variances in chrono's

[xdrocker]

What are some your experiences with different chrono's. While doing load work picking a starting pont is pretty tough for me. If I use the starting load I am way over major with most loads. Prime example, .40, WW website says 10.5 gr of longshot under 135 gr HP @1.125 = 1367 fps. I loaded 8.6 @ 1.160 and got 1320, 8.9 got me 189 PF and I'm still 1.6 grains under their STARTING load. I e-mail Winchester and they assured me their data was correct. Same with my limited 180 and 200 loads but not as extreme. So my question is; Is the chrony industry pretty tight or due they vary from brand to brand as far as accuracy goes?

[Lee Bell]

What are some your experiences with different chrono's. While doing load work picking a starting pont is pretty tough for me. If I use the starting load I am way over major with most loads. Prime example, .40, WW website says 10.5 gr of longshot under 135 gr HP @1.125 = 1367 fps. I loaded 8.6 @ 1.160 and got 1320, 8.9 got me 189 PF and I'm still 1.6 grains under their STARTING load. I e-mail Winchester and they assured me their data was correct. Same with my limited 180 and 200 loads but not as extreme. So my question is; Is the chrony industry pretty tight or due they vary from brand to brand as far as accuracy goes?

Frankly, I don't have a clue. I take my Digital Pro Chrono's word for what my rounds are doing. So far, I've not run into a problem, but I really have no easy way to check. Perhaps you, and I, should find someone else with a chrono and compare results. If you were to get anal about it, you could even line the chronos up to get a comparison of the same shot, then reverse them and average the variance.

I'm going to look for a chance to do this. If you beat me to it, let us know how it turns out.

Lee

[Mr Glack]

Have a similar thread going on chrono variability for revolvers shooting .45. The chrono pros will hopefully chime in. They commonly use two chronos (in line) to account for the equipment part of variability (chrono equipment that is). I understand there's not much difference there actually.

The table data is for a certain type of gun and/or barrel. Often it is a bench test standard barrel that allows them to test CUP pressure as well. Even if it's the same gun model it won't necessarily match the tables exactly. On the other thread we have the extreme example of 1911 .45 ACP ammo being used in a revolver. Can't expect the same results. Predicting the difference is also hairy. You must test.

You also want to get in the habit of testing something like 10 rounds for a load to get an average and I also evaluate the standard deviation to get an idea of the variability of performance. Even if your powder is very accurately measured there will be differences. In particular the arrangement of the powder in the case cavity (remaining space when bullet is seated). A .45 or .38 load for example will have a lot of empty space for the powder to rattle around in while a 9mm often is just the opposite. In my experience my 9mm loads typically are below 1% standard deviation (reflected as a percentage of the average velocity) while .45 or .38 loads are going to be well above.

In the other revolver thread for example. This results in a 95% confidence limit for one load example ranging from 713 to 763 fps.

So it's not necessarily the chrono's variability. The only real test is what the chrono pros do with two chronos measuring the same shot. I'm anxious to hear their thoughts.

[LPatterson]

xdrocker,

With velocities that much higher I would suspect the chrono. Find a friend that with another chrono and compare. My Chrony was about 200fps faster than the CED I bought to replace it after the deliberate homicide.

[moose]

hi

I hope my method can be of some help

my 2 cents

i tried to eliminate errors in chrono reading by placing a Chrony

in between the screens of a Pact mkiv.

When firing 1 shot i get 2 readings. Very similar readings, sometimes

only 0.5fps difference between the Pact and the Chrony.

[RogerT]

How do you evaluate the different readings when you set up two chronos in line?

Set up a third chrono in line and choose the value that is most similar?

[vonfatman]

I have found that if I aim high between the sticks on my Chrony, I can get errors...for example,

yesterday I was shooting a .44 Mag load that I knew was supposed to be coming out of the tube at roughly 1,000fps.

To save time, I set my Chrony up a bit low, thus I was shooting/aiming between the top of the sticks. My Model 29-5 six inch

was putting out slugs measured in the 1,200-1,250 fps range. Weird huh? I shot 20 rounds this way and found the Chrony to be consitantly in the 1,200 fps range. Then I switched to a 7.5" Ruger SBH and saw the darn readings drop into the expected 1,000fps range??? As I looked back later, I realized that when I was firing the Ruger I was holding a different point of aim. This was confusing me! Heck, I'm a little slow anyway!

So, elected to try what I thought might be an easy solution...I changed the 9volt battery and put in a fresh one. However, I had the same type readings, when I shot the Model 29-5 I got roughtly 1,200fps.

I then thought I'd set the Chrony up higher to get the slug closer to the Chrony's "eyes"...about 4" above the unit.

My readings with the Model 29-5 went right into the 1,000 fps range and stayed there. The Ruger's velocity was just a bit higher as was

to be expected with an additional 1.5" of barrel.

So, I think the point of aim over the eyes of my Chrony needs to be consistant (as has already been suggested) AND in the case of my unit, I need to keep the bullet flying closer to the electronic eye...about 4" worked in yesterday's situation.

I also had trouble getting a reading with a .22 rifle and .177 air rifle yesterday...again, I did my shooting towards the top of the sticks. As a matter of fact, I did not get any reading with the pellet gun until I lowered my point of aim.

Good luck.

Bob

Edited June 10, 2007 by vonfatman

[Joe4d]

You didnt mentioned your barrel,, most published .40 data is in a 4" standard barrel, as opposed to a 5 or 6' match grade. For what it's worth in a Limited gun using a powder as slow as Longshot isnt the way to go unless you enjoy extra recoil and muzzel flash.

[Lee]

I'm with moose on this one. Same procedure and results. So I gave the Crony away. Anytime I've gotten results way out of the expected range it turned out to be a lighting problem.

[shred]

Improper setup, Lighting and muzzle-blast from shooting too-close are the main sources of chrono error in my experience. If you shoot across them at an angle (up/down, left/right or some combination thereof), you'll also cause some error, but not as much.

Even the in-line same-brand chronos in a lighted box at major matches often differ by 10+ FPS, so don't believe everything up to and after the decimal point is perfectly accurate..

[Lee]

Thanks shred. Muzzle blast is a big problem. I never shoot closer than 15ft and don't have a problem.

[soaringf22]

thread revival.

i shot my chrony f1 and oehler yesterday to compare the two. Very sunny and about 65 +/- degrees. with my two guns shooting the same two different loads i consistantly got a reading of 30 fps higher in the chrony f1. my logic says to listen to the lower of the 2 readings because i dont want to under estimate a load that po.tentially go minor or even sub minor. not to mention the oehler was giving me the lower reading which is also the machine people seem to think is 100%.

anyone have similar situations?

if g-man is reading i think itll put a smile on his face to prove why you always go for +10 on pf.

[bbbean]

thread revival.

i shot my chrony f1 and oehler yesterday to compare the two. Very sunny and about 65 +/- degrees. with my two guns shooting the same two different loads i consistantly got a reading of 30 fps higher in the chrony f1. my logic says to listen to the lower of the 2 readings because i dont want to under estimate a load that po.tentially go minor or even sub minor. not to mention the oehler was giving me the lower reading which is also the machine people seem to think is 100%.

anyone have similar situations?

if g-man is reading i think itll put a smile on his face to prove why you always go for +10 on pf.

At BitB, he was only 9.8 over. Cuttin' it kind of close...

[medalguy]

I wondered about the accuracy of my chrono also so I got a second unit and placed it right behind the first one and fired several strings. I found about 3% variance constant. I also have found errors seem to be more common when firing at the top of the sticks. I believe the instructions say to shoot in the middle and that seems to work better. When all else fails....