Printed velocities vs reality

[Michael54]

For you guys using chronos I'm wondering how accurate the stated velocities in the reloading manuals are vs reality with the different listed loads.

 

[Rob5589]

Most seem to be reasonably close. I use a Barnes load in my 7RM and attained the exact velocity that was printed. I was surprised by that one.

 

[Wrench]

I have several rifles with the same chambering, some even cut with the same reamer. I don't always see exact copies of velocity in them when sharing ammo.

Lot to lot ammo variation, barrel difference, chamber difference....altitude, pressure, temp.... it all plays a part.

My advice if you do not have a chrono is to take the printed velocity and use it as a baseline. Take the rifle to 3,6 and 900 and see what it tells you. If you do this, you can back feed your ballistic program and get a corrected velocity.

If you're vertically stringing at long range you'll know the spread is not good.

Guys often balk at this method due to ammo cost, but the only way to get good at range is to shoot accurate rifles at range.

 

[wind gypsy]

Can be accurate or wildly inaccurate.

Barrel variance (fast vs slow, bore diameter, etc), bore condition and break in status, chamber spec, temperature, lot to lot powder burn rate variance, brass case capacity variance (fireformed vs virgin, lot to lot variance, brand differences) all plays a part.

 

[rayporter]

it is much better than pre-chrono days!!!

one reason for the book listing varying it the use of a pressure barrel. they gotta use it!

 

[Rich M]

It is an approximate number. Better than nothing.

 

[cobb]

Don't compare my CED chrono to manuals as a rule, did a couple weeks ago and my readings was +40 fps verse the manual for same load.

 

[dla]

Most rifle velocities are for a 24" barrel. I only have one rifle with a 24" barrel, everything else is shorter. I use the printed velocity as a reference point (sanity check) when initially working up a load with my chronograph.

I bought a chronograph long ago and I can't imagine doing load workup without one.