Home Forums Hunting & Shooting Ask The Gunwriters APRIL - Ask John Barsness Questions About "FLAT-BASE AND BOATTAIL RIFLE BULLETS"

Hi Guys:

I would like to thank John Barsness (Mule Deer) for his latest exclusive Campfire article, FLAT-BASE AND BOATTAIL RIFLE BULLETS , which is now on the Home Page (click link above).

Please use this space to ask John questions about the article. I hope you enjoy it.

Thanks again, John!

rb

Nice article John.

I've never bought the line that BTs lose their core / jacket more than FB bullets. While I've not documented recoveries of bullets like you, my casual observations echo your notes.

I also think for rough and ready handloaders like me, boat tail bullets tend to be easier to seat straight in the case because they start into the case mouth so easily. Whether due to this factor or not, I tend to see better accuracy with my BT handloads, all other things being equal.

Not sure that last bit holds water, but I'm going with it until proven wrong!

Enjoyed the heck out of the article John, thanks for actually keeping track of all those shots!

Last year I had four "big game" hunts on the schedule: black bear, antelope, mule deer and elk. I chose to use the same rifle and load for all four hunts; a .30-06 Rem 700 CDL with the 165 gr Nosler Ballistic Tip loaded to about 2900 fps.

People questioned me about my choice of the 165 gr Nosler Ballistic Tip for the bear and elk, but it worked out great on all four animals. I shot the bear while he was quartering away. The bullet went in the rib cage, and only the core exited through his off side chest/shoulder area. We found the expanded jacket hung up in his hide. Very quick kill, and he traveled only a few feet after being hit.

Also recovered one bullet from the mule deer, which was shot facing me. It retained much of the core, nicely expanded. The pronghorn of course didn't retain the bullet, and the bullet that took the elk was never located, though it went through the on-side shoulder causing tremendous damage in the chest cavity, then punched a hole in the off-side shoulder blade as well. All from a little 'ol Ballistic Tip.

Sometimes things are not as they seem. I had good reason to believe that "my" Ballistic Tips were plenty tough enough for the tasks. And accurate? Yes indeed... It pays to learn about the bullets we're going to use, for varminting, or for hunting larger animals.

Regards, Guy

I must admit I don't visualize this one. Is it a matter of the shorter shank exposing the throat sooner, or does the shorter shank permit more blow by early on, or does the boat tail deflect the early blow by more vigorously onto the throat, or ...

How strong is the effect, say in terms of % reduction in number of rounds fired before accuracy is affected?

(Thanks for the article.)

Lead-cored bullets tend to "obturate" (expand slightly) when booted in the rear by powder gas. The rear ends of flat-based bullets obturate quicker, due to more area exposed to the hot gas than the smaller flat area at the end of boattails.

Boattails tend to funnel some powder gas into the rifling, due to the angle on their sides, while flat-based bullets tend to have sealed the bore by the time their rear end passes the start of the rifling.

Or at least those are the conclusions of the research I found.

Excellent article, John. Thanks for sharing your experience with us.



Bobnob17,

I check a majority of my loaded rounds on a Sinclair Concentricity Gauge. I don't find that the boattail bullets necessarily seat any straighter than flat base bullets. They are just easier to handle getting started into the case mouth.

The factor that seems to make the most difference in how straight the bullets seat is how well the bullet seating stem fits the front end of the bullet.

Some of my older seating dies do not work well with sharp-pointed plastic-tipped bullets like the Barnes TTSX. I had a rough time yesterday seating 140 gr TTSX bullets in 7x57 cases with an older Forster Bonanza seating die. Many bullets were loaded out of round as much as .010", and I needed to use the Tru-Angle tool on almost very round to correct them to acceptable straightness (for me, .003" or less).

Redding offers an optional VLD style seating stem for their seating dies, to better handle the sharper-nosed bullets.

I am glad you are getting good accuracy with your boattail bullets. And as John noted in the article, the boattails do achieve less wind drift than the flat-base bullets.

