Is this 3.1fps SD really possible?

[sig2009]

I was doing a ladder test yesterday with the chrono and this happened. I find it hard to believe so I am going to rerun it. 3.1 fps SD!!!!!!!!!!

Tikka T3X CTR 6.5 Creedmoor 20" barrel

140gn Hornandy ELDM .040 thou off. IMR 42.2 S&B Large Rifle primer. Hornady once fired brass.

Temp: 77 °F

# FPS FT-LBS PF
4 2524 0.00 0.00
3 2517 0.00 0.00
2 2519 0.00 0.00
1 2522 0.00 0.00
Average: 2520.5 FPS
SD: 3.1 FPS
Min: 2517 FPS
Max: 2524 FPS
Spread: 7 FPS
True MV: 2521 FPS​

 

[ballison]

If you're asking if a 3.1 fps SD is possible from a 4 shot sample size using the same load, the answer is most definitely yes. I guess I'm a little confused on where the ladder test comes into play. A ladder test usually involves shooting rounds with varying charge weights. So if those 4 rounds were all with different charges (usually .3-.5 gr apart), then I would say something is out of wack.

 

[lash]

I've seen that before. But I also shoot more than 4 rounds to determine ES and SD. There is no way to get statistically valid SD/ES numbers using only 4 data points. I personally recommend 10 minimum for that. I have recorded an SD of 4.3 over ten rounds of my favorite.338 LM load, using 285 Hornady HPBT over 41.5g H1000. I give credit to consistent neck tension and loading practices.

Now if you were just checking to get a speed while doing OCW load workup, then...never mind...

 

[sig2009]

If you're asking if a 3.1 fps SD is possible from a 4 shot sample size using the same load, the answer is most definitely yes. I guess I'm a little confused on where the ladder test comes into play. A ladder test usually involves shooting rounds with varying charge weights. So if those 4 rounds were all with different charges (usually .3-.5 gr apart), then I would say something is out of wack.

Well. The ladder test is used to shoot different loads with different charges. If you read the OP they were with the same charge with the same bullet weight. I had about 10 different loads I took to the range to chrono. this was just one of them.

 

[JSTARSZ]

The answer is yes but...your sample size is too small to gain a true understanding of the results. If you shoot 20-25 rounds and you still have a SD of 3 count yourself extremely lucky or one awesome reloader.

 

[spife7980]

I had a similar experience recently. Thought I was on a balls to the wall amazing load recipe after 3-4 and then the next shot was 50 fps higher blowing it all to hell.

Ignorance is bliss sometimes.

 

[TripleBull]

I have recorded an SD of 4.3 over ten rounds of my favorite.338 LM load, using 285 Hornady HPBT over 41.5g H1000.

91.5 grains?

 

[lash]

91.5 grains?

Lol, yes, that's it. It's not a hot load, but gets me 2780 fps and sub 1/2 moa 3 shot "groups" out to 1000+. My Savage has a shortish throat or I would seat them out more and load a bit faster.

 

[_Raining]

Once I settled on a load I have shot two sets of 100 rounds. I have recorded 2.X up to 6.X SD, most falling in the 4.X range for 10 shot groups. I have not done the math yet for the full set but anything less than 10 is good enough for me when looking at cold bore up to very hot bore. Too bad my group sizes are only averaging .75ish, maybe one day i'll get consistent sub .5 moa 10 shot groups.

 

[Pakratt99]

Good article on necessary sample size for things like SD can be found here http://www.autotrickler.com/blog/practical-statistics-for-shooters . In short your sample size is on the small size but that number is not out of the question for a very consistent reloader using good components.

 

[usafa77]

I had an sd of 1 after four shots the other day- ended up at 16 after 10 shots.

 

[hic28]

Yes it's possible

 

[Sheldon N]

Just shoot the 6 Dasher... it's like cheating. I haven't ever seen a double digit SD. Most loads I've tested have an SD of 3, and even the load where I just throw powder charges on a progressive press has an SD of 8.

 

[sig2009]

Just shoot the 6 Dasher... it's like cheating. I haven't ever seen a double digit SD. Most loads I've tested have an SD of 3, and even the load where I just throw powder charges on a progressive press has an SD of 8.

Unfortunately not in my Tikka. I assume the 20" barrel is the culprit. Going to look at replacing it.

 

[Lunchbox27]

I would try a different powder before spending the coin on a new barrel. My 20" Tikka has given me single digit SD numbers with two different powders using the 140's

 

[user]

Good article on necessary sample size for things like SD can be found here [video]http://www.autotrickler.com/blog/practical-statistics-for-shooters[/video] . In short your sample size is on the small size but that number is not out of the question for a very consistent reloader using good components.

Great article.

 

[308sako]

Freak SD, unfortunately off the best velocity node.

 

[Pure-Precision]

As stated sample size is small but the numbers are still good. I got an SD of 2.0 with a 4fps extreme spread over 5rds of 7mm wsm with 162eld-m's a few weeks back, and it shoots .5-.6 moa. I've had freak loads with sub 3.5sd over 10rds and still only 1.25-1.5moa come to find out my "lightly used" barrel had a lot more rds than stated through it.


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[Clearlight]

Only 3 shots in these photos , but sometimes the ammo is near perfect .
Slower velocity is one of my 6.5 x 47's , 3019 vel is a friends 308 we were
tuning for the Aus Queens F Class Nationals . This load was good enough to
win F standard category , beating all the current Aus F class team .