N 150 versus N 550

[Richiew]

Hi all 

would like to know why when using n150 it seems to need less powder than N550 ,the confusion is that n550 is a high energy powder so why don’t we put more n 150 in as this should be a lower power powder .

cheers 

[henryo]

The double base powders have a less pronounced pressure peak than single base (occurs when the bullet is only a few inches down the barrel).

If you then load to the same peak pressures, you will have a greater 'area under the curve' on a pressure vs time plot - which is the delta v or muzzle velocity.

With a double base powder the best way to see it is you are using a slightly 'slower' (regressive) powder but it (normally) has a higher density letting you physically cram it all in the case. Hence more weight in grains for the same peak pressure, albeit a higher average pressure for a higher muzzle velocity. Obviously this is not 100% efficient so most of that extra energy is lost or goes in to the barrel...

I think the naming convention Vihtavuori uses for N1XX vs N5XX are more about applicability for certain cartridges, than absolute burn rate

[Richiew]

Thanks for reply , was just checking a few loading manuals for future reloading. Hornady has in its 9th edition a section on 308 win and a few pages on info for 308 service rifle showing some interesting info for viht powders .

[Laurie]

Viht shows its N100 powders and their N500 equivalents with the same burning rates ........... but they're not. The high-energy versions are slower burning, sometimes significantly so. QuickLOAD lists N530 as slower than N140 never mind N130 through N135 and N560 as being slower burning than N165. Changes in quickness in themselves affect the charge weights that produce peak pressures.

[Big Al]

19 hours ago, Laurie said:

Viht shows its N100 powders and their N500 equivalents with the same burning rates ........... but they're not. The high-energy versions are slower burning, sometimes significantly so. QuickLOAD lists N530 as slower than N140 never mind N130 through N135 and N560 as being slower burning than N165. Changes in quickness in themselves affect the charge weights that produce peak pressures.

Interesting Laurie.

Can I ask what do you know about temperature stability between the 100 and 500 series?

I remember reading somewhere recently that the 100 series was due for an upgrade in this regard?

[Laurie]

That's a good (and difficult) question Alan. Viht itself says the N550s are more temperature stable than N100s. Conventional wisdom says that it should be the other way round!

Search on forums etc and you find what are in effect opinions, not facts - and they are contradictory from US users claiming everything from excellent to terrible.

All I can say about N550 is that it appears to be a bit harder to ignite than N150 in cold weather conditions. (Lapua small primer 308 'Palma' which is ignition / temperature sensitive and N550 starts to lose MV / increase SDs at higher temperatures than N150 this being on or just above freezing.) Steve Donaldson, one of the UK's top F/TR shooters as was although he's now largely dropped out of League levels, has used Palma brass, Berger 210gn BT, and a stiff load of N550 for nearly 2,700 fps from a 34-inch barrel for many years with great results. Back in 2013, he dropped out out of the GB F/TR team and went to the FCWC in Raton, New Mexico as a privateer. Not being subject to team rules, he shot every competition and practice he could over the two weeks and put an enormous round count in - his rifle was borrowed by fellow Rutland team members too. With locally sourced primers and fresh N550, he used his UK load throughout without any charge weight reduction - and did very well in the US National F-Class Championships and then the World Championships. At ~7,500 ft ASL in a semi-desert climate and in a local heatwave temperatures went from cool first thing to very hot by our standards peaking in the mid to high 90s F in the shade by late afternoon on some days in week one, a little cooler (low 90s) in week two. Steve assured me his UK load worked fine throughout and he'd no pressure issues at any time. I believe many 'Match Rifle' competitors use N550 too with 200-230gn bullets in Palma brass and these lads and lasses go off to shoot MR in Australia in sometimes brutal temperatures as an NRA team.

Vihtavuori has quietly added anti copper fouling additives to their powders recently and says it will be reformulating most (everything?) in its range to be temperature insensitive in the near future. I'm not surprised - it's becoming increasingly difficult to sell propellants into both sport and military markets these days if they have the reputation of being temperature affected. Hodgdon / ADI has been in the lead for years with the Extreme range of extruded powders, but now IMR (General Dynamics, Valleyfield, Ontario) is adding new 'Enduron' grades which although not quite as good as ADI is still very good indeed, and Alliant ATK's recent additions from Bofors, Karlshoga, Sweden such as Re16 have a new 'TZ' technology claimed to rival the Hodgdon/ADI 'Extreme'. Certainly American users are raving about them in every respect. (We don't get any here as yet - I hope that is going to change.)

[Brillo]

Laurie,

Interestingly, I’ve just done some load development with my Berger 200.20X bullets using both N150 and N550. Needless to say the N550 produced much higher velocities for similar chamber pressures. 

Group sizes were promising with N550, slightly more so than N150. The only reason I didn’t continue with N550 is because of the concern about excessive chamber throat burning as I’m led to believe it’s similar to RS60 in this respect.

However, from what you articulated about Steve Donaldson’s loads my concerns might be unfounded.

[Laurie]

You can wear barrels out pretty quickly with N150 too if pressures are high enough. Some of the hot loads for 185/200gn Bergers with N150 in Palma brass only give a 2,000-2,500 round barrel life in 308 Win.

Steve D by comparison claims he gets around 3,500 with his N550 load, presumably running at lower pressures.

However, these are all small samples and barrel steel / rifling type affects barrel life significantly too.

I have a suspicion that if pressures are kept to moderate levels, most of the N500 series won't burn out barrels particualrly quickly. An exception may be N540 as it has a near 40% nitroglycerin content by weight - same as arsenal Cordite .303 British Mk.7. Powders with some nitroglycerin are almost becoming the norm now - the new IMR Endurons all have some and all Alliant powders whether from Nitrochemie, Bofors or General Dynamics St. Marks have this ingredient. All ball types are double-based, likewise Norma extruded powders.

I bought a secondhand Musgrave TR 308 many years back with a nearly new Maddco stainless barrel on it and developed a mild 155gn SMK / Alliant Re15 load for it, shot the rifle for three or four seasons and sold it. I meet the buyer regularly who still owns this rifle maybe 15 years on, and he still uses that Re15 load. The barrel round count must be astronomic by now, but he says it still shoots as well as he can, if not better.

[Richiew]

Thanks for the info boys , all very usefull I will use the data to make up long barrel life /accurate rounds ,would prefer the n150 as it comes in big tubs . latest results for n550 and berger 185 jugs in 308 were best accuracy at the bottom end of the load range ,started at 40g to 46g n550 and best results were at 41,5g on a hot heatwave day 22 to 24 deg c .got some loaded now for chrono test next time out to play . sets of 155/175/185 bergers   155/168 amax and sierra155tmks all at 2.9 coal which was the best for all the bergers . cheers