Posted: 10/18/2008 12:12:14 PM EDT
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Seeking advice on barrel length from those of you with experience. Regarding .308 / 7.62 calibre - have any of you shortened barrels ? How short did you go ? The loss of velocity - was it excessive ? |
Tricky one. 26" seems a popular length and I wouldn't have normally gone below 20", but having recently shot one with a 12", yes that's 12" barrel (with a claimed but personally untried accuracy of average 1.3moa 100 out to 500yds) I might rethink. Not sure on velocities as you reduce, 26" usually around 2600-2800. I think if you were tempted by the short stuff you would have to accept it would not be a precision rifle past say 600yds, but I'd very much like to be proved wrong..... 
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OK I've been playing with Quickload and have been doing some calculations which are listed below. For the purposes of this I have used Sierra's 150gn FMJBT bullet which is not dissimilar to the 144, 147 & 155 gn bullets available in NATO offerings. Powder chosen is W-748 and the load is 44gns which gives a chamber pressure of 53685 psi which is under the SAAMI max of 55114 psi. Column listings are as follows Barrel length, velocity, muzzle energy, powder burn percentage, ballistic efficiency, muzzle pressure 26" 2871 fps 2746 ft/lbs 99.35% 34.0% 6574 psi 25" 2850 fps 2705 ft/lbs 99.20% 33.5% 6896 psi 24" 2827 fps 2662 ft/lbs 99.07% 33.0% 7247 psi 23" 2803 fps 2616 ft/lbs 98.90% 32.4% 7630 psi 22" 2777 fps 2568 ft/lbs 98.70% 31.8% 8050 psi 21" 2749 fps 2518 ft/lbs 98.48% 31.2% 8513 psi 20" 2720 fps 2464 ft/lbs 98.21% 32.5% 9024 psi 19" 2688 fps 2407 ft/lbs 97.90% 29.8% 9591 psi 18" 2654 fps 2347 ft/lbs 97.55% 29.1% 10224 psi 17" 2618 fps 2282 ft/lbs 97.13% 28.3% 10934 psi 16" 2578 fps 2213 ft/lbs 96.63% 27.4% 11734 psi 15" 2534 fps 2139 ft/lbs 96.05% 26.5% 12643 psi 14" 2486 fps 2059 ft/lbs 95.36% 25.5% 13683 psi 13" 2433 fps 1972 ft/lbs 94.52% 24.4% 14881 psi 12" 2374 fps 1877 ft/lbs 93.51% 23.2% 16275 psi From that you get 500 fps less velocity between 26" & 12" legal limit barrels but there is still enough retained energy to keep it legal. More interesting though is the increase in muzzle pressure, which must have a detrimental effect on suppressors. As for what you're looking for, you only need a 1/8 barrel if you're going to shoot 240+ gn bullets and none of the rifles you mention has that twist rate, so a custom build would be necessary. Don't know about exterior ballistics but if anyone wants to punch these numbers into Infinity or similar, we'll get a better idea of drop and drift. I do know that it won't be good though |
Aiming to treat myself to a .308 for Christmas. Achieve ? Well, it has to be suppressed and its length has to be manageable for occasional stalking / foxing too. It needs to be deer legal. Target work out to 600 yards. I did once have a Remington 700 cut down to about 16". At the time I only did our local clubs 200 yard matches and 200 yard McQueen - never tried it out to 600. Bullpup such as DSR-1 would be ideal ( 26.5" barrel and suppressor and overall shorter than standard rifle ) but UK price is steep. I might be able to get it cheaper in Germany but not definate. The alternative is to cut down a standard rifle and use an over the barrel suppressor. Considering the Sako TRG22 or Unique Alpine TPG-1 at the moment. Sako do a folding version with 20" barrel but standard is 26". Unique Alpine is 25". I know there are fully suppressed rifles out there - The AWS from Accuracy International The Fully suppressed TRG22 from LEI The Fully suppressed version of the UA TPG-1 They are nice but - A 16" barrel is the norm for these fully suppressed rifles. BUT UNFORTUNATELY with a 1 in 8 twist designed for heavier subsonic bullets. I will be using standard match ammo so that twist would be no good. |
Mark, Excellent info - many thanks. Looks like the muzzle pressure stays reasonable to 18" - It gets more excessive shorter than that ! Assuming a 200 yard zero and 168 grain ammo - 26" barrel - drop at 600 yards is about 72" 20"..................................................81" 18"..................................................85" 16"..................................................92" 14"..................................................100" 12"..................................................111" So, looks like 18 or 20" is about the shortest to go for - the increase in muzzle pressure and bullet drop is not TOO bad there. |
Why would it be 'no good'? What do you call 'standard match ammo? Unless you're shooting extremely light bullets a 1:8" twist will be fine. You won't need a 1:8" or faster unless you want to shoot 240gn+ bullets but you can still shoot lighter bullets from fast twist barrels. I regularly shoot 52gn MatchKings and 50gn GameKings from a 1:7.7 barrel, they're really moving fast. Looks good when I punch paper and still messes up a fox's day. I've not seen evidence of bullet break-up. |
