Subsonic .308 loads out of 1:12 twist barrel

This is a discussion on Subsonic .308 loads out of 1:12 twist barrel within the Cartridges & Calibers forums, part of the Sniping Related category; I am considering working up some subsonic 308 rounds for my sps-v. I currently shoot 175 smk's at 2600 fps with less than 1/2 moa ...

Results 1 to 10 of 10
  1. #1
    Senior Member ddd oo7's Avatar
    Join Date
    Mar 2011
    Location
    Memphis, TN
    Posts
    2,118

    Subsonic .308 loads out of 1:12 twist barrel

    I am considering working up some subsonic 308 rounds for my sps-v. I currently shoot 175 smk's at 2600 fps with less than 1/2 moa accuracy. I was wondering if the smk's will stabilize at 1050fps? The loading data center lists clays and tightgroup as powders for sub sonic rounds, but on the IMR site they say that trailboss can be used. Do I work up these loads like any other starting low and working up or is there another way. I want to be sure not to stick one in the barrel Also, I have heard that 30-30 bullets stabilize better at slow speeds. If I use 30-30's, do I seat them to the cannilure? If I do they are less than 2.800.
    Rem 700 sps-v .308 in AICS
    Thunderbeast 30P-1
    Tac Ops Tac 51 .260 on Surgeon action
    NRA Life-Member

  2. #2
    Senior Member RocketmanOU's Avatar
    Join Date
    Aug 2010
    Location
    Ohio
    Posts
    620

    Re: Subsonic .308 loads out of 1:12 twist barrel

    They should stabilize in a 1:10 twist at that muzzle velocity, yes. You can check here:

    http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

    Generally, shorter bullets will stabilize at lower spin rates (velocities) than longer bullets, hence the flatter-nosed .30-30 bullets with the nasty BC's will tend to do so. They're also likely to have more bearing surface though, so I can't say that the pressures would be the same as published data for other bullets. If you're talking about just using RN bullets (for which, for example, Hornady's manual lists data for the 308), I'd use the listed COL for seating depth, then the powder data from the manufacturer. If you search around, you'll find a number of guys out there using RN bullets in 308 for subsonic loads. Just remember that the chamber of the .30-30 and the corresponding leade will be different than that of the 380, so the cannelure won't necessarily be in the right spot if you're using .30-30 specific bullets.

    As far as working up a load, I'd stick to published data. If you look at IMR's site, they list only a maximum load for the Titegroup and Clay's loads, possibly because using less actually created higher pressures. This phenomenon is noted in several reloading manuals. Hornady comes to mind, on its description of the 243 Win. in the 7th edition, for example. Remember that pressure can be highly dependent not only on burn rate, but air space in the case as well.

    Good luck.
    Let us recollect that peace or war will not always be left to our option; that however moderate or unambitious we may be, we cannot count upon the moderation, or hope to extinguish the ambition of others. - Federalist 34

  3. #3
    Senior Member RocketmanOU's Avatar
    Join Date
    Aug 2010
    Location
    Ohio
    Posts
    620

    Re: Subsonic .308 loads out of 1:12 twist barrel

    Just saw that you have a 1:12 twist, not a 1:10 (RIF). Also, had a bit of a brain fart - the Miller formula doesn't apply very well to subsonic projectiles. Give me a bit and I'll come up with another model I dug up a long while back.
    Let us recollect that peace or war will not always be left to our option; that however moderate or unambitious we may be, we cannot count upon the moderation, or hope to extinguish the ambition of others. - Federalist 34

  4. #4
    Senior Member RocketmanOU's Avatar
    Join Date
    Aug 2010
    Location
    Ohio
    Posts
    620

    Re: Subsonic .308 loads out of 1:12 twist barrel

    Found it. There's an older routine written in basic that can describe subsonic stability - you would need roughly a 1:9 twist to stabilize the 175 SMK subsonically, assuming my inputs were correct.
    Let us recollect that peace or war will not always be left to our option; that however moderate or unambitious we may be, we cannot count upon the moderation, or hope to extinguish the ambition of others. - Federalist 34

  5. #5
    Senior Member ddd oo7's Avatar
    Join Date
    Mar 2011
    Location
    Memphis, TN
    Posts
    2,118

    Re: Subsonic .308 loads out of 1:12 twist barrel

    Thanks for the info. I won't waste powder and bullets trying the smk's then. I have about 2,000 170g round nose. They are only 1.004" compared to the 175smk's at 1.245, so they might stabilize. The IMR site recommends 168g sierra, but length wise they are about the same as the 175's. I actually have a few hornady bthp 168's and they are slightly longer than the 175 smk's. the imr site recommends 8 grains of titegroup for 168 smk's. I like the FTX's and might move up to them if I can get the ones I have to stabilize. Would you recommend starting at 7 grains or lower? would you load to 2.800"? I have been loading 2.950 on the smk's but the round nose should hit the lands sooner I would think.
    Rem 700 sps-v .308 in AICS
    Thunderbeast 30P-1
    Tac Ops Tac 51 .260 on Surgeon action
    NRA Life-Member

