a lot ref rimfire, I'm learning as well, hope it helps. Right now, Center X Is the best I have.
I do like the Garmin to track velocity and the effect on target, at 100 it matters a bunch, although sometimes there's no explanation and the bullets grows wings!
 
#12
The chronograph shows an ES of 93 fps for 65 rounds of SK Standard Plus, with an SD of 25 and a spread of 913 - 1006. The temps were about minus 15 degrees Fahrenheit ("+\- 15 F").

The cold temperature explains the slow MV of the rounds (it doesn't take long for a warm round to cool).

The relatively large ES and high SD are not unheard of with an ammo like SK Standard Plus. At best SK Standard Plus is an entry level match ammo that can have some boxes with a number of relatively consistent rounds and other boxes with poorer performance. In other words, sometimes it can be good, sometimes it sucks.

The chrony results themselves show no reason to suspect that something is wrong with the barrel. If there is something amiss with the barrel it will show on the target rather than the chronograph.

For comparison, below are the basic chronograph numbers from three samples of SK Rifle Match, ostensibly a "better" grade of SK. The results are from October 5, 2021. The ES figures are high, as are the SD values.

The OP's high SD suggests that many of the rounds shot were nearer to the extremes in MV than they were to the average MV.





 
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#15
justin amateur said:
SK S+ is in the middle of the SK spectrum for quality.
SK Magazine being the bottom, SK Semiauto next,
with SK S + being 3rd from the bottom.
Pistol Match, Rifle Match and Long Range being the top 3.
Some boxes will produce better results than others.
Welcome to the assembly line lottery. ;)
Click to expand...

As I understand it SK is broken down as follows
They make 2 lines of ammo, one slightly faster than the other
The slower speed of the two is segregated, based on performance ,from low to high as:
Standard plus
Pistol match
Rifle match

The slightly higher velocity low to high
Pistol match special
Biathlon sport
Long range
 
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#16
According to a Capstone official, SK ammo is graded in the following hierarchy.

For SK varieties nominally rated 1073 fps it's SK Rifle Match, SK Standard Plus, SK Pistol Match, and SK Magazine.

For SK varieties nominally rated 1106 fps, it's SK Long Range Match, SK Biathlon Sport, and SK Pistol Match.

It should be noted here that this doesn't necessarily mean that higher graded varieties will always outperform lesser ones.



For the full article in which Esterline was quoted, see https://www.gunsandammo.com/editorial/cz-usa-model-457-22-lr/365081
 
#18
Compare price per cartridge to rank SK cartridge quality.
The lower the cost the less quality control is used.
Esterline's comment is slightly out of sequence.

I haven't been able to find SK Biathlon or Pistol Special for a while.
That's why I didn't include them. :cautious:
 
#19
Ammo branded specially for "Pistol" is a niche ammo, even though anyone can shoot it.

As a niche ammo, it's priced accordingly. Pistol ammo has no requirement to be a higher grade or to be better performing than "rifle" ammos. SK Pistol Match is graded below SK Standard Plus.
 
#20
Shot from my CZ 455 with a 16.5" barrel
 

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#22
justin amateur said:
Compare price per cartridge to rank SK cartridge quality.
The lower the cost the less quality control is used.
Esterline's comment is slightly out of sequence.

I haven't been able to find SK Biathlon or Pistol Special for a while.
That's why I didn't include them. :cautious:
Click to expand...
Have you checked Grafs? Also I have a brick of Pistol Special I could part with.

SK AMMO 22LR 40gr SOLID RN BIATH-SPORT 50b 100cs - Graf & Sons

The SK Biathlon Sport cartridge is a result of innovative engineering and a long history of close co-operation with top biathletes. This biathlon ammunition combines effective and reliable energy with the finest match standard accuracy. The SK Biathlon projectile has ideal velocity for frigid...
www.grafs.com www.grafs.com

 
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