Measuring fps

[Jeremiah P]

Wondering the correct way to measure fps when trying out loads. It seems with a cold barrel the speed is slower than that of a warmed up barrel, after first shoot the fps range stays within 10 fps. Also what chronos are you guys using?

[Huntbear]

Always shoot out of a cold barrel.  That is how you hunt, right?  I always wait at least 5-10 min. between shots, with the barrel pointed up slightly to help heat leave like a chimney.
I take a book or something to pass the time.

Chrony's do not vary much, but like all electronics, you get what you pay for.

[JoshT]

Chrony's do not vary much, but like all electronics, you get what you pay for.

I personally saw a test once where we took three of the exact same chronographs (Chrony Beta)... and set them up back to back so the round would go through all three right in a row. The velocities should have been very close... but there was as much as 100 fps difference between them. Sometimes the middle chrony was the fastest... sometimes the last one was the fastest. We rotated them around and got the same thing. My point is... there is no way to calibrate a chrony... and setting one up prefectly is nearly impossible.

Also, if the bullet does not travel through the lightscreens absolutely perpendicular to the screens and parallel to the bottom... then your readings will be eroneous. I use a Beta Chrony all the time... but I also take the results with a grain of salt. If you're looking for velocity to use for figuring a drop chart... you'll need to shoot the chart anyway... so an estimated velocity is a fine place to start.

[Antlershed]

Josh, we are trying to get as close as we can to 3250 fps cause we ordered turrets based on a velocity and bc and the original bullets didn't shoot worth a damn so now we are trying to match it if we can.

[littlebuf]

im not sure i understand, why are you trying to reach 3250 fps ?

[jeepasaurusrex]

The BDC on the scope is calibrated for that load at that velocity.

[JackOfAllTrades]

Shootin Chrony. Cold barrel.

I load for accuracy first, then velocity.

How close are you getting to that 3250fps?  Think of it this way.. The BDC is calculated for that bullet weight/design at that velocity... Oh, but wait! What bullet and ballistic Coeficient?  Round nose? Boat tail soft point? HP Spitzer? Each will have a different trajectory even if they were all fired at the same initial muzzle velocity.  So, getting that magic number for fps isn't all that important unless you can duplicate exactly what the BDC is set for. If you can't duplicate it, then what you're looking to do is match the middle range impact point of the bullet to that same mid range aim point of the BDC. You might have to set the scope to have impact 1/2" high (or low), at that mid range to be able to use the BDC through its whole range.

The idea is to get you in the kill zone, not necessarily get you to the point of clover leaf groups at 100, 200, 400yds by using the BDC retical.

-Steve

[littlebuf]

The BDC on the scope is calibrated for that load at that velocity.

but what if that velocity shoots like crap out of that barrel? ive never worried about how fast my rounds are going just how accurate they are. i zero my scope accordingly and go with the best load. more than once its been the slower load

[Jamieb]

antlershed.
What cartridge, what bullet?

[JoshT]

They're shooting the .300 RUM... 180 Accubonds I believe.

Let me get this straight... you guys ordered BDC turrets based on unconfirmed drops? That's just asking for trouble... make sure you verify them before you go launching rounds at critters.

[Jamieb]

I had a similar issue with my RUM/scope. I bought a shepard P-1A, I needed to get the 200 gr. accubond up to 3100fps to match the scope. 2 years of playing with loads and 1400 shots latter and I've got that load dialed in with the 200 gr accubond going 3175fps, it matches the cross hairs in the scope perfectly out to 1000meters. I'll never do that *censored* again. Plain old 1/4" or MOA turrets all the way.

[littlebuf]

1400 shots later!!! well now that you got your load you need a new barrel cuz that ones gotta be shot out

[JoshT]

1400 shots later!!! well now that you got your load you need a new barrel cuz that ones gotta be shot out

Hell no he don't... I'd hate to be a critter anywhere inside 1/2 a mile from that gun... that's for frickin' sure!

[AWS]

Now all you need is a place to hunt that has wind flags all the way to a 1000yds.

AWS

[Jamieb]

That remmy tube has almost 3000 rounds through it and its still shooting pretty good. I was out busting rocks at distances from 300 to 1100 yards a few days ago. I bought the rifle as a donor for a custom, made the mistake of shooting it.