  6. #6
    Senior Member ddd oo7's Avatar
    Join Date
    Mar 2011
    Location
    Memphis, TN
    Posts
    2,118

    Re: Subsonic .308 loads out of 1:12 twist barrel

    Oh yeah, I started playing with this because I have a Thunder Beast 30P-1 on the way. It should be at my dealer in a couple of weeks and walking home with me in about 7 months if all of the paperwork goes well. When I get a new barrel, I will go with a faster twist, but as good as this one is shooting, I don't intend to replace it just yet. I might order a blank and put it in the safe so I don't have to wait on it though!
    Rem 700 sps-v .308 in AICS
    Thunderbeast 30P-1
    Tac Ops Tac 51 .260 on Surgeon action
    NRA Life-Member

  7. #7
    Senior Member ddd oo7's Avatar
    Join Date
    Mar 2011
    Location
    Memphis, TN
    Posts
    2,118

    Re: Subsonic .308 loads out of 1:12 twist barrel

    Well, I loaded up some rounds this morning and tested them this afternoon. I used Lake City brass, cci 200 primers, 8 grains of titegroup powder (almost the same as my .357 load), and 170gr round nose 30-30 bullets.

    The velocities were not as tight as I would have liked. High was just over 1,100, and low was around 1040. I had to adjust up 15 moa off of my 2600 fps 175smk round that I normally shoot. These were holding about 1.5 moa at 100 yards. I did not test any farther and do not have high hopes for them much past 200, but it is interesting none the less.

    I did not notice any keyholes on the paper. Is there anything in particular I would notice, or if the holes are round then I'm ok? I don't want to rip the baffles out of my suppressor when I start shooting through it.
    Rem 700 sps-v .308 in AICS
    Thunderbeast 30P-1
    Tac Ops Tac 51 .260 on Surgeon action
    NRA Life-Member

  8. #8
    Member
    Join Date
    Oct 2009
    Location
    western NY
    Posts
    41

    Re: Subsonic .308 loads out of 1:12 twist barrel

    Hi, I am not a veteran reloader but used to do quite a bit with older singleshot rifles. In large cases with smokeless power you get a lot of velocity variation depending on where the powder lies in the case. near the primer or away from it. So we used a light dacron or polyfiber wad to hold the powder to the rear of the case. Alternatively we would tip the rifle up before each shot to settle the powder to the rear of the case. The second option might not work real good for snipers I tried some sub-sonic 22LR in my Kimber 1911 and they tumble beyond about 30 yards! I am actually surprised they cycle the slide OK.

  9. #9
    Senior Member ddd oo7's Avatar
    Join Date
    Mar 2011
    Location
    Memphis, TN
    Posts
    2,118

    Re: Subsonic .308 loads out of 1:12 twist barrel

    I have considered a fill, but I intend to use these with a suppressor when it clears the ATF. I'm not real excited about the fill running through and getting stuck in the suppressor.

    Since I wrote this post, I have purchased a single shot 300 blackout with a 1:8 twist 16" barrel. This round is much better tailored to subs as it can handle 220's just fine and the case volume is significantly smaller. Now I don't intend to shoot subs out of my 308.
    Rem 700 sps-v .308 in AICS
    Thunderbeast 30P-1
    Tac Ops Tac 51 .260 on Surgeon action
    NRA Life-Member

  10. #10
    Senior Member
    Join Date
    Jul 2009
    Posts
    455

    Re: Subsonic .308 loads out of 1:12 twist barrel

    Theres a substance in life jackets called Kay-Poc
    when burnt it leaves no residue and as stated above
    you should keep the powder against the primer.
    I take things and make them better

Ads

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Similar Threads

  1. 300 Win Mag subsonic loads
    By Flims in forum Cartridges & Calibers
    Replies: 8
    Last Post: 12-30-2013, 02:38 PM
  2. subsonic loads in my m-14
    By ekaphoto in forum SOP
    Replies: 3
    Last Post: 04-15-2010, 12:08 AM
  3. Subsonic 308 loads
    By perpetual motion in forum Cartridges & Calibers
    Replies: 10
    Last Post: 11-10-2009, 07:40 PM
  4. Subsonic Loads
    By doubledown1 in forum Cartridges & Calibers
    Replies: 7
    Last Post: 07-12-2007, 11:36 AM
  5. Reduced loads and Subsonic loads
    By in forum Cartridges & Calibers
    Replies: 21
    Last Post: 04-29-2005, 02:34 PM

Search tags for this page

.308 subsonic loads

,
175 smk sub sonic loads
,
220 rn subsonic 1:11.25
,
308 sub sonice load data
,

308 subsonic load data

,

308 subsonic loads

,
sub sonic 308 load data
,
subsonic .308 load data
,
subsonic 308 12 twist
,

subsonic 308 load data

,
subsonic 308 loads
,
suppressed 308 1/12 twist
Click on a term to search for related topics.