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Old November 3, 2011, 03:38 PM   #1
Scouter19D
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.308 How to get 178 gr faster?

I'm using the Hornady 178 gr. A-Max, and trying to figure out why the quickest load listed in the 8th Manual is 2400 max in service rifle and through 90% of other .308 loads listed. Not that speed is the essence of performance, but for those long, long, and longer shots, and after seeing what similiar weighted bullets have as velocities, why isn't it pushed faster in the book? Even alliants website lists WAY more powder and velocity for a 180 gr Speer. The M118LR has much faster velocities as well. Any thoughts?
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Old November 3, 2011, 03:54 PM   #2
mehavey
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See www.6mmbr.citymaker.com/f/Sierra308Win.pdf

I'm using the "usual suspect" powders loading the 175SMK to exactly 2,550 (chrono'd) to equal my `81 M118Match ammo with no problems.... and w/o straining any pressure limits (50-52ksi)
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Old November 3, 2011, 04:15 PM   #3
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Thanks for the site. Interestingly, the charges for any given powder are very similiar to Hornady's loading for the 178 gr AMAX. Only difference is, the velocities are at least 100 fps, sometimes 200 fps different. Can't see that happening in only 3 gr deviation in bullets.... Time to get a chrono and start working up a load. Perhaps 2400 fps is all I really need for the bullet in question....
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Old November 3, 2011, 04:28 PM   #4
Jim Watson
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Lyman has load data for the 178 Amax up to 42 gr IMR 4895 = 2600 fps just as an example with a common powder. But that is 60,400 psi, too.
Do you want to hammer your M1A that hard?
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Old November 3, 2011, 04:41 PM   #5
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Well, even with the Adj. Gas Plug up front, the answer is no. But I would settle for the 2500 fps range if its safe. Looking at the Hornady Manual, it's not even listed under Service Rifle, and only with three powders in .308 Section. Only one of which is locally available. None of which I use. Or want to use. May have to pick up a Lymans. Thanks for the heads up on that! Kinda makes my day.
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Old November 3, 2011, 05:21 PM   #6
mehavey
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Here is what produces a measured 2,550fps±12 @56°F out of my standard 22" M1A:

175SMK/IMR4895*/42.4gr/BR2/WWcase** 2.800"OAL
QL=2,554/50,448psi

*Lot#7984/Ba=0.512
**55.6grH2O

Note that I drop down to 42.0gr in the summer for similar velocities

Note also that this exceeds Hornady/Speer's Max, but is more than a grain under Lyman's Max
and 3.5 grains under IMR/Hodgdon's Max. Moreover, I would be flying blind doing this
(or changing powder lots) w/o both a chronograph & tailored QL burn rates.

My lawyer reminds me, of course, that YMMV

Last edited by mehavey; November 3, 2011 at 05:29 PM.
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Old November 4, 2011, 07:19 PM   #7
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mehavey

I'm using the same load you are 42.2 grains.
Standard 22" M1A @ 2575 here in Arizona at 90 degrees.
It's a great CMP comp load, grand kids are shooting up
my remaining stock
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Old November 4, 2011, 09:09 PM   #8
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If you pull the tables and take a look, even at 600yds, I bet the wind drift with an extra 100fps you will need the same number of 1/2MoA clicks.
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Old November 4, 2011, 10:10 PM   #9
mehavey
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The 175SMK/2,550fps figure is to guarantee the bullet doesn't drop below supersonic before
reaching 1,000 yards, even with a nominal headwind.

For practical hunting distances with the M1A, however, 2,400 at the muzzle would do just fine.
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Old November 5, 2011, 08:18 AM   #10
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Looking to do some target shooting, between 300 and 800 yards. No hunting. That's what ultimately drove the choice of the AMAX. I shot some Black Hills Gold and LOVED it, but can't pay $30 a box all the time. So maybe I don't need that much speed to reach 800 yards effectively? This is all pretty new to me. 350 is my longest engagement to date.
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Old November 5, 2011, 09:30 AM   #11
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2,300fps muzzle w/ a 178A-Max against a 15mph headwind will get you to 800 still doing 1200 -- comfortably supersonic
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Old November 5, 2011, 09:34 AM   #12
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The 175SMK/2,550fps figure is to guarantee the bullet doesn't drop below supersonic before
reaching 1,000 yards, even with a nominal headwind


Mehavey--- According to the riflemans journal you need a MV of 2850 to stay at Mach 2.1 at 1000 yards. Please elaborate on your post as i am trying and failing to get a 175 Serria Match to 2850. Best i can get is 2730 and that is showing pressure signs.

Any help would be great.
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Old November 5, 2011, 10:27 AM   #13
mehavey
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Supersonic = Mach-1 ~ 1,130fps at sealevel STP

The reason you don't want drop below s/s in precison shooting is that dropping through the shockzone perterbs flight. You either want to be definitely sonic or definitively supersonic -- but not "trans"sonic right at the target. (Then you don't know what's going to happen.)

Here's the exterior ballistic for an AMax starting at 2,300:



(If you bump muzzle velocity up to 2,550, you push that remaining 1,200fps/supersonic velocity out to 1,000 yards)
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Old November 5, 2011, 11:46 PM   #14
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If you are only shooting out to 800 you can even get away with 168gr bthp bullets at 2650 fps. I wouldn't shoot 168's past 800 but they will reach out there.

175s or 178's will do it with less wind drift though...

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Old November 6, 2011, 08:42 PM   #15
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I'd look at the 155gr SMK.
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