WIND DRIFT VS. B C QUESTION

[Thauglor]

Yes bullet weight matters. You can get the same BC bullet but the heavier one will perform better in the real world, no matter what the calculstors say. Lots of evidence for that in match results

 

[SKWERLZ]

Agree to a point, ERIC!!!!

However, BC changes as velocity decreases!!! Some forms increase BC as velocity drops, while other forms decrease BC as velocity drops!!! This is the problem with some bullet manufacturers stating a BC without stating the velocity for that coefficient!!! Look in a Sierra Manual and look at the BC for their bullets!!!

BC is directly proportional to the inverse of the deceleration (negative acceleration)!!! The deceleration rate can change!!!

Bill!!!

DSF addresses that on a kestrel 5700 but Ive only had to use it past transonic

The BC does a decent job out to 1000yd or so. Ballistic model calculations are based on the ideal G1 or G7 standard, and for our bullets is a ratio of this result but can be inaccurate as this drag ratio is not consistent across velocities. This is why Applied Ballistics offers custom measured drag curves to address the lack of fit.

I’ve had good luck well past 1000 with trued up G7’s
Straight G7 + speed got me on target from 600 to 2300 last Friday.

 

[Wild Bill IV]

DSF addresses that on a kestrel 5700 but Ive only had to use it past transonic

I’ve had good luck well past 1000 with trued up G7’s
Straight G7 + speed got me on target from 600 to 2300 last Friday.

The G7 narrows that window of BC change vs velocity drop do to the BT, 10 Cal length model!!! And, some, if not most, ballistic calculators are almost dead on using the G7 model!!! I do know, some bullet forms tend to upset more at the supersonic to subsonic transition!!
I truly enjoy the the expertise of LR and ELR competitors!!! The advice is excellent for my form of shooting to the extremes of ethical LR hunting ranges and one, and only one shot kills!!! In the field, 3 rounds in the shirt pocket on cool and cold days!!! Lock and load and try to pull that one shot off within 10 to 20 seconds after ranging and determining the firing solution!!
I practice for the cold barrel one shot on target!!! I also reload and test like the LR shooters!!! Except, I'm old school BR with inside reaming the fired formed neck, not resized neck!!! Never had doughnuts in over 45 years reloading!!!

 

[Erik Cortina]

Yes bullet weight matters. You can get the same BC bullet but the heavier one will perform better in the real world, no matter what the calculstors say. Lots of evidence for that in match results

Bullet weight was already taken into account when calculating BC. Bullets of equal BC perform the same at same speed.

Watch this video:

The answer to the question at the end is: The one with higher BC will have less drop.

 

[davidjoe]

David:

You will get a kick out of this!!! Before the Digital age, the exterior ballistics was determined with charts, tables, and/or slide scales. I have the charts for exterior ballistics (B size drawings)!!! Unfortunately, my 1:1, C size caliber to bullet form drawings (lay a bullet in the forms and find the best fit) were destroyed by a faulty timer on the water fill solenoid on an ice maker upstairs!!! This package was from DuPont with copyright year 1936!!!! The BULLET FORM was based on flat based bullets only, with different point shapes and types (pointed, hollow point, round nose, etc). With out knowing the form, the BC factor can not be determined with this packet!!!! The charts are logarithmic and linear!!! Depends upon finding the BC using the form drawings, Remaining velocity, angle of departure, time of flight, max height of trajectory, angle of fall, wind deflection, and energy!!!!!!

Pix is front cover page!!!!!

Yes, once our ancestors figured out laws of parabolic curves, it “sealed the fates”. That was a monumental achievement which directly opened space to us with pencils and reason. It has greater applications to life, not relevant here*

With absolute, uncanny mathematical certainty, a discerning person or computer can precisely determine where a superbowl pass will end up, within the first inch of separation of the fingers of the QB, but, you must have a minimum of two still images of the ball, and you must know “exactly” how much time elapsed between taking them.

