Are bullets the wrong shape?

[dcali]

Pointy bullets with modest boat tails are pretty well optimized for several reasons.

If you have a boat tail that's too long you get dynamic stability problems and long bullets require high spin rates, which reduce accuracy and put more stress on the projectile. Manufacturing a perfect football bullet is also problematic. Putting them in backwards wont work because it increases drag (the optimal nose is a pointed one, not a blunt one).

 

[dcali]

Maybe why rebated boattails show up every so often?

Rebated boat tails are an attempt to reduce the base area without increasing the boat tail angle or lengthening the boat tail. I know Lapua makes them, but I've heard others say they don't provide much improvement of regular boat tails. Not sure if anyone else does.

 

[mikecr]

Maybe why rebated boattails show up every so often?

Rebated boattails attempt to hybrid the benefits of both flat base and boattail. However, you don't get the best of either, but a compromise of either, so those seeking best would go right past RBTs.
With regard to muzzle pressures, as applied to greater boattail/rear ogive area(with a backward bullet launch), rebating would help accuracy a bit -while increasing base drag. Better would be to reduce muzzle pressures released against an ogive type base, and to do so while the bullet is still fully captured within the bore.
It's difficult for me to understand why this isn't common by now, as lower muzzle pressures would likely benefit release of any kind of bullet.

 

[redrockranger]

It's the 21 st century. I've got a colege edacation,it' tyme to reinvent the wheel.

 

[johnmventers398]

Rebated boattails attempt to hybrid the benefits of both flat base and boattail. However, you don't get the best of either, but a compromise of either, so those seeking best would go right past RBTs.
With regard to muzzle pressures, as applied to greater boattail/rear ogive area(with a backward bullet launch), rebating would help accuracy a bit -while increasing base drag. Better would be to reduce muzzle pressures released against an ogive type base, and to do so while the bullet is still fully captured within the bore.
It's difficult for me to understand why this isn't common by now, as lower muzzle pressures would likely benefit release of any kind of bullet.

would lower mussel pressure = lover velocity?

 

[redrockranger]

Rebated boat tails are an attempt to reduce the base area without increasing the boat tail angle or lengthening the boat tail. I know Lapua makes them, but I've heard others say they don't provide much improvement of regular boat tails. Not sure if anyone else does.

I believe the flat base bullet creates a better seal in the barrel.

 

[spclark]

Rebated boat tails are an attempt to reduce the base area without increasing the boat tail angle or lengthening the boat tail. I know Lapua makes them, but I've heard others say they don't provide much improvement of regular boat tails. Not sure if anyone else does.

David Tubb has a redesigned DTAC 115 6mm with a rebated boat tail. I don't know of anyone who's used them yet.

 

[Mr.Knowit all]

I've loaded bullets backward from time to time. BCs are horrible. Brush deflection is much reduced. You can also use a center drill in the exposed lead back side of an FMJ and make a bullet that will expand at subsonic velocities. Also works when you have a bunch of pointy bullets and need to shoot a 30-30.

Any way you slice it, it's a short range proposition.

Right. My friend loaded some and it split the necks on the brass like you said the accuracy was terrible. however when he did hit a target or gel it made a larger wound cavity. Obviously we need a semi-long 7 to 8 degree bout tail meeting at a flat base to get some kind stability in the "push" from the powder. I think in the last 10 years bullets have made TREMENDOUS progress. Some of the BCs are astounding..... JMO

 

[mikecr]

would lower mussel pressure = lover velocity?

Rewrite this and read it to be sure it makes sense, before posting , and I'll answer it.

 

[dcali]

would lower mussel pressure = lover velocity?

Muzzle pressure has little to do with velocity, at least not directly. The velocity is created by the pressure at every point from chamber to muzzle. The more pressure at each point, the more velocity. The trick to internal ballistics, in part, is to maximize velocity while leaving as little pressure at the muzzle as possible so as to avoid disturbing the bullet as it exits. That's a gross oversimplification, but you get the gist.

