Long range bullet drop affected by bullet weight variation?

[Nostrum Damus SASS #110702]

I'm trying to understand the significance of precision bullet weight control for CAS long range applications.  I can't seem to find a ballistic calculator that will answer the question for me, so I'm asking here.  I know some will say things like "other factors are more important" and that may be true, but that's not the point.  So:

If all other things are held equal, for a given RNFP lead bullet with muzzle velocity of 1200 fps, what is the variation in bullet drop at 600 yards between bullets weighing 495 gr,  500 gr, and 505 gr, in other words, what is the effect if nominal 500 gr bullet weight consistency is +/- 1% ??

[The Original Lumpy Gritz]

Weight variation leads to variation in MV. 

That leads to trajectory variation, and impact location 'walk'.

You also want to control bullet runout. Keep your T.I.R. to .003 or less.

[irish ike, SASS #43615]

It's physics. If velocity remains the same then the energy at the impact point will vary. Or, bullet drop. Is it 1 MOA or 3? same bullet shape so wind and air density should have an equal affect.

Also, the greater distance to the target the greater the variation.

[Nostrum Damus SASS #110702]

Thanks, I know all of that.  I know it makes a difference.  I want to know if the difference is one inch at 600 yards or 1 yard.  ALL OTHER THINGS BEING EQUAL.  Same TIR.  Same MV.  Same COAL (and, by the way, in the cartridge I am making, the bullet engages the rifling of the barrel when the cartridge is fully seated in the chamber, which I accomplish with a levering tool).  Same everything EXCEPT +/- 5 gr bullet weight.  What is the theoretical MAGNITUDE of the vertical variation in point of impact between the 495 gr and 505 gr bullets?

[Cpt Dan Blodgett, SASS #75655]

If you have a chrony and know the ballistic co-efficient of the bullet any number of ballistic calculators will give you the answer,  I use the one at hornady.com

You may well find the drop difference is negligible compared to the wind drift and one's ability to accurately dope the wind.

[Nostrum Damus SASS #110702]

Cpt Dan B, the problem I'm finding with all of the ballistic calculators is that they seem to round off your input data without telling you that they are doing it.  I have run the same inputs on multiple runs using the same BC and MV but with bullet weights of 495, 500 and 505 gr, and the bullet drop at 600 yards has been identical to the one-hundredth of an inch for all three weights -- which I believe is impossible.  My best guess is that the Hornady, Winchester, and other non-mfr online calculators are rounding 495 up and 505 down to 500 gr -- I can't think of any other possible explanation.  I'm looking for a better ballistic calculator, I suppose.

[Garrison Joe, SASS #60708]

With same muzzle velocity, any heavy and light bullets drop the same over distance except for the ballistic coefficient difference between bullets.  High bullet drag in flight slows the bullets, lightest bullets more quickly. If you have the BC of the two different bullet designs, one can plug the numbers into say the Federal Cartridge calculator and get the difference in drop at any reasonable range. 

 

The calculations I have found most useful are in the QuickLoad/QuickTarget calculator.  That will cost you $120 or so, but it is very valuable with both determining drops at various distances, and internal ballistics (pressures, time in barrel, pressure at muzzle, burn efficiency) for almost any jacketed or CAST bullet load, including cast bullets and powders that not even the Lyman Cast Bullet handbook shows loads for.   Several of the cast bullet mold makers provide BC numbers to plug into QuickLoad!

 

If you have the same bullet design, just light and heavy weights on slugs cast from the same mold, the weight won't make much drop difference at all.   BUT, what varying weights in such a cast bullet DOES indicate is that you have mold fill out problems or internal (non-visible) air cavities in your cast bullets.   Both of those problems give you off-centerline center of mass, which wrecks fine accuracy of the lighter slugs.   THAT problem is what folks are trying to find and eliminate when they weigh their cast bullets and toss out the lightest, and maybe also any that are heavier by far than the mean weight.  Not that it affects drop, but that it affects group sizes.

