predicting reload velocity

[JimmyHoffa]

How close are you guys with the velocity you think you're loading for and what the chrono actually spits out?
Reading the powder can/reload manuals/mfg websites, I thought I would be pretty close to published velocities.  But the chrono was either surprisingly low or high.  The loads were pretty consistent amongst themselves.
One example was 30-06 I was hoping to get around 2600 fps, but everything read about 2250 fps.  (the dang .30-30 can do that) So next batch gets a few more grains.  The other example was .338-378.  Expected to get about 2850, chrono is saying 3050.  And the charge was less than max published which had even lower velocity. 
Just kind of curious how closely your results match your predictions.

[jasnt]

What barrel lengths.  I normally get pretty close.   Books never right cause I've never had a rifle even close to books seating depth

[JimmyHoffa]

22-26"  Same barrel/twist and in a few cases same model.  pretty much same atmospherics as book. 
Within a 100 fps, I could've made up some reasonable excuse to convince myself.  Chrono was about 12 feet out, so nothing goofy there.  Made that mistake long ago....

[jasnt]

Which chrono?  I have a digital pro that every once in a while gets just the right light conditions and throws crazy speeds. Last week end for example it said my 243 was shooting a 95 vld at 5016fps. 4996, then it snapped out of it going back to 3100

[2labs]

Which chrono?  I have a digital pro that every once in a while gets just the right light conditions and throws crazy speeds. Last week end for example it said my 243 was shooting a 95 vld at 5016fps. 4996, then it snapped out of it going back to 3100

Those probably even sound different 

[Stein]

The moderately priced chonos are all wildly inaccurate.  Shot the loads out to distance and use calculators with known bc to calculate actual velocities.  Most of mine were a couple hundred off.

[headshot5]

The moderately priced chonos are all wildly inaccurate.  Shot the loads out to distance and use calculators with known bc to calculate actual velocities.  Most of mine were a couple hundred off.

With how wildly inaccurate ballistic coefficient values are (provided by bullet manufacturers) on most bullets it is hard to say it is just the chrono.   

[Bob33]

If you're that far off with multiple loads from multiple books it's probably the chrono. Test a known good factory load. Some barrels do shoot slower but not 400 fps

[theleo]

22-26"  Same barrel/twist and in a few cases same model.  pretty much same atmospherics as book. 
Within a 100 fps, I could've made up some reasonable excuse to convince myself.  Chrono was about 12 feet out, so nothing goofy there.  Made that mistake long ago....

Powders matter with barrel lengths. If your trying for a heavy bullet using a magnum powder in your 06 with a 22 inch barrel you lose more velocity per inch of missing barrel compared to what the factory used (probably 24" for the 06). Add in that they probably have tighter chamber dimensions on their test barrel than your factory rifle.

As for the Weatherby, I'd be checking for pressure signs. It's odd to me for it to be that much higher. If the published data is with a 24" tube I'd say 100 fps increase over published makes sense.

[high country]

The moderately priced chonos are all wildly inaccurate.  Shot the loads out to distance and use calculators with known bc to calculate actual velocities.  Most of mine were a couple hundred off.

Winner.

The reason we chrono loads is for accuracy. When we field validate the load, we don't NEED the bc or the velocity as we now have actual dope to work with. A bc or velocity can be calculated from the results.....and your confidence will be higher.

They're nice for load development, but at the end of the day 200 fps won't make any difference unless you need a vectronix range finder.

[Bob33]

They're nice for load development, but at the end of the day 200 fps won't make any difference unless you need a vectronix range finder.

At 400 yards the difference between 2600 fps and 2400 fps (with a 3" high zero at 100 yds) is about 8 inches. I'd be concerned about that.

[birddogdad]

so if you don't have a high end chrono, the  cheapest way is to reverse the math with a distance and drop calc... math never lies!

[JimmyHoffa]

22-26"  Same barrel/twist and in a few cases same model.  pretty much same atmospherics as book. 
Within a 100 fps, I could've made up some reasonable excuse to convince myself.  Chrono was about 12 feet out, so nothing goofy there.  Made that mistake long ago....

Powders matter with barrel lengths. If your trying for a heavy bullet using a magnum powder in your 06 with a 22 inch barrel you lose more velocity per inch of missing barrel compared to what the factory used (probably 24" for the 06). Add in that they probably have tighter chamber dimensions on their test barrel than your factory rifle.

As for the Weatherby, I'd be checking for pressure signs. It's odd to me for it to be that much higher. If the published data is with a 24" tube I'd say 100 fps increase over published makes sense.

No pressure signs at all.  26" (but that shouldn't be more than 20+ fps)  When I saw the chrono spit out 3096, I was thinking 'uh,oh...hope I can lift the bolt!'  It came up with ease.  Calibrate the scale every batch to eliminate that uncertainty.

[Stein]

The moderately priced chonos are all wildly inaccurate.  Shot the loads out to distance and use calculators with known bc to calculate actual velocities.  Most of mine were a couple hundred off.

With how wildly inaccurate ballistic coefficient values are (provided by bullet manufacturers) on most bullets it is hard to say it is just the chrono.

Look up the G7 values or buy the book, they are incredibly accurate.  Don't go by the manufacturer.  Even with their numbers, you can reverse calculate the velocity way more accurately than a chrono.

There is absolutely no substitute for taking your final load and shooting it from 50 yards to however far you can and base the drop charts off of that. Everything else is guessing.

[headshot5]

Look up the G7 values or buy the book, they are incredibly accurate.  Don't go by the manufacturer.  Even with their numbers, you can reverse calculate the velocity way more accurately than a chrono.

There is absolutely no substitute for taking your final load and shooting it from 50 yards to however far you can and base the drop charts off of that. Everything else is guessing.

LOL,

I was just pointing out that there are more factors than just the chrono.  I don't get too worked up over velocity, I go for accuracy and build all my drop charts based on shooting those distances   The way this thread makes it sound, chronographs are the most worthless thing since the snuggie.