Measuring muzzle velocity precisely

4runnerman said: I see what you are pursuing for sure ,but I don't think it matters to much. If you are carefully doing your hands loads you MV should not change more than 10 FPS between shots any how.
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You are right on the money. My reloads have shown an SD as low as 3 and as high as 8. I'm quite pleased with them, considering that most writers consider a SD of 10 good.

Geo_Erudite that is very good information to have, and I will follow up on it.

My thanks to all who have responded, something new is gained by all of us when we share or experience, knowledge and insight.

Kindest regards to all
 
Set up the chronograph at 7 yards. Shoot, record, average.
Set your ballistic calculator to 7 yard intervals. See how many fps are lost in those first 7 yards. Add that to the muzzle velocity.
Adjust muzzle velocity as necessary to get the program 7 yard velocity to match the chronograph reading at 7 yards.
 
At 15 feet I don't think you lose even 5 fps.
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Depends on the cartridge and bullet. At 15 feet BC is actually a factor as it will make a difference in velocity, especially in a fast cartridge with mediocre BC's like .204 ruger.

In .204 ruger with a 40 grain bullet you roughly lose 38FPS at 5 yards. This would pretty much be a worst case scenario. So you're likely not going to see a difference over 40fps. Besides, that's within margin of error. Velocity could change more than that if you hold the rifle differently, or if a cartridge sits in a hot chamber, and that's even within the normal velocity spread of some factory ammo.

At such a close range, you could probably estimate velocity directly at the muzzle, by using readings at 5 yards, and then plugging in the numbers in a ballistic calculator. By working backwards, plug in the data you know, BC, MV at 5 yards. Plugin your 5 yard MV and gradually add velocity until the velocity at 5 yards matches your chrono number, it should be very close to the actual number.
 
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At such a close range, you could probably estimate velocity directly at the muzzle, by using readings at 5 yards, and then plugging in the numbers in a ballistic calculator. By working backwards, plug in the data you know, BC, MV at 5 yards. Plugin your 5 yard MV and gradually add velocity until the velocity at 5 yards matches your chrono number, it should be very close to the actual number.
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This works if you know the BC of the bullet in question.

If not you'll need to get bullet drop along with velocity data from multiple ranges to use the same "plug and pray" process for estimating a BC using a ballistics calculator. Basically you use data points to define a curve, then play with the BC variable until you find one that fits the curve.

Then once you have your BC (or a close enough approximation) you can use the above method to calculate the exact muzzle velocity.

Jimro
 
Much ado about not much. Rounds of factory ammo in a box can vary more than 15 fps +/-, and it is about impossible to get even the most careful handloads much under that variance. Chasing a goal of having every round leave the muzzle at exactly 2600 fps is a fine, clean, hobby, but so is putting that salt on a bird's tail. Good luck!

Jim
 
I'll further muddy the velocity waters by stating that the same rifle and ammo combination can easily have near 100 fps difference in average muzzle velocity across several people shooting it. Bullets shot from the prone position typically leave faster than when shot from standing.

And if the barreled action shooting that ammo was clamped in a fixed mount (like SAAMI tests are), the average muzzle velocity attained in that environment will be faster than that of when people held the rifle. Plus, the standard deviation and spread will be lower, too.
 
Much ado about not much. Rounds of factory ammo in a box can vary more than 15 fps +/-, and it is about impossible to get even the most careful handloads much under that variance. Chasing a goal of having every round leave the muzzle at exactly 2600 fps is a fine, clean, hobby, but so is putting that salt on a bird's tail. Good luck!
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Amen...
I'll worry more about things like neck tension before minutiae like this that are beyond our ability to control. I'd bet you could put absolutely identical powder loads into identical cases with identical bullets and still get a velocity spread just based on how the powder ends up lying the case at time of ignition.

JMO, but learning wind calls is my priority. My time is better spent sending "reasonably" precise loads 1K yards downrange rather then spending days on end in front the Crony.
 
James K- My handloads are always with in 10 FPS. Maybe onece in a while I will have a crazy one,but 90% plus of the time I am in that 10FPS or less. My 308 for example- 175 gn Serria, 43.2 gn RL-15 and a GM Match primer, All rounds leave at 2640 to 2648 FPS. As for store ammo-Could'nt say, Never shot one yet.
And yes- I use my Chrony every time I shoot. Put the same distance away every time. I use a string attached to my Front Rest and to the Chrony too ensure I get same distance always. That is 15 feet away. My front rest and rear rest are also set by a string between them. Now unless my Chrony is bad ( pro chrony) I have to believe what it tells me.

