Range Report cronograph issues

[htorano]

So I got my CED Millenium 2, and headed out to the range with 5 different types of ammo. I set it up, about 10 ft from where I was shooting, and chronographed my rifle with the different ammo. Everything seemed consistent, until I got home and actually pue some thinking into it. I have an AIAE, 20" barrel. The readings that I got were between 2350-2410 depending on the ammo (everything was 168 and 175 grain). At the range, I didnt notice how low these readings were. I ran them through the software, regardless, and the dopes that I got are way off compared to what Im actually shooting.
Shouldnt my rifle be doing something closer to 2600fps? Any ideas as to what I might've done wrong?

 

[ChadTRG42]

Re: cronograph issues

I normally set my CED M2 out 4-5 yards, or as far as the cables will let me. Were you using the IR screens, or the standard sky screens?

 

[Fred_C_Dobbs]

Re: cronograph issues

Hanks, do I understand you to say you've been using dope for 2600 fps and it's matched your range data?

 

[Grump]

Re: cronograph issues

I would expect a 20-inch barrel to be about 2500 fps, maybe up to 2550.

The M14s with 173s ran the equivalent of 2580 or so at the muzzle/10 feet or so, 2550 at 26 yards.

My accuracy dropped of a bit when I went to 2630 at 10 feet with 175s.

Trust your dope over an electronic device that can fail...as long as your scope clicks and range numbers are BOTH correct!

 

[htorano]

Re: cronograph issues

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ChadTRG42</div><div class="ubbcode-body">I normally set my CED M2 out 4-5 yards, or as far as the cables will let me. Were you using the IR screens, or the standard sky screens? </div></div>

Ive been using the standard sky screens

 

[htorano]

Re: cronograph issues

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Fred_C_Dobbs</div><div class="ubbcode-body">Hanks, do I understand you to say you've been using dope for 2600 fps and it's matched your range data? </div></div>

If I use the dope at 2600 fps, I might have to adjust 1 click (1/10 mil) the most. Usually, point of impact is slightly above point of aim

 

[htorano]

Re: cronograph issues

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Grump</div><div class="ubbcode-body">I would expect a 20-inch barrel to be about 2500 fps, maybe up to 2550.

The M14s with 173s ran the equivalent of 2580 or so at the muzzle/10 feet or so, 2550 at 26 yards.

My accuracy dropped of a bit when I went to 2630 at 10 feet with 175s.

Trust your dope over an electronic device that can fail...as long as your scope clicks and range numbers are BOTH correct! </div></div>

I agree. But, Id like to be able to switch ammo, dial in the dope, and be reasonable close to my point of aim. When I used the dope for 2400fps, I was WAY off. On paper, but not acceptable....

 

[bubbapug1]

Re: cronograph issues

what were the loads, i.e. powder grains, caliber, etc.

 

[htorano]

Re: cronograph issues

/everything was .308

Lake City 175 gr
FGMM 168gr
FGMM 175gr
Black Hills 168gr
Black Hills 175gr

I must note that while the readings were useless, it was the FGMM 168gr that gave me the most consistent readings. I fired 10 rds, and everything was within 7fps

 

[Buford Boone]

Re: cronograph issues

Chronograph numbers don't sound right? First thing to check is the spacing of your screens.

I believe that system operates on a 2' spacing. I believe it also has a mounting bracket that folds. If you are using it on a tripod, the arms can overextend, thereby giving you more than 24" of spacing. If the machine thinks the bullet traveled 24" but it actually traveled 24 1/8", your readings will be low.

You can easily measure it but you must pick the same spot on each screen. I normally use the leading edge of the window.

If that is the issue, just brace it up so that the spacing is as close to correct as possible then shoot away.

Good luck.

 

[Ol' RD]

Re: cronograph issues

No Hanks, I agree with grump on this your going to loose about 25-35fps per inch of tube. So, 2500 fps sounds about right.

 

[htorano]

Re: cronograph issues

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Robot Doc</div><div class="ubbcode-body">No Hanks, I agree with grump on this your going to loose about 25-35fps per inch of tube. So, 2500 fps sounds about right. </div></div>

Ok, but, my readings were still just under 2400fps. I would also agree that somewhere in the low 2500's sounds more reasonable

 

[Timo Turl]

Re: cronograph issues

Sounds about right to slightly slow. I am getting 2,560 from 175 SMK with my 24" AIAE with the chrono at 20ft. Presuming you shot a decent number of rounds through and ensured that the infra-red monitors are firmly pushed in and locked then it is probably giving you an accurate reading (i'm assuming you had no error messages on the day). It might also be affected by temperature but I'm guessing Puerto Rico is fairly warm.

 

[CTone03]

Re: cronograph issues

My 20" gas gun averages 2,662 fps with the 168 FGMM using a CE chrono at 10', and 2,552 with 175 gr. FGMM using the CED M2 at 15'. I found the M2 sometimes gets two readings from one shot when I put it at 10'. So far it's been good to go at 15'.

 

[gau17]

Re: cronograph issues

This happened to me a couple of weeks ago. Next time you go out make sure your sensors are pushed in all the way. To prevent this from happening again I placed an outline on the bar so I know that sensors are in the correct position. Increasing the distance between the sensors will give you incorrect FPS readings. I was getting approx 200 FPS slower on all of my shots.