confusing chronograph results

[john_1182]

hi again, today i went out and started a litle bit of load development on the ..308 and i have come back with some chrono results that confuse me

.308, tikka t3, lapua brass, standard cci primers, ADI 2208 (Varget), 150gr winchester power point SP projectile

all rounds are loaded to the best of my ability, brass is cleaned, tumbeled, sized, trimed, tumbeled again (ect)and powder is measured with electronic scales and i dont load the powder untill the scales give me the same reading 3 times.

here are the FPS results i come back with

46gr
2821 fps
2866 fps
2914 fps
2918 fps

46.5gr
3042 fps
3020 fps
2929 fps
2911 fps

47gr
3033 fps
3073 fps
3017 fps
2955 fps

47.5
3028 fps
2864 fps
2998 fps
2988 fps

what is confusing me is the differance of almost 100 fps in all of the loads, i understand larger strings would give better results, but im still baffeled in the large variances, could it just me a shit load (brass powder prime combination for the rifle ect) or could somthing like out side weather conditions be effecting the chrono ? light, wind ect ? strings were fired over a 1 hr period at aprox 6pm tonight it was over cast, 30 kmph winds and sun was at about 4 o'clock in the sky..

also the chrono is a "shooting chrony" and i was using the sun shades it come with"

 

[Victor N TN]

Re: confusing chronograph results

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: john_1182</div><div class="ubbcode-body">
also the chrono is a "shooting chrony" and i was using the sun shades it come with" </div></div>

A long time ago I had 2 of these. I sold the first one after 2 months of head scratching. I gave the second one to my brother. They just have too much error in their software. Or very poor quality hardware.

The Pact I have has been very reliable. But hopefully this summer I'll be getting a new CED that can download everything to my PC.

See if you can find a friend with a more dependable chronograph. I'll wager most of the variance will disappear.

 

[john_1182]

Re: confusing chronograph results

ok, thanks for the reply, out of our group, im the only one with a chronograph, looks like its time to keep a eye out for a new one.

i hope there not as hard to find as primers and powdder here in australia ( i have to drive 300km 180mile to get my stuff, there not allowed to post it in the mail or courier

 

[308sako]

Re: confusing chronograph results

deleted in protest!

 

[Victor N TN]

Re: confusing chronograph results

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 308sako</div><div class="ubbcode-body"> That is with bulk style bullets there are sometimes lots which have a large difference in the finished diameter... .3065 to .309 <span style="font-weight: bold"> </span> <span style="color: #000099">(example only)</span>type variations. This will affect the pressure curves and therefore the powder burn and velocity yield.

I would try to shoot some match grade bullets in the same general weight area and see what the chrono does then. </div></div>

+1... Variances I am very familiar with. I'm glad you put it up. I forgot it.

 

[308sako]

Re: confusing chronograph results

deleted in protest!

 

[Victor N TN]

Re: confusing chronograph results

I'm sure that in my case I have already forgotten on a lot of subjects, more than some people will EVER know.

And the Swiss cheese just keeps getting more holes in it.

I hunt up math tests on the internet to try and keep so much stuff from slipping down the drain. Getting old is rough. Now, I think I would like to live until all my grandkids graduate college. I never thought I would live this long.

 

[john_1182]

Re: confusing chronograph results

ok, never thought of bullet diamiter variances, but makes perfect sence, i went out today with another 10 rounds just to check it again in different light conditions later in the evening, i tryed the low and high end of my loads and the 45gr charge gave me super shit readings 200fps ES but the 47.5gr charge gave me a ES of 80 would be less but i included the one odd ball reading (aprox 50fps lower then the others) and a SD ot 12, so im happy with that

i still have orderd a new CED chrono, it wont hurt to have a better quality chrono with more features, also when i was reloading i was using my fingers to adjust the loads (now im using a trickeler so im assuming that will make some sore of differance)

 

[bdh308]

Re: confusing chronograph results

Victor...you maybe old but your still one of the wisest and humbling man Ive ever talked to. Keep your chin up.

