.308 powder advice

[knewmans]

Need some advice for powder choice for .308. Everything works well at 600 but I want to see if I can nudge it upto supersonic at 1000yds.

Howa 1500 24" 1:12 twist. I don't know the history of the barrel but I suspect either the throat is long or rather worn as it is impossible to get a SMK 2156 near the lands.
PPU brass
Fed 210 primer
TR140 Powder
Temp about 13C for all testing

With 155gr SMK 2155 or 2156 I worked up to 46.2gr TR140 velocity peaking at 2710fps. There were no pressure signs I could see, primers still rounded. JBM suggests 2800fps would just be supersonic at 1000yds.

HPS factory 2155 ammunition chronos at 2735fps

It was suggested that a 175gr SMK might be more suitable. With 43gr TR140 (from Lyman manual but above Vhitavouri N140 max load) I had 2460fps with some primer flattening. JBM suggests 2650fps would just be supersonic at 1000yds.

I'm not particularly happy pushing the TR140 harder. The Vhitavouri data suggests that N550 could be an alternative and give me that extra velocity. The potential extra barrel wear of a double base powder doesn't worry me as I won't use it all the time and it could be an excuse to rebarrel anyway.

Does anyone have advice/experience to offer on a switch to N550?

[Laurie]

If you use a well reasearched G7 BC for these bullets, you'll find you need more velocity than 2,800 fps. The older 155 SMK (#2155) needs 2,950 MV to be reliably supoersonic at 1k, the newer higher BC model ~2,830-2.840.

But trans and supersonic boundaries are funny things and depend a lot on conditions applying at the time of shooting, so even those values may not be particularly reliable. The good news is that the older model has a reputation for respectable behaviour as it drops into transonic speeds, the last 100 fps above the speed of sound being the real problem zone, and usually goes through the sound barrier while maintaining stability. That's not to say there is therefore no problem as trans / sub sonic bullets usually see increased group dispersions, and wind effects may be dramatically increased.

Getting any bullet to stay supersonic at this distance from a 24-inch barrel .308 Win rifle is hard work, not to say getting on for risky pressure-wise or even near impossible.

N550 is not the powder to do it with in any event - too slow burning for 155s but well matched to 185-230s. If you want to risk peak pressure loads with an N500 series powder, use N540. You WILL see dramatically reduced barrel life though if you run it flat out.

Even then, you'd be lucky to get the required MVs - TR and F/TR rifles run 30-32 inch barrels because they're needed, not because the owners think they loook pretty.

With 155s, Ramshot TAC and better still Wild Boar (double-base ball types) will get you into the right sort of bracket and at higher MVs than N540. The alternative is to keep N550, but go to a heavier bullet. The Berger 185 Juggernaut is the obvious choice - if you can find any in stock of course, and if you don't mind prices at >£0.50 per bullet now. The old Sierra 190gn MK was a long-time favourite for very good reasons with 'Match Rifle' competitors to 1,200 yards before the 210gn VLDs appeared. It stabilises fine in a 1-12" twist rate (as does the Berger 185), and has a reputation for excellent manners approaching and at the speed of sound.

If you're going to run things on or straying beyond the red line, and you will with this set-up, you need a strong and preferably roomy case, and will also have to accept short case life with standard LR primed brass. That's Lapua or Norma cases to be used. However, for those who run hard and hot and want some sort of case life and personal safety margin for the sake of their eyes remianing in working order, THE case to use is the Lapua Palma with an SR magnum or BR primer. I don't know how PPU runs capacity-wise, but you need a fired unsized case to hold at least 56gn of water when filled to the brim. Thick wall cases hold appreciably less and increase pressures substantially.

[Dannywayoflife]

Laurie would ramshot big game be the right powder for the 190smk?

[knewmans]

Thanks for that reply Laurie. Certainly appreciate that 24" is less than ideal. Just looking to make the best of a mediocre job and you've given me some direction.

[User702]

I'm using pretty much the same setup as you (if you swap the howa for a remmy 700!) And i'm using 47.5 grains of TR 140 to power my 2156s. In the test shots i hvae done there have been no signs of pressure and the mv was a healthy 2883 fps 10 feet from the barrel.

How come you aren't happy using more powder than that?

[knewmans]

Although I don't seem to have pressure problems approaching the max load I've used there is very little change in muzzle velocity as if its approaching a limit. I can go higher and may well just to see but I'm not hopeful. Just wondered if there was a better solution than keep pouring more in the case.

