I have observed in comparing several Accubonds with their Ballistic Tip counterparts [ .284-140, .277-140, .308-180], that the AccuBond is slightly longer in each case. Can I take this to mean that the jacket may be slightly thicker on the AB? Is the BC also slightly higher on the AB? Just curious. Eagleye.
Ballistic Tip BC vs Accubond BC?
- Thread starter Eagleye
- Start date
- Thread starter
- #3
So far, I'm really impressed with these AccuBond bullets. The accuracy is on at least a par with the ballistic Tip, and it is a sturdier bullet. Of course, It will not make me switch completely over, I still have the utmost trust in your Partition, which has NEVER failed me. But in my rifles they are accurate!! Even my 7x57 mountain rifle printed groups under 1" at 100 meters with the 140 AB. Posted here is a typical group from my STW with the 160AB. Eagleye. 
While I hate to disagree with the poster NOSLER (here of all places! :shock: ), it should be understood that length has very, very little effect on a bullet's Form Factor. Bullets of similar shape (caliber, meplat size, ogive, boattail length) that are longer and heavier get their higher BC's from the weight (increased Sectional Density)--not the length.
I'd put money on side-by-side tests between the BT & AB showing the difference to usually be within the variation caused by differing twists, velocities, etc and that the BT would come out on top as often as not. Maybe NOSLER could ask around the office and see if such tests have been conducted by his company--my guess is they have.
It's a very common misconception.
I'd put money on side-by-side tests between the BT & AB showing the difference to usually be within the variation caused by differing twists, velocities, etc and that the BT would come out on top as often as not. Maybe NOSLER could ask around the office and see if such tests have been conducted by his company--my guess is they have.
It's a very common misconception.
Pretty sure....S.D. has to do with it as well but the design, longer bullet, with increase in jacket construction has made the B.C. higher on the AccuBond. There is a reason we can't make heavier weight bullets in the AccuBond on certain products. The 25-110 was originally a 120gr, but the length was WAY to long.
Statistically, the 180gr AB in 30 cal is published at .507, same with the 180BT. In lab results the 180 AB's B.C. is closer to .530, while the 180BT is at .507
B.C is defined as the ratio of a bullet's S.D. to its coefficient of form.
The S.D. in ratio to the design
Statistically, the 180gr AB in 30 cal is published at .507, same with the 180BT. In lab results the 180 AB's B.C. is closer to .530, while the 180BT is at .507
B.C is defined as the ratio of a bullet's S.D. to its coefficient of form.
The S.D. in ratio to the design
I just think people don't realize what a small factor length is and what a large factor weight is. Of all the factors in a bullet's shape (form factor) length makes about the least amount of difference. But the BC is directly proportional to the SD, which is directly proportional weight for a given caliber. It's that directly proportional part that makes a big difference for a given shape.
Just looking at the 30 Cal BT's, for example:
125 g, BC = .366. By just adding 25 grains to the same shape you'd expect the BC to be .366*150/125 = .439. And yet the 150 is only advertised at .435.
The 150 has a BC = .435. Add 15 grains to the same shape and you could expect .435*165/150 = .479 but the 165 is only advertised at .475.
Do this for the rest of them and it seems, if Nosler's advertised BC's are accurate, the 30 cal BT lost a little BC every time it got longer (a fair amount in the case of the 180) because the increase in weight more than covers the difference.
Don't get me wrong, I'm not questioning your statements that the 180 AB has a slightly higher BC than the 180 BT. That's good news. :wink: Some of that certainly could be due to length, differing CG location and resulting differing stabalization effects depending upon the twist, etc.... Lots of different variables.
My point was weight is the heavy hitter here. If length by itself made that much of a difference, Barnes' advertized BC's might actually be somewhat realistic instead of extremely inflated such as they are. That's a good thing for you guys. :wink:
Just looking at the 30 Cal BT's, for example:
125 g, BC = .366. By just adding 25 grains to the same shape you'd expect the BC to be .366*150/125 = .439. And yet the 150 is only advertised at .435.
The 150 has a BC = .435. Add 15 grains to the same shape and you could expect .435*165/150 = .479 but the 165 is only advertised at .475.
Do this for the rest of them and it seems, if Nosler's advertised BC's are accurate, the 30 cal BT lost a little BC every time it got longer (a fair amount in the case of the 180) because the increase in weight more than covers the difference.
