Thread: Boat tails v.s. flat base projectiles

My 243 groups better with flat base projectiles than with boat tails, and Ive seen someone else say the same on a US hunting forum. Any thoughts on why that could be?

Flat base projectiles are less sensitive to an less-than-perfect barrel crown, is one theory I've heard. Makes some sense to me but I've never tried to prove it.

They fly shit shorter....can fill a worn bore better,the moon was in correct alignment when made. Just go with it. Boattails are easier to load as sit nicely in case to start seating but other than that tiny quirk ,I have never seen advantage....but I don't shoot long range either.

Some of mine prefer FB as opposed to BT. Is common with BSA's.

Different projectiles... different harmonics.

Some guns just like some combinations.

I.e. your gun might like a different boat tail projectile better still, or different powder... etc...

Not necessarily boat tail vs flat base.

Originally Posted by Husky1600#2

Some of mine prefer FB as opposed to BT. Is common with BSA's.

Think older slightly worn bores....may find Speer projectiles go very well in it for same reasons...they squish out to fill grooves better perhaps.

The theory is that a boat tail in certain bores may allow propellent gases to flow past the base, decreasing obturation of the projectile in the bore, and potentially allowing these gases to exit around the projectile at the muzzle unevenly, thus upsetting accuracy. By comparison, the flat surface area of the flat base, holds back more of the propellant gas, which pushes against this larger flat area, causing better obturation and sealing the gases behind the projectile.
Or something like that...

Over the Year's, I have found flat base easier, to get to shoot well, with several powders and OAL, Boat tails, seamed to require a bit more tuning, always exceptions, but all the best target bullets, in my 3, 6mm PPC, were flat base.
good old soft point, flat base for bush work, Boattail for way out there.

Flat base bullets are typically easier to find accuracy for but have a lower BC so not as good at long range.
If you are shooting inside of 300m then it probably doesn't matter.

If you tell us what your ammo is or the bullet + velocity, can easily plug into a ballistic calculator and see if it's worth wasting time on boat tail bullets for your use.

It's actually more complicated than flat base vs boat tail, it comes down to bearing surfaces length, boat tail length, ogive shape, basically the better the bullet is aerodynamically the more sensitive it is to twist rate and seating depth.
The newer TMKs, SMKs, ELD-M/X, Berger Hybrids do a good job of making a high BC bullet that is easier to find accuracy with.

Most 243s are slow twist so shoot shorter bullets better. Boat tail bullets are usually longer so need a faster twist rate.

Originally Posted by -BW-

The theory is that a boat tail in certain bores may allow propellent gases to flow past the base, decreasing obturation of the projectile in the bore, and potentially allowing these gases to exit around the projectile at the muzzle unevenly, thus upsetting accuracy. By comparison, the flat surface area of the flat base, holds back more of the propellant gas, which pushes against this larger flat area, causing better obturation and sealing the gases behind the projectile.
Or something like that...

And the proof of what -BW- said is in writing and pictures. This is from an early Lyman reloading guide from a time of white shirts thin black ties, black rimmed glasses, pocket pen protectors, slide rules and right clever bastards.

older and still, most factory 243s are a 1-10 twist
They're built for a 100 g Max flat base bullet
people see the new bullets and go, oh it's 3gn heavier or lighter 95 or 103ish gn, and think that will be sweet
Twist rates are more to do with bullet length than bullet weight. A 95 gn boat tail is way longer than a 100 gn flat base, and a 103 etc is longer again
Some rifles will shoot them just fine, others don't. This is just because you are pushing the twist rate to its limits

with most modern bullets being long boat tails, arms makers should go to a 1-8 in 243. This would fix those issues and make it easier, as they can use the same barrel in all of their 6mm offerings

it's already been done with 223. The norm used to be 1-12, but you struggle to find a new one any less than 1-9 now

Originally Posted by Warthog

My 243 groups better with flat base projectiles than with boat tails, and Ive seen someone else say the same on a US hunting forum. Any thoughts on why that could be?

My son 2 weeks ago shot 4 deer including 3 stags all head shot with 85gr GMK out of his T3 243 using 2 stainless DPT baffles on his MK1 can.The 85gr is inherently accurate.Reckons the 2 stainless makes it quieter and better to shoot. Proof in the pudding.

I'm guessing trajectory wise there isn't much in it out to 250 yards.