Accuracy of Chronographs and reliance on SD's

[remaction]

SD is a statistical function and the more shots over it result in better SD numbers due to a larger sample size.
The chronographs I have used have a .5% - 1% accuracy range. At 3,000 fps this is a range of 15 fps at .5% or 30 fps at 1% error.
At 1%, a recorded shot of 3000 could be from 2970 to 3030 and the next shot recorded at 3060 could be from 3030 to 3090. Due to the accuracy of the chrono, they could really be the same speed at 3030. We can reduce weather conditions by proper setup of the chrono, but if the accuracy range is .5%-1% that still leaves a pretty large gap in velocities. In the meanwhile, we are fretting over getting an SD of less than 10.

Chrono's are the best tool we have but they are not perfect.
I'm guessing shooters are not further proofing by running larger strings, say 25 shots, for verification.

How much faith do you put in the chrono SD or ES numbers without shooting a larger sample (25?) over the chrono?

 

[spife7980]

http://www.appliedballisticsllc.com/Articles/ChronographChapter.pdf

Get yourself a good one and you dont have that much to worry about. The lab radar in tests is always right about the same as the magneato speed as well.

I use a small 3-5 rounds if I want a general reference but when I have finalized a load I do a test of 10 for the baseline number I plug into my calculator.

 

[OLD308]

I once tip toed around Bench rest shooting back in the day. They were the only ones with chronographs. We all figured velocity the old fashion way by comparing drops and distance. Here is what they told me. Load development was done in lots of 50. Crazy I know. But the reason they did that was to get the best picture possible. They also told me that it was impossible for a human to shoot at distance (caliber dependent) better than 10 SD and 20 ED.

Years later while trying to match military match round, 118 something or another, I was told it had a SD of 20 and ED of 40 on 10 round lots. I did test this as I had a Cronograph at the time. 10 round strings did get close to the 20 SD and 40 ES. But 20 round strings shot it all to hell. That’s when I quit trying to match that junk and never bought any more. Just some info, hope it helps.

 

[ken4570tc in WY]

Good info guys! I'll be starting load development soon for my .243 Ruger Precision Rifle and using the Magneto Speed to assist. I won't be looking to load for velocity but mainly for accuracy. I don't plan to burn up the barrel looking for the Holy Grail. I'll be starting out with the Speer TNT 70gr FB bullet over minimum charges of A4064 to select a primer, then move on to increased charge weights for the possible nodes, followed by changes in seating depth. This will be for short to moderate range varmints and coyotes. I'll gradually move on to the heavy bullets over H4350 for long range steel, critters and competition. Anyway, that's the plan. However, with the information above, I will certainly shoot additional larger strings to verify and re-verify chrono data.

 

[_Windrider_]

http://www.appliedballisticsllc.com/Articles/ChronographChapter.pdf
View attachment 6943477

Get yourself a good one and you dont have that much to worry about. The lab radar in tests is always right about the same as the magneato speed as well.

I use a small 3-5 rounds if I want a general reference but when I have finalized a load I do a test of 10 for the baseline number I plug into my calculator.

i use both. Ill shoot 10 rounds with the magneto and Labradar and record the numbers. then i use the average of both. then i take off the magneto and run the lab as i shoot to track the numbers. this way i record as many shots as i can when i shoot. of course this is only done prone. when doing alternate positions and barraceades and stuff i dont use anything, i rely on my DOPE at that point.

 

[Milo 2.5]

SD is a statistical function and the more shots over it result in better SD numbers due to a larger sample size.
The chronographs I have used have a .5% - 1% accuracy range. At 3,000 fps this is a range of 15 fps at .5% or 30 fps at 1% error.
At 1%, a recorded shot of 3000 could be from 2970 to 3030 and the next shot recorded at 3060 could be from 3030 to 3090. Due to the accuracy of the chrono, they could really be the same speed at 3030. We can reduce weather conditions by proper setup of the chrono, but if the accuracy range is .5%-1% that still leaves a pretty large gap in velocities. In the meanwhile, we are fretting over getting an SD of less than 10.

Chrono's are the best tool we have but they are not perfect.
I'm guessing shooters are not further proofing by running larger strings, say 25 shots, for verification.

