How important is bc?

[Michael Eichele]

Steve,

I cant argue whether or not flat base bullets are more accurate than boattails. I dont have enough experience to make a conclusion but I have read a number of opinions that they are so I'll accept it. Question is, how much more accurate are they? Boattailis are apparently accurate enough for 1K plus hunting so I think accuracy is a moot point. And boatail bullets, having a better BC, are less affected by enviromental conditions making them potentially more accurate in a sense at longer ranges.

Mark, you are 100% correct. That is why flat base bullets work well for 100 yard BR and boattails work well for LR matches and hunting.

 

[Fitch]

Sorry if I mussunderstood you. I was refering to your response to Jon A and not Steve. It appeared that you were dissagreeing with him and felt that he was spot on. I cant say you were wrong as you were not. I just thought you missunderstood what he stated.

M

No problem. I misunderstood you on my end as well. We are both looking for the truth.

I am enjoying this thread a lot. It was a good question that started it. I've learned quite a bit just thinking about it.

Thanks
Fitch

 

[RockyMtnMT]

I will have to agree that the boat tail does more for wind drift than I thought. The consensus is that the boat tail is directly responsible for the bullets wind drift.

I ran some #'s on two drastically different hunting bullets that pretty much backs up what everyone has said about bc's.

7mm Nosler AB 160g bc=.531
7mm RuM
3300 fps mv
3000 ft elev.
40 deg temp
300yrd zero
600yrd drop=39.4" or 6.3 moa
600yrd drift=18.8" or 3 moa (10mph)
vel=2318fps
1000yrd drop=188.3" or 18moa
1000yrd drift=59.2" or 5.7moa
vel=1772.3fps

7mm GS HV 120g bc=.390
Same rifle and atmosphere
4200 fps mv
600yrd drop=26.8" or 4.3 moa
600yrd drift=20.1" or 3.2 moa
vel=2653.2fps
1000yrd drop=138" or 13.2 moa
1000yrd drift=64.9" or 6.2 moa
vel=1867fps

Interesting to compare.

Steve

 

[Ridge Runner]

Good stuff. I'll also add another perspective into the mix people don't think about much (but should). Higher BC bullets are less sensitive to changes in weather.

Much like wind drift, for any given temp or pressure change, the error will be less with the higher BC bullet. Or looked at another way, the higher BC the bullet you use and the faster you shoot it the farther you can go with simple drop charts before needing to worry about weather changes.

If using a PDA for every shot it's not that big a deal, but understanding when you actually need to use a PDA and when you don't is something people should know. That distance being farther increases the odds when speed is needed in the field.

We all know our charts can't be perfect, the things we can control we can get darned close but not perfect, so the less we can dial and still make zero the closer the POI will be, the higher the BC the less you have to dial, the closer to perfect things are. Thats why I chose high BC bullets if there is one that is suitable.


Also shooting nosler accubonds, I've had matching exit holes from 500 yards to 1350 yards, the impact velocity at 1350 was 1650 fps, so even the bonded accubond will expand some at 1650 fps.
RR

 

[Movin]

Do rebated boat-tails give the best of both types? Do driving band bullets work like rebated boat tail?

 

[elkaholic]

Do rebated boat-tails give the best of both types? Do driving band bullets work like rebated boat tail?

IMO the rebated boat tails are the way to go. I make my own in .308 and they perform very well at 100 yards as well as 1000. Having said that, I've also had Bergers , A-Max and SMK shoot near one holers at 100 yards as well so go figure. The idea with the rebate is to insure uniform gas pressure as the bullet leaves the barrel. A normal boat tail has a greater chance of being unequal (unless the bevel is perfect) Apparently many of the normal boat tail manufactures are near perfect....Rich

 

[Mikecr]

Rich, have you observed any specific RBBT influences to BC and Sg?

 

[elkaholic]

Rich, have you observed any specific RBBT influences to BC and Sg?

I don't have a std. boat tail die so I don't have anything to compare apples to apples. Everything I make is RBT and they are accurate at all distances. It WOULD be an interesting comparison. Maybe I'll turn some SMK's into RBT's and compare the two against each other!!.......Rich

 

[MontanaRifleman]

Maybe I'll turn some SMK's into RBT's and compare the two against each other!!.......Rich

Good idea!

 

[Movin]

IMO the rebated boat tails are the way to go. I make my own in .308 and they perform very well at 100 yards as well as 1000. Having said that, I've also had Bergers , A-Max and SMK shoot near one holers at 100 yards as well so go figure. The idea with the rebate is to insure uniform gas pressure as the bullet leaves the barrel. A normal boat tail has a greater chance of being unequal (unless the bevel is perfect) Apparently many of the normal boat tail manufactures are near perfect....Rich

Nice! you must have checked Corbon out. Are you making any bullets heavier ( better BC ) than the 240 SMK? It sure would be interesting to see a 300 RUM in about 7 twist with a 295 grain high BC projectile!! For a little more money the same set up in a 30-378 ....

 

[elkaholic]

Nice! you must have checked Corbon out. Are you making any bullets heavier ( better BC ) than the 240 SMK? It sure would be interesting to see a 300 RUM in about 7 twist with a 295 grain high BC projectile!! For a little more money the same set up in a 30-378 ....

Believe me, I've had an awful lot of interest. If I could only figure out a way to make it worthwhile I would do it in a heartbeat! I could probably make up to about 260 in .308. That WOULD be a thumper in an ultra at about 2900' ....Rich
p.s. with a brass ballistic tip the B.C would be off the charts

 

[Movin]

A brass ballistic tip on a VLD should open at low velocity, high BC starting at 2900 out of a fairly light hunting set up...wow!! Long, long action to build off of...Money and time, we need money and time!!

 

[elkaholic]

a brass ballistic tip on a vld should open at low velocity, high bc starting at 2900 out of a fairly light hunting set up...wow!! Long, long action to build off of...money and time, we need money and time!!

yes we do!!:d