I have been out with my 7mm-08 this weekend. I loaded some loads with the 150 Swift SII (42gr H414, new Norma brass, cci 200 primer). I know this load is not going to break any speed records. It has been 90° where I'm at both days. I was wondering from experience how much I may have to adjust this load in colder weather say around 35° and do I need to switch to a mag. primer? This combo is shooting really good. I have some H4350 to work something up with an extreme powder if the H414 doesn't like the cold. This is a MCR built rifle with a 22" pac nor super match barrel.
I don't have a 7mm-08, however I do use H414 in a .30-06 Springfield and .243 Winchester and .243 Ackley Improved. It is a very good powder for both families of cartridges.
I hunt in temperatures from 0 degrees up to 90 degrees using h414. My rule of thumb is that the .30-06 family always uses a magnum primer, loads are developed in the summer in the heat to insure no pressure spikes. You will lose some velocity in the extreme cold, but I wouldn't adjust the load at all. The magnum primer helps remedy this problem.
The .243 cartridges I also load with magnum primers. This isn't necessary per-say, because of the shorter powder column, however, I was always told by my handloading mentor that ball powders should always use magnum primers for consistant and through ignition and that loads should always be worked up using the magnum primers (for the ball powders). You don't want suprises when shooting in the summer.
H414 is really close to H4350 (I use this for a .30-06 AI) and is also an excellent choice for the 7mm-08. You'll be happy with either, H414 is also known as W-760 and is 100% compatable with h414 data, It's generally cheaper and h414 is usually $2 cheaper than h4350.
I have some cci mag. primers, I will load my next rounds with them and see what happens.
This is my first try at the 7mm-08 with the 150 to 162 bullets. I've not been able to spend a lot of time with this one. I started out shooting Varget. It would produce 1" groups with the 162 AMax in the upper end of the load range. It would shoot around .6" with a light charge. I don't have a chronograph, just going by published data saying these are slow loads. I will say that the Nosler manual has been pretty close to the most accurate loads with this gun (unusual from my research). With a light charge of H414 and the 150 Swift SII, I shot a group Saturday around .45" and one yesterday that was the same. This was on the ground using a bipod and rabbit ear bag on the back (not the best setup for shooting good groups). I do have a range finder, these were at 105 yards. If the Nosler manual holds true, with H380 powder, it shows most accurate and best velosity. I might give it a try next, it's a ball powder so I assume mag. primers will be best with it also.
When developing my load data, I like to use the powder manufacturers data. I generally will use Hodgdon.com . I also will use Quickload data (my friend has a copy) especially for my wildcat cartridges as it gets me close and keeps me within safe limits. Then I will start my load development going in 1/2g increments until I find my rifles sweet spot. It sounds to me that .45" is your rifles sweet spot. Remember, Accuracy always trumps velocity!
I've shot some of my best groups prone using a bi-pod and a rear bag. It's a very natural way to shoot. I've also taken almost all of my game in the last 10 years using a bipod. I even shoot chucks laying in the grass shooting prone. I's my favorite way to shoot.
Most of my experience with H414 has leaned me towards heavy charges. infact I had gotten the best accuracy with the .30-06 with maximum loads.
H380 is a good powder, don't overlook Hodgdon's BL-C(2), It too is a ball powder, not the fastest, but very consistant. H4350 shows the highest velocity, and if you can group it well.....It would be hard to beat.