Rifle bullets; accuraracy question

[Fumbler]

I know that the most accurate bullets are BTHPs.
My question is does the uneven soft point of typical jacketed soft points hinder accuracy compared to FMJ and ballistic tips of equivalent quality?

For instance would Federal Premiums with Nosler ballistic tips generally be more accurate than Fed Premiums with the same weight Sierra Gamekings?

My Tikka T3 Lite in .308 win is more accurate with ballistic tips than soft points of equal ammo grade and I wondered if it was just my gun or the majority of guns.

 

[uglygun]

Boat tail bullets are not always the more accurate bullet.

in some instances a flat base can be more desireable or sometimes more accurate, bench rest shooters seem to have a preference for some flat base bullets for shorter range work.

theories are on how the bullet gets "kicked in the pants" by the expanding gasses at the precise moment the bullet exits the barrel and the gasses blow past it.


As for ballistic tips versus open tip match or even open tip lead spire points, could boil down to center of gravity. Having the center of gravity centered rewards in the jacket is supposedly better for the bullet stability in flight. Think of the polymer insert that makes up the volume of the projectile somewhat as well as projecting forward from the tip, compared to a lead spire point the ballistic tip will have a slightly more rearward center of gravity. Open tip match bullets are much the same way with the lighter mass jacket being drawn over the core which resides lower towards the end of the jacket.

An old picture I took of some ballistic tip style bullets I cross sectioned,
Nosler 50grn Ballistic tip on left, Hornady 40grn Vmax middle, and Sierra 40grn BlitzKing on right.

 

[Fumbler]

Thanks for the comments. I didn't know having a center of gravity further back is better.

I guess what I'd like to know is whether or not spire points and soft points have degraded accuracy due to having a lead tip that is often not concentric or is marred up and has lots of irregularities.

Looking at HP's and ballisic tips those have very even points while SPs don't.

 

[TooTaxed]

Deformed bullet tips should increase yaw and therefore accuracy. In my experience, boat-tailed bullets perform better at long ranges, but under about 200 - 300-yds the difference is negligble. Note that this is well within the range of most hunting and combat shots.

 

[Grump]

Search around for the very controlled bullet deformation experiments conducted about 100 years ago by legendary barrel-maker [Harry?] Pope.

To sum it up, it took a lot of ugly damage at the tip or even the ogive to degrade accuracy much. The bullet heel turned out to be the critical area. Greater precision and repeatability in manufacturing HPBTs and HPs in general, when the jacket is a closed cup in back and open in the front, is why the old 173-gr conventional FMJBT M72/M118 bullet in .30 caliber could never match the Sierra 168-gr Matchking for accuracy. They could do between .75 and 1 MOA out of bolt guns, but no better, according to reliable reports I've seen over the years.

Is it enough of a difference to affect your score on a target or a good hit on game? For game and any load shooting 2 MOA or lessI wouldn't worry about a half-minute difference in accuracy until I'm holding so hard that I can TELL that the bullet hit a half-minute off call.

For targets, that Highpower 10-ring is a full 2 MOA (bigger at SR), so I would worry about a half-minute difference in accuracy that puts my groups OVER 1.5 MOA as fired from position.

 

[Gewehr98]

Depends on what your game is.

Ask the benchrest gang what the tail end looks like on the bullets they use. I'll give you a hint - it's not a boat-tail.

That's not saying you can't have an accurate boat-tail bullet. Lately, I've been shooting the Lapua Scenar bullets in my 6.5-06, all the way out to 1000 yards. I'm very much convinced that the folks at Sierra need to make a trip to Finland.

 

[JohnKSa]

The flat-based bullets are more accurate (and easier on the bore too.)

However, at longer ranges the wind becomes a major issue and a well made boat-tail bullet will buck the wind better since it loses velocity slower than a flat-based bullet.

