Subsonic .308 loads

3

308Loader

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Minnesota finally decided that I can own a suppressor. I will be applying for my stamp soon:D. Supersonic v/s subsonic loads in .308 Win suppressed? To take full advantage of the suppressor at 100yrd targets, would it be wise to load subsonic? Only looking to shoot at small game targets like, prairie dogs, rabbits, soda cans and such. Moreover what would a subsonic load component list look like?

barrel length & twist
Brass
Primer
Powder
Bullet
 
Hodgdon 2015 Annual Manual:
150 Nosler BT
Win brass
Fed210M
24" barrel-1-12"
COL: 2.8"
Trailboss
10.0gr 1176 fps @ 25800 PSI (start)
14.0gr 1417 fps @ 27100 PSI (max )

There are many others but this manual was on top of the pile. I would be cautious about going to heavier bullets unless you happen to have a fast twist barrel as the longer bullets combined with low velocity may not provide satisfactory accuracy.
 
A good buddy of mine shoots .308 "S/S" and those loads are SO quiet. Not sure exactly the charge but I do know he prefers the 200 gr SMK's and Trail Boss powder right about 9gr if I remember correctly.
 
TRAILBOSS!!!!

175gn Nos HPBT

Im not in front of my load data right now but its silly quiet thru my SDN-6. Loads of fun (pun intended)
 
In my old Savage Hog Hunter which had a 20" barrel and a 1/10 twist I would load Hornady 208 A-Max's with 11gn of Trailboss. With my AAC SDN-6 can on it you could literally hear the hammer hit the firing pin.
 
The longer and heavier the bullet, the easier it is for Trail Boss to keep you sub-sonic. You will, however need faster twist as the bullet gets longer. It's just not as much difference as most people suppose because you are staying out of the transonic range and air resistance (drag) applies less force to destabilize the bullet.

Keep in mind the 10" twist, if you have it, was originally chosen for the 30-40 Krag to fire 220 grain round nose bullets. Round nose bullets are short for their weight, making them easier to stabilize.

Another trick that works at subsonic velocities but not at supersonic velocities is to try to achieve some static stability to assist the spin. This is done by choosing a bullet whose center of gravity is in front of its center of pressure. Most any boattail bullet turned backwards will fit that description. Just be aware you are reducing powder space when you do that, so it cuts down on the maximum powder charge. That a common trick in Finland and other countries where the Hollywood hype about suppressors hasn't entered the "common knowledge", and not overwhelmed the good sense to reduce noise pollution. They even consider you rude for not using one out of consideration for your neighbors. Therefore, suppressors may be purchased over the counter as a standard gun accessory in that country.

If you try that trick for increasing stability a little, then you will be up against having a much lower ballistic coefficient. The assumption is you will shoot small game at fairly short ranges with it.
 
I shoot subsonic 308 in my backyard, use cast and coated 150's with 10gn of trail boss.

Pretty useless really, might as well get a 45 acp and shoot 230s, will cost less and have more energy than a 220g 308 bullet at the same speed and punch a bigger hole.
 
Guess it depends on what your doing. Guess I really don't do much more than play with my subsonic 308 and 300 blk loads, the same thing that I do with my 45 and 9mm loads too. That said I do have pistol caliber rifles, so it is not like comparing a pistol to a rifle in terms of accuracy.

If I am hunting with SS and it's not just an armadillo tearing up the yard or some other small pest, I generally use a 405g or heavier with my 458, brings a lot more energy than the others can deliver.
 
As far as the center of gravity forward on the bullet, and a heaver bullet with more bearing surface to deliver more energy accurately, what about round nose jacketed bullets? What is the trail boss powder that suites it well for subsonic loads? looked for it at a few stores couldn't find any.
 
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Trailboss is a donut shaped pistol powder that is pretty fast and very bulky. It comes in 9oz containers (&5lb) but costs as much as a pound of other powders.

http://www.imrpowder.com/trailboss.html

If you try and down load a rifle powder to subsonic you will not develop enough pressure for good results. Pistol powders will allow you to though and TB allows fairly high load densitys because is it so bulky. 10 gn's fills a 308 case over half full.
 
308Loader said:
As far as the center of gravity forward on the bullet, and a heaver bullet with more bearing surface to deliver more energy accurately, what about round nose jacketed bullets?
Click to expand...

The round nose's CG is still behind its CP, but not by nearly as much. The reversed boattail gives you a longer thinner bottle rocket stick hanging out behind it, and that's what any additional stability comes from. AFAIK, the hollow base wadcutter is the only standard commercial design where CP is behind CG.

Long bearing surface prevents tilting a bullet as much, but even a short bearing surface bullet has a limit to how tilted a barrel will let it be. The first study I saw was for the FMJ 173 grain M1 Type bullet, which is the match version of the old M1 Ball bullet, with the difference being the M1 Type has no crimp cannelure. The bearing surface on it is only about 3/4 of a caliber. Not a lot. But even that bullet, tilted to the maximum a barrel will allow without straightening it (about 0.004" off-axis), only opened groups about 1 moa. Most bullets you load will have less tilt than that and you can take steps to minimize the tilt if you choose to, eliminating the issue.
 
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