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

a.JR · #8 12-25-2003, 05:05 PM

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 · #9 12-28-2003, 06:04 PM

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

a.JR · #10 12-28-2003, 07:08 PM

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 · #11 12-28-2003, 07:42 PM

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... [img]images/icons/grin.gif[/img]

Len Backus · #12 12-28-2003, 09:09 PM

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 · #13 12-29-2003, 02:46 AM

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 · #14 12-29-2003, 06:07 PM

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.
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