Boattail VS Flatbase

[onesonek]

I did a quick search and didn't really see what I was looking for.
If it has been brought up before, I missed it, so bear with me please.
What is your preference of the two, for hunting bullet. Not restricted to a particular mfg, or individual design characteristics, other than being a flatbase or boatail design? And then why?

 

[efw]

Whatever my rifle likes best; I don't shoot game at distances long enough to matter whether the projectile has a flat base or BT so I just let the rifle tell me what she likes and then go with it.

 

[DrMike]

My observation is that I more easily wring greater accuracy out of a flat base than out of a boat-tail. There are fewer angles to complicate matters. I shoot a number of boat-tails, but when I'm simply looking for a hunting bullet, I gravitate to a flat base bullet.

 

[Jimbeaux82]

DR Mike,

I find your observations very interesting indeed. I have always thought that the Nosler Ballistic Tip bullet was by far the most accurate hunting bullet in most cases and all of the target bullets tend to be BTHP, but that could be for use at long range. But how can you account for the fact that the NBT groups so well in most guns?

I do understand that some people feel like the flat base engages the rifling better , especially in rougher bores like a mil surp, so that may be the answer.

Jimbeaux

 

[onesonek]

My observation is that I more easily wring greater accuracy out of a flat base than out of a boat-tail. There are fewer angles to complicate matters. I shoot a number of boat-tails, but when I'm simply looking for a hunting bullet, I gravitate to a flat base bullet.

Same here Doc. Beyond the heel and muzzle crown, I also believe BT's are somewhat more subject to barrel harmonics. Although that would more difficult, for me to prove.

Whatever my rifle likes best; I don't shoot game at distances long enough to matter whether the projectile has a flat base or BT so I just let the rifle tell me what she likes and then go with it.

I agree Eric, accuracy is king. As you touched on it, I suspect there will be some, where distance is deciding factor,,,assuming the desired accuracy is there. Even if it takes more extensive load work up, to find an accurate load.

 

[filmjunkie4ever]

Hate to sound like an echo but that is exactly what I have found to be the case as well. Since I use Nosler bullets almost exclusively for all of my big game (and most small game) hunting, I usually get some Accubonds and Partitions and see who shoots the best. Although lately I have been having uncannily good luck with the E-Tips as well. The E-tips and Accubonds shoot to the same point of impact in my 300 WSM and so that is a nice bonus; my 30-06 has always prefered the Partitions in 180 grain but the Accubonds in 150 and 165 grain shoot very well; my 308 likes flatbase bullets with the one and only exception being the Sierra Gameking and my 25-06 likes all of them except the 110 grain AccuBond...go figure! :wink:

You know for what its worht I will add this, most hunters and I say most because I know that there are both huters and shooters which do frequently perform outside the following parameters, will not be shooting far enough away to notice a huge difference in having the improved ballistics of a boat tail bullet versus those of a flat base. However as Dr. Mike said and we always listen to the doctor :grin: the answer is to shoot the bullet which shoots the most accurately.

 

[onesonek]

Jim,,,I can't answer for Doc's thought's.
I however, attribute the accuracy of the NBT to couple of aspects. #1 would be Nosler having some exceptionally close tolerence's in that heel angle, and also great quality control. Then too, the BT has a realtively short tail, that is likely more forgiving than some other designs.

 

[DrMike]

I attribute the accuracy of the NBT to close tolerance in the manufacturing. Based on my experience, however, I would not be at all surprised to find that if Nosler manufactured on the same line a flat base bullet, it would prove more accurate (even if marginally) than the BT. Obviously, boat-tail bullets can be very accurate. Realistically, in the field, few of us are really capable at the usual hunting ranges of distinguishing the differences between a flat base bullet and a boat-tail bullet. Moreover, few of us are able to take advantage of the differences. I concede that at distances beyond, say 450 yards, the better BC of the boat-tail confers an advantage. However, at closer ranges, due to the fact that there are fewer angles, a flat base bullet will likely meet closer tolerances, and hence generate a higher degree of accuracy. One of the advantages of hand loading is that we can adjust charge or other factors to compensate for these slight discrepancies that are introduced by design. Nevertheless, it remains a truism that the more complex the design, the greater the potential for inaccuracy introduced.

 

[SJB358]

I generally shoot a ton of Noslers. I really don't think of the BT or AB's as true BT's. Yes, they do have a slightly beveled heel, but they are far from the deal on a GK or Berger bullet. As all the rest said, I shoot was is most accurate in my rifle and luckily, with few exceptions, I have had little trouble making either or shoot in my rifles with good hunting accuracy. Scotty

 

[onesonek]

Realistically, in the field, few of us are really capable at the usual hunting ranges of distinguishing the differences between a flat base bullet and a boat-tail bullet. Moreover, few of us are able to take advantage of the differences. I concede that at distances beyond, say 450 yards, the better BC of the boat-tail confers an advantage.

