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Ace12
February 6, 2006, 06:02 PM
Im shooting 130 grain in my 270wsm right now with a BC of .433. The 140 grain has a BC of .496. Does this mean the 140 grain will shoot better groups?

J.D.B.
February 6, 2006, 06:44 PM
Nope, BC refers to how well the bullet cuts through the air. Lower= easier. How closely a bullet is matched with it's mission,gun,and loading, and how good the gun is, how well the shooter can shoot.......these all bear on the group size one can achieve with a given combination of all these things.
Josh

ocabj
February 6, 2006, 07:43 PM
Higher BC is better for longer ranges, which is where BC comes into play.

You will notice that a lot of the varmint bullets have a fairly low BC, yet shoot amazingly small groups up to 200 yards simply due the the chambering of the gun and the velocities used to push the bullet.

TX_RGR
February 6, 2006, 08:26 PM
no.

impact
February 6, 2006, 08:30 PM
Im shooting 130 grain in my 270wsm right now with a BC of .433. The 140 grain has a BC of .496. Does this mean the 140 grain will shoot better groups

No

A boat tail bullet will have a better BC than a flat base bullet with the same weight bullet. The boat tail will have less drag. But the boat tail will not stabilize as well as a flat base bullet right out the barrel. (sometimes) A boat tail can yaw or wabble but stabilize quick. I have heard of BR guys saying that some boat tails will shoot better at 200 yards than 100 yards. I'm sure twist come into play with all this as well.

I have had good luck with boat tail bullets. I do however have one gun. Falling block in 218 Bee. A three inch group is about all the gun will do with boat tails bullets at 100 yards. Reload with flat base bullets and it becomes a tack driver.

But I will say there is way more to accuracy than FB or BT type bullets!

P-990
February 6, 2006, 08:37 PM
BC just indicates air resistance (hopefully I've got that right). Higher BC bullets just cut through the air better.

Anyway, the boat-tail versus flat-base thing seems to indicate that flat-based bullets are better for groups at 100 yards. This is a blanket statement though, for I have a .260 bolt-gun that shoots its best 100-yard groups with 140gr Sierra Gamekings, which are a boat-tail. I have noticed in my AR-15 that 1-MOA accuracy at 100 yards does not always translate to 1-MOA at 300 yards, depending on the bullets used. Dinky little 50-55gr pills shoot great at 100 yards; not so good at 300 for me. Big 77gr slugs group wonderfully at 200 and 300, but aren't so photogenic at 100-yards, though not bad either.

armedtotheteeth
February 8, 2006, 07:46 AM
I hope you enjoyed your class in Ballistic coeffecients. Tonight , read pages 102 -234 from your reloading handbook and write an essay on hand casting bullets.
High Bc = good (IE 50 bmg 650 gr fMJ)
Low bc = bad ( 45-70 Flat nose),
This is for long range shooting. I aint looking to start a war about the 45-70 here, JUst for comparison purposes you guys, Calm down!

I hope you get the picture

ConRich
February 8, 2006, 09:31 AM
It is my understanding that high BC = less drag which means less drop in velocity as the bullet travels down range. This should result in a flater trajectory. This would be more noticable at longer ranges but probably not at all at 100yds.

Rich

Jim Watson
February 8, 2006, 10:41 AM
A friend of mine has a .223 that was set up for the 69 gr SMK before heavier .22 bullets came out. It will stabilize the high BC 75 gr A-Max but will not group it as close... in calm air. When the wind blows, the heavier/longer bullet is moved less.

The effect is small at short to medium ranges and I doubt it matters much in a hunting rifle.

armedtotheteeth
February 8, 2006, 07:17 PM
I am not so sure it is a slipping through the air thing as much as it is a resistance to change in trajectory. I amy be way off track here , but a heavier bullet of one shape will always have a higher Bc than a lighter bullet of the same shape . ( or something :confused: ) I see and understand it as it resists changes in velocity better. I think heavier bc bullets are effected less by wind than lighter ones. Assuming they are at the same velocity. The more i talk the dumber i get. Im going to get another beer. anyone else want one. I like mine half beer half v-8, with a healthy dose of Habenero sauce

30Cal
February 8, 2006, 07:25 PM
A higher BC bullet will be less susceptable to environmental factors (drop and wind mostly). It usually works out that bullets with significantly better BC's are higher quality bullets IME.

armedtotheteeth
February 8, 2006, 07:29 PM
Yeah, i think thats pretty much what i said. Or something. we are on the right track. Any engineers out there??

P-990
February 8, 2006, 09:03 PM
attt,

I've always thought that BC measured aerodynamic drag. Maybe we're both right? Or maybe both wrong? :confused:

But I tend to agree with 30Cal; speciality high BC bullets tend to be better bullets from what I've seen as well. I know one long range shooter with a .284 Winchester. He was throwing some 185gr 7mm Bergers that were ridiculously flat shooting. He mentioned something like only a 5-6 minute change from 2 to 6! :eek:

Gewehr98
February 8, 2006, 09:53 PM
I hope you enjoyed your class in Ballistic coeffecients. Tonight , read pages 102 -234 from your reloading handbook and write an essay on hand casting bullets.
High Bc = good (IE 50 bmg 650 gr fMJ)
Low bc = bad ( 45-70 Flat nose),
This is for long range shooting. I aint looking to start a war about the 45-70 here, JUst for comparison purposes you guys, Calm down!

I hope you get the picture

Somewhat broad brush strokes in the .45-70 description. While they're not suitable for leverguns, meet these high-BC .45-70 bullets, either available online or cast from readily-available moulds. All sport a BC greater than .400, with some approaching .500:

http://www.bpcr.net/site_docs-results_schedules/documents/Dan_Theodore_NASA_Bullet_Report_MAR_2005_files/image002.jpg

http://www.pauljonesmolds.com/45013.jpg

http://www.buffalobillsshootingstore.com/images/product/963.jpg

I shoot the second bullet from the left in the assortment immediately above, it's become one of my favorite long-range Creedmoor loads for .45-70. Flat nosed .45-70 bullets do have their purposes, but not everybody has to be handicapped with low-BC bullets in that chambering. ;)

impact
February 8, 2006, 10:38 PM
I think I was reading somewhere in my Lyman book that a bullet flys from the base not the nose. In other words the base of the bullet is more of a factor than the nose.

A boat tail bullet allows air to fall in behind the bullet and creat less of a vacuum. That = more BC. The flat base bullet has more vacuum behind the bullet because of the design of the bullet. That = less BC. It's all about the drag or the ability of the bullet to fly through the air.

Because a flat base bullet has less BC it will shoot better at close range. The vacuum acts like a stabilizer for the bullet. But it will also shoot good at long range but will have more drop.

This is one reason I take such great care in not to damage the base of a bullet when reloading. If I just nick the base while seating the bullet you will have a flyer! Now boat tails will seat better or easyer than flat base bullets.

More BC = Corvette. Less BC = Hummer:D

Speaking of cars! You know that in NASCAR they put tails on the cars to push the back of the car down to give the rear of the car more traction. Take the tail or wing off and the car and it goes squirrelly. Kinda the same thing with bullets