BC numbers for 142 long range accubond

[redside]

Hello all,
I've read most everything I can on this forum trying to figure out what would be a safe BC number to use for my custom CDS dial on the leupold scope. I've seen everything between .570 to .620. My barrel is a 1-8 x-caliber 6.5 barrel. Should I just go with about .6 and I should be pretty close out to my self imposed limit of 700 yards.
Just looking for a little direction.
Jim

 

[el matador]

There are too many variables to say for sure. The best thing to do is go shoot your gun at 700 yards and see where it hits. There will be a little bit of error in your scope adjustment (4 clicks might not be exactly 1 MOA), the BC might be off a little, the muzzle velocity, etc. By validating your drops you will know exactly how many clicks it takes to get there.

I like to verify at 3 different distances: Where I'm zeroed, max hunting distance, and somewhere in between. This way I can fit the trajectory curve pretty well by adjusting BC and muzzle velocity. If there's no way for you to practice at 700 yards then you shouldn't be shooting at game that far anyway

 

[Bullet bumper]

Nosler says the G1 BC is .719 and G7 BC is .320 . If I had all the exact dimensions of the bullet and the muzzle velocity it will be launched at . I could model it and predict a list of BC's to average . Without the bullet in front of me it's not really an accurate option .
I suspect that the high SD of the 6.5 bullet throws the BC up a bit more than it actually is in flight . .6 G1 BC might be a reasonable average .

 

[bigngreen]

A .293 G7 BC is what I have listed from Litz.

 

[LongBomber]

.293 G7 bc is what matches up with what I have seen from my couple 6.5's. From what I have seen shooting them, you are better off starting off with the 129 LRAB. There is not enough difference in bc to make up for the velocity.

 

[BallisticsGuy]

Hello all,
I've read most everything I can on this forum trying to figure out what would be a safe BC number to use for my custom CDS dial on the leupold scope. I've seen everything between .570 to .620. My barrel is a 1-8 x-caliber 6.5 barrel. Should I just go with about .6 and I should be pretty close out to my self imposed limit of 700 yards.
Just looking for a little direction.
Jim

I don't know where you're getting your BC numbers from but it's nowhere near what it should be. Nosler shows .719 G1 and .291G7. Now then...

BC varies with velocity and drag becomes much less severe with altitude so I'd need your MV and the elevation range you plan to hunt in in order to give a really good answer. The best way is to go out and do some 700yrd shooting at your hunting elevation, get your drops and use that to back into the averaged BC that matches. It matters most at the long end anyway.

I would personally go ahead and use .719 myself based on my experiences with the 7mm 168gn LRAB with regard to advertised BC versus real world results. I shot a box of them in a long range match, did very well. Had no trouble using indicated elevation corrections from 200-1000m with my ballistics apps (ballisticxlr.com and KAC BulletFlight M) using their advertised G1 number.

 

[LongBomber]

I would personally go ahead and use .719 myself based on my experiences with the 7mm 168gn LRAB with regard to advertised BC versus real world results. I shot a box of them in a long range match, did very well. Had no trouble using indicated elevation corrections from 200-1000m with my ballistics apps (ballisticxlr.com and KAC BulletFlight M) using their advertised G1 number.

There is an older thread on here which has verified bc's of all the lrab bullets. The 6.5 142 is actually pretty disappointing, it is no where near .719. It is well under a berger 140hybrid for bc. The .293 g7 bc was from Bryan Litz data, which is about as good as it gets.

 

[Bullet bumper]

This is Noslers info on the 142 grain Accubond LR
Litz's G7 BC may well be more realistic.

