Actually, I find CF a bit easier than shot shell. With shot shell you have to use exact components for a load, there is not minimum or maximum, nor substitution, everything is maximum, you have to load as stated, primer, hull, wad, shotsize.
With CF there is at least a little room to play. If you cannot find an exact component, start at the minimum or start load and work up. It is possible and actually frequently done, to substitute a primer or bullet for in load for a given weight. Just be sure in substituting that you don't put a 55 grainer on a 45 grainer load. (there are a few exceptions, sounds like you may not be there yet) It sounds like the Winchester white box 45 grainer is THE load in the NEF 223, so working to duplicate it's performance is the place to start if it shoots well or very well in your rifle. In past, most anything we put together was better than what we could get off the shelf, these days it seems that the object is to beat the best the factory can make. I didn't read all the responses, so if I'm repeating what others have said, ignore as needed.....
Get a couple of reloading manuals, the Speer and the Lyman are good places to start, the Hornady and the Sierra with either of the above would be a good place too. Visit each powder manufactuers site and request a reloading manual. This will be a simple paper bound, often center stapled booklet with a selection of recipies for each chambering. These days a few are offering only a downloadable version, Winchester is an example of this. You are going to see some variance from say a Winchester load published by Winchester and a load using the same powder/bullet weight by Speer for instance. Thats ok. What you want to look at are the similarities. Not how different they are but how alike they are. If there is a large variance, ie, Speer says 30 grains where Winchester says 35 for the same bullet weight (even though the bullets may not be the same) it is time to research further. A 5 grain difference in a 223 case is time to go?
?? A 5 grain difference with a 45-70 may just be the difference in components and lab equipment and even the makers own judgement.
A bit at a time you will get a good handle on this. One must get is a chronograph. Without knowing the true velocity of your loads, you've no way of judging your pressures other than through very subjective methods. Once you begin working with a chronograph, you will understand more and more that in a given cartridge, "X" amount of velocity is produced by "X" amount of pressure. You simply ain't going to get a 150 grain bullet to go 3000 fps without being very, very close to 55,000 psi in a 30-06 regardless of the powder or the bullet. The bullet weight and velocity may vary a little for a 223 but the concept is the same. Velocity is the only real factor a handloader has to determine the saftey of their loads. Other pressure signs don't begin to occur untill you are getting beyond safe limits. So if a bolt is sticky on lifting, you know you are well beyond the limit. In a Handi, a sticky case may not be a sure over pressure sigen, but a barrel that didn't readily fall open would sure be one, as would a primer that had completely lost the radius at the edge of the pocket.
I have never questioned the strength of the NEF, and in 223 you have all kinds of built in strength. Stay inside or at the maximum listed loads and you will be fine.