How much faith do you put in the chrono SD or ES numbers without shooting a larger sample (25?) over the chrono?

I have both a LR and a magneto, only when the load is not good do I see numbers like you mentioned. 5 charges are enough for me. To me, it does not matter what the numbers are, shoot your load at 1k and observe what just happened. if the load is decent, your vertical dispersion will be tight. Find a calm day and find out, even under 12 mph, you can decipher shitty load or wind deflection.

 

[remaction]

Thanks for the link Spife, good article. My question came about after reading another thread regarding SD. It got me to wondering about the accuracy of the chrono's and if we sometimes chase a ghost based on too small of a sample if we are rushing to find a load. I believe my ProChrono must be decent as 1,000 yard results match up really well with the drop tables in Strelok across several guns. I tend to overthink things but it's not necessarily a bad thing to question our processes and equipment.

 

[47guy]

i shoot my entire load development over the magneto speed once I find a load I’ll shoot at least 25 over it...I’ve got several 0-1 and 2fps ESs with 5-10 shots but when I run 25+ over the chrony I always end up in the
Teens.

 

[remaction]

i shoot my entire load development over the magneto speed once I find a load I’ll shoot at least 25 over it...I’ve got several 0-1 and 2fps ESs with 5-10 shots but when I run 25+ over the chrony I always end up in the
Teens.

You are much better than I at loading details and consistency, I've never gotten 2 ES over 10 shots....

 

[CUBUFF89]

I've recorded data using my Oehler 35 for years and looks like I can trust its validity. I switched recently to MS thinking it was more accurate. That may not necessarily be true but the MS is much easier to use and not sensitive to light conditions. It's the only one I use anymore.
Note: I have yet to try them both at the same time. Might be enlightening.

 

[47guy]

You are much better than I at loading details and consistency, I've never gotten 2 ES over 10 shots....

The first two are the same load...5 rounds then 24 rounds...3rd is a different load.

 

[remaction]

Awesome results 47guy.
What caliber, case, powder and primer? Do you anneal and if so how often?
Any secrets?

 

[47guy]

6.5X47
lapua
varget
FED 205M
every second firing

i dont do any prep work anymore because for the type of shooting i do its not worth the extra work...i tumble every time because i like shinny stuff and i FL size every time.

 

[remaction]

Looks like I need to try the 205M's, I've been using 450's. Everything else is the same, although I haven't annealed my cases yet. I'm in the 8-12 range for SD's.

 

[47guy]

i know everyone swears by the 450s but in 3 barrels now the 205Ms have produced lower numbers and much better consistency...so much so that i sold off my 450s and bought 10k 205s.

 

[remaction]

Good to know, I have been a sheep following the flock...

 

[47guy]

not sure what bullets your using...but since your breaking away from the flock...you might want to try the 123g lapuas...these bullets are IMHO the perfect bullet in the 47...im running them(easily)at 3020fps out of a 8 twist 26" hawk hill...6.8mils confirmed at 1000yds...at 850yds in the same 830 wind a couple weeks ago i was .3mils less drift than 2 6.5CMs running 140 ELDMs at 2800fps.

also ive always shot heavier berger bullets and was very sceptical about the lighter 123s...im a believer now and this will be my go to from now on the plus is i can find 123g lapuas anytime and just about anywhere and they are priced right.

 

[remaction]

I've tried 130 Bergers and 123 A-max. I looked and I guess the ES's are better than I remembered. The 123 has about a 6 ES but is a light load, that's where it shot the best and for my casual use that's fine in my shorter barreled rifle (22"). The 130 Bergers run at 2,855 with an ES of about 10 on average. Therefore, the SD's are pretty good.

 

[47guy]

Yeah those are decent numbers.
I shot 130s outta my last barrel 24” at 2950 that’s was leaning on them a little and why I’ll stick to 26” now

 

[mcfred]

FWIW, per the manual of my Öhler 35P:

 

[Deleted member 10043]

Take a weighted average of a string and eliminate shots > < 1% of the mean or average. You will see that it doesn't make a material difference. Also, it is really not a statistical sample chosen from a population. We don't even load 500 cartridges and then properly randomly select 10 to shoot a string. Thus, these well known +/- 1% inexpensive chronographs are well within an acceptable statistical error rate and are still relevant if that is all you have to work with. Statistically, you don't need more shots to get a better SD when your population is unacceptable to begin with. So, don't sweat it unless you are really shitty at reloading.

