why are my speeds so far off?

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Mikeyman

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So I was out today with my 23inch barrel rossi 243 1-10" twist single shot.

I worked up to 44gr of RL22 behind hornady 100gr btsp. The hornady book shows this travelling at about 2950 fps.

My chrony showed it at 2650 plus or minus consistently. Is my chrony fubar?

The hornady data was developed with a 24in barrel also with 1-10 twist. Would one inch difference make much difference? :confused:
 
Nope, but your barrel tolerances might, as could your:
seating depth
crimp
air temperature
powder lot
chrony accuracy
chrony set up (you could actually check this - how far away is the unit from the muzzle?)
and a bunch of other variables.

I wouldn't worry about it - figure out how to use your chrony to get an accurate and safe load and don't worry about squeezing out the last fps.
 
Mikeyman said:
So I was out today with my 23inch barrel rossi 243 1-10" twist single shot.

I worked up to 44gr of RL22 behind hornady 100gr btsp. The hornady book shows this travelling at about 2950 fps.

My chrony showed it at 2650 plus or minus consistently. Is my chrony fubar?

The hornady data was developed with a 24in barrel also with 1-10 twist. Would one inch difference make much difference? :confused:
Click to expand...

Welcome to the dream world of newer American reloading manuals. To avoid law suits they have kept the pressures down, but to make shooters feel happy, they put unrealistic velocity figures in.
Your chrono will be correct.
 
I agree, in the past as well there were always hidden reasons for upping the published velocities, whether it was to sell that companies bullets, powders, rifles, calibers, etc. Look at Weatherby stats. for both factory and reloads, all overly optimistic, to sell rifles. Hogdon data showing other makes of powder always showed higher vel. with Hogdon powders, until they bought the other powder company. Folks have to get used to the fact that most of the published stuff about powders, bullets, performance on game, etc. is B.S. in an attempt to sell products. Even the magazines are bought off by the companies or sponsored or at least thrown a bone...
This even goes back to the 1940s when Ackley published loads and velocities that were way to optimistic, just to sell his wildcats/gunsmithing bus.
 
Just firearm to firearm can make a difference, as mentioned, chamber dimensions, barrel dimensions, how smooth the barrel is and god knows how many small issues.

I have fired identical 375H&H rounds out of two different rifles, same day, same ammo, same chrony etc, and one has consistently chronied almost 100fps faster, we tried 2 or 3 different loads, and with each load the one rifle was consistently faster.
 
It's not unusual for a shooter finds his rifle to come in a couple hundred "under the book". About the time he proclaims to the world the manuals are full of crap and writes three magazine articles about it, someone with a minimum chambered match barrel will come along and get 200 over the book with the same load.

These two guys aren't going to get along.;)
 
Thanks for the input guys, it's my first time playing with the chrony so I am sure there is a learning curve.

I had the chrony on a tripod about 15 feet from the end of the muzzle. Should it be closer?

I know too close and the gas from the muzzle will throw it off and much farther and I would have a hard time reading the readout.

The bullets were seated to the published COL - and I will have to double check the die but I am pretty sure it wasn't crimped just a seater die - RCBS
 
Most bullet seaters crimp as well if set up properly, the exception is some in-line seaters don't have the crimp function.
 
I have found some rifles actually produce more velocity than listed in the book for a given load. Two of my Cooper rifles produce book velocities with less than book powder charges.
 
All that being said, how were the groups? ;)

Always nice to see your buddies whizz banger miss the pop cans you set out at 3 or 400 meters and your slow poke SA get em every time.

Lots of different factors that determine velocity, forget the numbers and worry about accuracy.
 
Unfortunately was a disappointing range trip because my new scope was FUBAR after zero'd. The POI was all over the place without any adjustment to the scope. Atleast I could check velocity though.
 
Well hopefully you have some speeds with little deviation, then you at the very least have a good starting point.


Mikeyman said:
Unfortunately was a disappointing range trip because my new scope was FUBAR after zero'd. The POI was all over the place without any adjustment to the scope. Atleast I could check velocity though.
Click to expand...
 
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