As far as chronies go..I do own a Beta and I havent seen any errors in it yet. Course I may have gotten lucky and purchased one that actually got inspected properly too...lol. I honestly think its the ladder with your bullet variances. It sounds like you do well in taken extra precautions in your reloading but sometimes even the best can overlook something so simple causing extreme spreads.

 

[Enios]

Re: confusing chronograph results

This is not an exact answer but something I found very interesting in running some test today with my Chrony Master Alpha. Your speed variations can be from many things just in the load process, also.

Victor, for you maybe week after next I'll try to set up the Millennium and Chrony back to back and see how they compare readings. I'm pretty sure the Chrony reads about 35 fps faster but we will see. I love the Millennium for the data storage and the fact we can down load it all to the computer. It is in a class all to itself but if I'm going to shoot a chrony I had rather it be the Chrony. Little brother has wasted one from muzzle blast from his 7MM RUM already. Shook something loose but they replaced it with no questions asked. Here's what I did today.....


Well....Got to run test today at 15 ft from Muzzle 100yds and 175's. Ran into problems on the second test because the chrony got in the shade at 175 and numbers won't work out any way I ran them. May go back and look at the speeds it hit on each round and see if one of them works out that way. If it does I'll post something later.

I tried every way I could think of to make the numbers work out. Changed BC of bullet and got with in about 40 fps of the same at 100 yds and 14 fps at 175 which I was pretty happy with that until calling Little Brother and he said did you try changing Muzzle speed and I said OOOOPS. My average muzzle velocity was 2513 15 feet away and nothing worked out until I changed it to 2550 which is the speed I thought it should have been close to anyway and Bingo I was 2 fps slower at 100 yds and 4 fps faster at 175. Which could have easily been from not shooting over dead center. Hard to get ever thing lined up just right at those distances and just picked a spot as close to middle of the screens as I could get. First bullet on each five shot group was the slowest of the bunch. I might could go back and drop them out of the works and number could be even closer.

On the 175's if I also add the 35 fps to the muzzle speed I am 2 fps away from my 100 yd speeds that I know were good.

At 100 and 175 yds Chrony was against the targets so you could get no closer at knowing the speed at the target. Will this work every time? I ain't got a clue but it showed me right quick why I haven't been able to get any closer with a program and every thing read as it should.

Will it help anyone? I ain't got a clue but it sure made me feel better today and I don't feel like it was wasted time. Using the actual speeds I had recorded at 15 ft from Muzzle I was off as much as 50 fps at 100 but about half that 175. Made my come up clicks on the money at 175 yds.

One other thing I noticed was the SD's while bad at muzzle were single digits at 100 and not to bad at 175. I think this was because at 100 I got close to the target and centered the diamond and keep them tight. At 175 it didn't work out as well and I shot higher and just trying to hit in middle of things and not my chrony.

Anyway just wanted to share hope it helps someone out!

 

[Fuzzball]

Re: confusing chronograph results

"what is confusing me is the differance of almost 100 fps in all of the loads, i understand larger strings would give better results, but im still baffeled in the large variances"

John, first, larger strings would improve the statistcal accuracy of the averages but it would do nothing for the ES.

You didn't say how far your Chrony is from the muzzle and blast can make for some squirelly readings. I prefer a distance of 15 ft. from the start screen.

Many people think the magic to obtaining low SD/ES is measuring powder with a consistancy of +/-.0000001 gr.. That's not so.

Much more important than any such dead-on charge accuracy is the consistancy of case internal volumes, bullet tension (real tension, not the commonly misintrepted neck-to-bullet diameter difference), primer consistancy and working inside the optimum pressure range. Any or a combo of these out of whack can easily make 100 fps or more difference.

 

[Victor N TN]

Re: confusing chronograph results

Depending on weather conditions, could the muzzle blast being throwing the screens off? I know sometimes my Pact catches shots from the next bench over and I haven't fired a shot.

Just a thought.