looking to load up some subsonic loads for my Tikka t3. Anyone have any advice? Does the twist make a difference on the loads?
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subsonic 308?
- Thread starter atracksler
- Start date
It might, its twist + speed that creates stability. Also .308 has pretty dismal ballistics sub-sonic; speed is it's biggest asset.
Yes. Slower bullets need a faster twist to stabilize.
This calculator will help you to determine whether or not the bullet will be stabilized:
http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi
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When I was in Africa I met with several biltong hunters who used a subsonic load in their rifles. They loaded the bullets backwards. I thought they were crazy but they swore it gave them better accuracy and better expansion because the base of the bullet was not jacketed. When I got home I researched it on the net and found that there was actually some truth to what they said.
What number am I driving for here?
The calculator will color code your results as not, somewhat, or completely stabilized.
Click on Terms and it will tell you that you want 1.3. When you run it it will give you an output with red, yellow & green. Just like a stop light. Technically anything over 1 is stable, but 1.3 is a better real world number.
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Just out of curiosity, what are you planning on doing with these loads?
I ask b/c pistol bullets (in the form of pistol chambered carbines) perform better subsonically for hunting applications (eg Light loaded .357 Mag). Even a sub-sonic 30-30 might work better.
I've been tempted to experiment in the past, but always end up convincing myself to try a different platform.
I ask b/c pistol bullets (in the form of pistol chambered carbines) perform better subsonically for hunting applications (eg Light loaded .357 Mag). Even a sub-sonic 30-30 might work better.
I've been tempted to experiment in the past, but always end up convincing myself to try a different platform.
cockpitbob
NES Member
Makes sense. For stability you want as much weight in the nose as possible. Hollow-based rifled shotgun slugs and badminton birdies are the ultimate examples. If you aren't going to spin them fast, the last thing you want is a light-nosed, long-nosed hollowpoint.
Be careful. I've seen write-ups of people working up low velocity loads and had them stick in the barrel. Try to find published "reduced loads". The old reloading manuals used to list those.
ETA: the JBM calculator uses equations assuming round nose bullets which are more nose heavy than most.
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CockpitBob, you reminded me of something. I think in the article that goes with the Miller Stability Formula states that is primarily intended for supersonic flight. I'm not sure how correct those numbers will be at subsonic flight.
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cockpitbob
NES Member
Look what I found in a box in the basement. From the 1987 Speer #11 reloading manual. The slowest they go is 1600'/s, but it could act as a sanity check on other info you get. ("Red load" = reduced load)
I think the version on JBM corrects for even subsonic velocity.
He can check it against Greenhill which was intended for subsonic projectiles.
The Hodgdon site has a 150gr load using IMR Trailboss that's close to subsonic - 1176 fps.
I think that this would vary greatly from rifle-to-rifle and bullet-to-bullet. I can't imagine that a flat based bullet jumping into a sharp angled leade would be very accurate. I wouldn't doubt that it's hard hitting at short range though.
Ok after spending 45 minutes looking through Don Miller's article and other resources, I tried google.
Bryan Litz made a sniperhide post about the MSF saying that it had some limitations for subsonic projectiles. No further details as to the why though.
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Bryan Litz made a sniperhide post about the MSF saying that it had some limitations for subsonic projectiles. No further details as to the why though.
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38ExtraSpecial
NES Member
does anyone have a copy of bryan lit.'s book? he does some talk about sub sonic ballistics. pretty cool stuff. i let my uncle borrow the book so i can't look anything up
definitely a must have book for anyone that shoots long range rifles
definitely a must have book for anyone that shoots long range rifles
I have both of Bryan's books. His chapter on bullet stability does not speak to the M.S.F. and it's use for predicting stability factors for subsonic projectiles. If his book had an index (my one minor gripe), I might be able to determine if it was hidden somewhere else in the book, but it's not in the stability chapter.
I hope the OP posts his results. Should be interesting.
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I hope the OP posts his results. Should be interesting.
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Regarding load data, the lowest velocity published data (Lyman 49th) I could find used 190 gn cast bullets and 10.5 gn Unique (1289 fps) or 10.0gn SR-7625 (1174 fps), which are both pistol powders.
Those loads are still obviously supersonic, but I think the only way you get there is with even lower charges of pistol powder...which will result in a very low density case fill. My only experience with this are some plinking loads I've made with 45-70 and small charges of Unique. Different animals...45-70 is a much heavier bullet, w/ a slow twist and a straight wall cartridge.
For .308 there will probably be a fine line between sub-sonic and no-sonic (read: stuck in barrel).
Those loads are still obviously supersonic, but I think the only way you get there is with even lower charges of pistol powder...which will result in a very low density case fill. My only experience with this are some plinking loads I've made with 45-70 and small charges of Unique. Different animals...45-70 is a much heavier bullet, w/ a slow twist and a straight wall cartridge.
For .308 there will probably be a fine line between sub-sonic and no-sonic (read: stuck in barrel).
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Seems like this would be a poor idea for me...
just quieter....
Do you have any information I could read on that? I have been running my .44 with some hot loads for hunting and if I get better results with lighter loads I am all for it
You won't get better results w/ light loads, but if having a sub-sonic bullet is a requirement you'd be better off using a pistol bullet vs a rifle bullet b/c they are designed to perform at much lower velocities.
Normally a 158 grain .357 Mag out of my 18" Marlin will go ~ 1600 to 1800 fps using full charges of magnum (slow) pistol powder like WW296. However if I take that same bullet and load it w/ <6 gns of a fast powder like WW231 or Unique then I get ~1100 fps (sub-sonic) and its much quieter.
At these low speeds I would expect the .357 Mag HP bullet to perform better than a .308 spitzer.
If the rifling twist is fast enough to stabilize it, you're going to get much better medium-long distance performance with a spitzer bullet than with a pistol bullet at subsonic velocities.
True enough, I assumed short distances (0 to <100 yards). Pistol bullet BC's are comparatively awful so they slow down really fast.
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