*Where something has just been, determines where it is going.*

 

[Wild Bill IV]

Yes, once our ancestors figured out laws of parabolic curves, it “sealed the fates”. That was a monumental achievement which directly opened space to us with pencils and reason. It has greater applications to life, not relevant here*

With absolute, uncanny mathematical certainty, a discerning person or computer can precisely determine where a superbowl pass will end up, within the first inch of separation of the fingers of the QB, but, you must have a minimum of two still images of the ball, and you must know “exactly” how much time elapsed between taking them.

*Where something has just been, determines where it is going.*

Off subject!!!

Past technology leads us into the future!!!
And sometimes, the past technology has consequences!!!
If terrorist groups (hijackers) would have not harvested the Cordite in new ammo from the 1970s to build non metallic bombs, we probably could be using plastic explosives instead of smokeless powders today!!! The cases would smaller, but thicker walled!!! And, there were also some caseless rounds then too, using plastics explosives!!! And, we would only have to worry about copper fauling in the barrel!!!!

 

[davidjoe]

No one ever seems to account for form factor and no program I'm aware of uses a G8 reference. So, we're stuck with using a G7 bc as the best case, G1 worst case. In the field, I've noticed that regardless of BCs being very close or identical, the smaller diameter bullet has less surface area for the wind to push against, and I've noticed I have to hold or dial less wind with 6mms and particularly 224s, than what the calculation calls for. I believe that we'd have to more complex ballistic solvers, using sectional density, true diameter and the length of said diameter, form factor, and a G7 or G8 BC, to obtain the absolute best solution. Even then, human error in data entry or a bad wind call, still puts you back outside of where you want to be. Example of the previous, I typically shoot field steel matches with my custom 223, which is a 30" 7 twist .090" freebore, I shoot 80grn 80ELDMs at 3206 avg with PP2000MR and a corrected G7 of .239, which has worked for me, all the way to a mile, and does phenomenal in our typically setting of 1130yrds and in. However, I'm typically using around 60% of the wind call from the solution. If it calls for 6moa, my hold is typically 4-4.25moa. Bryan Litz and a couple others address these in more detail, but there is indeed more to it, than just velocity over G7. Mostly it's over looked because a lot of people are shooting moa or 2 moa sized targets and being a few percent off in your solution, is still a hit, and a minor correction on the fly, can center it up. Unfortunately most don't take notes on what they had to do, to center it up. Sorry for the long winded answer.

It’s an interesting set of observations but it would suggest the .223 would be more widely used in F-TR. We just don’t see them out there, especially at long range, and few at midrange, either.

We know BR guys are certain that small groups are shot with small bullets. If it’s not a problem of inherent accuracy, and if they do even better than the tables suggest in wind, which is already at or above the much bigger and heavier .308, I am wondering why we don’t see them out there.

 

[Jeff Porter]

Related to this, I have been following a conversation in podcasts where a PRS shooter is finding that a much lighter bullet at a much higher velocity is making hits more dependably than a heavier higher BC bullet (6.5 Creedmore 100gr @ 3100 vs. 147gr at 2700) inside 900 yards due to flatter trajectory ( more forgiving to range estimation) and shorter time of flight having less wind deflection than the higher BC bullet going slower. A case where looking at the paper it would say use the higher BC round but out in the actual field situations, speed wins. Again this all falls apart past about 900 yards when the light bullet bleeds off speed and becomes unstable but if you are shooting at shorter ranges, may be worth a look at a speedy bullet.

When I shot service rifle I would use 52gr bullets for 100/200 reduced course practice and matches. They always printed tighter than my 77's but after 200 yards, 77's were better. The target tells the truth even if you lie to yourself.

 

[Will Henry]

I skipped through a lot of the thread so my post may or may not be relevant. I have always felt, given the same BC and velocity, the larger diameter bullet will be slightly less susceptible to the wind, due to greater cross-sectional density. I also don't think it makes much difference. Blow a wind call and you're still shooting an eight! WH

 

[RegionRat]

Related to this, I have been following a conversation in podcasts where a PRS shooter is finding that a much lighter bullet at a much higher velocity is making hits more dependably than a heavier higher BC bullet (6.5 Creedmore 100gr @ 3100 vs. 147gr at 2700) inside 900 yards due to flatter trajectory ( more forgiving to range estimation) and shorter time of flight having less wind deflection than the higher BC bullet going slower. A case where looking at the paper it would say use the higher BC round but out in the actual field situations, speed wins. Again this all falls apart past about 900 yards when the light bullet bleeds off speed and becomes unstable but if you are shooting at shorter ranges, may be worth a look at a speedy bullet.

