Why Cannelure?
Some ask me why I use a cannelure at all. I started using cannelured bullets nearly from the beginning when I started reloading over 30 years ago because a good crimp in a cannelure was the best way to insure the round I sighted in on the bench would still be the same as the round that was fired under adverse field conditions. There are many reasons why I use cannelures on my bullets and sometimes cases, and why I was so thrilled to buy this unit when they came available here. Some of those reasons are for reliability, safety, ballistics, and terminal performance. Here are a few of these common issues where cannelures can be useful.
Set-Back
Set-back is when a bullet is inadvertently forced INTO the case mouth, and can happen in a variety of ways.
Semi Auto Pistol Rounds
It can be crucial to put a good cannelure on some projectiles and/or cases of finished rounds for some semi autos (especially 40 S&W) to avoid setback during repeated loading and unloading of that first round on top of the mag. I read setback has blown up more than a few 40 S&W guns, especially with people who carry every day and have to load and unload the weapon frequently. That repeated loading and unloading can eventually loosen and set-back the bullet in that first round, increase pressure dramatically due to compressing the power charge, with disastrous results. This is especially true for any reloader who does not have access to the higher pressure crimping options used on factory rounds. The 357SIG is a great round, but because there is so little neck to bullet friction due to the short neck on the case, set-back can easily occur with this round as well in the same way as the 40 S&W. In the 357 SIG, also being a high pressure, high performance round like the 40S&W, set-back can be disastrous.
Tubular Magazines
Set-back is a common potential problem in firearms with tubular magazines as well, like many lever action rifles, because repeated firing of the weapon causes the rounds in the magazine to hammer against one another. The more recoil, the harder the hammer effect. Most factory rounds intended for use in leveractions use a cannelured bullet due to safety and reliability issues, and therefore reduce liability issues for the cartridge manufacturers.
Military Rounds
Dropping rounds or dropping magazines can also cause set-back. That is one of the primary reasons almost all military rounds have a cannelure, because in combat, magazines full of ammo can go through much abuse before they are used, and the operator’s life could depend on the reliability of the rounds and weapons. In a presentation on military ammunition failures and solutions to the National Defense Industrial Association, Dr. Gary K. Roberts, a noted expert in the field, stated 13 essential design criteria for any military round. One of those essentials was a “cannelure for functional reliability in adverse conditions.” How many people depend on defense rounds with no cannelure?
300 BLK
Another situation where set-back can cause seriously dangerous detonations is where a 300 Blackout round is loaded into a 223 gun by accident. Since they both share the same parent case and use the same magazine, this is an easy mistake. With all the multiple calibers being used in identical looking AR platforms, mistakes can happen. Theoretically, the round "should" just fail to chamber, but without a cannelure and a strong crimp, that 30 caliber bullet can reportedly set back far enough to allow the bolt to go into full battery and allow the gun to fire a .308 projectile into a .224 bore. There are internet reports of just such accidents happening resulting in explosions and destroyed weapons, and the potential for serious injury. Bad news!
If you reload, putting a cannelure and good factory crimp on each round can help prevent these kinds of problems. Even if you do not reload at all or your department won't allow you to use reloads, you can make some factory rounds much safer and more reliable to load and unload repeatedly by just carefully adding a properly placed cannelure to the straight wall case of an otherwise great factory round.
Set-out
Set-out is when the projectile is forced to slide OUT of the case neck before the round is fired. This can also happen in different situations with unwanted results.
Semi Auto Rifle
Set-out can easily occur in any semi-auto, or full auto rifle due to strong recoil springs and high bolt velocity needed for these weapons to function reliably. This is often an unknown culprit contributing to less accuracy in semi-autos as opposed to manually operated firearms like the bolt action rifle. Richard Mann, in his June 2014 article for Shooting Illustrated entitled "Handloading the .300 AAC Blackout," stated the following:
The only problem I ran into while handloading the .300 Blackout was with bullet set-out when the cartridge was chambered. With some loads—particularly those using the 125-grain Nosler AccuBond and 150-grain Nosler Ballistic Tip—the bullet would migrate forward in the case when the cartridge entered the chamber. This had a horrible effect on accuracy. Set-out was a noticeable problem only with the Nosler bullets, but it could have been occurring with other bullets, too, and just not showing up as glaringly on target. I spent several hours chambering dummy cartridges with a variety of bullets and measuring set-out, and in fact, I found it occurred to some extent with every bullet tested.
...After speaking with Nosler, I think we found the cause. The AccuBond’s jacket is thicker than most conventional bullets, and the core is not pure, soft lead, making it harder for a taper crimp to take hold. My conclusion is the 125-grain AccuBond needs a crimping groove.
The type of set-out stated above is simply caused by the force of the round being chambered in a semi-auto or full-auto rifle. I always use a cannelure and factory crimp die when reloading rounds to be fired in a semi-auto rifle.
