column By: Dave Scovill | January, 18
There is a photo in the 1955 issue of the Ideal Hand Book on page 25 that shows a .30-caliber jacketed bullet with the base expanded to what appears to be about .40 caliber. The bullet was fired from a .30-caliber barrel cut off in front of the receiver. The text next to the photo states: “It will be obvious to the reader that the gases were driving the base faster than the point after the bullet left the short barrel, causing the decided upsetting of the base.”
The text goes on to state expansion, aka upset, at the base of the bullet is common to flatbase bullets. The base of boat-tail bullets does not expand, owing the gas pressure around the surface of the tapered portion, but explains why boat-tail designs must be of heavier construction at the base, with thicker jackets and harder cores, to prevent collapsing.
The implication is that the base of the bullet must be tough enough to withstand the shock of the pressure that pushes the bullet forward, but the rear half, which for a moment (less than 1.5 millionth second) wants to remain at rest as well, but is confined by the gilding metal jacket that is supported by the barrel wall. The ogive, however, that is not supported by the barrel, wants to expand owing pressure from within by the lead core.
If all that is not enough to give engineers a headache, a bullet should expand, but not blow to pieces or behave like a monolithic solid, when it hits the intended target, the chest of a deer, for example.
Of course, this all assumes the bullet is capable of some measure of acceptable accuracy from a run-of-the-mill sporting rifle. The problems associated with achieving accuracy were summarized in the Hornady Handbook of Cartridge Reloading, 3rd Edition, and has been printed in each edition since then. The graphic illustrations show how the center of the bullet form may vary from the center of gravity, causing the bullet to veer from its intended path. The challenge is to maintain near flawless jacket thickness as it is progressively formed from what was originally a flat sheet of metal. As the text in the successive Hornady handbooks indicates, we’re talking about maintaining jacket thickness, which routinely tapers from the base to the nose, to within .0001 inch for millions of bullets.
Other problems surface as well. It is normal for tooling used to form jackets to wear out, making it necessary to retool for up to 10 or 12 stages of the forming process. Where a handloader sets his/her dies up for a particular bullet, the bullet seating punch normally contacts the bullet ogive to prevent the punch from putting too much pressure on the nose, especially if the bullet has a lead tip.
If bullet seating depth is set up to touch or come within a couple thousandths inch of the lands (rifling), it is quite possible that another batch of the same bullets from a different lot may have a slightly different ogive shape as the result of retooling by the manufacturer. This may not affect the overall loaded length to the tip of the bullet but might result in the ogive being jammed into the lands or backed off more than expected. This sort of problem is rare, but variations from one batch of bullets to the next, or with bullets packed in the same box, do occur.
In the earlier days of jacketed rifle bullets, it was not unusual for the lead core to shift forward upon impact in an animal, which in effect fed the core forward, feeding the mushroom at the front while leaving a void at the rear of the jacket. The Speer Hot-Cor was an effort to minimize core shift. Hornady ultimately introduced the InterLock, a shelf around the inside perimeter of the jacket designed to restrain core movement. Then Speer came up with the dual-core Mag Tip. Custom bullet makers like Jack Carter resorted to bonding, soldering the core to the inside of the jacket. More recently, we have the Swift A-Frame, which emulates the design of the Nosler Partition, both of which allow the front of the bullet to expand while holding the rear half intact.
Of course, the other problem associated with lead core bullets was the lead tip was/is easily deformed while being slammed back and forth while riding out the effects of recoil in the magazine box. The lead tip also had a tendency to become soft by absorbing heat due to friction generated by acceleration in the barrel and by high velocity in air.
Canadian Industries Limited, as I recall, was one of the first, if not the first, to install a polymer tip (SabreTip) to minimize deformation due to bouncing back and forth in the magazine box, and we might assume, enhance ballistic efficiency. Nosler adopted the idea as the Ballistic Tip. At that time, Remington already had its Bronze Tip, and Winchester had the Silvertip, actually a cap covering the tip of the lead core. Since then polymer tips are commonplace, with Sierra being one of the most recent to add the green tip MatchKing (TMK), while Remington added an AccuTip and Winchester has the XP. To steal and paraphrase a rebuke offered by a friend on occasion: “It appears you cannot toss a dead cat around here without hitting a polymer tip bullet.”
Polymer tips, or concepts thereof, are not immune to their own problems, however, since they too can flatten somewhat or break off while waiting respective turns up to bat in the magazine. So, like the old nemesis lead core designs, it pays to rotate cartridges with polymer-tipped bullets through the magazine to avoid deformation or breaking off.
With the advent of monolithic bullet designs, problems resulting in excess pressure surfaced. When the Nosler Partition was made on screw machines back in the late 1940s, a bore-diameter groove was cut on the outside of the bullet over the solid wall between the front and rear cores, an apparent effort to abate pressure when the wall encountered the rifling. When production was switched to forming dies, the groove was eliminated. Years later the Nosler Zippido had a solid base, up to the ogive, and grooves were added around the solid shank to mitigate pressure. The more recent monolithic Nosler E-Tip, however, has one shallow groove to accommodate a crimp. Notes in the Nosler Reloading Guide No. 8 state loads for the E-Tip should begin with suggested starting loads for its other designs of the same weight.
The late Fred Barnes, Colorado Bullets, came up with an all-copper, monolithic bullet design sometime after the introduction of the Nosler Partition but encountered accuracy and fouling problems. When Randy and Coni Brooks acquired the company from Barnes, the copper bullets resurfaced as the Barnes X-Bullet. Grooves were added a few years ago in an effort to reduce pressure and fouling while improving accuracy. The Triple-Shock (TSX) is a hollowpoint design, and a polymer tip was added to the Tipped Triple-Shock X (TTSX).
When the Arizona Game and Fish Department requested that hunters on the Arizona Strip use bullets with nonlead cores, recommending the Barnes TSX/TTSX as a readily available option, outfits that avoided monolithic bullets for whatever reasons got the hint, although the lesser-known North Fork designs, originally offered by Bob Fulton of Hawk Bullets, were available at the time as well. Then the state of California banned the use of lead and lead-core jacketed bullets across the board, which pretty much opened the flood gates for monolithic bullets.
It is interesting to survey the evolution of hunting bullets over the years, mostly because the original challenges, regardless of the “cool” factor associated with polymer tips, monolithic designs, etc., sometimes appear to be overlooked. That is, a bullet must hold together and penetrate at relatively high velocity at close range and still do the job downrange where velocity drops accordingly, for as far out as might be required, which from what we see on TV and read in print in the last few years, seems to be evolving toward infinity.