When I shot service rifle I would use 52gr bullets for 100/200 reduced course practice and matches. They always printed tighter than my 77's but after 200 yards, 77's were better. The target tells the truth even if you lie to yourself.

Just out of curiosity... I ran the two cases side by side with AB Analytics.
I used the same bbl twist for both runs, a 1:9 but it wouldn't have made a difference if I ran a faster twist for the 147.
By using the velocities you stated, here are the runs.

The faster bullet may have a flatter trajectory, but it doesn't have the wind advantage at all. We tend to know the distance and not the wind. There is already a 1 MOA windage advantage to the 147 at 400 yards in a full value 10 MPH wind. YMMV

Here is the 100 grain at 3100 fps.




And here is the 147 at 2700

 

[BoydAllen]

Somewhere I read that experienced F Class shooters see an effect of heavier bullets that goes beyond BC. In other words if you have bullets of different calibers with the same BCs shot at the same velocity, the heavier, larger caliber bullet will have a slight wind drift edge. Ballistic software attempts to mimic real world but it may not do so exactly.

 

[Jeff Porter]

Just out of curiosity... I ran the two cases side by side with AB Analytics.
I used the same bbl twist for both runs, a 1:9 but it wouldn't have made a difference if I ran a faster twist for the 147.
By using the velocities you stated, here are the runs.

The faster bullet may have a flatter trajectory, but it doesn't have the wind advantage at all. We tend to know the distance and not the wind. There is already a 1 MOA windage advantage to the 147 at 400 yards in a full value 10 MPH wind. YMMV

Here is the 100 grain at 3100 fps.

View attachment 1676863


And here is the 147 at 2700

View attachment 1676864

Yeah that is what the computer says … no personal experience, just a well known shooter reporting that the faster lighter bullets are drifting less than predicted by the AB and other calculators. Chris Way of Rifle Kraft on Frank Galli Snipers hide podcast. Frank seeing similar speed effect with 6ARC using 80gr varmint vs 108 ELDM

Edit to add .. just went back and checked that part of the podcast. 100’s are 3200 fps. His time of flight limit was the distance you would get in 1.2 seconds. After that , high BC heavies win. No dog in the fight but some thing to check out some day when I get all my other stuff done.

 

[jelenko]

Somewhere I read that experienced F Class shooters see an effect of heavier bullets that goes beyond BC. In other words if you have bullets of different calibers with the same BCs shot at the same velocity, the heavier, larger caliber bullet will have a slight wind drift edge. Ballistic software attempts to mimic real world but it may not do so exactly.

I've heard the same.

I lean towards beliefs impacting perception.

The equations used are well used in testing by militarys and bullet manufacturers. If anyone is going to find higher order effects I would think they would.

 

[RegionRat]

As a very young student, I was a skeptic too.

Every time I bet against the ballisticians and aerodynamicists, I lost that bet. Then they educated me and then I started taking bets from the skeptics. We call that a learning curve.

The equations used are well used in testing by militarys and bullet manufacturers. If anyone is going to find higher order effects I would think they would.

Now imagine a place where the guns might be near static in human hands or on the ground, versus the ones that are on fast moving ships, airborne fighters, C-130s, or under the chin of a helo.... and then come see me about ballistic solvers, wind, and the BC of bullets.

The same physics gets involved with optics and lasers going through the atmosphere at distance. It is always difficult to know what is happening downrange in terms of the climate and atmosphere we are sending bullets or photons.

So if the comments are about not knowing the wind and DA downrange, then I am with it. If the comments are about the difference in low BC bullets versus high BC bullets, then I just have to let it roll.....