Bullet base style = accuracy?

dcloco

Any experience with different base styles in regards to accuracy? Any trends noticed?

muss

Boat-tail bullets are typically a little more accurate. At least in my rifles.

bpost

Hi dcloco,
A boattailed bullet may load easier and is possibly easier to get started straight without base damage. The boattail itself reduces base drag on the bullet in flight. The reduction is almost nothing until bullet speed drops to sub-sonic then there is a huge difference in the base drag the different bullet styles experience.

If you look at the type of bullets used by Benchrest guys it seems there are two groups of shooters.

Both groups use a deburring tool like the K&M Services unit. It deburrs the inside of the case mouth at a very shallow angle. This protects the hyper-critical bullet base from scouring damage as it is seated. They shoot flat based bullets like those sold by Fowler out to 300 yards.

The other group seem to be the 600- 1,000 yard guys. They know the bullet will be sub-sonic at 1,000 yards and the boat-tailed design is used a lot. The VLD (very low drag) bullet designs are all boattails. Boat tails may buck the wind better but I've not seen proof of that.

I was shooting mostly boat tails for the loading ease in all my rifles. After getting the K&M tool loading flat based bullets is a breeze. MRBRUCE gave me some Fowler 80 grain flat based bullets to try out. The have proved to be the most accurate bullet I have ever shot.

The key seems to be the deburr tool tapering the inside case mouth at just the right angle so there is no damage to the bullets when seating them.

Another trick is to pull the handle just far enough to start the bullet, raise the ram and rotate the round about 90 degrees and go about 3/4 of the way down. Then rotate it once again and seat it all the way. This helps keep the bullet concentric in the case.

Carefully check the case mouth after the bullet is seated. If you see any shavings on the lip of the case the bullet was damaged during seating. You need to get the better deburr tool IMO.

Best

JustC

flat base will be as accurate and maybe a tad more to 300yds and beyond that, the boat-tails are the thing to have. They reduce drag and therefore have a higher BC. Unless they are experimenting, you'll not see a flat base pill in any benchrest match past 300yds.

I like VLD pills for longer range as they simply buck the wind better and allow the shooter to score higher if they missed a condition change such as a wind flag or mirage change.

that's my .002"

nononsense

dcloco,

Base shapes:

Flat (with a pressure ring and hollow point)

Flat FMJ (lock base style exposed lead with closed point)

Boat tail

Boat tail VLD

Rebated Boat tail

This question can get into a huge dissertation involving physics and aerodynamics of shapes. There are many other factors that require analysis along with the shape of the base but this can fill volumes rather than few paragrphs on a forum.

Right now, it's pretty hard to make absolute definitive statements regarding accuracy and base shapes because there are many variables that can have an effect on accuracy.

Point blank shooters tend to prefer the flatbase with a pressure ring. The long range folks like the VLD boat tail because the Ballistic Coefficient is better. But now we see a group of long range experimenters that are using and succeeding with the flat base long range bullets from Randy Robinett and a couple of other bullet makers.

I think it's easier to get a load worked up using the flat base bullets and I think the VLD boat tails can be picky about loads. The Rebated boat tail is supposed to solve the turbulance problems of the standard boat tail. The flat base bullets do solve the turbulance problems but you lose BC slightly. Land and groove design, velocity and surface finish of the bullets can have a huge effect on accuracy with any of these different bullets.

Is there a blanket statement regarding base shape and accuracy? Nope.

The Corbin brothers both have websites dealing with bullet making equipment and supplies. This site has software and some rather detailed explanations of bullet design:
http://www.corbins.com/dc-1015.htm

This is an FMJ .308 Win. traveling at supersonic speed. Note the disturbance at the cannelure:


This is an FMJ 9mm Luger flatbase:


This is a .32ACP subsonic:


"The shadowgraphs have shown that the flowfield in the vicinity of a bullet most generally consists of laminar and turbulent regions. The flowfield depends in particular on the velocity at which the bullet moves, the shape of the bullet and the roughness of its surface, to mention just the most important factors. The flowfield obviously changes tremendously, as the velocity drops below the speed of sound, which is about 1115 ft/s (340 m/s) at standard atmosphere conditions."
http://www.fulton-armory.com/fly/fomo.htm but originally from a treatise titled "How Bullets Fly" by Ruprecht Nennstiel, Wiesbaden, Germany.

dcloco

Whoa...interesting...to say the least!

D.S.COLE

in years of rifle reloading and shooting in answer to your question ,as to trends, boat tail bullets have been more accurate than flat base . while I havent kept written logs on this ,memory seems to say that in working up loads for a lot of cartridges and rifles over the years the boat tail has won by probably a 2 to 1 ratio. my experience or 2 cents worth.

nononsense

That may be all well and good for the past but the current trend is towards the flat base bullets taking the honors at the long range competitions. Shooters are seeing that the flat base are easier to develop loads for and are not as fussy as the boat tails.

Now that doesn't mean that things won't change next year or the year after that but the flat base is ruling the roost these days.

Best.

fire for effect

Boattail bullets make the transision thtough the Sound barrier better than a flat based bullet.prior to this point, flat based bullets will be just as accurate as a Boattail