You have told us how you load, but you have not told us how that ammo performs in your rifle. Your targets will answer your question.

Lee is in the precision rifle building business, so his rifles are not the average. His ammo is also put together with great care so it is not the average ammo either.

Therefore I would say your groups would be somewhat larger, but there are so many factors I would not risk saying anything more.

I load most of my ammo like you do, Dillon 550, full length resize, thrown charges, primers seated by the press. I have a heavy barrel Savage 308 that I've tried to work up super accurate loads for. I've gotten to where my groups are hovering in the 1" range at 100 yds. shooting off a bipod, which is not that great but not that bad either. I think the ammo will do better and what's holding me back is consistent shooting technique.

So, I'm making a real effort on educating myself on how to correctly hold and support the rifle, and plan to concentrate less on ammo and spend more time on the range, keep myself square and straight behind the rifle, trigger pull straight back, consistent hold, breathing, etc., just really pay attention to everything I'm doing behind the rifle. I'd love to go somewhere for a week of precision rifle training next year if I can manage it.

I'd imagine your ammo would perform very well in the custom rifle, and the shooter behind the rifle is equally important.

either with the rifle, optics, or shooter if ammunition produced on a 550 with a modicum of care won't shoot somewhere about 1" @ 100yds. Not necessarily MOA at longer ranges, tho. That's where shooting technique, lock time, expensive optics, and fancy tricks make a huge difference.

In a basically stock rifle, all the other feel-good stuff generally doesn't pay off at reasonable ranges.

Here's a pic of what a 1909 Argentine Mauser with Shilen barrel will do with 550 reloads - repeatedly.

I do process the primer pockets with one of those Sinclair carbide cutting tools that references off the base of the case before I reload the cases. It does give a consistant and repeatable depth to the pocket.

Byron, To me ammo is the secondary component. Start with a perfect bbl. A blue-printed or Custom action. A pillar and steel bedded stock, or one with an aluminum V bedding block. A Niteforce Scope, Jewel and or Basix trigger. Then you can see the results of your handloads. This is not to say you cannot making good ammo on a 550 but not BR quality. At least to my way of thinking.
I see all kinds of Ads on so called precision Varmint rifles on the AR platform, but never saw one shoot to my Varmint standards. But that also doesn't say they can't make a good Varmint rifle.Its all in the eyes of the beholder. I have had good luck with Leupold scopes too. They are just not Nightforce standards. FWIW dept.