How to get an accurate G1 BC number? Is it even possible?

[alexnelon]

So I'm pretty new to long range shooting in general and naturally am now knee deep in ballistic solvers trying to figure out how to put good data in so I can get good data out. I'm going to shoot NRL Hunter in West Texas at the end of May, so trying to get my head on straight before then.

The issue I'm struggling with now is; what the heck is the ACTUAL BC of the bullets I'm shooting?

For reference, I'm shooting a Howa 1500 in 30-06 with factory Federal Fusion 180s. Getting basically box velocity (2702fps avg)

Federal lists the G1 for this load at .498, pretty good for a soft point right? Here's where they make my brain mush though.

Federal offers this same bullet as a component as well as 4 different cartridges. All with different BC numbers...

.503 - .308 @ 2600fps
.498 - 30-06 @ 2700fps
.484 - .300 WSM @ 2950fps
.485 - .300 WM @ 2960fps
.483 - Component

I know different velocities generate different BC, but my cursory knowledge of physics tells me this is trending the wrong way.

With the numbers already probably fudged to look good, are the smart shooters just completely ignoring these and going straight to truing at range?

How close can I expect to get to the actual BC after truing? How close is "close enough"?

 

[BBob]

Overthinking it. That range of BC numbers won’t make a drastic change. Plug in the average, go shoot. Tweak the velocity and final trim with BC and you’ll be fine.

There’s plenty of sources to help with how to true. Here’s one:

Trajectory Validation: Ten Steps for Success

Trajectory validation is the final step for building confidence in a long range precision rifle. Also known as drop truing, it’s the process of tuning a ballistic solver to a scope, rifle, and its …

panhandleprecision.com

 

[Shō[t]gun]

What he said

 

[180ls1]

The best that you could probably do without actually validating it yourself is to switch to Hornady Match ammo and use 4dof.

 

[wind gypsy]

Applied ballistics has a 180 federal fusion listed as 0.380 G1. Not sure if there has been different versions of that bullet but that's a far cry from the numbers in the OP and that's what I'd start with unless I knew better.

 

[hereinaz]

Federal may be playing with the velocity they are publishing. BC varies with velocity, and the G1 velocity they are using varies the most.

Variation in BC with Velocity

Any bullet can have both a G1 and a G7 BC, it’s just a matter which one is more representative for all speeds. G7 BC is typically more reliable.

bergerbullets.com

 

[alexnelon]

Applied ballistics has a 180 federal fusion listed as 0.380 G1. Not sure if there has been different versions of that bullet but that's a far cry from the numbers in the OP and that's what I'd start with unless I knew better.

Man I hope that's a typo on their end.

Hornady has their 180 interlock listed as .452 G1 and the Rem Core-Lokt with a flat base is listed at .383.

The Fusion 180 is a boat tail and looks a little more slick than the Hornady bullet so hopefully it's at least on par with that...

 

[Rippey715]

Since this is for NRL Hunter 800 yds should be your max. So just plug in the velocity and G1 written on the box into your solver. Make sure your environmentals are correct. Shoot at the farthest target you can or at least 800 and true what your solver says to what you actually have to dial for dope. Inside 800 there isnt too much difference for truing usually but this will have you all set for NRL hunter.

 

[wind gypsy]

If actual BC is 0.380 as tested by Applied ballistics and you use 0.483-0.503 from the OP, dope is going to be off quite a bit at 800.

I'd start with what AB measured it at unless you know the 180 Fusion has changed a bunch somewhat recently.

By all means run what ya got but a fusion isn't a good candidate for shooting a long ways. A 223 with a 73 ELD or 77TMK would buck the wind better than that 30-06 load if AB's #'s are correct.

 

[alexnelon]

If actual BC is 0.380 as tested by Applied ballistics and you use 0.483-0.503 from the OP, dope is going to be off quite a bit at 800.

I'd start with what AB measured it at unless you know the 180 Fusion has changed a bunch somewhat recently.

By all means run what ya got but a fusion isn't a good candidate for shooting a long ways. A 223 with a 73 ELD or 77TMK would buck the wind better than that 30-06 load if AB's #'s are correct.

I sent them (AB) an email to try to get some more info on their number.

I'm just super suspicious that they might have either a typo or used a version or bullet that is different that what Federal is using now.

My evidence is as follows;

Flat base soft point bullets from everybody are listed right around that .380 G1BC

.383 - Federal Power-Shok
.383 - Remington Core-Lokt
.425 - Hornady Interlock (Flat Base)
.381 - Winchester PP

But the soft point boat tail bullets are all around .450-.500

.452 - Hornady Interlock BT
.475 - Nosler Partition
.505 - Sierra SPGK
.498 - Federal Fusion

I admittedly WANT AB to be wrong on this, but even accepting that I think it's still pretty reasonable to see the numbers and think it looks fishy.

