Flat Base VS Boat Tail?

[Utah Shooter]

Sorry if this has been here before. I am curious as to why the flat bases seem to shoot better at short ranges that the boat tail.

[trotterlg]

One thing is that the flat base bullet spends less time in the transition point at the muzzle than the boat tail does, so it is effected less by any crown problems or any effect from going from the bore to free flight. Larry

[dungheap]

Originally Posted by Utah Shooter

Sorry if this has been here before. I am curious as to why the flat bases seem to shoot better at short ranges that the boat tail.

Please clarify what you mean by "short ranges."

If we're talking 100 yards give or take, I don't think that's necessarily so. I get some super groups out of Z-max (boattails) and have had some really lousy groups with flat base (notably Remington 50 grainers). Midsouth Varmint Nightmare Extreme flat base and the Zmax's seem pretty close in performance in many combinations.

My conclusion: "There ain't no such absolute." JMO

[Utah Shooter]

Out to 250-300 yards. I know that there is no absolute to reloading and projectiles. There however can be a curve. I guess it would be interesting to have a poll of what shoots better in ones rifle and then go from there.

[Johnly]

Each rifle has it's own quirks making "rules" difficult to define. I've tried a dozen different boat tail bullets 7mm-08 and maybe get them to deliver 1.25 MOA three shot groups. Switch over to flat base bullets, Hornady, Speer, Sierra and the rifle prints 0.75 MOA groups with the first three shots out of a cold clean barrel.
I can compensate for drop and drift, but not accuracy.

John

[george ulrich]

Originally Posted by trotterlg

One thing is that the flat base bullet spends less time in the transition point at the muzzle than the boat tail does, so it is effected less by any crown problems or any effect from going from the bore to free flight. Larry

This pretty much nailed it, its refered to as aerodynamic jump. Flatbase are less affected because of drag. b.t. with less drag take more twist to stabilize.

[Daryl]

Each rifle shoots best to it's own preferences.

There might be a multitude of reasons or maybe as simple as trotterlg noted - time at the crown or crown quality - or throat, or something else?

For many years, BT's were THE bullet for 1,000yard accuracy shooting, but now, it seems, flat bases rule n .30 cal. and above - go figure. That was a few years back with the 1 5/8" 5 shot record group, which was beaten the next year I think, but the same calibre and same flat based bullet in 1 3/8" group or some such size. I expect THAT record has perhaps been beaten with a boat tailed projectile and on it goes, back and forth.

Tried to find those in a search - but failed. Perhaps they were not ratified?

I did find a 10 shot group just over 3" at 1,000yards shot with a .30 cl and .187 FB bullets- in 2009.

[george ulrich]

It still comes down to math bullet length to twist rate, a bad crown is a bad crown , changing from one form to another will not correct a problem. Aero dynamic jump to drag function will basically give stability factor. Key word is basically, its a little more complicated but these are the basic rules...

[trotterlg]

A bad crown affects a BT bullet much more than it does a FB bullet, probably why lots of people think a FB bullet is generally more accurate than a BT bullet. Not talking about a big ding on the crown, but very small things that affect how the hot gasses exit the muzzle as the base of the bullet clears the rifling. Over stabilizing a bullet can keep it from being upset when it exits a badly crowned barrel, so I guess that spinning a bullet faster can make it more accurate, but only because there are other problems with the rifle. Larry

[george ulrich]

Which brings us back to aero-jump that is the reason the b.t. is affected more. I don't quite understand the bad crown theory unless we are talking about factory crowns any gunsmith that isn't getting crown square should probably be avoided.