Used it behind some 130 gr Sierras to run a new barrel in, and have chrono’d 41.5 gr of it behind some 143 eld-x at 2680 through a 26” barrel. I’ve loaded another .5 grains in the next batch, and Viht data tells me there’s still another full grain to go. Grouping nicely so far, some serious development on the way, so will check back if the threads still going.
It’s a bit bulky. It’s already getting near the top of some star line LRP cases, nothing a bit of tapping and settling won’t fix. and it somehow doesn’t flow very freely
Vihtavuori developed this grade with the 6.5 Creedmoor and similar applications very much in mind, so it ought to perform at least reasonably. By 'high-energy' (infused nitroglycerin) powder standards it is very mild, the lowest specific energy rating of the N500 series by far and in terms of 'combined heat of explosion' energy levels the same as some N100 series grades.
Burning rate wise, its designation might make people think it's close to the longstanding N550 - it's not, being a very much slower burning grade. Look at Viht's loads data for the 12 cartridges with N555 data so far and for bullet combinations with N550, 555, and 160 powders and you see a large gap between 550 and 555 in maximum charge weights, but a close correlation between maximum charges for N555 and N160, at least until you get to the two largest cased cartridges listed (30-06 and 284 Win) where N555 drops down a grain weight or two.
I've tried it in 260 Rem and 7mm-08 and it looks like it'll be a good alternative to the now lost 4350s. The former cartridge's results can be seen here:
and the 7-08 findings will be published within the next few weeks.
(Incidentally, if looking for an IMR/Hodgdon 4350 replacement in cartridges like the 6.5 Creedmoor or similar mid-sized cartridges, the single-based Reload Swiss RS62 is an excellent choice and difficult to improve upon with the exception of those looking for absolute top MVs.)