Sorry, but I have to disagree with yor post.

Oops- Correction- Thats a 168 Serria.
 
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43.2 gn RL-15 and a GM Match primer, All rounds leave at 2640 to 2648 FPS.
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So 43.2 gr of Reloder 15, gives you precisely the same mv all the time, regardless of temperature?

I tried it in 54R and .308 loads, and went back to Varget due to what I perceived was temp sensitivity, and found a lot of other similar findings online...
 
tobnpr- Yes it does. I get to range in morning at 5 AM,maybe low 50's and leave around 1 or 1:30 Could be as hot as 85 by then. My MV stays the same. I shoot 5 rounds,Clean Barrel, have a sip of pop,pick up brass,text the wife,chat, and then shoot 5 more. MV stays the same. I tried Varget in 308 and went right back to RL-15. I also try to stay with RL-15 in my 6mmbr for matches also. As of latley it has been very hard to find. I will switch to varget in the BR if I have to,but the 308 is RL-15 only.
RL-15 is not temp sensative.
Will my MV change at -30, Yes I am sre it would somewhat, Maybe I should re-word my phrase to- At any given temp,my loads will be with in 10FPS of each other, and not list the MV. I just know in summer ( when I shoot ) It is 2640 to 2648 FPS. My point was-To get loads with in 10 FPS is the norm.
 
James K said: Much ado about not much. Rounds of factory ammo in a box can vary more than 15 fps +/-, and it is about impossible to get even the most careful handloads much under that variance.
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James, here's two of my chrono reports. The first one 2 sets Federal Gold Medal Match and a string of ten shots loaded with a Harrel volumetric powder measure.

T= spread from high to low M= median S= standard deviation

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This second one a few days later show three groups loaded with a RCBS ChargeMaster that individually measures each load. I was also testing different neck tension. As you can see in two out the three groups the T= spread from high to low is less than 15fpts. So, it is not only possible but it is doable.

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"doesn't it make sense to get the most accurate MV possible for a little bit incremental effort?"

You could always invest in a doppler microwave radar unit.

Probably only cost you a couple of million.
 
Mike- It's not a effort to get it. I used a digital scale and make sure all loads weight the same. Not much effort there. Cases are weighted to with in 3 gns-Again no effort.

Most in here have been loading a considerable time longer than me. In my 3 plus years of loading I have learned Accuracy demands Consistency. I don't hunt, I target shoot, so Accuracy is my goal. 25.5 gns is not 25.4 nor 25.6 . Does it take longer to be so picky- Yes it does- Do I care-No.
I am really thinking now of putting one of my other Chronys out at 200 or 300 yards to see what I am getting compared to what I should be getting.
 
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One thing that really helps muzzle velocity to be consistant is how the primers are seated. If they're not deep enough to compress the priming pellet between cup and anvil, they'll not detonate the same for every firing pin impact.

Another is denting them enough with the firing pin with a strong enough firing pin to do it right. Replace firing pin springs every couple years. Ensure the pin tip sticks out of the bolt face at least .060" but no more than .065".
 
Bart-- Funny you should say that, about pin protrusion. I read a article about a lot of Bench Shooters now that are going the opposite direction. I replaced my spring last year. Spent some time doing some research on it. I now have my firing pin back off to 35 thousands and seem to be in a better world. Have you heard anything at all about it?.
 
Accuracy does demand consistency, but it rarely demands absolute, slavish repeatability in weights.

The most accurate load I ever put together in my .243, a true quarter inch load if I did everything right at the trigger, had a swing of nearly a grain in powder weight - half grain low to half grain high.

The big secret, I found, was tapping the ammo box, case head down, gently on the table for about a minute before shooting.

That compacted the powder to the same degree in the case.

I never sorted my brass by weight, I never sorted my bullets by weight. I did all of the standard prep actions, but didn't go out of my way to micro-debur the case mouth or anything like that.
 
Thanks for the tip Mike. I will have to try the tapping thing once or twice and see what hapens. I am always open to new Ideas.
 
I should have noted that I was using IMR-4064, a long stick powder, and a charge that filled about 85% of the case. It was a load that was near the bottom of the power spectrum, but it was a tack driver.

It wasn't necessary with loads that were near 100% capacity or which were slightly compressed. Those types of loads benefit from being loaded with a drop tube to get the most consistent loading density.

With the load I was using, tapping the box on the bench reoriented the powder and compacted it uniformly.

With a short cut stick powder, or with a ball powder like one of Winchester's, those powders tend to reorient and compact naturally and easily.
 
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