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I've a 20" barreled .308 T3 Tactical. Outstandingly accurate at sensible ranges like 600 yards with most ammuntion. Also if I do okay (I'm not a brilliant shot) it will pull regular V bulls on the 1000 yard target at Bisley. I'm sure a better shooter and handloads would improve on that. I'm not sure what the size of the V is on the 1000yard target, I think it's 20" When I bought it, my plan was for a one stop shop no gun smithing required rifle ie it has a Picatinny rail, was threaded with a brake, has a great trigger, detachable mag and a very smooth action and adjustable cheek piece. I didn't envisage taking it to 1000 yards, as I'd listening and reading different things suggested that a longer barrel was required for this as velocity and acuracy would go tits up. This might be of interest to you about what happens to velocity when you take a hacksaw to a barrel. www.tacticaloperations.com/SWATbarrel/ I had planned on selling it after a time and upgrading, but I just can't justify it. It's too good! If you want something compact, what about a Remmy 700 LTR in an AICS folding stock? -although there is a bit of a weight penalty for the stock. |
Only going by the research I have conducted and the advice given by various manufacturers. Most .308's with full length barrels are offered in 1;12 - Sako in 1;11 ( claimed to be a compromise when shooting heavier buttets at extended range. Most .308s DESIGNED / INTENDED for subsonic bullets are in 1;8 - the subsonic ammo used tends to be 200 grain plus and at low velocity. It is claimed that a 168 grain .308 at 2600 - 2800 fps through a 1;8 barrel will not stabilise properly and accuracy will suffer. Therefore I believe that as I shall be only shooting match ammo at supersonic speed, the 1;8 barrel will be unsuitable for me. Having said that I would LOVE to be wrong as the fully supressed rifles I have seen with 1;8 twist would be very desireable if I can shoot supersonic rounds accurately through them. Anybody here have a .308 with 1;8 twist ? |
Interesting article - thanks for the link. |
I have two 30cal rifles, one with a 1:8" twist (300Whisper) and one with a 1:10" twist (308Win). Both shoot great. I mainly use 150 grain FMJBT bullets in both and in the Whisper I occasionally use with 220 subs. The 308 will have 168, 175 and 200/220HPBT bullets when I feel flush. Never seen any problems with either rifle with any of the bullets. Speeds are around the 1950-2200 fps with the 150gn bullets (Whisper) and 2500-2850 (308Win) depending upon powder and load choice (I just happened to testing both these today and the damn chrono decided to jump in the way of the bullets  but that's another story) and around the 1150fps with 220gn MKs. The 168 and 175s in the 308 were going at between 2650 and 2700, again depending upon powder/load/etc.OK, so it's only the Whisper that's a 1:8", but if you want more precise info on the 308 loads and speeds I got today, let me know. |
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If you want to shoot 200+ gn bullets subsonically, all you'll need is a .300 Whisper, but it won't be Bambi legal One other thing, in my experience, and that of others, you can not over stabilise a bullet. As Zediker said "I'd love to see something overstable" Slow twists don't shoot heavy bullets, but fast twists shoot everything |
I once saw/read an article that claimed you could overstabilise a bullet. Essentially it claimed that in a stabilised bullet the linear axis of the bullet would always be coincident with the path of the trajectory, whereas an 'overstabilised' bullet would always fly 'nose high', if that makes sense. Is that bollocks then? |
I've said it loads of times, you can't over stabilise bullets! However, too fast a spin rate could cause bullet break-up but I've not seen it (I've driven 52gn bullets extremely fast from a 1:7" and still had great groups). Just one point though it has nothing to do with bullet weight. Ever wonder why tracer doesn't stabilise in your 1:12" barrel? It's only 63gn after all. It's to do with the bullet length, or bearing surface actually. Tracer bullets are long (about as long as a 80gn Sierra) and so need the faster twist. Military barrels are 1:7" or 1:7.7" for this very reason, otherwise they'd only need to be 1:10" or 1:12" for those greeny weanies at 63gn. |
Yes and no. It's true that's the theory, but it's unmesureable. It may have an effect at extreme range, but for the lclubman shooter, which is us, we'll never know or be able to measure the difference. I built an AR a while back for an avid fox shooter who was adamant he wanted to shoot lightweight bullets. I convinced him to have an 8 twist as it'll be good all round. Well, he's a total convert and it turned out to be one of those genuine one hole group rifles. As for the over-stabilisation theory......when someone here can convince me that it makes a difference to their world championship winning score, I might begin to listen. |
Clucking bells - it seems everywhere one goes on this interweb thingy, one gets conflicting opinion - aarrgghhh So, if I am reading the above correctly, I should not worry too much about a 1 in 8 being too fast ? It should stabilise / overstabilise 168 grain bullets ? If I got the 1 in 8 barrel and found that it preferred heavier bullets - what is the heaviest .308 bullet available ( in UK ) in factory match ammo ? |
Federal GM 168 IIRC or you could be a real man and roll yer own 
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Use the Quick target program that was given to you. Follow the instructions to import the data from quick load and it will give you exterior ballistics which seem to be quite accurate. |