seating depth changes

[Lefty7mmstw]

That's opposite from what's popular with folks shooting long range matches. They seat bullets out far enough to engage the rifling for best accuracy in barrels with groove diameters much smaller than what the bullet is. I've got best accuracy with all bullets jambed into the lands; even .3092" diameter 30 caliber ones into .3075" groove diameter barrels. That barrel's almost 2 thousandths smaller than those bullets.

All 30 caliber jacketed bullets starting into a barrel have the same force pushing them in for a given chamber pressure. Their diameter's all the same once they're into the rifling. With the same pressure behind one, that means the force pushing them in's the same. Doesn't matter what the shape of their hind end is.

That's a rather gross oversimplifacation since most boattail bullets are built differently than their flatbase cousins with a much heavier base. Not to mention the extra manufacturing steps introducing more run-out in the bullet jacket itself with a boattail. Yes they see the same pressure, but the way they see it can be awfully different.
A 30 cal will run .300 bore and .308 groove for the most part. I've shot .311 bullets through a 30 cal and they did fine too, albeit they were a bit stout on pressure rather early. The beaufiful thing about a lead core bullet is they can move a bit either way in daimeter and still be usefully accurate.
You are talking about the exact opposite thing that I am with running oversize slugs down a bore however. I'm talking about getting undersize slugs to work in a given bore.
We once got a savage 243 that was accidentally put together with a 25 cal barrel(yes a 25 cal barrel) and the only bullet we could get to moa accuracy was the 243 cal 70 grain speer TNT. It was soft enough that it ubdurated and filled the bore. All flat base bullets and boattail bullets with heavier heels and jackets shot terribly. The rifle was eventually sent back by the gun shop, but it was interesting.

 

[Bart B]

That's a rather gross oversimplifacation since most boattail bullets are built differently than their flatbase cousins with a much heavier base. Not to mention the extra manufacturing steps introducing more run-out in the bullet jacket itself with a boattail.

It cannot be a gross oversimplification because I've not stated it even close to 144 times.

All the Sierra boattail bullets I've seen cross sectioned have the same wall thickness from base to heel to body; same as their flat based ones. Even asked Sierra about this years ago; answer: all the same thickness.

Sierra did have the runout problem with their first 30 caliber boattail match bullets; the FMJBT ones of 180 and 200 grains. That was fixed when they came out with their 168's and later 190's then all of them had hollow points; the solution to out runout issues at their back end.

 

[Lefty7mmstw]

It cannot be a gross oversimplification because I've not stated it even close to 144 times.

All the Sierra boattail bullets I've seen cross sectioned have the same wall thickness from base to heel to body; same as their flat based ones. Even asked Sierra about this years ago; answer: all the same thickness.

Sierra did have the runout problem with their first 30 caliber boattail match bullets; the FMJBT ones of 180 and 200 grains. That was fixed when they came out with their 168's and later 190's then all of them had hollow points; the solution to out runout issues at their back end.

Nosler and speer are built significantly whether bt or fb. Nosler doesn't do much other than varmint in fb(not counting the partition h-frame), but their bt bullets have a very heavy base on them. Speer are cored entirely differently.
In the end it really boils down to will it shoot. I really don't care to waste my time arguing subtle differences between bullets that may or may not really make a difference. I know I've had good luck getting stubborn rifles to shoot with either sierra or hornady fb bullets, and that's good enough for me. I'll put a good fb bullet up against any bt for mid to long range accuracy.
Just a thought, how many competitors use bt bullets in their ppc's?

 

[Bart B]

Just a thought, how many competitors use bt bullets in their ppc's?

More these days than they used to from what I've been able to find out. The best ones are probably made by Bart's Bullets. (no relation at all......)