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140 gr .277 Nosler Accubond

 
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  #1  
Old 04-14-2013, 12:32 PM
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140 gr .277 Nosler Accubond

Users of the above bullet, what "real world" BC do you see?

Just curious as I have to change BC to ~0.6 in the shooter app to match observed drops.

Wondering if either my chrono is way off, or this is common with these bullets.
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Old 04-14-2013, 08:57 PM
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Re: 140 gr .277 Nosler Accubond

I would have a really hard time believing that the .277 140 gr nosler accubond has a .6 BC. A lot of times, people's chronos are giving them false readings or something else has been inputted into the ballistic app incorrectly. People fudge numbers in Shooter all the time and if you fudge BC, you will find that your actual drops will be off a lot more as you get a lot further out.

Really, the only thing that I mess with is velocity and then I go test it out as far out as I want to shoot. In the end, testing your set up as far out as you want to shoot it is the most important part. Then you can tweek BC and velocity to make them match as far out as you need. Nosler is notorious for fudging their BCs on the higher side to start with. So if anything, the BC would be lower than published by them.
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Old 04-14-2013, 09:52 PM
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Re: 140 gr .277 Nosler Accubond

Thanks for the reply.
Using .496 advertised BC and a muzzle velocity of 3225 matches actual drops as well.
Chrono velocity is 3080 fps, roughly 150 fps difference.

With a actory tube and mild load (63 gr RL22), 3080 seemed reasonable, but perhaps it is faster.
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Old 04-14-2013, 10:55 PM
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Re: 140 gr .277 Nosler Accubond

You may have one of those super fast 270s.

I've been accused of having the fastest 270 Win out there. Been shooting it since 1966. She's on her second barrel.

In mine, 28.5gr RL-22 pushes the 140 NAB right at 3200 FPS according to the Chrony Beta.

I don't trust the Chrony much. Only use it for ES and SD calcs on promising loads. I then go long range and watch for vertical dispersion.

I use the 0.496 bc and adjust velocity to get the drops correct.

Each rifle will produce a different bc for any given bullet. I don't suppose the difference is all that large but is observable as distances increase.

The main objective is to hit the point of aim and I have better luck using the published bc and adjusting velocity.

To get a 0.6+ bc with the 140 NAB and 150 BT I had to repoint the bullet with a brass tip which also increased the weight almost 10 grains.

55.5 grains of PP 4000 MC causes the chrony to read 3225. I'll validate that velocity as soon as the wind quits.

7828ssc gets the old girl well over 3300 fps mv which sure seems a bit much for the winny. However, barrel and case life has got to suffer. Thus I backed down to the PP 4000 MC velocity which produced exceptional groups.
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Old 04-15-2013, 12:33 AM
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Re: 140 gr .277 Nosler Accubond

Quote:
Originally Posted by BlackSS View Post
Users of the above bullet, what "real world" BC do you see?

Just curious as I have to change BC to ~0.6 in the shooter app to match observed drops.

Wondering if either my chrono is way off, or this is common with these bullets.
BC's are usually going to run a bit lower than the mfg's listed bc's but they are going to vary in the real world due to a lot of factors starting with your muzzle velocity.

The best thing to do is just once you have a load you are liking validate your drops at three different ranges beyond 100yds and then adjust MV and BC in your program until it matches those drops.

Once you do that you should be very close to right at just about any range out to the point of the bullet becoming transonic.
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  #6  
Old 04-15-2013, 09:04 AM
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Re: 140 gr .277 Nosler Accubond

3200 fps? Are you guys shooting .270 WSMs? With the Nosler book's middle load of Ramshot Hunter (54.5) and a 24" factory barrel, I'm getting an expected 2850 fps with the 140 accubond. I know it could be loaded hotter, but an additional 350 fps is astonishing.
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  #7  
Old 04-15-2013, 10:46 AM
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Re: 140 gr .277 Nosler Accubond

I am shooting a wsm
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