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208 AMax in 1/12 twist 308Win, Range Report

 
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  #1  
Old 01-12-2008, 07:11 PM
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Join Date: Dec 2001
Location: Canyon Ferry, MT
Posts: 245
208 AMax in 1/12 twist 308Win, Range Report

This might be of interest to the 308Win shooters.

Bought the 208s primarily for the 30-06. Figured I'd give them a whirl in the 308, even though I kinda expected stability issues at relatively low MV, and 1/12 twist. Here's what I found:

Load:

Brass: Win
Bullet: 208gr AMax, moly'd
Powder: RL15, 44.5gr
Primer: CCI 200
OAL 2.90"
MV: 2480 fps


Rifle:

Rem factory bbl/chamber 700 VS cut to 22"
1/12 twist
A5 stock
Leupold MK4 3.5-10x40 M1, GenII mildot from Premier Reticles
Badger Ord hardware


Did some 100 yard shots to get a zero. It was windy, but all looked fairly good, at sub-moa.


Went out to 560 yards to see if stability would be an issue at midrange. Results were sub-moa, at about 20F, in 5-15 winds from 9 0'clock.

Here's a pic of the 560 yd results:



Stretched it out to 1120 yards in 15-25 mph wind from between 1 and 2 o'clock (About half-value). Temp 35F.

Took a couple rounds to get on steel. I was at 40 moa up, and 7 moa right. I put 10 downrange. 6 hits, 4 misses left (wind wasn't my friend). The black square is 5" by 5" at the outside edges. I'm kinda surprised it was stable out to this distance, at 1/12 twist, 2480 fps MV.

Here's a pic of the 1120 yard target:



Did more load development using W760 to maximize velocity. Here's the meat and potatoes,

Moly'd 208 AMax
Win brass
W760
50.0gr
2560 fps
22" barrel
OAL 3.002"

That OAL gives a .002" crush on chambering.

After the relative success at 1120 yards, I wanted to go to an extended range in the transonic region, to see what would happen.

Results are interesting, but inconclusive as to stability. I THINK the bullets were stable, based on one recovered jacket, and relative size of the "group", or more accurately, "beaten zone".

Shot the 50gr W760, 2560 fps load at a range of about 1850 yards. That distance is beyond the ability of my laser. I went to a lased 1000 yards, then got in the truck, zeroed the trip odometer, and drove .5 miles further out. The odometer isn't too precise, but I figured I had to be somewhere between 1800-1900 yards.

I had mounted the MK4 16X, to give the little 308 some longer legs, in regards to internal travel. I had 83 moa "up" available.

