I have all of these components available but my older Hornady manual has no load data for N150. Rifle is a Remington mod. 600 in 308 Win. The current on-line Vihtavouri data only lists loads for two 150g boat tail bullets. I believe the Hornady (non-boat tail) SP would have a little more surface area in contact with the bore and might increase pressures. The max load listed for one of the boat tails is 49.9g. Question is how much should this be reduced when using SP's instead of boat tails...or does it matter?

It doesn't matter. You can reference several load data and for example, Speer, they show charges for all of their bullet weights starting the same regardless of bullet type. Like the 270, for instance: Speer will list their 150 boat tail, spitzer flat base, etc.

If you feel any safer, then start one grain less than a boat tail minimum charge. I don't think it is necessary though.

I treat all loading data for normal cup and core bullets as the same.....as long as we're talking same caliber and weight....and we're starting at the start point and working up! I'll even throw in Northforks, Swifts, partitions, and most bonded bullets.....

Doc/Dog...thanks for the comments. I'll start at least a grain low and see how it goes. I've not used this rifle for a few years and will be taking it on a high altitude (Lake Tahoe area) deer hunt in a few weeks. It's always been a very accurate little rifle and, as the years pile up, it's light weight is appreciated. Thanks again for you're help.