Hi BigBore,
Good to meet another European shooter on the forum. I'm using a 300 gn jacketed flatpoint bullets, and I've loaded them to the N110 SAAMI max, which is 28.7 gn, or 1.86 grams. Using RCBS' .454C dies (not .45LC dies), I have no problems at all at the prescribed 44.5mm total cartridge length.
The SAAMI max is a bit on the 'better safe than sorry' side, that is to say, it's a bit mellow. Vihtavuori used to publish two different reloading tables, one for the lawsuit sensitive Americans (SAAMI standard), and one for us 'sensible' Europeans. (I'm kidding guys, don't shoot). For N110, the European tables used to rate about 5-8% heavier loads. Alas, the new Vihtavuori reloading tables are all SAAMI, and the old ones do not contain .454C data, so the beefy Ruger sort of shrugs away each of my handloaded rounds.
I have purchased a box of Winchester .454 factory ammo for reference, and even without a chronometer it is obvious that this factory round is a more powerful cartridge.
However, I cannot increase on the max prescribed 28.7 gn N110 load on the 300gn JFP, because N110 is much more voluminous than H110; the brass simply cannot contain any more, because the bullet already compresses the powder down when it is seated. The grains of N110 powder are cylindrical in shape, and each of these tiny cylinders has three microscopic holes running along their length to ensure sufficient air for a clean and calculated burn. This is why N110 is (relatively!) more expensive, but make no mistake; it is superior to H110 in every aspect. You (like me) are having a hard time finding N110 reloading data on the net for the .454C because most such publications are American, and the Finnish N110 is hard to come by in the States, and even more expensive for them to buy than it is for us Europeans. So most Americans stick to H110, and yes, it burns slightly faster than N110, especially when case volume gets a bit tight.
To cut things short, stick to the book when you use N110, that is to say 33.5gn for 225gn jacketed bullets (42.7mm tot length), 30.7gn for 250gn jacketed bullets (42.8mm tot length) and 28.7gn for 300gn jacketed bullets (44.5mm tot length).
I have ordered a chronometer, and when it arrives I will emulate the performance of the fierce Winchester factory ammo using the slightly faster burning Vihtavuori N105 gunpowder. There is no doubt in my mind that this will prove to be a more constant, more reliable performer that any H110 round.
Mind you, the listed N110 charges are by no means plinking loads. They'll stop a charging T-Rex dead in its tracks, and the recoil of thirty or so of these rounds tears the skin off the base of my thumb. So whatever you do, start 15% under max load as usual.
Anyway, as to the charges you are using, I have no data on 350 and 400gn bullets, so we'll have to make an educated guess. The 350 is 17% heavier than the 300gn bullet, which, given the same charge and case volume (seating depth!), will give you approximately 14% of pressure increase. But you wisely do not use the same charge, you use 25gn instead of 28.7gn. A 10% decrease in charge will yield approximately 20% decrease in pressure, and you have decreased about 13% for a 26% pressure decrease.
At first glance, your 350gn load is a safe (26-14=) 12% under max pressure... BUT!
1. What type of bullets do you use? Lead bullets seal better than jacketed ones, so that will INCREASE pressure.
2. How deep do you seat this bullet? The deeper you seat the bullet, the less the case volume. A 10% decrease in case volume will get you an approximate 13% (!!) increase in max pressure, and wadcutter types of bullets need to be seated especially deep.
If I put your 400gn charge under the same calculations, extrapolating from the SAAMI 300gn standard, you are about 20% under maximum, but 400 gn bullets are BIG, and even if you seat them as high as your Raging Bull can take them, you're bound to end up losing a lot of cartridge volume. So no way that 20% is accurate!
To summarize, the charges you use appear safe, but only as far as I can tell. You need a chronometer if you want to find the limits. If you have an accurate charge, I'd say stick to it. If you're an on the edge fps-junkie like me, buy or borrow a chronometer and look for fps data on the exact type of bullet you are using, and match it using Vihtavuori powder. But keep in mind that seating depth is critical, as is the fact that neither your Raging Bull nor my Super Redhawk can match the max pressure a Freedom Arms can safely take.
Greetz, and sorry for the long post,
db