Years ago, before the Ballistic Program, I shot at longer ranges to find out was going on with bullet drop, as the tables seem to always have discrepencies I could quite figure out at the time. Now I could only attribute those to the law of averages. The BP, still has some law of averages by necessity, or rather limitations due the variables of design minutiae, but are pretty close to what my records showed.
So I concur with Doc, and even at 500 yds., the difference is still less 1.5" with a flatbase against a G5 boattail I just compared at the same velocity. In actual shooting, that could be slightly different however, but not usually to any great degree. Beyond that, the 2 designs seperate, and at much faster rate beyond 600.

 

[onesonek]

I generally shoot a ton of Noslers. I really don't think of the BT or AB's as true BT's. Yes, they do have a slightly beveled heel, but they are far from the deal on a GK or Berger bullet. As all the rest said, I shoot was is most accurate in my rifle and luckily, with few exceptions, I have had little trouble making either or shoot in my rifles with good hunting accuracy. Scotty

I understand what you're saying Scotty,,,,with GK and Berger's, you are refering to, I believe are figured at G5 and G7's. The NBT and NAB are boatails, but if I had to guess, they are likely to be in the G2 may be G3 arena if there's such a drag function. I haven't quite got that meticulous to measure with them, in order to figure out exactly, and plug in another Drag function,,,, my program operates on G1,G5 , and G7's. But still, even among the 3 and bullets mentioned and a flatbase, the difference's aren't great until 500 yds and more. So unless its something like a VLD G7 or specified other, I treat all the boatails as a G5 for the most part . I can fudge for the NBT and be close enough. But again, the differences are small enough, under 5 - 600 yds that is isn't a major factor.

 

[JD338]

I am a Nosler boat tail kind of guy. :grin:

JD338

 

[SJB358]

I am a Nosler boat tail kind of guy. :grin:

JD338

Me too I guess :grin: Heck, I like them all if they shoot decent! Scotty

 

[6mm Remington]

I love the boattail and used to just shoot the old Nosler solid base boattail in everything! When they first started making the Ballistic tip I had to now change to Partitions as I just was not happy with the BT's on game. They have both shot very well for me. First bullet and load I'm working on in my son's new 300 WSM is a 180 gr. AccuBond. I've only tried a couple powders so I'm not there yet. Thinking about trying some 180 gr. E-Tips though as I sure am impressed with it in my son's 6mm. Short answer is I will end up loading an AccuBond, Partition, or E-Tip (all Nosler :shock: ) and I am sure I will find one of those three that shoots really well and I'll be very happy with. Short answer, which one shoots the best in my rifle!

 

[atmoshpere]

As far as accuracy is concerned, I've read quite a bit about the theoretical benefits of flatbase over boattail when using shorter for caliber bullets. The idea is that the shorter boattails have a higher likelyhood of starting down the bore slightly canted to the bore's axis because they are more oval shaped if you will. Even a small cant of .5 degrees can affect dispersion a measurable amount at 100 yds. The longer full diameter area of a flatbase bullet in the lighter weights with the 90 degree angles at the back supposedly helps keep the bullet's centerline parallel and centered on the bore's centerline.

From what I understand, most bench shooters for 100-200 yard comps use flat base bullets, but then I think longer range marksmen print some impressive groups with predominantly boattails so it may be half a dozen to one and six to the other :mrgreen: I guess most long range boattails are fairly long tho and have plenty of full diameter bullet shaft, so they may not qualify under the previous theory.

I don't have enough experience to really say one or the other, just sharing some things from a book that I've been finding very interesting.

atm

 

[Oldtrader3]

I use a lot of BT's for general shooting and range work. For serious hunting though, I stick to PT's. I usually only shoot one weight in any given rifle. So I will sometimes shoot CT's, BT's and PT's in the same rifle in the off season. If I need a bigger hammer, I use a bigger caliber rifle!

When its time to go to work on game, the PT's come out.

 

[BeeTee]

In the "for what it's worth" category...

According to the U.S. Army's Marksmanship Training Unit, as discussed in an article entitled "Designing an NRA Match Rifle", ideal dimensions for a 30-cal bore is: groove diameter of .3083" +/- 0.0001" and a land diameter of .3006" +/- 0.0001". Further, "there should be no distinctive tools marks and if there is any taper to the bore, it should be chambered at the largest end."

I've thought that the length of the full-diameter bearing surface of a bullet, in relationship to its total length, has an effect on concentricity as it travels down the bore. A shorter bullet is harder to align to the bore axis during the first moments of firing. So, a shorter bullet (like a 125/150gr 30-cal) doesn't have the accuracy potential of a longer bullet, but a flat base design would help the shorter bullets.

