BC confusion

[Tex_Hunter]

So Im new around here, been reading the forum and various discussions for probably 3 months and finally registered tonight because I have a question that has been burning a hole in my brain for quite a while.

I currently own a .308win that has recovered 95% of the deer it has been aimed at over its lifetime (5% were definite operator error), absolutely love it, but recently read a ballistics table I stumbled upon for a 270WSM and fell in love. I know for paper punching the 7WSM and 300WSM are probably better but for hunting out to 600yds on East Texas whitetails a 270 WSM in 150gr is about to make my wallet lighter... gotta convince the wife why I need to replace a perfectly good hunting rifle first (shes sitting on the couch across from me scowling as I write so my case may not be so strong right now).

Anyways, back to the question that has driven me crazy for nigh on a month. I load my .308 with 180gr nosler ballistic tips, I know that's way too much bullet for whitetails but my gun loves absolutely loves the 180grainers and printing .25-.50MOA 100yd groups out of model 70 featherweight with nothing more than a massaged trigger makes me feel like a real hero from time to time, my excuse is that I hunt in heavy brush and Im lazy and dont like walking around in the cold among huisache thorns trying to find a deer that ran. Anyways, I also like the 180BT because of the .507 BC they make a nice long range load, as I get a chance to shoot at 1000yd plates from time to time. Anyways, to my new love, the 270WSM I noticed the 150gr nosler BT's for this check in just shy of .5BC at something like .493 whereas a Hornady interbond of the same weight is a whopping .525 which at the advertised MV of 3100fps is a mere 6MOA holdover at 500yds when sighted at my preferred 200yds. For hunting I don't care much past 500yds because that is the longest I can viably shoot at my current hunting spot, so a >.500 BC is really not a big deal. Now when I read this I looked up the 180gr interbond for .308 a respectable but not astonishing .480, I was a little bit baffled because my findings from the .277cal bullets would suggest it to beat out the Nosler BT but for some reason or another the .308cal Nosler is better BC wise than the Interbond despite being similar bullet designs to their smaller .277cal little brothers. Anyone have a guess as to why?

 

[Michael Eichele]

Welcome to the site.

There are many factors that will come into play as to why one manufacture publishes a value and another manufacturer posts another for a very similar design. One may test them at 100 yards where the other tests them at 200 yards, small differences is design (it does not take much design difference to make a 3-5% difference). There are often times differences between manufacturer's testing systems etc.....

That said, the difference between the IB and the BT is about 5%. Like you said, at the ranges you are talking, 5% does not matter much. Factory published BC's are more of a better place to start than an absolute anyway.

If you really want to open the can of BC worms:

http://www.longrangehunting.com/forums/f19/lets-argue-about-bcs-68234/

That will keep you up all night once or twice.

Good luck!

M

 

[MontanaRifleman]

So Im new around here, been reading the forum and various discussions for probably 3 months and finally registered tonight because I have a question that has been burning a hole in my brain for quite a while.

I currently own a .308win that has recovered 95% of the deer it has been aimed at over its lifetime (5% were definite operator error), absolutely love it, but recently read a ballistics table I stumbled upon for a 270WSM and fell in love. I know for paper punching the 7WSM and 300WSM are probably better but for hunting out to 600yds on East Texas whitetails a 270 WSM in 150gr is about to make my wallet lighter... gotta convince the wife why I need to replace a perfectly good hunting rifle first (shes sitting on the couch across from me scowling as I write so my case may not be so strong right now).

Anyways, back to the question that has driven me crazy for nigh on a month. I load my .308 with 180gr nosler ballistic tips, I know that's way too much bullet for whitetails but my gun loves absolutely loves the 180grainers and printing .25-.50MOA 100yd groups out of model 70 featherweight with nothing more than a massaged trigger makes me feel like a real hero from time to time, my excuse is that I hunt in heavy brush and Im lazy and dont like walking around in the cold among huisache thorns trying to find a deer that ran. Anyways, I also like the 180BT because of the .507 BC they make a nice long range load, as I get a chance to shoot at 1000yd plates from time to time. Anyways, to my new love, the 270WSM I noticed the 150gr nosler BT's for this check in just shy of .5BC at something like .493 whereas a Hornady interbond of the same weight is a whopping .525 which at the advertised MV of 3100fps is a mere 6MOA holdover at 500yds when sighted at my preferred 200yds. For hunting I don't care much past 500yds because that is the longest I can viably shoot at my current hunting spot, so a >.500 BC is really not a big deal. Now when I read this I looked up the 180gr interbond for .308 a respectable but not astonishing .480, I was a little bit baffled because my findings from the .277cal bullets would suggest it to beat out the Nosler BT but for some reason or another the .308cal Nosler is better BC wise than the Interbond despite being similar bullet designs to their smaller .277cal little brothers. Anyone have a guess as to why?