Thanks for the article, JB,
I knew there was a reason those Sierra Pro Hunters shot so well, just wasn't sure why.

Great article

most metals flow on compression, and any small elements (slices) will have a later moment of interia than slices close to the nose. Whether this is a "sealing" process is open to debate

because

the surface area of truncated cone is larger than the surface area of a circle having the same diameter. If nothing more than its a 3 dimensional surface rather than 2.

Im not going to say that the base of a boat tail bullet sees more pressure than a flat base because I know what kind of names I will be called.

A boattail's base obviously "sees" more pressure than a flat-base, because there's more area to the base behind the full-diameter bearing surface of the bullet, and PSI is pressure per square inch.

But with a boattail much of the pressure is applied to the side of the truncated cone, not directly forward on the flat base. This difference is larger in high-BC boattails with very small flat bases and more elongated truncated cones.

Or at least that's the way I'd read it. Whether or not that's correct, the military studies documented quicker throat erosion with boattail bullets, after firing hundreds of thousands of rounds, and attributed it to gas blow-by.

Makes sense as well.

For my big game rifles I work hard to achieve consistent MOA accuracy for three shot groups. Hardly the most exacting standards.

For my long range rifles I work towards 0.75 MOA and I do find those VLDs tricky to seat at times.

You've given me something to think about...

A BT base may "see" more pressure, but I've always understood FB bullets develop more chamber pressure because of the base obturation. One can increase charges with BT because less obturation tends toward lower chamber pressures, however increased charges may not be possible due to BT length extending into the case volume. The same powder charge behind a FB and BT will typically result in higher velocities with the FB, true or is there more to the story?

There's a little more to the story: Flat-base bullets of the same make as boattails also have more bearing surface against the bore, increasing pressures slightly, often increasing velocities as well. Which just illustrates, once again, that pressure on a bullet works in various ways, so simply calculating the PSI against the base area isn't the entire influence of pressure on velocity.

So can we conclude, MD, that any slight increase in flat-base bullet psi will not exceed any book "redline"? Or was that even taken into account when testing was done? The exception being mono-metal and high BC designs.

Also if pressure is applied more to the side of the truncated cone, does that result in accelerated barrel wear?

John,

That was a thorough and very informative article full of the kind of well backed up technical information we've come to expect from you.

I would like a clarification though. I suspect I already know the answer.

You mention that hollow point bullets don't fare as well over longer distances as tipped bullets but the obvious fact is that so many target bullets don't have tips. I assume that by "hollow points" that you don't mean the typical Berger or Sierra target bullets (the ones I'm most familiar with) but rather a true hollow point meant for violent expansion in varmints?

Clarification please.

Thanks,
$bob$

Have a little different question for Mule Deer > I have a Win Featherweight in .300 Win mag that I just had bedded by a supposedly competent shop in CO...When taking rifle out of stock I saw that it had not been done with any type epoxy but has a type of hard plastic square ( about 1" ) that curves up sides by lug and at rear where bolt goes through...Seems to be ok but will it last or is it a gimmick..?..Found when I installed a Timney trigger..Barrel is floated fine..Shots before trigger change were 3/4" at 100...Thanks ahead of time !

Sounds like they just put a plastic shim in it, which often works very well for floating a barrel. I've done the same thing many times with the flat plastic "closers" on loaves of bread and other groceries that come in bags. It's a good way to test whether floating the barrel will help accuracy, and sometimes just leave 'em in there rather than bothering to epoxy-bed the action. Why not, if it works?

Thank you for your article, your accurate analysis and your great write up!!

Question: "What was the twist -- your 6.5-06 barrel?"

That was a 1-9, but I never had any problems stabilizing even 140 Berger VLD's no doubt because I never shot the rifle at less than 4000 feet above sea level, on up to 7000 feet.

I see that E.R. Shaw has 1 - 8 and 1 -7 besides the 1 - 9.

Say a fellow wanted a rifle for 1000 ft elevation up to tree line. Hugh bc vld bullets primarily.

1 -8?