Don't get me wrong, I'm not questioning your statements that the 180 AB has a slightly higher BC than the 180 BT. That's good news. :wink: Some of that certainly could be due to length, differing CG location and resulting differing stabalization effects depending upon the twist, etc.... Lots of different variables.
My point was weight is the heavy hitter here. If length by itself made that much of a difference, Barnes' advertized BC's might actually be somewhat realistic instead of extremely inflated such as they are. That's a good thing for you guys. :wink:
- Thread starter
- #7
Not trying to be a smartass here, but if weight, and not length is the real factor in the BC of a bullet, tell me why a Norma 6.5mm 139 grain SPBT has a BC of .402, while the Lapua Scenar 6.5mm 139 grain HPBT has a BC of .615. No weight difference, but a heck of a difference in the BC!!!!
I'm not sure which Norma bullet you're talking about (I didn't know they made a 6.5 139 SPBT?), but the Lapua is one sleek bullet.
The overall shape (meplat size, ogive, boattail length, etc) is just as important as weight (that's why round noses never have very good BC's even when heavy) it's just that the length is only a small factor for the overall shape compared with the others listed. Now some of those things cause the length to be longer--for example a 13 cal secant ogive and a long boattail will both make a bullet longer. But they are what give the bullet the higher BC--not the resulting increase in length.
Swift A-Frames, TBBC's, etc are usually longer than plain spitzers for a given caliber/weight and yet have much lower BC's. The flat points kill them more than the length helps them.
So of course shape is important, but of the various dimensions that describe that shape, length is about the least important.
Weight is important because holding everything else constant, an increase in weight will give a proportional increase in BC and it's what sets the practical limits. You're never going to get the highest BC's with light bullets. Sleek light ones can have higher BC's than blunt heavy ones...but not heavy ones equally as sleek.
The 200 AccuBond is as long as the 220 Matchking. It has an overal sleeker shape due mainly to its sharper point. And yet, its BC is a fair amount lower. This is simply because of its lighter weight. Add 20 grains to its weight without changing its shape or its length (thinner jacket, tungsten core, etc) and it would have a higher BC than the 220 MK. That's just the way it works.
Ballistic Coefficients tell you the rate at which a bullet will lose its velocity. Aerodynamic drag is not the only factor--that's half of it. The other half is weight. Because a given force of drag will decellerate a bullet that weighs 1/2 as much twice as fast. F=ma....
The overall shape (meplat size, ogive, boattail length, etc) is just as important as weight (that's why round noses never have very good BC's even when heavy) it's just that the length is only a small factor for the overall shape compared with the others listed. Now some of those things cause the length to be longer--for example a 13 cal secant ogive and a long boattail will both make a bullet longer. But they are what give the bullet the higher BC--not the resulting increase in length.
Swift A-Frames, TBBC's, etc are usually longer than plain spitzers for a given caliber/weight and yet have much lower BC's. The flat points kill them more than the length helps them.
So of course shape is important, but of the various dimensions that describe that shape, length is about the least important.
Weight is important because holding everything else constant, an increase in weight will give a proportional increase in BC and it's what sets the practical limits. You're never going to get the highest BC's with light bullets. Sleek light ones can have higher BC's than blunt heavy ones...but not heavy ones equally as sleek.
The 200 AccuBond is as long as the 220 Matchking. It has an overal sleeker shape due mainly to its sharper point. And yet, its BC is a fair amount lower. This is simply because of its lighter weight. Add 20 grains to its weight without changing its shape or its length (thinner jacket, tungsten core, etc) and it would have a higher BC than the 220 MK. That's just the way it works.
Ballistic Coefficients tell you the rate at which a bullet will lose its velocity. Aerodynamic drag is not the only factor--that's half of it. The other half is weight. Because a given force of drag will decellerate a bullet that weighs 1/2 as much twice as fast. F=ma....
- Thread starter
- #9
It seems to me that "shape" and "length" are related, at least to some degree. I certainly agree that weight is a most important factor in the BC, and as you have observed, with the same overall shape and length, the heavier bullet will always be better than the lighter equivalent. For your info, I have included a picture of: From left to right: Norma 139 SPBT; Norma HPBT and Lapua Scenar. Regards Eagleye.
Similar threads
