BC of Nosler BT 6mm 55grn too good to be true?

[RAG]

Using nothing more than my judgement, I question the accuracy of Nosler's claim that their 55grain 6MM Ballist Tips have a BC of .276; I just don't see how it can be that much higher than the 58 grain V-max which claims a BC of .250. Shoot, even the 65 grain V-max only claims .280.

Because of the reported BC, I've tried to get the Nosler to shoot in my 6BR/6PPC Varmint/Benchrest combo rifle, but the Nosler's seem to group about .15 worse than the V-max,and .2 worse than the 55 Blitzkings) in my rig...which has bothered me because I want the higher BC for varmint shooting...but the more I think about it, the more I doubt Nosler's claims.

Anyone set up a couple of Chrony's and tested these claims out for themselves?

Thanks.

 

[AckleymanII]

You really never can believe what you read.

Here is how I over come the BS.

Since we are varmint hunters and not paper punchers, launch time is cricical along with accuracy.

I worked up a super accurate load with the 70g Blitz king and the 55g Nosler. I shot them both at 300 yards. They both grouped the same,about 3/4', you gotta love Lilja barrels) but the 55's shot 7 inches flatter...they are smok'en.

Next test is to shoot them at 400 at little bitty creatures that like to crawl around and destroy pastures.

 

[RAG]

I'm with you on the 55s for sage rats - at 3,800 FPS they do the trick. But I would be happy if I could get the 55 Nosler BTs to shoot groups like that...I can get the 55 BKs to hold 1/4 MOA out to about 300, but not the Noslers...according to manufacturer claims, I'm giving up a big differnce in BC to shoot the flat base BKs. Consequently, I'm going to rechamber a spare 6PPC barrel to 6BR in hopes of getting the Noslers to shoot in the 2s,or at least low 3s).

 

[RJinTexas]

I agree with Kieth, both my old 6mmRem and 243Win performed spectacularly with 55NBT's. They both shot the 70NBT's well but out to say 500yds the splatter factor was more impressive with the 55's and with a 50yd zero it enabled me to shot the x-hairs out to 300yd before I had to start clicking. Now I'm wondering why I've always favored 75Vmax's and not even tried the 55NBT's in my 14tw 6BR???
RJ

 

[RAG]

Agreed, I highly favor the 55s for the splat factor, especially in the lower capacity 6BR. But does anybody at least know anybody that has tested the BC themselves to determine if the 55NBTs really match the ballistic coefficient of the 65 V-max...looking at the two side-by-side, I really don't see how they could have virtually the same BC; in fact, I'd be surpised if the 55NBT had any greater BC than the 58 V-Max.

 

[Bryan Litz Ballistics]

I haven't tested the 55 grain BT's for BC, but I did test the 70 and 80 grain ballistic tips which have about the same G7 form factor of ~1.18. IF the 55 grain BT has the same ogive and boat tail as the 70 and 80 grain bullets,which it probably does) then it has an average G1 BC of 0.220.

Here are the advertised/measured BC's for three Nosler BT's:
80 grain: .329/.323,2% high)
70 grain: .310/.279,11% high)
55 grain: .276/.220*,26% high)

* This is the estimated BC based on the measurements of the 70 and 80 grain bullet.

I suspect there's more error in the lighter bullets advertised BC's because Nosler only measures BC over short range. For the lighter bullets, this means they're being tested at higher speeds than the heavier bullets. My measured BC's are average values for 3000 to 1500 fps. I realize these bullets are shot much faster than 3000 fps, but it's the standard velocity window I use to allow apples-to-apples comparisons.

At ranges up to 300-400 yards, I suspect these bullets, at the speeds you're shooting them, will be quite flat and not highly sensitive to small errors in BC. However, if you want an accurate trajectory predicted beyond that range where the bullet has lost significant velocity, I recommend using the measured BC's above,.220 for the 55 grain BT).

Take care,
-Bryan

 

[RAG]

Bryan,

Thanks for the detailed response. And it's too bad there isn't a little better 'uniformized' standard for reporting BC for various velocities, allowing us to accurately compare one bullet over another. I'm really not too concerned about it, but I just didn't like the thought of giving up a couple hundred fps of critter impact velocity from one equa-weight bullet to another...which probably isn't the case, as I would guess .276 would be an exaggeraget BC,at any velocity) for the 55 NBT. I don't have two working chronographs anymore, but I'll just have to shoot the various bullets in question though a chronograph at 200 or 300 yards and see if there is truly a distinguishable difference in velocity at this range.

 

[Alycidon]

I tested some 55gr NBTs against my usual 65gr Vmax and 68gr Barts match that I use for fox busting in a 6mm PPC.

I used the same powder load under all three but the velocity readings were all pretty close,,within 100fps) as was placement on the target. I was expecting at least 200-250fps difference.

They did though shoot some really nice cloverleafs at 200 yards. I did find when I was using then in a 22.250 that expansion on fox was pretty slow. Good on rabbits and crows though but normally just a small exit on a chest shot fox. Not actully tried one in 6mm on a fox yet though.

A

 

[shootsanything]

I think what is missing from the discussion is the fact the reported BC for any bullet is either a mathematical estimate or a number derived from a test barrel. Since firing distorts the bullet its BC will change slightly. The only way to know what the BC is for a bullet in your gun is to test it in your gun. One method is to know the velocity at the barrel and measure drops at known yardages, but this has to be compensated by how high the scope is from the barrel. The other and more reliable is to measure the velocity at multiple yardages. I only attempt to do this when I am alone at the range.

 

[Bryan Litz Ballistics]

shootsanything,

Bullets actually fly very consistently from all rifles. There are many things that can give the perception that the bullets are flying differently from different rifles,like inaccurate scope adjustments, errors in range measurement or velocity measurement, misunderstanding of BC dependence on velocity, atmospherics not accounted for, etc.)

If a bullet is properly stabilized, meaning you're using the manufacturers recommended twist or faster, and the bullets are not being fired at such a high velocity that they're actually 'slumping' or failing, the bullet will fly the same from any rifle in a given atmosphere.

Slumping is not very common, and when it happens, usually happens inconsistently causing poor groups. In other words, if your rifle is shooting small groups, the bullets are flying 'properly', and are flying the same as they would from any other rifle that shoots small groups. The effects of various rifling numbers and depth is practically insignificant.

Take care,
-Bryan

 

[243jimb]

I too found that this bullet did not live up to its published BC. When I worked out the supposed bullet drop for the MV I was getting it was way off. I found it very refreshing that Berger has restated the BC on their bullets, I congratulate them on that. It's a pity that some other manufacturers don't see the need to follow suit.
Jim.