Velocity E.S. vs Vertical Dispersion at 1,000 yards

[Len Backus]

How low do you tune the muzzle velocity ES (10 shots)of your loads in order to shoot small groups at 1k?

Ballistics programs tell us that a 30 to 50 fps velocity difference will cause a vertical spread of quite a few inches, depending on the bullet's BC. How much correlation do you actually see (as opposed to theory) between ES and vertical dispersion at 1k?

 

[Michael Eichele]

Hi Len,

I have shot some factory ammo that was about 60 FPS ES and it would group 10" at 1k. I have some home made loads that have shown me as much as 70 FPS differance and they give me less than 4 or 5" of verticle separation at 1k. Strange huh??

 

[LDO]

typically 1k shooters try to tune there loads so that the ES is in the single digits.i know i dont have to tell u this but the key to lr. accuracy is consistency,a ES over 20fps is not considered consistent enough.with tiny groups being shot all the time by a number of shooters ,its important to use any edge u can get,a low ES would be one of those competetive edges.my-2 -dave-merry christmas

 

[milanuk]

This is one of those 'weird' subjects. I agree, by my beer logic, a lower E.S. (and by way thereof, S.D.) should be a given for long range shooting. Makes sense. But from time to time, I hear shooters (good, long range competitive shooters... not BR, but Palma) mention that when they got around to chronographing a load that they'd been knocking out the 10/X rings w/, the chrono numbers seemed to indicate that they shouldn't even be able to keep them on the paper at distance. And that's one *big* honkin' target frame! Almost seems to indicate that there might be something else at work here?

Kind of a sub question that's been bugging me every time I come across it in 'Handloading For Competition: Making the Target Bigger' by Glenn Zediker. He mentioned something he'd heard second hand, so I don't know who started the rumor, but supposedly some people who had the setup and patience to do so had chrono'd their loads both at the muzzle, and at 1000 yds. The weird part was that the individual rounds showed much, much less E.S. *at the target* than they did at the muzzle. Any ideas on how that works?!?

TIA,

Monte

 

[a.JR]

Most of the chrono's used by the average shooter do not have the capability of resolution of any less than 15 fps,Mainly because of the screens capability, so the guys that have the need for single digits do not have the full story..Obviously if you have figures of 75 fps you are not going to be kickin "A" at Hawks Ridge,but concentration on group size at the chosen distance will net more positive results than focusing on the chrono ..JR..Jeff Rogers.. pic of 3 targets shot during the state champs @547 yds they are 1.230 /1.910 /2.400 = agg 1.84ins and these were shot with a rifle that has a variation of 25 fps on my chronograph

 

[STL_Shooter]

That would seem possible given the bullet leaving the barrel at a different point in its vibration...

 

[RBrowning]

You not only have faster and slower bullets leaving at different times in the barrel's vibration pattern, you have the bullets leaving at different points in the recoil cycle. Logically we assume, supported by all of the balistic printouts, that the lighter bullet will shoot flatter and hit higher. I have seen many times when the lower velocity bullet hits higher. The slower bullet is in the barrel longer and the muzzle has raised farther due to recoil. Not a big issue with a 50 pound bench gun but more obvious with sporter weight rifles. This becomes very obvious when changing to heavier bullets in a pistol and your point of impact at 100 yards goes up instead of down.

 

[a.JR]

Any ideas how that works?!?....Monte,The reason for the differences you see "at the Target" is mainly from the discrepency in the B.C. from bullet to bullet...If you are not carefully qualifying all of the bullets used in competition you will never reduce the vertical dispersion...If you were to shoot a set of cartridges(10 say) with a magical spread of 20 fps at the muzzle and you also had 10 bullets with a B.C. spread of .510 to .530 ,then the speed difference at 1K could be as high as 50 fps or.... To make all 10 shots on the "paper" as close to the same as possible is my quest,the use of chrono's and ballistic programs only serve to confuse the issue during my research and testing ...JR..Jeff Rogers

 

[Len Backus]

So, Jeff, how do you reduce the BC discrepency in order to shoot small groups like in your picture?

 

[a.JR]

Len,My procedure is to 1st start with as many bullets of choice as i can get,then batch into 2 lots of approx 5 to 6 thou diff in aol...Any that go high /low outside of this are sent to the fire form bin...I then cut the length of the tip down to the shortest ,so i end up with 2 batchs out of say a 1000 would give me approx (using a hand made comp benchrest bullet)480 bullets @1.325 and 480 bullets @1.330...Then i use a cutter i made that looks like an elaborate pencil sharpener to equalise the meplat at 60 thou...I now have say batch #1 all the same length with the same dia tip(meplat) and so on...The next step is to batch into lots of equal ogive to base dimension...then batch again into equal bearing surface ... The degree of how tight u batch has to do with the match weather conditions you are up against,it is a waste of time running bullets that are quailified to 1 thou if there is at least a mminute of mirage movementon your target...When i travel to shoots i do not have the privilege of knowing the weather(my nearest big comp is a 1000 miles away)so i go with the best i can make...This will NOT make a 10in gun into a 3in gun,but once your on top of the brass and the tuning it'll come...I am stickler for details in every area,for instance i went to the match where i shot those targets with 60 loaded rounds that varied from 484grains to 484.6 gns total weight ..JR..Jeff Rogers..ps i have a pic of the prepared projectile beside the standard unit if your interested.

 

[chris matthews]

Len,
Just to throw another monkey into the equation.... while it's true, big ES accounts for vertical, just think what it does for horizontal also. That slower bullet will get blown around a bit more than the faster one. Just more pieces in the puzzle...

 

[Len Backus]

Jeff

Can you proffer a guess as to how much accuracy is gained from the sorting you describe? Yes, I would like to see a picture of your trimming device.

Chris

Good point. At 3150 fps and bc of .750 the wind drift (10MPH) difference with a 50 fps variance is about 1 inch at 1K.

At the same time the drop difference would be about 7 inches.

Add to these Jeff's effective .020 bc difference and you get an additional 2 inches of POI deviation.

 

[a.JR]

Len ,Sorry i don't have the 2 meplat trimmers here at the moment ,i have loaned them to a shootin buddy for testing on some 7mm bullets, can take a pic and send later if ya like?...I can't really guess what difference an untreated bullet vs a treated one is because i have never done it on a fully treated one...I started in '97 by batching both oal and base to ogive and saw a real improvement over un checked projectiles,by 2000 i moved to bearing surface and saw another improvement and then in '03 i started to modify the meplats and have not had good enough testing conditions to confirm or deny the results.(i will soon be testing again as my good test weather is just about here...I did the other checks of bullet dia and weight and got no where but i still qualify as explained each time, as i figure that each bit of equalization i do can't hurt...On my light gun the biggest gain was in the bearing surface ,realy quite strikeing,it pulled the V.D. from 5.5 inches down to less than 2 inches..Smallest group with the 106CLO's was 3.400 wide and 1.700 high at 1K..JR..Jeff Rogers..ps.pic of modified 187BIB

 

[chris matthews]

xring...
Just a suggestion... I would spend more time shooting and LESS time at the bench.
All this stuff is good points to consider, but the honest cold hard truth is most of us do spend to much time at the computer or the reloading bench or in front of the TV and not enough behind the trigger.