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> Revisiting .308 twist, in cold weather and with a suppressor
Revisiting .308 twist, in cold weather and with a suppressor
@ 09:45 pm (GMT) |
Federico CalboliHi All, I hunt with a .308 with the old 1/12 twist, with a suppressor. I go up to 9.7 grams (155 grains) because when it is cold (say, -20C) I feel that that all the barrel can safely handle without a baffle strike (not that I ever had one, and I plan never to have one). In fact if someone said go down to 8 grams in cold weather I'd say they have a point (but it is pretty light for moose, even at the distance we hunt at).I plan to get another .308, and I basically can get it as 1/10 twist. How much heavier could I go with bullet weight? One thing I would like to do is to use subsonics to hunt beaver, but Lapua suggest a 1/9 twist for their .308 subsonics (they are 13 grams), something that would be extremely aggravating to get (I can get 1/10 for quite a lot more cash, I doubt I could justify 1/9, even if I could get it). So bonus question: would 1/10 be OK with subsonics (at seriously close range I accept) without accidentally making the suppressor explode? Extra info: moose range is 100 metres max, beaver I'd say 30 max. Which I understand makes me a total wuss in a long range forum, but TREES! |
Replies
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@ 09:47 pm (GMT) |
Federico CalboliRe: Revisiting .308 twist, in cold weather and with a suppressorAnd if it not clear, all the questions also imply a suppressor in cold weather. |
@ 08:25 am (GMT) |
Nathan FosterRe: Revisiting .308 twist, in cold weather and with a suppressorHi Federico, this might be another instance where the delivery (wording) of information is counter productive. The big problem we have at the moment is that folk think of bullet stability in black in white terms - the bullet is either stable or in a state of such yaw that all sorts of bad things can happen such as baffle strikes, keyholing etc. But its not that cut and dried.If you are using the Berger calculator, you will see that it has a below 1 section titled unstable. The next section is titled marginally stable (1.1 to 1.5). The issue here is the use of the word marginal. For a guy shooting out to 300 yards, an SG of 1.3 is quite all right (think 190 to 200gr BTHP bullet at 2400fps in a 12 twist at 15C). It only becomes a problem if attempting to reach way out. At -20C, a very long projectile may become unstable in a slow twist barrel but in your case, if you are using a flat base bullet, the SG will remain high even if using a heavy weight bullet. In my experience, an SG of 1.4 is very good. The bullet remains stable out to long distances without bullet jacket / core stress that can be induced when the SG is over 1.5 (specifically fast twist magnums). As for baffle strikes, one must factor in the actual baffle bore diameter and concentricity of the suppressor relative to the bore. These are the major issues with bullet stability (within reason reason) being secondary to these. If we take the ASE suppressor as an example, the bore is 10.4mm (.409"). The bullet diameter is 7.82mm (.308") which is a generous amount of room (2.58mm or 1.29mm per side) for the bullet, provided the unit is square to the bore. The bullet would have to be quite unstable in order to produce 1mm yaw per 100mm. But if you are extremely worried, there is a simple solution - don't use the suppressor. The 10 twist will stabilize some subsonic loads - ideally a round nosed / wide HP style bullet. The Lapua 200gr FMJ might be a bit of a moot point because it produces pin hole wounds and even small game will run after being hit unless head shot. As you know, if a beaver runs its basically goodbye. This kind of set up is generally quite a let down. Other examples include M1 carbine, 9mm and Blackout if using anything other than specialized projectiles such as the Hornady Sub-X which still putts out (wounding) after about 75 yards . In practice, a .22LR with suitable projectiles produces a larger internal wound / faster killing than some of these cartridges (FMJ's) including the M1 carbine. If you are able to obtain the Hornady 190gr Sub-X and hand load it, it will stabilize in a 10 twist. The 190gr Sub-X bullet length is 1.3" and the G1 BC is .437. An increased twist rate would help a bit with expansion but I would not get too carried away with it as you will likely find that the whole thing is a bit bla after you have played around with it for a bit. OK, hope that helps a bit. All the best. |
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