 

[Rippey715]

Also take note of the difference between G1 and G7 profiles.

"G1 – also known as Ingalls, G1 projectiles are flatbase bullets with 2 caliber nose ogive and are the most common type of bullet. G7 – Bullets with the G7 BC are long 7.5 degree boat-tails, with 10 caliber tangent ogive, and are very popular with manufacturers for extremely low-drag bullets."

What solver are you going to use for the match? Does it have a profile for this bullet?

 

[wind gypsy]

I sent them (AB) an email to try to get some more info on their number.

I'm just super suspicious that they might have either a typo or used a version or bullet that is different that what Federal is using now.

My evidence is as follows;

Flat base soft point bullets from everybody are listed right around that .380 G1BC

.383 - Federal Power-Shok
.383 - Remington Core-Lokt
.425 - Hornady Interlock (Flat Base)
.381 - Winchester PP

But the soft point boat tail bullets are all around .450-.500

.452 - Hornady Interlock BT
.475 - Nosler Partition
.505 - Sierra SPGK
.498 - Federal Fusion

I admittedly WANT AB to be wrong on this, but even accepting that I think it's still pretty reasonable to see the numbers and think it looks fishy.

I wouldn't put too much faith in manufacturer listed BC in this class of bullet. They all have lousy BCs and are rarely used to shoot at distance so they probably don't get much attention for the fact that the listed BCs are frequently not accurate. AB lists the 180 Partition @ 0.359 for example (edit: maybe that's the "protected" point though?)

Not all boat tails are equal. Look at the one of the 180 game king SBT (AB BC of 0.473) and then compare it to the shorter one on a fusion.

A 180 Accubond is 0.482 which I'd expect to be above the fusion.

All that said, 0.380 does seem low. Let us know if AB gets back to you.

 

[alexnelon]

Also take note of the difference between G1 and G7 profiles.

"G1 – also known as Ingalls, G1 projectiles are flatbase bullets with 2 caliber nose ogive and are the most common type of bullet. G7 – Bullets with the G7 BC are long 7.5 degree boat-tails, with 10 caliber tangent ogive, and are very popular with manufacturers for extremely low-drag bullets."

What solver are you going to use for the match? Does it have a profile for this bullet?

Trying to decide which solver to use.

I’ve been messing with GeoBallistics and AB the most because they both have profiles for this bullet.

GB seems to just list mfg BCs though. I want to use AB since they actually test the bullets but obviously need to true my dope either way because I don’t know what to believe.

 

[Bluefish]

If you don’t have access to a 500+ yard range, you can get an approximate bc from a radar chronograph. this won’t be a popular choice, find someone who has a LabRadar and set it to return 25,50,75, and 100 yard velocities. Then plug that into a BC calculator. It will quickly tell you if it’s .380 or .480. Not accurate enough to tell between .480 and .485, but an easy way to get in the ballpark on a short range.

 

[SDHNTR]

I’m taking Litz’ word over the manufacturer’s any day, IMO.

 

[alexnelon]

From Applied Ballistics:

"Hello,

The BC we provide is the averaged BC from 3000+ fps down to below 1500fps. The BC we provide is the tested value from the bullets we purchased at a retailer than tested in our laboratory. What you see is the performance of the bullets we had.

Thank You"

Not super helpful...

 

[SouthPaw]

From Applied Ballistics:

"Hello,

The BC we provide is the averaged BC from 3000+ fps down to below 1500fps. The BC we provide is the tested value from the bullets we purchased at a retailer than tested in our laboratory. What you see is the performance of the bullets we had.

Thank You"

Not super helpful...

A lot of manufacturers market their BC measured at very short range, sub 200 yards. BC degrades as a bullet slows down at distance. As I understand it, AB takes averaged doppler BC values for velocities from muzzle down to below 1500fps or sometimes near transonic. Thus the bullet has slowed significantly and averaged BC over the entire trajectory path is much lower than what is advertised by manufacturers. Your bullet's approximate G1 BC from your rifle setup might be around .480 at muzzle velocity, and .380 at 1500fps.

For examples, below Hornady posts different BC's for their bullets at different speeds in the trajectory:

Ballistic Coefficient - Hornady Manufacturing, Inc

A-Tip®, ELD® Match, and ELD-X® Ballistic Coefficient Values Hornady originally published “800 yard”* average Ballistic Coefficient (BC) values for ELD-X and ELD Match bullets. This was done to provide the most usable BC from a trajectory prediction st...

www.hornady.com

Just plug in a reasonable value and go true your solver beyond the farthest distance you'll shoot at the match. Maybe also try to find some Hornady 178g ELDX 30-06 ammo for a big bump in ballistics.