I have found that flat base bullet shoot much much better than boat tails in the 55 grain with a 1:7 twist.
My Sierra boat tails are about 1.5-2 MOA, and the flat base are about 1 MOA.
This with a Noveske N4 and a Nightforce 10X.
Has anyone else compared boats to flats?
For a given bullet weight, flat base bullets have a longer bearing surface. That could be helping them to shoot more consistently.
Maybe try comparing the 55 gr flat base with 77 grain boat tails?
Interesting idea - bearing surface and stabilization.
The Sierrra 77’s shoot pretty good - mostly around an MOA - sometimes better.
I like 55’s cause their less expensive. Midway’s Dogtown 55’s are about 55.00 per 500, and I get about an MOA with them.
Boat tails are not as accurate - I’ve only shot these to 100 yds. I need to check this at some greater distance to see if the accuracy holds up.
Physics tell me that the boat tails should stabilize in flight better because of less wake turbulence.
Please be mindful of where you are posting. We have an ammo related area.
77s are longer- more bearing surface, BT or not
FB’s out to a couple of hundred yards shoot better than BT’s. BR competition has proven this. Once you get out beyond 200-300 yards the BT’s shoot better.
It’s been posted many times that FB bullets are easier for a mfg to mfg. There’s less involved to go wrong. I don’t know the ins and outs of manufacturing, but I’ve seen some really impressive groups posted with FB bullets. It leads me to believe there’s some truth to the claims.
Yeah, but the boat tails are easier for me to get started in those little 223 case necks without pinching my fat fingers! 
Exactly which 55 grain boat-tail bullet and which 55 grain flat-base bullet are you comparing?
If you have space on your progressive, or if you want to add a simple and quick operation on your single stage, add a Lee Universal Flaring die. I use one in station #1 of my 550 and I have it adjusted to add just a touch of flare to the case mouth. It makes seating FB bullets a snap. I know what you mean about trying to seat a FB on a resized case mouth w/o any flare.