Welcome to LRH Tex Hunter!

I think for close in in brush hunting it doesn't make much difference what your bullets BC is. My uncle in PA was the most successful PA deer hunter I ever knew and he used a .308 back in the day when when no one hardly ever heard of a bullet's BC.

On the next subject of "manufacture's published BC's", you gotta take them with a real big grain of salt. First off, they are G1 BC's which are more suited for bullets that are not low drag boat tail type bullets. Next, you simply can not trust what most of the major bullet manufacturers are listing for BC's. Bryan Litz, who is Berger's chief ballistician, has done a lot of testing of many of the more popular low drag bullets. If you go to this Ballistic calc site, his BC's are factored into these bullets which you can select on a drop down menu.

JBM - Calculations - Trajectory

It looks a little intimidating at first, but you'll get used to it.

The .270 WSM is a real sweet cartridge, but it's a barrel burner too (you might check out "nitiriding") That cal is not know for high BC bullets.

308 or 270 WSM... both will do the job for you on TX whitetail (hope your wife isn't reading this ), but the 308 will make a bigger hole.

Anyone have a guess as to why?

Because they all have their own criteria and agendas

Hope that helps,

Mark

 

[Tex_Hunter]

Thanks for the early replies, like I said, I was more interested as to why for the .277cal bullets the Interbond has a 6% higher BC than the equivalently weighted .277cal Nosler BT but when you step to .308cal projectile it is now the Nosler BT has a 5-6% higher BC than the Interbond, even though the respective bullet construction for each type didn't fundamentally change. It just made me think (a dangerous road to go down, I know) that for one caliber Bullet A has a higher BC, but in a bigger caliber Bullet B is now the higher BC, because reason would suggest that the proportions simply grew between the .277 and .308cal projectile and thus if bullet A has the edge in the smaller caliber, it continues to have the edge against bullet B in the larger caliber as well, assuming of course you are comparing equivalent weights. Although I guess the long skinny 150gr .277 projectile could potentially lend itself to the design of the Interbond and the stubbier 180gr .308 bullet tips to the Nosler BT, or as Michael and Montana both mentioned the mfg is BSing me and I need to just get a box of both and see where Im at after some paper punching.

On a side note, Montana you mentioned the 270WSM as a barrel burner, that mean its more so than the other WSM's or their long action big brothers? Or the same?

 

[MontanaRifleman]

Thanks for the early replies, like I said, I was more interested as to why for the .277cal bullets the Interbond has a 6% higher BC than the equivalently weighted .277cal Nosler BT but when you step to .308cal projectile it is now the Nosler BT has a 5-6% higher BC than the Interbond, even though the respective bullet construction for each type didn't fundamentally change. It just made me think (a dangerous road to go down, I know) that for one caliber Bullet A has a higher BC, but in a bigger caliber Bullet B is now the higher BC, because reason would suggest that the proportions simply grew between the .277 and .308cal projectile and thus if bullet A has the edge in the smaller caliber, it continues to have the edge against bullet B in the larger caliber as well, assuming of course you are comparing equivalent weights. Although I guess the long skinny 150gr .277 projectile could potentially lend itself to the design of the Interbond and the stubbier 180gr .308 bullet tips to the Nosler BT, or as Michael and Montana both mentioned the mfg is BSing me and I need to just get a box of both and see where Im at after some paper punching.

On a side note, Montana you mentioned the 270WSM as a barrel burner, that mean its more so than the other WSM's or their long action big brothers? Or the same?

Tex, basically the smaller the hole (cal) the powder has to go through and the more powder, the more it will burn the throat. The 7 and 270 WSM's are barrel burners for the most part. The 300 WSM has a rep for good barrel life, up to 3000 rounds.

bigngreen shoots a 270 WSM and maybe he will chime in.