Chronograph question

[Starado67]

Hello everyone! I am puzzled! I bought a magnetospeed c3 chrono and did a ladder test using IMR4451. Ten 5 shot loads to a max of 41.3 in .2 increments! The load book says I should be getting 2600fps+ and the most I got out of the max load was 2250fps!

 

[SeabeeKen]

I'll consult my crystal ball for more details about cartridge, rifle, twist rate, etc, but in the meantime, how many data sources did you consult and did they agree?

 

[RegionRat]

I will add bbl length and action type to Ken's comments too, but it does sound like a really big difference to account for....

 

[SSL]

Load books "say" a lot of things. They also are only a snapshot of a load using specific brass, bullet manufacturer and style, powder lot, primer, barrel length and etc. as used in their test piece. I've run across data that was much lower than listed and others that were far higher than my results. The same goes for pressure values. Assuming the chrono is working correctly, I would bet on it before I would take loadbook velocities, even if they are that far apart. As @SeabeeKen said, we need a lot more data from you.

 

[Starado67]

Oops sorry guys! RPR 6.5 cm. 1:8 rh twist, 24” bbl, using Hornady 140gn ELDM

 

[RegionRat]

Yup, something isn't right and it would be time to double check everything.

Was it possible that you shot any similar factory ammo and timed it just for reference? This would help divide the problem between the new measurement system, versus the ammo.

The Magnetospeed is fairly straightforward and should be difficult to goof up, but if it is brand new and new to you, then having something other than your ladder test rounds might help sort out if the results are some problem with your chrono versus the loads.

If we don't find a problem with the chrono, and it really is the ammo, then you will want to double check your weight calibration for a first order error.

 

[SSL]

Yeah...that looks wrong. I understand there are sensitivity settings on the Magnetospeed. Possible setting is wrong? Just throwing spitballs here. Don't have a Magnetospeed, but I agree that that much difference is odd.

 

[Starado67]

As a matter of fact I shot some that was loaded with H4350 and they performed within expectations

 

[RegionRat]

How do you charge powder?
Sure you were calibrated?
Anything left from those samples to disassemble and check?

It is easy to be off by 50 fps, or even in some instances up to 100 fps when lots of things combine the wrong way, but things are off by roughly 400 fps so we should be able to find an error that large.

 

[std7mag]

My thought is you shot "10, 5 shot loads".

So 50 rounds, and you didn't think something wasn't right after 3-5 rounds??

 

[wkdickinson]

My experience, the MagnetoSpeed V3 is almost idiot proof. I think you need to be looking somewhere else for your problem.