Is your's a 24 or 26" barrel?

[knewmans]

Having read your Target Shooter article on the Ramshot powders Laurie Wild Boar seems like a good option to try. Time to measure my cases.

[Laurie]

TR140 (Reload Swiss RS50) has a suggested max charge around 46-46.5gn for a 155 with Commonside recommending 45.5gn in an RWS case under the old Sierra MK 155 to duplicate the NRA factory ammo which in turn produces maximum allowed CIP Maximum Average Pressure in a tight-bore TR rifle with a Bisley 150, Palma 95 or similar reamer used to cut the chamber.

Current .308 Win Remington 700s are produced with notoriously slack chambers with massively long throats which when coupled to a much slacker bore than used in a typical GB TR rifle drop pressures (and MVs) substantially. The long throat usually means that performance is substantially degraded too with 155gn length bullets due to large amounts of jump. Many US F/TR club shooters using factory 700 Police rifles load very heavy / long bullets starting with the Berger 185gn Juggernaut, but in some cases up to and including the 230gn Hybrid over scary amounts of Hodgdon VarGet. Transfer of these loads to other people's rifles, even factory models, may prove to be a recipe for disaster. The moral as always is to beware (greatly) of other people's loads, or in this case to beware Remy owners bearing loads data gifts. My own Howa is pretty long-throated too, ~2.900 suiting most tangent ogive bullets, but that's not to say that it's akin to Remington 700s.

The logical conclusion for short-barrel long-throat factory rifle owners attempting to reach out beyond 800 yards is to 'go heavy', but that assumes the rifle likes such bullets. My particular rifle doesn't perform well with them unfortunately. At a heavy sporter weight, recoil starts to become unpleasant and intrusive too with 185s and max loads, 200s not being at all nice in use.

The problem with most single-base powders in the 308 in this dilemma is not finding examples with approximately suitable burning rates of which there are several, but those with enough energy to get the desired results into a usable charge weight. Viht N140 has a lowish specific energy rating of 3,720 Joules per gram weight, while N540 high-energy runs at 4,100 J/g, and Hogddon VarGet / H4895 4,050-4,060 J/g exceptionally high for sigle-base types. I don't where TR140 fits in, but since the RS high-energy grades (with nitroglycerine infused into the base NC propellant sticks) are listed as "around 4,000 J/g", that would suggest that the untreated RS50 / TR140 will be in the same ballpark as the Finnish number - and in fact they give near identical performance in real life.

Ramshot double-base ball types are rated at 3,910 to 3,950 J/g depending on grade, quite 'cool' actually for D-B types and presumably linked to their development for military smallarms applications where barrel life is a big factor to the procurement officers. (Manufacturers of such modern versions of the ball varieties such as PB Clermont which makes Ramshot and GD's St. Marks Powder Co. in the US which makes Winchester, Hodgdon and now some Alliant ball based powders and nearly all those used in current US milspec 5.56 and 7.62mm stuff claim that their ball powders have lower flame temperature values and are less erosive than single-base extruded types at any given pressure / performance level.) Allied to a good specific density levels that allow case-filling charges under 155s without seeing excessive compression - that can and will change a powder's behaviour in some cicumstances - they're pretty well suited to this factory rifle problem with 155s in 308.

Of the 'traditional' powders, that are actually available to us in the UK this year, the best to try with 155s in the quest for ultimate MV is IMR-4895 which is another unusually hot-rated powder at 4,080 J/g, higher than nearly all ball powders and most high-energy types. It's marginally slower burning than its Australian manufactured H namesake and can give surprising high MVs in this situation.

[User702]

fYI, i have a 26" barrel, so will be gaining some velocity compared to you.

[TJC]

Not wishing to hijack this thread but I too am looking for .308 powder for a 24" as an alternative to Varget and was wondering what's the difference between IMR 4895 and H4895 ? They appear to have pretty similar MV in a 24" according to the Hodgdon reloading site.

Is one more temp sensitive than the other (is that really a material factor in the UK ??), does one burn faster than the other, is one easier to measure than the other and is there is a major difference in price & availability in the UK ?

They both appear to have similar start loads but H4895 appears to require a lot less powder at max loads to attain pretty comparable velocity in a 24". Is that telling us anything material ?

I'm no benchrest shooter and just want to find a decent alternative to Varget esp with respect to MV, that's all.

Cheers