My experience has been the bullet being the single biggest difference maker. I'm pretty much convinced (not to be argumentative, just my own experience) no amount of load variations will make a bullet that doesn't shoot well in a particular rifle, shoot well. And I've wasted a lot of powder trying to make the bullets "I wanted" to shoot work. These days I read up on which caliber I'm loading for in a comparable length and twist barrel before I even start. I look for what's commonly working as far as primer, powder, and bullet weight. That's where I start. As far as brass, Winchester is typically the most uniform lower cost. Lapua is preferred. I also use Hornady and with a 30-30 that only needs to kill deer not really further than 150yds, once fired Remington brass of different lots gets it done. I like to buy 150 cases all the same lot per rifle. I shoot some competition bench rest even with my factory rifles. 3 groups of 50 keeps me with 50 loaded, some of another group left over from a shoot, and another group of 50 to be working on reloading. I try several different bullets and weights. It takes minimal time to find the bullet your gun likes best. Then I play with powder charge weight and different powders. A good load will have a very comparable point of impact within a small range of powder weights. Once you've worked out your load, then it's time to "fine tune" it with seating depth. I start load development with all bullets .005 off the lands. For me, I typically find the sweetest spot from .010 jump to .010 jam. I only have one rifle that shoots better jammed. And it is a custom barrel in 6br shooting Berger VLD's. The rest usually end up doing well enough with Hornady bullets jumped. Not that Hornady are always the best shooters, but they usually end up close enough in my factory rifles with a price that's hard to beat for a few 10th's of an inch. Most of my rifles are short actions, and I've yet to have one that I couldn't touch the lands and still use the magazine. Maybe I've just been lucky.
Since you mentioned you're shooting a 308, for target I've gotten very good results with Federal 210m primers, Varget powder, and Hornady 168 A-Max bullets. Short jump between .005 and .010. That's also out of a 26" barrel.
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