 

[Greg Langelius *]

This reality is one of the reasons why I limit my reliance on chrono's to gleaning basic MV data to be used for plotting initial 'just get me on the paper' trajectories. I can often tell from the target pretty much all the data I really need for finding good loads and determining real-world dope.

For example, for 600yd, I train at 100yd, and confirm 300yd drops to true my ballistic projections. It gets me on the target at 600yd, and in the 9 ring after the two sighters. I make my final in-comp zero correction off that.

I'm not a sniper, and I don't compete any more in such comps. I know my methods do not deliver, for me, a first round hit capability; and refrain from doing what for me is the impossible. I leave it to others to confirm that such a capability well and truly exists.

Put most simply; I trust the target more and the chrono less because, for me, the chrono can lie, but the target seldom does.

Greg

 

[Deleted member 10043]

Correct, you can get your +/- 1% from your chronograph and true up at distance. We do it no matter what type of chronograph we use, anyway. Your calcualted SD will not show up down range on target. Mathematically, it would not be a good idea to back into the SD from target results because now you entered yourself and the environment into the equation. Your own induced SD on any given day will always be greater than the calculated one from the chronograph. We are never out-shooting our own rifles no matter how bad or good the rifle performs. Don't fool ourselves into thinking just because we have great chronograph results that we are going to have great results downrange. The chronograph is just there mainly for safety reasons when working up a load. Just because you have a great single digit SD and low ES with safe MV doesn't mean you are going to see that downrange. All you have determined is that your reloading is fine. That you have eliminated that factor in a series of many factors. For some people that is the end of the game and there is nothing wrong with that if that is what you are into. It is a goal that is not difficult to reach and is highly overrated.

 

[remaction]

"Don't fool ourselves into thinking just because we have great chronograph results that we are going to have great results downrange. The chronograph is just there mainly for safety reasons when working up a load. Just because you have a great single digit SD and low ES with safe MV doesn't mean you are going to see that downrange."

Bingo! I started this thread after viewing another thread, where SD's were good but accuracy downrange was not. I wanted to see what others thought about chrono accuracy, but in the end game the chrono info is just one part of the information available to us.

 

[47guy]

I’ve only had a couple of times where the numbers where good but the load was not but it does happen.

After shooting with some buddies shooting factory rifles and factory ammo and seeing the numbers and the results down range I don’t worry about the numbers much anymore...or should I say as much.

 

[Deleted member 10043]

The shot simulators we see that come with a few shooting apps are cool to determine the error rate we can call the wind and show the statistical percentage of hits.

 

[gunsnjeeps]

Most ammo seems to perform better than the chronograph would indicate. It is a tool to use while working up loads but it is still just a tool. I can use my chronograph velocity and 100 yard zero and be in an 8 ring at 1000 yards. M118LR looks bad over the chronograph and with a run-out gauge but works fairly well at 1K, kind of makes one question the conventional wisdom. Now if I could find a true pulseless sling. PS: or make pistol ammo that had factory SD.

 

[OzzyO20]

Looks like I need to try the 205M's, I've been using 450's. Everything else is the same, although I haven't annealed my cases yet. I'm in the 8-12 range for SD's.

I'm heading in the opposite direction at the moment. There was an interesting read a week or two ago from Hornady stating that SRP was dangerous in the 6.5 CM designed for LRP. That didn't add up to me since so many have been running it without issue, and Lapua I'm sure did their research when they released the SRP 6.5 brass. What was interesting was the CEO of Alpha advising against using SRP match primers in the 6.5 CM. Then I found where the CCI 450 was the primer of choice for most top PRS dudes, so I got 1,000 to try.

Currently I'm getting an ES of 15 and SD of 6.6 in a solid 1/2 moa load using Federal GMM 205M's. I'll report back when I get the 450's worked up to the same charge weight safely (if it happens) as to if the SD and ES opened up or shrank any.