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Re: Long range with a short barrel .308 ?
Posted: Mon Oct 03, 2016 6:51 am
by meles meles
The DTA SRS Covert with a 16" barrel seems to do well at 'extended' ranges, ie from 800 to 1000 mards, but then that has a 1 in 8 twist to the rifling. Is that (along with a 'efty load of course) the major factor in keeping the bullet fast and stable?
Re: Long range with a short barrel .308 ?
Posted: Mon Oct 03, 2016 7:30 pm
by Scarface
Laurie wrote:VLDs aren't great at transonic speeds, although as always there seem to be exceptions. Traditional blunter designs often do better in this role, hence a number of older Sierra models such as the original shorter 155gn MK (#2155) used in the NRA ammo.
Berger makes a 175gn BT specifically for this role, the OTM Tactical designed to be fired from 20-inch semi-auto military 'sharpshooter rifles' and tested by its designer Bryan Litz successfully (claimed 1-MOA grouping) at 1K fired from a 20-inch barrel Larue at around 2,650 fps. Unfortunately it's as rare as hen's teeth in this country and uncommonly expensive with it. Incidentally, it was also specifically designed for the 11.25-inch twist, this being what the US military have adopted as a standard spec for sniper / sharpshooter rifles.
The 185gn Berger BT LR Juggernaut is the obvious and outstanding choice, an excellent long range design at any velocity, and generally stable in all speed zones. An older and bit cheaper alternative is the antediluvian 190gn Sierra MK, long used by Match Rifle shooters because of its proven trans and even subsonic good manners. Both designs are fully stabilised in your rifle's rifling pitch. Another superb and very old L-R design is the rebated boat-tail Lapua 185gn D46, a .30 match variation of the Finnish military 7.62X53R machine-gun bullet designed to wring maximum range out of the belt-fed guns.
In either case, to get them moving as fast as possible, use Lapua 'Palma' small primer brass with SR Magnum primers and consider a 'high energy' powder, Reload Swiss RS52 or Viht N550 being the obvious candidates. Plain single-base Viht N150 also achieves surprisingly good MVs from the 185 Juggernaut in the Lapua small primer brass. You will cane the barrel throat with any of these combinations, so it's best to restrict them to very long range shooting. You will also need a lot of elevation adjustment available in your scope set-up.
Hi Laurie
Just the sort of info I was looking for thanks for taking the time to reply. If I go the Berger route what sort of MV can I expect using Palama brass and the Vit powders, is 2600fps a possibility from a 20 inch barrel ?
Also what about COL will the jug need to be close to the lands or will it handle a bit of a jump.
Vit 550 & 150? Do I take it if the bullet weight goes up the burn rate needs to be slower ? Even with a short barrel?
Scope wise I have a Vortex HSLR 6-24 x50 with a 20 MOA rail that gives me about 55moa on the turret and another 30 on the reticule from a 200yd zero. At the moment I only get to shoot on the longer MOD ranges about five times a year so I'm not too worried about throat wear I'll just enjoy the day
Re: Long range with a short barrel .308 ?
Posted: Mon Oct 03, 2016 8:33 pm
by WelshShooter
I can get over 2600fps with a 167gr Lapua Scenar using Reload Swiss RS50 (similar burn rate to N140) from a 20" barrel. If you're using the double based Vihtavuori N5xx powders then you should be able to manage 2600fps using a 175gr bullet.
Re: Long range with a short barrel .308 ?
Posted: Mon Oct 03, 2016 10:05 pm
by Laurie
2,600 fps should be just on using Palma brass. Can't be certain though as every barrel and throat are different. Use hard bolt lift and/or any appearance of ejector marks as high pressure indicators - primers won't show anything until they blow. This is very tough brass and will give multiple firings with pressures that kill standard Lapua brass in three or four such heavy loadings.
The heavier the bullet, the slower burning the powder needed. Some don't burn entirely in the barrel and in any event, you'll likely get a fair muzzle blast.
You'll likely need around plus 40-MOA on a 100 yard zero to be 'on' at 1,000, so your scope and mounting arrangements will be fine.
Re: Long range with a short barrel .308 ?
Posted: Tue Oct 04, 2016 1:06 am
by stu47
I've just finished load work up for a TMK175 with RL15 through my Tikka M55 22" 1in12 twist - accuracy won't worry the F Class or FTR lads but I can hit a figure 11 with 7 out of 10 fired. The misses are my bad wind calls - still learning!
This has replaced my go to load of SMK175 with RL15 but the TMK's use 0.2grains less to achieve the same 2545fps.
I tried N140/ 150, IMR4895, H4895 and H4064 but RL15 came out on top - again.