Flat base or boat tail?

[nvbroncrider]

Is there any explanation as to why a rifle will shoot a flat base but not a boat tail or vice versa?
Or why a rifle will shoot both?

 

[Gunner46]

Some guys like blondes, some like redheads......

 

[FOTIS]

On rifle's trash is another rifle's treasure.

 

[DrMike]

While there may be a formula allowing prediction of accuracy with one type of bullet or another, I would assume that the variables would introduce an astounding complexity. The bearing surface, degree of angle and even jacket thickness would all contribute as least somewhat to consideration of the bullet itself. Chamber dimensions, barrel twist and groove depth would likely contribute to the factors that would need to be considered. And then, start pressure and burn rate would be a contributing factor. I can imagine that any formula would be complex. Ultimately, Fotis and Gunner46 have offered the most realistic appraisal of why one rifle prefers one bullet type and another rifle tolerates another. In general, it is my experience that the less complexity in bullet design (i.e., flat base) the easier to wring accuracy out of a bullet. Then, when we begin shooting at distance and seeking a bullet with a higher ballistic coefficient, the requirements change again.

 

[Elkman]

Nope, as already stated. Rifles are like women, all have the same basic parts, all preform the same basic functions, they are of varying quality, and no two are exactly the same.

 

[truck driver]

Jake like you I have always wondered why I could get flat base bullets to give me better results than boat tails. I've read lots of articles published on the subject and I can not explain or reason why it happens. There are lots of learnered people here with more experience and knowledge than I have and won't even think about trying to explain why it happens but I think DrMike covered it very well as did Fotis and Gunner46. I do know that a custom cut barrel will shoot boat tails better than most factory barrels.

 

[Vince]

Nope, as already stated. Rifles are like women, all have the same basic parts, all preform the same basic functions, they are of varying quality, and no two are exactly the same.

Best summation yet.


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[Horsethief]

1. Dr. Mike's explanation is very good. I will save this for reference when someone asks the question about flat base vs boat tails so I won't have to think.
2. I had a 270 Win that would not shot 130gn Interbonds anywhere near as well as 130gn Interlocks (flat base) or 140gn Interlocks (boat tail) bullets. They only thing I could determine was the bearing surface of the Interbonds was just below what that barrel would tolerate. I won't go into the things I tried to make the Interbonds group better, but I failed in that endeavor. The other bullets had longer bearing surfaces that turned into better harmonics.
3. I sold that rifle and a bunch of very well tuned, hand loaded ammo to a good friend. He liked that I had done all the load testing.

 

[Vince]

1. Dr. Mike's explanation is very good. I will save this for reference when someone asks the question about flat base vs boat tails so I won't have to think.
2. I had a 270 Win that would not shot 130gn Interbonds anywhere near as well as 130gn Interlocks (flat base) or 140gn Interlocks (boat tail) bullets. They only thing I could determine was the bearing surface of the Interbonds was just below what that barrel would tolerate. I won't go into the things I tried to make the Interbonds group better, but I failed in that endeavor. The other bullets had longer bearing surfaces that turned into better harmonics.
3. I sold that rifle and a bunch of very well tuned, hand loaded ammo to a good friend. He liked that I had done all the load testing.

It is but is more highly technical than many can stand.
Bill's way is short and sweet which is what most of the general population wants. Don't get me wrong as I favor the good Doctor's explanations but I also like sorry and sweet. Especially when I'm tired.

Vince

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[JD338]

Nope, as already stated. Rifles are like women, all have the same basic parts, all preform the same basic functions, they are of varying quality, and no two are exactly the same.

Exactly!

JD338

 

[1Shot]

I had a custom Rem 700 26 " #6 Shilen select match barrel rifle in 25-06 Rem built. When I started load testing I was using 117 Sierra Game King BT bullets. No matter what I did I could not get that rifle to shoot under 3/4" groups at 100 yards. I had a friend suggest that I try the 117 Sierra Pro Hunter FB bullet. BINGO! Bug holes at 100 and 3/4" groups at 300 yards. Fast forward 20 years and much more experience loading and shooting many different caliber and style rifles. If you are not shooting over 300 yards you are wasting money using BT bullets because they don't start to show any benefit in wind and trajectory over FB bullets which are usually cheaper. But with some makes like the Ballistic Tip you don't have a choice.

 

[Oldtrader3]

I suspect that the most straight forward way to predict pitch and yaw with the BT bullets are bearing surface length and the incident angle of yaw and pitch in the barrel due to short bearing surface. The amount of this phenomena will be much less with the flat based bullet and longer bearing surface. I will need to dig out Col Whelen's book to find out how to calculate this.

Also knowing that out at longer ranges this yaw and pitch will stabilize and give better results in accuracy.

 

[Horsethief]

The most accurate 3-shot groups @ 300 yards with my 300 Weatherby were made with RL-19 and H-4831 pushing flat bottom 180 grain Hornady Interlocks. The RL-19 made a 1.25" group. The H-4831 had a group 2.2" wide.

 

[rick3]

Wow, good info.

I'm new to this board, but I've been shooting for many years and handloading for my rifles for about a year. I had been reading about all the BT bullets used at longer distances, and thinking that my inexpensive FT bullets were "beginners stuff", but I guess that's not exactly true. I wondered why I was getting such good groups (.4" @ 100yds), for me anyway, with my new .243 and the "cheap" FT bullets...now I know!

 

[DrMike]

Welcome aboard, Rick. You'll find a good group of people around here willing to exchange intel to make the sport more enjoyable. Trust you'll enjoy yourself as much as I do.

 

[nvbroncrider]

Thanks for the thoughts. Something that passed through my mind the other night and was looking for answers.

I like your opinion Bill sounds good.