Vihtavuori powders under 155SMK

[Lukas_K]

Well, reaching the bottom of the Accurate powder bucket there´s time for new load development soon.

 

The pills are for a Quadlite repeater in 308, 26"bbl. I´m talking only Nosler CustomCompetition 155grs bullets here since I still have over 4.000 left in my stockpile. They´re accurate copy of Sierra´s original #2155 Palma. So far they were loaded over Lovex powder, equivalent to AA2460. Had best results near max loads giving cca 2800-2850fps. I´d like to keep the bullets in that speed range, maybe faster.

 

At the moment, I have option to stock on enough Viht. powder to last along that bullets´ stockpile. Options are limited to N540 and N550, have to buy an entire lot to significantly save on the price.

 

A consultation with QuickLoad determines the N540 better (47.5grs, 2860fps, 55000psi chamber, 6700psi muzzle, 100% combustion) as opposed to the N550 load (offering 50grs compressed load, 2834fps, 48500psi chamber, 7500psi muzzle, 96% combustion).

 

Lapua loading data says otherwise and N550 shows higher speed results (refer to 155grs HPBT Sierra figures): http://www.lapua.com/en/products/reloading/vihtavuori-reloading-data/relodata/5/70

 

I´d love to hear opinions from actual experience; anybody loaded a siila combination for FTR maybe, what gave you the best results?

 

Lukas

[Laurie]

N550 is a bit too slow burning for 155s in 308 - it comes into its own at around 185gn bullet weight, although I know of at least one person getting good results and very high MVs with the powder and 155s - although I can't imagine how he stuffs enough into the case to do this!. N540 was very popular in F/TR around three or four years ago with this bullet weight giving some excellent MVs, but there has been a wholesale switch amongst national league shooters to H. VarGet, H4895, and IMR-8208 XBR, all Thales / ADI manufactured Australian powders from the Hodgdon stable. This is partly because of lower temperature sensitivity, but much more to do with barrel life. Using N540's potential, likewise N550 with the heavier bullets wrecks barrels pretty quickly.

 

If you don't want or need very high MVs, there is simply no benefit in using N500 series powders. N140 and N150 work better with 155s in moderate loads, N150 being my personal favourite with 155s at a cost of a little velocity over N140. N500 series powders need higher pressures than their N100 equivalents to work with full efficiency. However, you're already using a double-based ball powder and getting high MVs for a 26-inch barrel, so switching to another D-B type may not worry you too much. If so, use N540 rather than N550.

 

There is a very reasonably priced alternative - TR140, the prototype Swiss powder which is likely to replace the old Finnish made version as Eurenco runs the existing Vihtavuori plant's output down, or may indeed have already replaced 'genuine N140'. In any event, it gives near identical results, but only costs ~£55 per kilo. It's available from Fox Firearms at Diggle Ranges, Dolphin Gun Co. in Louth, Lincs, and HPS Target Rifle on Bisley camp that I know of, but likely other retailers too now. Incidentally, don't use Viht's data as a velocity guide - much of its 308 Win loads are ridiculously low pressure, particularly for N140. As you've got QuickLOAD, run the company's maximum loads through the program, and you'll find many produce very low pressures. Even if your rifle is so short-throated that you're restricted to the SAAMI 2.800" COAL, it takes 46.8gn N140 and a moderately compressed load to reach the CIP PMax with the original 155gn SMK and my chamber's case capacity with Lapua brass (56.1gn water) according to QuickLOAD.

[Lukas_K]

Laurie, thanks a lot for such extensive writeup! You´re right on my take on the barrel life - I bought 5000 bullets last year when the rifle was nearly new and I expect rebarreling when I get to the bottom of that bucketload. Still, it´ll probably take me two more seasons to get there.

 

Here (CZ) the reloading market isn´t so big, so the choice is often limited and deliveries uncertain. One can´t seriously prepare for any competition that way. One of the facts is, I don´t buy small batches anymore - in a few months´ time, the product won´t be available and i´d be forced to replace it, creating gazzilions of combinations over time - and doing load development all the time instead of actually competing. These two choices were now made available to me in sufficient volume - and since I can purchase the amount of powder to last until I run out of bullets, I´ll do just that, although from a limited choice.

 

N540 it is then. Thanks, L.