AROUND A DOZEN years ago I was telling a friend about a long trailing job on a Montana whitetail buck shot with a 125-grain Nosler Partition from a .260 Remington.  This friend happens to be a custom gunsmith (many rifle loonies would recognize his name) and an avid deer hunter, and he said, “That bullet’s designed for the .264 Winchester Magnum, so is too hard for the .260.”

He sounded very sure so I didn’t argue, but during a conversation with somebody named Nosler a few months later I found out my gunsmith friend was quite mistaken.  It turned out Nosler actually designed that bullet for the 6.5×55, because when the 125 Partition appeared the old “Swede” was by far the most-reloaded 6.5mm round, due to tens of thousands of surplus Model 94 and 96 Mauser military rifles.  The number of bullets handloaded in higher-velocity 6.5mm rounds such as the .264 was comparatively small.

He went on to say that Nosler uses a relatively soft lead alloy in the front core of all Partitions, to make sure they expand even on relatively light game at modest velocities.  The rear core is a much harder alloy, and sometimes varies in antimony content depending on the bullet.

Bullet companies can be very secretive about exactly how their bullets are made.  I’ve toured several bullet-making factories (including Nosler’s) where I’ve been asked not to photograph certain areas, or have been fed information so vague it’s useless.  Sometimes, however, they let something slip.

One tour was led by the plant supervisor, and he said every bullet they made featured the same 3% antimony lead alloy core.  A month or two later I started working on an article about bullets and phoned the company’s public-relations guy to confirm that number.  He told me, somewhat curtly, that their bullet-core alloys were “proprietary information.” This was fine with me, but I suspect the plant supervisor got a little lecture.

A different bullet company once told another gun writer they use 4% antimony cores in most of their big game bullets.  This may be true, because their cup-and-core bullets have a somewhat better reputation for holding together than the bullets from the company that may (or may not) use 3% antimony cores.  But when I asked the 4% company about it, they clammed up too.

Not many hunters discuss the cores of big game bullets, instead preferring long arguments about jacket design.  This is understandable, because jacket conformation’s far more obvious.  We can section a bullet and actually see variations in jacket thickness and design, though we have to be careful to section the bullet right down the middle.  If the cross-section varies a little, so can the appearance of the jacket.

When I first started sectioning bullets, it appeared the jacket of a 180-grain round-nose Core-Lokt was thicker around the middle of the bullet — exactly what Remington had claimed for years.  I mentioned this to the head production guy at another bullet making firm, and he asked me to send him the sectioned bullet.  After receiving it, he called and explained my mistake: My sectioning — done with a file — wasn’t precisely down the centerline of the bullet, making the jacket appear heavier in the middle than at the rear.  In reality, Core-Lokts merely have heavy but uniform jackets over the shank of the bullet.  Or at least some of the few round-nose models do.  Remington changed to somewhat thinner jackets in the Pointed Soft-Point Core-Lokts over 20 years ago.

Core hardness also has a definite effect on how bullets perform when they hit game.  Some bullet companies tweak the core alloy, depending on the job the bullet’s intended to do, some adjust the jacket, and some do both.  A prime example is the Nosler Ballistic Tip.  When first introduced in the 1980’s, Ballistic Tips were a plastic-tipped version of their lower-cost Solid Base bullets, with no changes in jacket thickness or core alloy.

Solid Bases didn’t expand very violently, and in fact in some models, in some cartridges, acted a little “hard” on occasion.  I once put a 25-caliber 120-grain, started at about 2850 fps from a .257 Roberts, just behind the shoulder of a big mule deer buck at the modest range of 100 yards.  The buck traveled around 200 yards before falling, a hole less than the diameter of a quarter through both lungs.

But adding the plastic tip really changed the way Ballistic Tips opened.  Recent high-speed digital photography shows this isn’t due to the tip “wedging” the bullet open, as many people believe.  Instead photos taken through clear “ballistic” gelatin show the tip actually traveling in front of the mushrooming bullet.  Instead, apparently plastic-tipped bullets cause bullets to open wider (and, often, more violently) because of the large hollow-point necessary for inserting the tip.