 

[bernie]

Somebody correct me if I am wrong (like I even need to ask!) but the Army did studies on boattail bullets and they do NOT increase barrel wear, that is an old wives tail. The boattail also primarily gives an advantage at long range because the boattail does not yaw as much (I have no idea why) as a flat based bullet when it breaks back below the sound barrier. For most calibers this is beyond the normal range most of us shoot. I am thinking off the top of my head this usually occurs between 600 to 1000 yards but I am really reaching on that one.

 

[Fumbler]

To sum it up, it took a lot of ugly damage at the tip or even the ogive to degrade accuracy much. The bullet heel turned out to be the critical area. Greater precision and repeatability in manufacturing HPBTs and HPs in general, when the jacket is a closed cup in back and open in the front, is why the old 173-gr conventional FMJBT M72/M118 bullet in .30 caliber could never match the Sierra 168-gr Matchking for accuracy. They could do between .75 and 1 MOA out of bolt guns, but no better, according to reliable reports I've seen over the years.

That pretty much answers my questions.
I guess there's no correlation to bullet type and accuracy...for me at least (shooting deer and punching paper for fun).

 

[JohnKSa]

bernie,

The boat-tail's long range accuracy is due to the fact that it holds velocity well and therefore is less affected by wind. The FIRST consideration in long-range target shooting is picking a rifle/load combination that keeps the bullet supersonic all the way to the target. All bullets are perturbed by the supersonic to sonic transition and no one trying for long-range accuracy picks a load that would cause this transition before the target range was achieved.

Here are some quotes from the web and books in my library about boat tail bullets as regards accuracy and barrel wear.

"The base of the bullet is the full-diameter bottom of the bullet. It is one of the most critical areas of the bullet for accuracy. The gas seal or pressure ring area of the bullet must be even and perfectly square to the axis of the bullet. Any variation or unneveness in the base of the bullet will result in an uneven exit if gasses (sic) around the bullet when it clears the muzzle. This results in instability and loss of accuracy. Most bench-rest shooters use flat-based bullets for their 100- and 200- yard competitions, because the perfect exit of gases behind the flat, square base is optimal for accuracy. "

And, further on in the same book.

"Where boattail bullets come in to their own, however, is past 400 yards, where the benefits of reduced air resistance decrease the flight time of the bullet in contrast to its flat-based counterpart, making range estimation and windage adjustments less critical."

Here's a quote from a glossary of terms found on the web.

"Boat Tailing - Tapering that part of the projectile behind the driving band to reduce air resistance, especially at low velocities. This type of design gives a projectile greater range but tends to increase wear on the gun barrel. "

And another excerpt from the history of the .338 Lapua:

"Accuracy and velocity at long range are greatly facilitated by the design of the Lapua projectiles, which have had a reputation for extraordinary long-range performance since the 1930s, when Lapua developed a special bullet with rebated boat tail designed to give Maxim belt-fed machine guns unprecedented accuracy at ranges of 1,500 meters and beyond, while minimizing barrel erosion commonly associated with boat tail bullets of conventional design. "

 

[Gewehr98]

JohnKSa hit the nail (or is that bullet?) on the head.

If your bullet goes trans-sonic before it gets to it's target in long range competition, you're going at it wrong.

Keep the bullet supersonic all the way. Do that either by utilizing a ballistically-clean bullet in an efficient case, like the .260 Remington or 6.5-284, or the brute-force approach, like the .300 Win Mag or .30-378 Weatherby Mag.

Or, you avoid the transition by starting out subsonic to begin with, like the .300 Whisper. Other rounds really don't care a lot about the shock wave transition as they reach way out there, to include the .40-65 Winchester and .45-70 Government, but they're not exactly the highest Ballistic Coefficient bullets in the charts anyway.

 

[30Cal]

Match bullets come in hollowpoint only because they are the easiest to make consistant. FMJ are what I'd consider fodder. They get there, but with unimpressive results. Based on my experience, you can beat up the tip of a bullet pretty good and it won't really matter--at least at short range (300yds or less).

As far as boattails, they come in handy past 300yds, but the edge isn't all that significant really. As far as the military is concerned (and I tend to agree with them), long range starts at 600yds.

Ty