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same weight/ same POI ?

 
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  #15  
Old 03-09-2012, 09:17 AM
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Re: same weight/ same POI ?

Quote:
Originally Posted by Mikecr View Post
Another qualifier to the question is changes to seated ogive distance to lands -w/resp to a gun's personality. This, because tune greatly affects POI.
And going from a tangent ogive to secant for example, all else equal, can have a big affect on POI and performance in general until optimum seating is again determined.

I can't imagine changing bullets, even lot to lot of the same, without seeing some difference.
In two different 30 caliber rifles shooting both 150 and 172 grain bullets, each with different ogive and jump to lands distances varying about .040", the difference in point of impact at 200 to 300 yards was less than 1/2 MOA.

And across several .308 Win. barrels shooting different lots of 168 and 190 grain bullets in each one, I never saw more than 1/4 MOA change in each ones point of impact from 200 through 600 yards.

I can imagine changing bullets, even lot to lot of the same, without seeing any significant difference. Especially at the shorter ranges.
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  #16  
Old 03-09-2012, 09:39 AM
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Re: same weight/ same POI ?

Mada I generally have more than 1 bullet with me. a tough heavily constructed hunting bullet and a long range Target type bullet. The my rifles are set up for maximum expected yardages with the long range bullets and generally carried with hunting bullets. An Example: if a 10 inch group is acceptable at 1000 yds. ( vitals zone) then it is also acceptable at 100 yds. the differences are not that dramatic for the hand loader but that is the idea. If the same 100 yard zero is actually the goal the answer is definitely yes but both loads would probably need tayloring'. but at short ranges for hunting no practical difference and easy to do if that is your goal.
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  #17  
Old 03-09-2012, 09:57 AM
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Re: same weight/ same POI ?

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Originally Posted by ken snyder View Post
An Example: if a 10 inch group is acceptable at 1000 yds. ( vitals zone) then it is also acceptable at 100 yds. the differences are not that dramatic for the hand loader but that is the idea.
I doubt anyone on these forums will put their first shot inside that 10 inch vital area at 1000 yards more than 10% of the time in hunting conditions afield.

I know I can't even do that on a thousand yard rifle range with known zeros and a .6 MOA rifle and ammo.
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  #18  
Old 03-09-2012, 10:44 AM
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Join Date: Jul 2010
Posts: 420
Re: same weight/ same POI ?

Mada I generally have more than 1 bullet with me. a tough heavily constructed hunting bullet and a long range Target type bullet. The my rifles are set up for maximum expected yardages with the long range bullets and generally carried with hunting bullets. An Example: if a 10 inch group is acceptable at 1000 yds. ( vitals zone) then it is also acceptable at 100 yds. the differences are not that dramatic for the hand loader but that is the idea. If the same 100 yard zero is actually the goal the answer is definitely yes but both loads would probably need tayloring'. but at short ranges for hunting no practical difference and easy to do if that is your goal.
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  #19  
Old 03-09-2012, 02:01 PM
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Re: same weight/ same POI ?

The answer is that the trajectories are different.

The question is whether or not it's significant for your situation.

Here's an example based on 2 factory loads...

Federal Gold Medal: 308 Win 168g Sierra MatchKing BTHP
BC=.463
2650fps, 10mph wind from 3 o'clock
100yds, elev=0, windage=.75
300yds, elev=4.75, windage=2.25
500yds, elev=11.75, windage=4.25
700yds, elev=21, windage=6.50

Federal Gold Medal: 308 Win 175g Sierra MatchKing BTHP
BC=.513
2600fps, 10mph wind from 3 o'clock
100yds, elev=0, windage=.75
300yds, elev=5, windage=2.25
500yds, elev=12, windage=3.75
700yds, elev=20.75, windage=5.75
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  #20  
Old 03-09-2012, 02:33 PM
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Re: same weight/ same POI ?

Quote:
Originally Posted by rscott5028 View Post
The answer is that the trajectories are different.

Federal Gold Medal: 308 Win 168g Sierra MatchKing BTHP
BC=.463

Federal Gold Medal: 308 Win 175g Sierra MatchKing BTHP
BC=.513
That's the difference between the short boattail on the 168 and the long one on the 175.

Sierra changed their original 30 caliber 180-gr. HPMK's boattail from the long one to a short one made to the same specs as their 168. It never shot as accurate as their old ones. The US Army team contracted Sierra to make their 180's with the longer boattail under special order; they knew they were more accurate at the longer ranges.
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  #21  
Old 03-09-2012, 06:34 PM
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Join Date: Sep 2011
Location: Las Vegas, NV
Posts: 92
Re: same weight/ same POI ?

Quote:
Originally Posted by justgoto View Post
I shoot a Hornady 150gr FMJ and a Hornady 150gr SST in the same rifle. The charge weight is .5grains different, the BC is .017 different; the POI difference is less than moa at 400 yards.

So I practice with the FMJs that are 2/3s the price of the SSTs.
This is exactly the answer I was hoping for.. See, what I want to do is use Hornady 162gr SST and 162gr A-Max. So I can switch between the two bullets depending on my target. THANK YOU !!

May I ask why the your charge weight is different? Is it just because. Or velocity issues. Or whatever the case may be..
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