This hollow-point changed the impact performance of the sedate Solid Base so much that Nosler had to make changes in the “hunting” Ballistic Tips to calm them down.  (The violent expansion worked great in the varmint models, of course.)  The first and easiest solution was to add more antimony to the core alloy, hardening the lead, but eventually the jackets in some models were beefed up as well.  As a result, a few Ballistic Tips now behave much like Nosler Partitions.

Plastic tips also affect the way monolithic bullets expand, the reason Tipped TSX’s open so well, even at extended ranges.  Of course, the ballistic coefficients of Tipped TSX’s are also higher than those of hollow-point versions, resulting in higher impact velocities at longer ranges.

The most common method for bonding lead-cored bullets involves slightly melting the core after the bullet’s swaged together, essentially soldering the lead to the jacket.  However, the heat also anneals both jacket and core, and must be taken into account when designing bonded bullets.  This is probably why only the front core in Swift A-Frames is bonded.  The rear core sometimes also expands on impact, especially at close ranges or when the bullet hits bone, but would probably expand even more if the entire bullet was heated, softening the rear core.

Some hunters believe Speer Hot-Cors are bonded, since their cores are formed by injecting molten lead into the jackets.  However, bonding only occurs when both cores and jackets are heated simultaneously, and the cores of Hot-Cors don’t stick to the jacket.  This is easily proven by placing a Hot-Cor nose-up in a vise, then splitting the front end with a hacksaw and peeling the jacket off the core.  However, the shank jackets of many Hot-Cors are pretty thick, and injecting the got core doesn’t heat them enough to anneal the jacket.  As a result they hold up pretty well on game, especially when started at no more than about 2800 fps, or used only at longer ranges.

Out of curiosity (and because bullet companies can be so secretive) I decided to test the cores of some .30 caliber bullets with a SAECO hardness tester, usually used on cast bullets.  The SAECO works by screwing a sharp cone into the nose of a bullet, then looking at a scale to “read” the relative hardness.  A reading of 0 means the lead is essentially pure, and “harder” readings go up to 10.  In my tests I added a plus or minus sign to some numbers, indicating the readings were slightly to one side or the other of the hashmark.

To perform the test, the noses were filed off bullets until a flat section of the core at least 3/16” wide appeared, the minimum width suggested in the directions for cast bullets.  From the results it’s obvious the cores of most big game bullets are on the soft side:

The big problem, of course, is that hunting bullets are used in different cartridges at widely varying velocities.  Along with impact velocity, this also affects rotational stress, something frequently encountered today with the rising popularity of faster-twist rifling.  Faster twists don’t have a huge effect on the expansion of harder big game bullets, partly because the difference between a “slow” and “fast” twist barrels is usually only a couple inches.

But the effect of widely varying twists can be substantial on thin-jacketed varmint bullets with softer cores.  For a prairie dog shoot with the first Nosler Varmageddon bullets, I loaded some plastic-tipped 55’s in a tang-safety Ruger 77 .220 Swift with the traditional 1-14 twist.  At a muzzle velocity of 3800 fps they expanded great, of course, but my shooting partner used a .223 with a 1-8 twist barrel, and the same bullet at only 3100 fps expanded more violently.  We saw this repeatedly at ranges from 30 to 300+ yards, because Varmageddons have thin jackets and relatively soft cores.  (Do the math, and you’ll find the bullets from the .223 exited the muzzle spinning 43% faster than the bullets from the Swift, despite starting out 700 fps slower.)

Differences in velocity have always been a problem for makers of big game bullets.  Some have tried to cope by designing bullets specifically for various velocity ranges.  Winchester tried this with the Fail Safe bullets in the 1990’s, offering one bullet for .308/.30-06 velocities and another for “magnum” velocities.  The concept evidently confused handloaders, probably because most humans don’t read directions, but some apparently believed the “magnum” Fail Safes would provide magnum performance in the .30-06.

Only one thing’s certain in manufacturing expanding rifle bullets: Some hunters will prefer softer bullets, and some will prefer harder bullets.  Luckily, today’s bullets provide something for everybody.