I have a hunch that flat base bullets are more accurate because of their overall shorter length (for their weight) than boat tails, not because the flat base has an intrinsic benefit to how it leaves the muzzle, but it's just a hunch. I'm not aware of any serious testing that puts the issue to rest one way or another. Although I have seen some back of the envelope calculations that lead me to believe that muzzle exit is not as big a deal as some might think, but the context there was military ammunition, not benchrest.

 

[johnmventers398]

Rewrite this and read it to be sure it makes sense, before posting , and I'll answer it.

Ha nah I think I will leave it the way it is. The power of proof reading eh?

 

[johnmventers398]

Muzzle pressure has little to do with velocity, at least not directly. The velocity is created by the pressure at every point from chamber to muzzle. The more pressure at each point, the more velocity. The trick to internal ballistics, in part, is to maximize velocity while leaving as little pressure at the muzzle as possible so as to avoid disturbing the bullet as it exits. That's a gross oversimplification, but you get the gist.

I have a hunch that flat base bullets are more accurate because of their overall shorter length (for their weight) than boat tails, not because the flat base has an intrinsic benefit to how it leaves the muzzle, but it's just a hunch. I'm not aware of any serious testing that puts the issue to rest one way or another. Although I have seen some back of the envelope calculations that lead me to believe that muzzle exit is not as big a deal as some might think, but the context there was military ammunition, not benchrest.

Thanks that was a really well explained answer. To the point and not overly complicated.

 

[spclark]

I'm not aware of any serious testing that puts the issue to rest one way or another.

While I don't shoot benchrest it seems the most popular bullets are flat-base, at least out to 200 yards. Out farther the boat-tails are most often used.

As for serious tests... I suspect B. Litz has done something along this line but he's probably busy prepping for the BSWN events week after next to stop by here much.

 

[mikecr]

There are a lot of reasons PB BR would center on short, light, FB bullets.
And that's where 'serious testing', which would actually cause only one change at a time, is difficult.

 

[dcali]

The trouble is it's hard to tell how much of the advantage of flat based bullets is due to how they leave the muzzle and how much is due to their inherently more accurate shape. The latter is well established theoretically, and the former not so much. But either or both could be the case.

 

[geo.ulrich]

While I don't shoot benchrest it seems the most popular bullets are flat-base, at least out to 200 yards. Out farther the boat-tails are most often used.


I'm not sure where this information is coming from but the last 10 or so years short range br has been dominated by b.t.'s .....George

 

[spclark]

Came strictly from my memory George, back from when I took up highpower around 2001. Never shot benchrest while there were a few at the club I joined who did. All seemed to be using flat-bottom.

Everything I read in & from Precision Shooting back then suggested FB's were their preferred style.

I'd have to believe recent developments in bullet design had had an influence on benchrest so it's not hard to accept BT's are used more now than before.

 

[geo.ulrich]

Came strictly from my memory George, back from when I took up highpower around 2001. Never shot benchrest while there were a few at the club I joined who did. All seemed to be using flat-bottom.

Everything I read in & from Precision Shooting back then suggested FB's were their preferred style.

I'd have to believe recent developments in bullet design had had an influence on benchrest so it's not hard to accept BT's are used more now than before.

Well lets see about " recent developments in bullet design" b.t.'s were being used in the late 70's then went to f.b. and went full circle to b.t. mid to late 90's. Precision Shooing pretty well had stopped being a b.r. magazine by 1990 and went a different direction which it seems didn't really turn out to well. The only gage I have is bullet die sales and bt's are an easy 10/1 over flat base even though there seems to be more interest being generated lately. George

 

[clams243]

Google "telescoped ammunition" very interesting concept.

 

[redrockranger]

For sale:

.243 ,105=106 gr. REBATED BOAT Tail bullets. Hand swaged on J4 jackets.