 

[codyadams]

Nosler has GREATLY inflated their numbers. They are nowhere near what they advertise. In my personal opinion, Nosler flat out lied to the consumers on this bullet. If they would have just been honest with real world capable b.c. #'s, they still would have sold because it is still a decent line up of bullets, but have caused alot of headache with their dishonest real world bc numbers. Do some research h in this thread

http://www.longrangehunting.com/forums/f19/nosler-lr-accubonds-bc-testing-results-137554/

 

[BallisticsGuy]

Nosler has GREATLY inflated their numbers. They are nowhere near what they advertise. In my personal opinion, Nosler flat out lied to the consumers on this bullet. If they would have just been honest with real world capable b.c. #'s, they still would have sold because it is still a decent line up of bullets, but have caused alot of headache with their dishonest real world bc numbers. Do some research h in this thread

http://www.longrangehunting.com/forums/f19/nosler-lr-accubonds-bc-testing-results-137554/

Greatly? That's simply wrong. Did you even read the stuff Bryan wrote? I'm really doubting that. If you did you'd have seen that the advertised BC's were stupid close to actual IF and only IF the bullet was aggressively stabilized. If Sg was on the low side then you get bad results, like 10% out. Well, that should tell you right away that the problem is precession of yaw at moderate gyroscopic rotational speeds. Beyond that, the velocities used by Litz were not disclosed meaning that the data presented cannot be analyzed for error. This is because velocity and BC are related. Further, you might understand what BC is derived from and how it's presented. Since the advertised number is an average, it's averaged by the manufacturers normally for the velocity band that the bullet is meant to operate in. Target bullets get used commonly all the way out to the transonic velocity regime. Game bullets simply do not as a generalized rule. They're generally meant to hit at fairly high velocities in order to initiate expansion.

The article you linked doesn't debunk Nosler's BC numbers very well. It describes clearly the effect on BC of insufficient twist rates and how the LRAB seems to respond.

 

[codyadams]

If you did you'd have seen that the advertised BC's were stupid close to actual IF and only IF the bullet was aggressively stabilized.

Yes, aggressively stabilised. That is not very common in real world ballistics, especially in factory rifles. So pretty much, they are ONLY telling the truth if you have a rifle with a non conventional twist. Not very honest in my opinion.

 

[LongBomber]

Greatly? That's simply wrong. Did you even read the stuff Bryan wrote? I'm really doubting that. If you did you'd have seen that the advertised BC's were stupid close to actual IF and only IF the bullet was aggressively stabilized. If Sg was on the low side then you get bad results, like 10% out. Well, that should tell you right away that the problem is precession of yaw at moderate gyroscopic rotational speeds. Beyond that, the velocities used by Litz were not disclosed meaning that the data presented cannot be analyzed for error. This is because velocity and BC are related. Further, you might understand what BC is derived from and how it's presented. Since the advertised number is an average, it's averaged by the manufacturers normally for the velocity band that the bullet is meant to operate in. Target bullets get used commonly all the way out to the transonic velocity regime. Game bullets simply do not as a generalized rule. They're generally meant to hit at fairly high velocities in order to initiate expansion.

The article you linked doesn't debunk Nosler's BC numbers very well. It describes clearly the effect on BC of insufficient twist rates and how the LRAB seems to respond.

But it does debunk the one single bullet we are talking about. Plain and simple, no matter how well you stabilize the 142gr it isnt going to get to .719. It needs to get from just over .6 up to .719 which isn't going to happen. You are right for the other offerings, there is a high velocity band that will produce noslers numbers, or reasonably close. Just not on the 6.5mm 142.

 

[redside]

First I want to thank everyone for you input, second I think I'm just going to go with a BC of around .61 and see how that plays out. It is really disappointing that Nosler didn't really make an effort.to get the correct BC out rather than inflate it for marketing. I still love the looks of the bullet though.
Thanks all.

 

[LongBomber]

Other than the inflated bc ( i use .29-g7 or .6- g1) they are a good bullet. Bonded to hold together somewhat, but still very soft. I had to be very careful with neck tension, just a bit much and I deformed noses seating. I ended up making a new seating plug and used exopy to fit it for the bullet to help.