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  1. #1
    Member pocketshaver's Avatar
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    subsonic .308 win/7.62x51

    anyone successfully find subsonic loads that will expand say out to 50 yards?

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    Really Senior Member Bruce_in_Oz's Avatar
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    Never tried to brew sub-sonic .308.

    For a given bullet, the lower the muzzle velocity, the faster the required twist-rate. Most .308 barrels are 1:12" twist.

    What you need is a light-jacketed bullet with a pure lead core, something like 170-ish gn bullets used to load .30-30 Win. IF you can achieve stabilization at 950 FPS or less, you are on a winner.

    Finding a suitable "bulky" propellant may be an interesting challenge, as well.

    If you want to cough up for a custom barrel with a 1:7 inch twist, as used on the .300 AAC Blackout, go for it.

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    Really Senior Member Sunray's Avatar
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    The A-Max bullet isn't designed to expand at all. They're Match bullets. Not made for hunting anything but varmints either.
    Use a cast bullet. A cast bullet will expand or break up at lower velocities than any jacketed bullet. An HP requires velocity to expand in any cartridge.
    Spelling and Grammar count!

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    Really Senior Member Bruce_in_Oz's Avatar
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    Long, pointy bullets with plastic tips / hollow points are base heavy. They can be stabilized in flight through air in the traditional way.

    However, there are ALWAYS "imperfections" in any bullet. These will produce tiny deviations from a perfectly smooth trajectory. Furthermore, such long, rear-biased bullets take LONGER to "settle down" in flight than shorter, denser, flat-based bullets. At "short" ranges they have a tendency to upset during the transition from air to big, warm, wet targets, like deer. If a bullet strikes bone on the way in, it will definitely become distorted and thus erratic in its further travel.

    The front of a JHP is quite thin and thus subject to this distortion on impact. This will start to alter the rotational behaviour of the bullet. Bear in mind that we are talking about rotational speeds of thousands of revolutions per SECOND. Your basic wood-working router runs at something like thirty thousand revs per MINUTE; 500 per second. However, a router bit is (hopefully) not also traveling forward at a couple of thousand feet per SECOND, unlike a bullet. There is a huge amount of energy in the forward AND rotational speeds of a bullet.

    The catch is that in the stability stakes, rotational speed is the prime factor. Thus, to achieve minimal stabilization, the bullet has a "minimum" spin rate that will keep it pointed at the target. A bullet is a "wrongly designed" gyroscope. You can go with a slow twist and outrageous velocity or a very fast twist and low velocity. As in most of the rest of engineering, there are limits on the variables and I am leaving gravity out of it for the moment.

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    Member bcd8238's Avatar
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    Subsonic 308 7.62 x 51 loads

    Hi,
    This data was taken from the current ADI (Australianicon Defense Industries) reloading manual. The manual doesn't specify an action that was used to test these loads.
    :150 GR. Nosler Ballistic Tip Trail Boss .308" 2.800" start load 10.0 grain Vel 1176 fps @ 25800 psi Max load 14.0 grain Vel 1417 fps @ 27100 psi

    : 168 GR. Sierra Hollow Point Boat Tail AS30N .308" 2.800" - - - Max load 8.0 grain 1060 fps @ 26800 cup

    Maybe of some help.

    Rifle - ADI World Class Powders and Ammunition

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    Really Senior Member Bruce_in_Oz's Avatar
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    Trail Boss is a "bulky" powder designed for things like .44-40 and .45 Colt.

    It seems to be a sort-of "smokeless" Pyrodex.

    A .308 case has a lot more volume than a .44-40 or .45. Getting a consistent ignition and burn in that larger volume may be a challenge. Some folk use "fillers" like oatmeal (rolled oats) or Dacron wadding ( like the "Innerbond' used in loud-speaker damping or dress-makers "padding").

    The other catch is bullet seating. You can seat the bullet further back into the case to occupy some of this excess volume, but that is also tricky with bullets with long ogives. It's a bit difficult to get neck tension on the bullet ogive. Hence the use of round-nosed bullets with long parallel surfaces.

    With ALL of the various suggestions, however, whilst you will lose the sharp "supersonic crack" of the bullet traveling downrange, you cannot get rid if the obvious problem, muzzle-blast. It is interesting that the "boom' from muzzle blast is relatively easy to locate. The supersonic shock front gets reflected from every tree in the near vicinity and this results in a weird "whooshing" sound if you are some distance off-axis. If you are pulling targets on a range and supersonic bullets are flying overhead, the noise is definitely loud enough to cause hearing damage. This is why all "serious "reduced signature" systems go for reducing the muzzle blast before reducing muzzle velocity. It is very hard to locate the source of a supersonic bullet fired from a distance through a "can". The impulse of the shock-wave of the passing bullet hitting your eardrums will also temporarily "shut-down' your hearing to the point the residual firing "thump" will be inaudible.

    One further twist is the concept of a "reduced capacity, full-sized cartridge case for "discrete" shooting, consider the WW2 Germanicon "Nah-Patrone". One useful site (especially if you read what looks like Finnishicon /Suomi, and I don't), is here:

    7.92x57 Nahpatrone - Waffenlager.net

    The idea was to introduce a cylinder of solid "filler" inside the case to greatly reduce capacity. This provided optimum (smaller) combustion space for the reduced load of fast-burning powder. If someone has a nice picture of e sectioned cartridge, could they please share it?

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    Really Senior Member Bruce_in_Oz's Avatar
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    Was just talking about this subject to a mate. He tells me that on page 440 of "The Germanicon Sniper, 1914-1945", by Peter Sennich, there is a photo of a Nah-Patrone as made by Finnower Indistrie in 1943.

    Part of the "package" that included the various "Schalldaempfer" "mufflers".

    Apparently, the Russians were using silencers on M91/30 Mosin Nagants quite early in the war. There's a whole other ammo rabbit-hole to explore.

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    Contributing Member CINDERS's Avatar
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    My friend played with this in a 308 he is a gunsmith and used trail boss shooting off a rest to 100m and it was practically one holing them with minimal report from the shot was interesting to watch I have some and when I decide to go back to burning gunpowder will try some in a APRS 308 with 168gn Honrnady A-Max. Don't wait up it's Spring here and the M/bike riding is far more fun than lying prone baking in the sun....?

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    With a body like yours Cinders, you wouldn't be game to lay in the sun.

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