 

good luck, GJ

[Garrison Joe, SASS #60708]

8 minutes ago, Nostrum Damus SASS #110702 said:

I have run the same inputs on multiple runs using the same BC and MV but with bullet weights of 495, 500 and 505 gr, and the bullet drop at 600 yards has been identical to the one-hundredth of an inch for all three weights -- which I believe is impossible.

 

Nope, it's just that those ballistics techs know a lot more about external ballistics than you do.  What you just reported squares exactly with what I wrote while you typed your last post.  Same MV and BC and you get the same flight path, even including drop.

 

good luck, GJ

 

 

[Colorado Coffinmaker]

 

The answer(s) you seek are not necessarily available with simple math.  With all the variables, the only way you are going to be able to answer the question, is with range sessions.  With exactly the same temperature, humidity, wind speed, wind direction and most important, whether you hold yer tongue right as you squeeze the trigger.     Best of luck in your quest  

[Nostrum Damus SASS #110702]

OK, well, Garrison Joe says that for a given MV and BC, and all other variables held constant (including at least wind speed and direction, altitude, barometric pressure, temperature, and relative humidity), THE FLIGHT PATH IS IDENTICAL FOR ALL BULLET WEIGHTS.  That may seem counterintuitive to some folks, but assuming that gravity is constant, it makes perfect sense.  Remember the old demonstration where a feather and a lead fishing weight are both dropped inside a vacuum chamber and they fall to the bottom at the same velocity and hit the bottom at the same time?  It is the same basic idea.  Trajectory is projectile weight agnostic; bullet weight affects only terminal energy.

 

OK, now that the science lesson has been concluded, here is my next question: why do precision long range shooters weigh and sort their bullets by weight if variations in weight make no difference to point of impact?  I'm not talking about weighing in order to detect major casting errors that affect the uniformity of the bullet; I'm talking about guys who say they will discard a bullet if it is more or less than one percent of their target bullet weight.  I don't get it -- two bullets coming out of the same mold but that are several grains more or less than average will fly with exactly the same trajectory, all other things being equal, as Garrison Joe states correctly.

[Ranger Dan]

No 2 bullets fly the "exact" same trajectory. Too many variables. Flawed projectiles is just one of them that they try to eliminate by discarding any that are not as perfect as they can measure, weight, concentricity, etc. The difference in weight has less to do with the actual weight but where the difference is. Not being able to see inside a bullet all you can do is weight them and discard those with the flaw of not weighing within your standards. They also discard any projectile that has visible flaws even if they weigh exactly what they are looking for. You are trying to put a number to a variable so miniscule as to be unmeasurable. If you really want to know, load 5 of each weight exactly the same and fire them at your target. I'm sure you will find no measurable difference in the elevation of the groups, mostly because all the other variables exceed the miniscule difference in bullet weight. Although I expect you will find that one of the weights, probably the heaviest will be measurably tighter group, because the lighter bullets have flaws you can't see.

[The Original Lumpy Gritz]

And then, there's the  barrel fouling to contend with. 

[Nostrum Damus SASS #110702]

Yes yes yes, I get it -- no two bullets are likely ever going to travel exactly the same path at 600 yards, try as I may to make it happen.  But at least I am now comfortable with the notion that there is no need to separate bullets by a few grains light or heavy (in a 500 grain bullet) because those differences can't be significant enough to matter and overshadow all of the other differences.  If I miss the large plate at 600 yards with a 505 grain bullet, odds are that I would have missed it with a 495 grain bullet too.  Conversely, hitting it with one probably means I would have hit it with the other, as well.  Not always, but most of the time.

[Garrison Joe, SASS #60708]

Go read my post again.  Long range shooters OFTEN sort bullets on weight, and shoot the heaviest, because the heaviest out of the mold are likely to have fewer defects in them.  Be better filled out on the surface, and less likely to have cavities in the bullet.   It's group size they are optimizing, not DROP.  I just started doing that for 30 caliber rifle bullets. Once I found loads that shot close to MOA in cast bullets at desired velocity range, now I'm tuning using heaviest bullet weight from a mold, and matching the lube selection to velocity.