From my drop chart, it looked like I would need about 87.5 moa at 1800 yards.
Code:
Gunsite altitude : 4500 ft.
 Bullet weight    : 208 grains or 13.48 Grams
 Muzzle velocity  : 2560 fps
 Crosswind speed  : 10 Mph 
 Ballistic Coefficient:  .648
 Range  Velo Time of  Energy   Path    Deflection    Total  Sight correction  Target
        city  flight            to    at crosswind    drop   for setting new   lead
                                LOS    of 10.0 Mph             zero range     33 fps
-------------------------------------------------------------------------------------
ˇYards   fps     s    ft.lbs.   in.    in.     MOA     in.   Clicks     MOA     yds ˇ
-------------------------------------------------------------------------------------
|    0  2560  0.0000   3027    -1.9    0.0   -----     0.0   ------    -----    0.00
X  100  2445  0.1190   2762     0.0    0.3    0.30     2.7      0.0     0.00    1.30
|  200  2334  0.2442   2515    -3.9    1.7    0.83    11.2     +5.5    +1.88    2.67
|  300  2225  0.3765   2286   -14.3    4.4    1.40    26.1    +13.3    +4.57    4.12
|  400  2119  0.5151   2074   -31.7    8.2    1.95    48.1    +22.1    +7.60    5.63
|  500  2016  0.6597   1877   -56.7   13.0    2.48    77.7    +31.6   +10.86    7.21
|  600  1915  0.8101   1694   -89.7   18.8    3.00   115.3    +41.6   +14.30    8.86
|  700  1818  0.9713   1527  -132.9   26.6    3.63   163.0    +52.8   +18.15   10.62
|  800  1725  1.1428   1375  -187.3   36.1    4.31   222.0    +65.1   +22.38   12.50
|  900  1636  1.3233   1237  -253.6   47.3    5.02   292.8    +78.3   +26.93   14.47
| 1000  1551  1.5117   1110  -332.2   59.8    5.71   376.0    +92.3   +31.75   16.53
| 1100  1469  1.7080    996  -424.0   73.7    6.40   472.3   +107.1   +36.83   18.68
| 1200  1392  1.9177    895  -533.4   90.0    7.16   586.3   +123.5   +42.47   20.97
| 1300  1322  2.1400    807  -662.0  108.5    7.97   719.4   +141.5   +48.64   23.40
| 1400  1257  2.3722    729  -809.7  128.8    8.78   871.7   +160.7   +55.24   25.94
| 1500  1198  2.6168    663  -980.5  151.2    9.62  1047.1   +181.6   +62.43   28.62
| 1600  1146  2.8728    607 -1176.2  175.6   10.48  1247.3   +204.2   +70.21   31.42
| 1700  1102  3.1400    561 -1399.1  202.0   11.35  1474.8   +228.6   +78.59   34.34
| 1800  1063  3.4173    522 -1650.8  230.2   12.21  1731.1   +254.7   +87.58   37.37
| 1900  1030  3.7039    490 -1932.7  260.0   13.07  2017.6   +282.5   +97.13   40.51
| 2000  1001  3.9995    463 -2246.5  291.4   13.91  2335.9   +311.9  +107.24   43.74
I dialed up 80 moa on the erector, and applied an additional 2 mils via reticle holdoff. About 87.5 moa total. 3-5 mph wind from 3 o'clock, I dialed 5 moa windage into it.

Touched off the first round, and waited the approx 3.5 seconds for it to get there. Didn't see or hear anything. Snow on the ground made seeing misses nearly impossible. I fired four more rounds with the same data, and figured I'd find craters somewhere near the target.

I drove back to the target. Found my 5-shot group in the dirt about 15 paces in front of the target. My wind call was good. Had I opted a 3 mil elevation holdoff, instead of 2, I would have likely connected with a few.

View of target, note hits short of target.


I only found remnants of one bullet. It appears to have hit point first.


The overall "group" on the ground, viewed from the perspective of the trajectory, appears about 12" wide, with one flyer to the right about 24" out. Vertical spread looks like about 24".

Picture of the individual craters are here:
montanamarine/Targets/1850 yards - Photobucket - Video and Image Hosting

To me they look pretty much like they were coming in point first.

When the snow melts and the ground is dry enough to get a dust signature, I'll try this again. Bullet splatters on the steel should be very telling in regards to stability.
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  #2  
Old 01-12-2008, 07:38 PM
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Join Date: Jan 2005
Location: OK
Posts: 2,145
WOW, thats interesting, really stretching the old .308.

If I read that chart right you have 140+ feet of drop at 1800 yards!
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  #3  
Old 01-12-2008, 08:07 PM
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Join Date: May 2005
Location: Montana
Posts: 432
Where do you live, Townsend?

We need to get together and do some longrange shooting.
__________________
Magic
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  #4  
Old 01-12-2008, 09:31 PM
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Join Date: Dec 2001
Location: Canyon Ferry, MT
Posts: 245
magicofmt,

I'm about 25 miles NNE of Townsend, about 20 miles E of Helena. Near the NE corner of Canyon Ferry Lake.

Are you nearby?
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  #5  
Old 01-12-2008, 09:35 PM
Silver Member
 
Join Date: Dec 2001
Location: Canyon Ferry, MT
Posts: 245
Coyboy,

LOL, yes, it's sorta like a mortar at that distance. I figured it's dropping about 2" per yard, at 1800 yds. Max Ord. a little over 50 feet above LOS, at about 1100 yards.

Last edited by MontanaMarine; 01-12-2008 at 10:00 PM.
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