I suspect a typical bullet will "upset" to some degree due to the tremendous pressure at ignition. A flat base bullet, and the Nosler Partition in particular, will upset more, allowing it to better swage to bore diameter - sorta like a Civil War minnie. Boat-tail bullets may be more resistant to swaging. If so, then a rough or oversize bore would be more accurate with a flat base bullet that offers more upset potential. Of course, if your rifle has a match quality barrel, it probably doesn't matter all that much whether you're shooting high quality FB or BT bullets out to ~300 yards.

Just my thoughts...

 

[Oldtrader3]

I think that the Partition bullet will obturate in the bore of a rifle more easily than a cup and core bullet because the Partition bullet is an open gliding metal cup at the base into which a lead slug is swaged. This design should promote obturation more readily than a cup and core bullet, particularly a boatail design because that design is not only jacket metal at the bottom of the bullet but also the boatail shape would lessen obturation of the bullet while travelling down the barrel despite pressure behind it.

 

[onesonek]

shorter boattails have a higher likelyhood of starting down the bore slightly canted

I would attribute this to a few things that allow this to happen. #1 would be if the throat slightly oversize in dia.. #2 uneven neck thickess is more critical with the boattail in general. #3 short necks with longer throats.
While these things would affect a flatbase much the same, just the FB has less sq. area in contact with the expanding gas.

longer range marksmen print some impressive groups with predominantly boattails

This generally is due to the reasons I mentioned earlier, in regards to entering the transonic zone. Which iirc, is 1435 fps at sea level with 70% humidity, or generally 200 fps above the speed of sound for the elevation and conditions you are shooting.
Also I believe most target guns, as mine, are built around a dummy round with a particular bullet in mind, so the tolerences are much tighter than production guns, that generally are a tad bigger in most dimensions beyond headspace

 

[onesonek]

In the "for what it's worth" category...

According to the U.S. Army's Marksmanship Training Unit, as discussed in an article entitled "Designing an NRA Match Rifle", ideal dimensions for a 30-cal bore is: groove diameter of .3083" +/- 0.0001" and a land diameter of .3006" +/- 0.0001". Further, "there should be no distinctive tools marks and if there is any taper to the bore, it should be chambered at the largest end."

I've thought that the length of the full-diameter bearing surface of a bullet, in relationship to its total length, has an effect on concentricity as it travels down the bore. A shorter bullet is harder to align to the bore axis during the first moments of firing. So, a shorter bullet (like a 125/150gr 30-cal) doesn't have the accuracy potential of a longer bullet, but a flat base design would help the shorter bullets.

I suspect a typical bullet will "upset" to some degree due to the tremendous pressure at ignition. A flat base bullet, and the Nosler Partition in particular, will upset more, allowing it to better swage to bore diameter - sorta like a Civil War minnie. Boat-tail bullets may be more resistant to swaging. If so, then a rough or oversize bore would be more accurate with a flat base bullet that offers more upset potential. Of course, if your rifle has a match quality barrel, it probably doesn't matter all that much whether you're shooting high quality FB or BT bullets out to ~300 yards.

Just my thoughts...

I agree again, that a shorter bearing is more susceptible to variation in concentricity. Which again is compounded in a roomy throat, uneven neck thickness. Even the concentricity, of the chamber itself. Also the seated bullet, as it is not uncommon common to seat with some runout. Which generally isn't a lot, but even .0005" in any, can make a difference. The seating runout can be corrected easy enough with concentric gauge/aligning tool. I do this with most my target/long range rigs. However, another way for less needs,,,, is to short stroke the seater by starting 1/3 to 1/2 way, then rotate the case a 1/2 to 1/3 turn 1-2 times before the full seating stroke.

I also agree and think different types of bullet obturate differently. And while I can't prove it, I think that is the reason, why certain bullets have particular seating depth wants, and then again design come to into play. I find with FB's, the generally excepted standard of .010" off the lands, is a good starting place. However, with BT's, I generally start at .002-3" off. And with some, I seat so I am bumping the leade pretty hard.
I think all bullets obturate to some degree, with the exception of extremely hard core AP's. Even the monometals will obturate to some extent I think. Albeit, I can't prove this either, but believe obturation to be the reason most mono's like being seated farther off the lands. Sometimes as much as .100" off the lands, according to some reports and recommendations I have read, along with some limited personal experience. I think this is because they like a hard fast launch, literally slamming into the leade, resulting in better/quicker obturation at the start, hence better accuracy. It's just my opinion, but when seating that far off the lands, the more concentric everything needs to be, the more even the neck thickness, and tighter tolerance's of the throat dia. is needed. But I also think that of any BT design in general, regardless of seating depth.

All that said, one thing I always do with boattails, regardless of weight/length, and individual design or composition characteristics, is turn the necks. And on the sharper shouldered cases, ream the neck every firing, needed or not