 

You have everything pinned on DROP.  Winning is more about precision, not drop.  Yes, with rainbow trajectories, you have to get sights on at long distance - that is where range time really helps.   But you can get PRECISION by work at the reloading bench.

 

good luck, GJ

[Caladisi kid]

Short answer...YES.

Long answer.....YES

Ballistics.......HHHMMMMM   Well if all the things are the same, as stated, the shot per shot will have....

All the bullets IDENTICAL in size and dimensions, which they are not.....

The lube amount and placement is IDENTICAL on every bullet, which it is not......

Each grain of powder is the same size, amount and density with every pour, which it is not.....

Every case has the same weight, dimensions, metallurgy, which they are not.......

The primer has the same IDENTICAL primer compound in it, which they do not....

Each case is placed in the chamber IDENTICALLY  every time, the butt of the rifle is placed on the shoulder with the same pressure. with an IDENTICAL cleaned bore, temperature of barrel is the same,  placement on the shooting sticks the same,  the wind from the same direction and steady, the Earth has not rotated from the previous shot, etc., etc., etc.

This all makes it so fun to try to make every shot count.  There is no perfect formula, just the best we can do.  Ask any bench rest shooter how well they can do with what they have, they are not perfect either, though they are very repeatable.

What a fun game we have!

My 2 cents,  CK  

 

 

 

[Buckshot Sheridan]

As mentioned in various ways above. The difference in weight either affect an aspect of the ballistics, or more so is an indication of something else that will cause an issue.   When calculating trajectories a ballistic calculator is looking only at velocity and BC. So of course the program is going to give you the same drop number, the inputs that it uses for that calculation haven’t changed. That being said weight is going to have an effect on your velocity. That change in drop will be measurable, but the bigger issue is that a light bullet is also going to be out of balance virtually every time, and when you spin it at roughly 80-100k RPM it’s not going to follow a consistent path from one to the next. 
 

This all being said a 10 grain spread is huge. I cast a 207gr bullet for my 44-40 and after a visual inspection a random sample of 20 from a 4 cavity mold casting about 1000 per session will rarely show more than 1.5gr from lightest to heaviest. The 715gr I cast for the 50-90 all get weighed and I discard anything that is not +_ 0.5gr. Usually this results in about 10-15% going back to the pot. Each casting session I get more consistent and the weight does as well. Last time the 50-90 went across the chronograph the 10 rounds gave an average of 1320 with a total velocity spread of 3. The consistency of the bullet, the powder charge and how the cartridge is assembled I can make as precise as my equipment and patience will allow. 

[Griff]

The difference between winners & also-rans is that winners pay attention to all the details.  From case selection, prep, bullet choice, production, on thru assembly.   You're entering a match, plan on building match grade ammo.  Be assured that amongst your competitors some are!  When my eyesight was above par and I wanted to win a long range match, there wasn't a bench rest trick I didn't use.  It's hard to get as enthused when the best you can see is to line up this closeup fuzzy ring with the fuzzy post at the end of the barrel and that far away fuzzy blob.  

[Sedalia Dave]

" For the more technically minded, ballistic coefficients are derived from the mass of the object divided by its diameter in the airflow squared, divided by the form factor, i, that relates to the aerodynamics of its shape.

 

Two bullets that are cast from the same mold but different weights CAN NOT have the same ballistic coefficients as their mass is different.

 

This is where your problem lies, you have assumed that the bullets of different weights have the same BC, when they do not.

 

G1 & G7 Ballistic Coefficients... What's the Difference?