Big Bore Revolvers
Set-out is also a common problem for powerful revolvers like the 44mag, 454, and the 460 and 500 S&W rounds. Under heavy recoil, the bullets in the cylinder can “walk” forward in the case and cause the cylinder to bind. This can render a 6 shot into a single shot. Which could prove deadly if it happens at a very inopportune time if you are using that revolver for protection. I always use a cannelure and strong crimp on heavy revolver rounds, as recommended in nearly all reloading manuals. Many factory bullets come with cannelures, but due to powder volume with some loads, they are in the wrong place. Some factory bullets even come with dual cannelures to address the problem. A cannelure tool can solve that problem precisely.
Bonded Cores and Terminal Ballistics
Precision
A good cannelure can help bond the bullet’s core to the jacket. This can improve accuracy by not allowing the lead core to slip inside the jacket as the spin is imparted by the rifling. Multiple cannelures can be used if desired. Consistency in velocity shot to shot is also improved at times with a good crimp and cannelure because the pressure between case mouth and projectile is more consistent round to round.
Terminal Ballistics - Rifle HP Expansion Control
In addition to benefits in exterior ballistics, core bonding also benefits terminal ballistics as well. Chuck Hawks, on his fine web site, talks about the benefit of cannelures for limiting bullet expansion and holding the base of the bullet together.
Some bullets also use a cannelure (crimp in the jacket) to help keep the jacket from peeling back beyond that point and keep jacket and core together. The cannelure also allows the bullet to be crimped into the case.
Nathan Foster, in “The Practical Guide to Long Range Hunting Cartridges,” states the following when talking about 7mm Magnum hunting loads:
Federal’s150 grain GameKing is an interesting load. This is a proprietary bullet as opposed to the standard 150 grain GK that hand loaders have access to. The Federal version features a cannelure which helps arrest expansion, either minimizing or delaying jacket core separation. The 150 grain GK is explosive at impact velocities above 2700 fps and equally violent but not prone to total disintegration at lower velocities. This load is best suited to lighter medium game up to a maximum weight of 80kg (180lb) and the cannelure helps greatly to minimize early bullet blow up.
Terminal Ballistics - Rifle FMJ Fragmentation
In his famous work, “Military Rifle Bullet Wound Patterns”, Martin L. Fackler stated a little known reason for cannelures on military FMJ rounds. Fackler pointed out that a cannelured FMJ bullet that strikes its target at a relatively high velocity will travel straight at first, then yaw sharply in the target and break at the cannelure. This causes the pointed portion of the bullet to flatten and tumble through the target sideways, and causes the base end of the bullet to fragment. The target must be within about 100 yards for this to happen with the standard military 5.56 round. At longer distances (i.e. slower impact velocities) the 5.56 bullet will yaw and break at the cannelure, but not fragment. At yet longer distances ( 300 yards +), and even slower impact velocities, the 5.56 bullet will not break or yaw, but simply pencil through the target. Fackler also indicated that if the target isn't deep enough for yaw to take place, the bullet will just make a straight wound and not fragment. I believe he said for the standard military 5.56 round used in Viet Nam, it would yaw after about 12cm travel through the body. Since all military rounds are required to be FMJ by the Geneva Convention, I guess military researchers discovered long ago how to get a FMJ to fragment. Drive a relatively slender bullet at very high speed to induce yaw, and use a cannelure to cause it to break if/when it yaws.
Oddly enough, the same cannelure that helps an expanding hunting bullet hold together due to core bonding (i.e. the 7MM MAG), helps the FMJ at very high speed break and fragment due to yaw ( i.e. the 223). Ballistics are sometimes interesting and counterintuitive.
Other Advantages
There are other little pluses for using a cannelure, like the fact that they can provide a sharp edge on the bearing surface of the bullet that can help clear fouling from the barrel as each round is fired. If you have a bullet with a short point and long bearing surface, you can add an addition cannelure ( or several ) to reduce friction against the barrel, therefore achieving higher velocities within safe pressures with the same weight bullet.
Conclusion
For anyone who reloads, and even in some special cases for non-reloaders, a cannelure tool is a must in certain circumstances for safety and reliability (i.e. 40 S&W, 357 SIG, 300 Blackout, lever action rounds, and powerful revolver rounds). It is also a wonderful tool for improved performance in other circumstances (i.e. hunting rounds and defense rounds where bonded cores or FMJ fragmentation are a real advantage) The first time you prevent any of problems mentioned above with a good cannelure and crimp, the tool has more than paid for itself in saving the cost to repair or replace a firearm and/or saving a great hunt, not to mention the incalculable benefit of preventing injury or loss of life. The first time a cannelure contributes to reliable performance in a self-defense situation and averts a tragedy, the value of the tool has become priceless. There are so many good answers to the question “Why cannelure?”, it begs the question “Why not cannelure?”
