Accuracy or low ES?

[J E Custom]

I used to do random testing for the best load/accuracy and found that it required many test loads at times.

So I decided to address one issue at a time, and it saved me many firings.

I look at SDs as one element and accuracy as another.

SDs are a measurement of volume used, (I prefer 98% to 100+% case density) powder choice, powder amount and primer used to create a consistent Pressure and velocity load (The better the combination the lower the SDs).

After Good SDs are found. (I also look for less than 10 ft/sec SDs and prefer 5 ft/sec SDs if I can get them) I start looking at the bullets (Brand ) and seating depths to improve accuracy.

With a good load (SDs) and a premium bullet it normally doesn't take long to get good accuracy at long distances.

Group size is normally effected by bullet barrel combinations. Vertical stringing is effected by SDs
And horizontal stringing is normally the bedding, trigger control OR THE SHOOTER.

This is just the way I approach accuracy development/Testing to save time, money and barrel life but also end up with the best accuracy that the rifle is capable of with me shooting it.

Just the way I do it.

J E CUSTOM

 

[KYpatriot]

Ridgerunner and dkhunter have said it best but my two cents is....you dont know much about the true accuracy or velocity of a load with a single 5 shot group. The difference in drop at the range you will be shooting represents your maximum accuracy potential and should be easy to determine, so if you are happy with it then load devlopment is done. I cant really imagine being happy with 100 fps ES for 1000 yard shooting though unless i was shooting at some large targets.

By the way shot dispersion is NOT linear. It varies with time of flight, not distance. A 1 inch group at 100 yards does not mean 10 inches at 1000 yards. Rather, you take the time of flight to 1000, divide it by the time of flight to 100, and myltiply that by the group size at 100.

For example lets say you are shooting a 308 winchester at 100 yards. Accuracy is consistent at .75 inches, time of flight is 0.115 sec. At 1000 yards in the same conditions, time of flight would be 1.713 sec. What would we expect the group size to be with this load at 1000? It would be (tof@1000 / tof@100) * group size at 100. In this case (1.713/0.115) * 0.75 = 11.17inches, not the 7.5 inches As commonly thought. From this we see that instead of group size increasing by a factor of ten like we would expect, it is closer to 14 for this load. Better bc and higher velocity can bring this down, but it will always be more than the ratio of the target ranges because it is the ratio of times of flight that really count.

 

[barefooter56]

BT,
Of the two measurements SD is the most important. On German Salazar's website is a great article on load testing and ES/SD for long range shooting by Jerry Engleman very good read and may clear more things up along with the previous posts. Also Bryan Litz has two books ACCURACY AND PRECISION FOR LONG RANGE SHOOTERS that goes into detail on ES &SD . And MODERN ADVANCEMENTS IN LONG RANGE SHOOTING that has more great information and tips on chronographs and how to set them up to get the most accurate readings. You can find them on the Berger or Applied Ballistics web sights and Sinclair/Brownells. Hope this helps!

 

[bill123]

By the way shot dispersion is NOT linear. It varies with time of flight, not distance. A 1 inch group at 100 yards does not mean 10 inches at 1000 yards. Rather, you take the time of flight to 1000, divide it by the time of flight to 100, and myltiply that by the group size at 100.

KYPATRIOT I see how this is true for vertical dispersion but why would horizontal dispersion be affected by TOF?

 

[dkhunt14]

CONDITIONS, CONDITTIONS IS the biggest factor. Matt

 

[barefooter56]

bill123,
Longer TOF = more time for mother nature to push your bullet sideways. KYpatriot, Ridgerunner and dkhunter have great advice and answers to help. The only thing I would add is make sure your rifle is fouled enough that the bullet strikes on the fouling target have stopped rising and are now clustering for BOTH your group shooting and Chronograph testing. If you want to take the factors of light, and height of the bullet over the sensors get a Magneto Speed . It reads off the magnetic field so you can test velocity in any light condition and comes with spacers to adjust the bullet flight height over the sensors. Many shooters have reported no affect on point of impact on the target even though the unit attaches to the barrel. Also keep good notes in your reloading log book and ONLY CHANGE ONE THING AT A TIME WHEN YOU TEST!! SD is the most important unit to pay attention too as has been said before. But the TARGET is always the final arbiter no matter what the distance. Lots of good advice here Bill , but it will take some work. There are no shortcuts to accuracy unless you get lucky and the first combination works.

 

[Pdvdh]

If you want to take the factors of light, and height of the bullet over the sensors get a Magneto Speed . It reads off the magnetic field so you can test velocity in any light condition and comes with spacers to adjust the bullet flight height over the sensors. Many shooters have reported no affect on point of impact on the target even though the unit attaches to the barrel.

And many shooters have reported an affect on point of impact (POI). This is another unknown and has to be tested on every rifle in order to determine the affect on precision and accuracy. The heavier contour barrels could be expected to be less affected than lighter, sporter-class contoured barrels. Any time you fasten weight to the end of a long rifle barrel, there should be no surprise if the weight causes a change to POI and/or precision (group size).

 

[barefooter56]

phorwath,
Very true. Should have added that . Thanks !

 

[coyotezapper]

And many shooters have reported an affect on point of impact (POI). This is another unknown and has to be tested on every rifle in order to determine the affect on precision and accuracy. The heavier contour barrels could be expected to be less affected than lighter, sporter-class contoured barrels. Any time you fasten weight to the end of a long rifle barrel, there should be no surprise if the weight causes a change to POI and/or precision (group size).

+1. I have a hard time believing that there would be no POI change no matter how heavy the barrel. HARMONICS.

 

[barefooter56]

Coyotezapper,
I have talked to shooters and have seen that in some cases it didn't change the POI. But as stated previously you must test. In any case they seem to have a leg up on the regular style chronographs. Bryan Litz did a test of chronographs and laser rangefinders in his "Modern Advancements I Long Range Shooting" book that has a ton of real world testing done and what the positives and negatives are of each unit. Lots of good info there to help one make an informed decision.