 

 

[Happy Jack, SASS #20451]

^^^^^^^  This

[Happy Jack, SASS #20451]

I have an Oehler system 89    And even the best available bullets  (example Berger 140hybrid match) vary.  Bullets tested varied by LESS than +- 1 grain.                         Out of my match JP rifle The following     BC   G7

3169  3157  2989  3021  3100  3132  3119  3171  3144  2768      Avg: 3077      Extreme spread  0403      SD  0121

 

Attempting to get G1 BC on lead bullets has been very frustrating.. Even on 535 +- .1 grain they are all over the place  So to answer the original question,  YES +- 5 grains makes a huge difference.

[Nostrum Damus SASS #110702]

So, guess what I'm doing today ... sorting bullets!

[Nostrum Damus SASS #110702]

I sorted a mostly full box of Acme Bullet Co 500gr coated RNFP bullets.  I decided to keep all that were within +/- 2.0gr of 500gr.  That resulted in 8 discards that will be turned into 357 or 45 cal bullets for regular SASS work.  Of the 8 discards, 5 would have usable if I set my limiter at +/- 3.0gr, and the other 3 were wildly out at 491gr, 492gr, and 509gr.  Interesting.  Had I not wised up to this, I could have shot bullets differing by 18gr on consecutive shots.  And I've probably done so already, which explains a few truly surprising long shots that went nowhere near where I thought they would hit.  Thanks to all for straightening me out.

[Tequila Shooter]

@Nostrum Damus SASS #110702  you may be able to get a little better grouping with a different design bullet, like a New Postel or a Creedmoor.  If you decide to cast your own try Brooks Moulds, I found him very helpful and his moulds are top quality. 

[La Sombra]

And since I am Tequila Shooter's bullet sorter and lube master, the bullets that we cast from the Brooks Mold are weighing 525 grains +/- 2 grains.  Everything else goes back into the recast bucket.

 

My thoughts on SASS LR, not BPCR or Quigley matches, is that 300-400 yard minute of man accuracy is good enough. Any other Long Range discipline  you need to shoot and cast more bullets to achieve the distance accuracy you desire.

 

Nostrum, GW Ketchum is a great resource for you in Texas. I suspect that he has forgot more on LR than I could ever know.

 

La Sombra

[Nostrum Damus SASS #110702]

I agree that all I need is about 3-4 MOA accuracy for my purposes.  And of course I study GWK's every move when we shoot together.  But ... all of those folks who shoot each month up at Willow Hole Cowboys are WAY MORE SERIOUS about it than I am, with their long heavy barrels, tuned barrel support positions, etc etc.  I'm shooting a Browning 1885 High Wall, so I consider myself to have a handicap from the outset.  I'm only in it for the fun and still do pretty decently, in my own estimation.  But I think my performance can only improve when I trim all cases to the exact same length and use bullets sorted to +/- 2 grains.  I was already weighing my powder charges to 1/10 of a grain, and recently picked up an electronic powder measure for even greater accuracy (and reduced pain in the butt of measuring each charge by hand).

[Happy Jack, SASS #20451]

Nostrum Damas, You DO NOT have a disadvantage with a 45-70  Browning High Wall.  I shoot one myself and do quite well out to 1666 yds (my longest target for BP guns.) I shoot a Postel bullet design but the old standard 500 gr round nose performs remarkably well out to 1600. Weigh your brass to +- 1gr and your bullet to +- 2 gr.  you will do about all you can.  I personally have found no value in tuning a barrel rest point. The seemingly best spot varies +- 5 " from day to day. Pick a spot about 2/3 of the way down the barrel and shoot.  JMHO

I have an Auto Trickler which is wonderful for weighing charges.   The OEHLER 89 system cost$$$$ it is worth it to me, but I am a serious long range shooter.

[Bison Bud]

As Garrison Joe already stated, at the same velocity the weight of the bullet should make no difference in the bullet drop.  Gravity simply doesn't care how much something weighs!  However, variations in weight will affect the standard deviations in velocity and the ballistic co-efficient of the bullet also has a lot to do with it as well.  As also previously mentioned air bubbles inside cast bullets can cause quite a bit of deviation in accuracy as well.  If extreme accuracy is the desired result, then I'd weigh each bullet and use the heavier ones of consistent weight.