Lead vs jacketed vs the chrono?

[steel1212]

At area 6 I chronoed my lead SWC load with 4.1 TG and came in at 801 FPS at A6 but the bullet was actual 204. When I was chronographing them they where in the 850s on 2 seperate occasions and one I put a no shoot over top the skyscreens. Now my buddy was using jacketed 180 precisions, actual weight was 181, at 917 at A6 but chronographed at 931 using my chronograph.

Now 12 fps diffrence isn't a whole lot but 50 fps is in my opinion. All the chronographing was done the same day the same ways. Any Ideas?

[steel1212]

I'm so confused it hurts. I chronoed my limited gun yesterday with 4.4 and 4.5 TG under 180 MG JHP at 1.180 OAL and was getting 900-930. I want about 950 or so. It was bright sun so I put a no shoot, white side down, over the chrono. Today I loaded up some 4.7 and went back. A little overcast but bright sun behind that. My 4.7 loads where coming in at 1030 WTF! I rechronoed the 4.4 and 4.5 and the 4.4 gave me a 174 PF avg.

Only thing diffrent between the 2 days is yesterday I had the chrono at 10 feet and a no shoot do to sun. Today I went to about 13-15 feet without a no shoot do to overcast skys.

Edited May 1, 2008 by steel1212

[LPatterson]

I am not a chrono expert and I did not stay in a Holiday Inn Express but it sounds like your chrono is very sensitive to light conditions. The bright sun and the white no shoot could have created a condition where the chrono was not seeing a distinct shadow. Years ago when I started people told me to put black magic marker on the Montana Gold bullets I used because the chrono didn't read as high with the gold colored bullet. I don't think increasing the distance from the muzzle to the chrono is going to increase velocity unless you were too close to start with, but my CED says 10 feet so 13-15 feet shouldn't be the problem.

The sun is the major factor and for me at certain times of the day can be shining down into the window of the chrono. To eliminate this I add a strip of duct tape to the front and back of each sun screen arm to lessen the amount of stray light. To further eliminate errors I take along a .22 with some target ammo that I have chronoed before and use it as a control check.

[HSMITH]

I have a Pact and my buddy has an Oehler, neither one of us have problems like that. If mine see's the bullet it is recorded and doesn't wander. The Oehler is infrared and it just plain works no matter what it seems like, it is extremely stable in readings too. What type of chrono are you using? Sounds like you might need to build a box......

[Catfish]

Something I noticed at Area 4 last year ....

They had two chronos set up, one behind the other (the screens, that is).

The screen that was closest to the gun (10ft) had me making pf at about 168-169. The screen that was farthest from the gun (11-12ft) did NOT have me making pf, at about 163-164.

So from that particular experience, I would say that distance to the screens will make a difference in the outcome.

Whenever I chrono now, I take as many variables out of the equation:

- shoot at 11-12ft instead of the 10 that's supposed to be standard.

- set up the chrono under an awning to take away any difference in sun/no sun

- record the temperature and then monitor during the year to see if the powder I'm shooting is consistent over the course of the year.

[lcs]

In bright sun (depending on the position of the sun) I have got "no reading" or "erratic readings" with shots fired. I then moved the angle of the chrono (in reference to the sun) and the shots started to register correctly. I have never covered the chrono with a target.

I have been chrono-ing for two years and always record temp, time, and sun conditions. I have chrono'd all kinds of bullets (and powders and varing temp conditions) and for two years my loads have been + or - 1PF at every major match. I also use all kinds of mixed brass.

You might try changing the angle in bright sun and try to test at the same distance most chrono stations do. In my experience, most of the chrono distances at matches seem to be less than the distance I use.

It may seem like a simple "fix", but it work'd for me and I don't have the most expensive chrono.

Hope this helps.

[steel1212]

Its a shooting chrony beta master.

I went out today and tried again and it was overcast, read getting ready to rain, and my 4.7 grains of TG 1.180, with 180 MG out of my limited gun came in where I thought it shoudl around 171 PF. I had the sky screens setup and it was as far back as that phone cord would let me be. My 200 LSWC out of my .45 still says 850. No matter what I do they alway say 850 except at A6 where it was 801.

If I end up building a box I'll go all out and get a CED M2 and build a box around it.

[BSeevers]

Chronys are usually consistant but high

[waynewal]

I am not a chrono expert and I did not stay in a Holiday Inn Express but it sounds like your chrono is very sensitive to light conditions. The bright sun and the white no shoot could have created a condition where the chrono was not seeing a distinct shadow. Years ago when I started people told me to put black magic marker on the Montana Gold bullets I used because the chrono didn't read as high with the gold colored bullet. I don't think increasing the distance from the muzzle to the chrono is going to increase velocity unless you were too close to start with, but my CED says 10 feet so 13-15 feet shouldn't be the problem.

The sun is the major factor and for me at certain times of the day can be shining down into the window of the chrono. To eliminate this I add a strip of duct tape to the front and back of each sun screen arm to lessen the amount of stray light. To further eliminate errors I take along a .22 with some target ammo that I have chronoed before and use it as a control check.

Wow, I knew there was knowledge in here somewhere! The duct tape sounds like a great idea to block the direct sun onto the senors! I will do that next time I go out. was having spurious problems with 2x the normal velocity readings with my Pact Mark 3. Was trying to build a cardboard shield, but this spounds better!

Thank you!

Wayne

[RiggerJJ]

I have to use shading for mine in direct sunlight, but putting a white tgt on the screens (white facing down so the pickups see white) was bad. I finally ended up with a cardboard (brown down) shade for the screens with a hole cut out for each sky screen. this works just as well as a cloudy day with even lighting.

I think the pickups need to see the bullet pass each of the sky screens...? but if you face a white down tgt on them it gets confused...

jj