That would certainly work with any bullets in the 140-grain range.

Well another good read for sure. Always enjoy these and thanks for writing them.
Here in the North East we are limited in ranges where we can open it up to the Western distances. The flat base Speer and other brand bullets work very well in our one to three hundred range window, but your not going to hear that from many guys on the benches on a Saturday afternoon........
The straight scoop is always a welcome reminder.

John, very good article. FWIW, I've recovered every bullet I've shot deer with, if they didn't pass through. It's a very interesting pursuit, and though educational, CAN at times pose some real questions. One I'd like to add, is whether you've noted any "improvement" in Speer's "Hot Core" flat base bullets' retaining their cores, vs. more conventionally formed flat base bullets? I've never gotten anything but excellent expansion from the Speer bullets I've used, and I've used a fair number of them for one lone hunter.

I think the story of the flat base vs. boattails is a lot like most everything concerning ballistics - there's a LOT of factors acting that we don't always consider, or even know about. Sure keeps a fella' humble!

Blackwater,

Sorry I missed your question!

The Hot-Cor bullets, contrary to what some believe, aren't "bonded" because of the molten-injection cores. This can be easily proven by putting one in a vise upright, then hacksawing it down from the nose and prying the jacket away from the core. Dripping hot lead into a cold jacket isn't anything like the typical bonding process, which involves swaging the core inside the jacket first, then heating both until the core melts slightly, essentially soldering it to the jacket.

In fact, a Speer Hot-Cor was one of the very few bullets I've seen lose the jacket immediately when it hit an animal. It was 105-grain 6mm, started at 2800 fps from a .243 Winchester. The deer was a forkhon whitetail buck, and the range around 200-250 yards. The bullet hit a little high, and the core went into the spine, breaking it, but I found the empty jacket right at the entrance hole when I skinned the buck. On the other hand, have never had that happen again with a Hot-Cor.

At the other extreme, years ago I used 140 Hot-Cors from a .264 Winchester Magnum at 3200 fps to cull deer on a ranch, and they all penetrated completely, with no sign of coming apart. Also have a 165-grain .30 Hot-Cor in my collection shot into a whitetail buck maybe 100 yards, as the deer ran angling away. Muzzle velocity was around 2800 fps, and the bullet landed in the rear of the ribs on the left side. Found the bullet perfectly expanded, retaining 85% of its weight, in the right shoulder.

Eventually I concluded that Hot-Cor performance depends on several factors.

Thanks. I've long had the idea, and that's all it was, that the hot core process MAY bond some jackets, but probably not all. Your observations kind'a lend at least a little credence to that "opinion." I've never personally had one separate, but that's also true of the BT versions that do not "benefit" from the hot core process. I just haven't had the chance to see enough examples in recovered bullets (most pass through our smallish southern whitetails) to be able to get some good field "proofs" of my theory one way or another. I've always had really good results from Speer cup and core bullets, whether FB hot core or BT's. But then, I tend to use calibers that are legitimately "overkill" on these game animals, and once I get one in my crosshairs, they usually don't have a chance, whatever bullets I've stoked my loads with. But .... the field is a strange place, where most anything, even the "unthinkable" CAN sometimes happen. And being as sure as humanly possible is never a bad idea "out there."

And BTW, thanks for some very clear-headed articles on a very consistent basis. You seem to always wait for empirical "proofs" before opining firmly on any subject. That makes your articles highly valued. Thanks.

John:

There is an article in this month's G&A about barrel wear. I've heard that boat-tail bullets erode barrels faster than flat-based bullets, primarily because of the difference in the way the gas impacts the base and bore. Do you find this to be the case? And, more importantly, in your experience what do you think the round-count difference might be?

Edit note: I just saw the last paragraph in this article. Ok, given that erosion is a proven thing, any idea of the round-count difference?

Thanks

RM

John,

What about mono metal as it pertains to bullet shape? I have been a fan of Hornady GMX and Barnes TTSX bullets.

Please be more specific about what you want to know. Ballistic coefficient? Expansion? Penetration?