In his book, “Student of the Gun,” author, firearms instructor, and former Marine Paul G. Markel succinctly describes the journey through firearms proficiency from novice through “expert.” More importantly, he describes the attainment of “expert” not as indicative of the end of the journey, but a firm commitment to being a life-long student. Through my personal journey, I’ve had the opportunity to train, compete, and instruct in firearms disciplines… and there are still many things I learn every day. Although I’ve studied and written extensively on ballistics and considerations for personal and home defense ammunition, I recently “re-learned” a valuable lesson on bullet set-back that I’d like to briefly share with you.
For a number of years, I’d kept a 1911 in .45ACP as my home defense firearm and loaded it with 185 grain jacketed hollow-point cartridges. During this time, I’d followed the advice that I’ve often dispensed to “routinely train with the firearm, firing the personal defense ammunition to ensure 100% reliability and then thoroughly clean the firearm and the magazines.”
Well, in the last two years, I switched my home defense firearm to a Sig P227 in .45ACP for the higher capacity (14 versus 8), the integral light rail, and the choice of Double Action or Single Action. Feeling confident with the 185 grain jacketed hollow-point cartridges, I kept the P227 loaded with this ammunition as well. At first, I routinely trained with this handgun/ammunition combination and found it to be as reliable as the 1911 that formerly held this role.
Another Step in the Journey
However, I “fell behind” on training with this system as often as I had in the past… opting to just unload the firearm and the magazines, clean and lubricate both, conduct a non-live-fire function check, re-load, and replace.
Recently, when I conducted this routine, I noticed how the Sig P227 failed to feed the first cartridge into the chamber which jammed the gun out of battery. Whereas a “tap” to the rear of the slide would normally return to the gun into battery, chamber the cartridge, and lock the slide and barrel to the frame, this cartridge was firmly jammed against the barrel’s feed ramp. For a home defense firearm that must be 100% reliable, I found this to be discomforting.
When I unloaded the gun, the cartridge in question fell free from the magazine and I noticed that it looked “a little different.” Well, it looked a lot different… and so did the second cartridge in the magazine. THEY WERE SHORTER!!!! This different dimension, the overall length, is one of the contributing factors that led to the jam. Other than the obvious concern that these cartridges could potentially jam my firearm when I needed it the most, I wondered how many other cartridges in the magazine were “shorter?”
With a digital caliper, I measured the overall length (from the end of the cartridge rim to the leading edge of the projectile) of the ammunition from the box which had not been chambered into the Sig P227 and they measured 1.206 inches. This measurement was consistent with all other un-chambered cartridges.
The measurement on the “short” cartridge was 1.103 inches! Although this is only about one-tenth of an inch, it was enough to jam the gun. So, I did a quick test with a “good” cartridge and chambered it repeatedly while taking a measurement between each iteration. I had found that each time I chambered the same cartridge, the bullet “set-back” about five thousands of an inch (0.005″). This could be caused by an insufficient crimp (pressure from the inside of the cartridge case against the outside of the projectile), the edge of the blunt-tipped jacketed hollow-point impacting the feed ramp, or both.
The bullet set-back was not only altering the external geometry of the cartridge as it fed from the magazine into the chamber which increased the potential for a jam, it was also changing the dimensions within the cartridge itself.
Internal Ballistics, Pressure, and Bullet Set-Back
If you recall from the Ballistics Series, there are four components to a metallic cartridge: the case, the primer, the propellant, and the projectile. Ideally, the composition/density of the propellant fills the otherwise empty volume of the cartridge case for a uniform ignition. You may also recall that while many people discuss firearm ballistics from a standpoint of projectile velocity or kinetic energy, PRESSURE is really the key element to safe firearm function. Proper propellant ignition creates the rapid gas expansion and pressure to press the case against the chamber’s interior, forming a tight seal which sends the projectile firmly through the bore while also providing enough residual pressure to cycle a semi-automatic firearm. There is a brief moment, about five ten-thousandths of a second (0.0005) between primer ignition and projectile movement where the pressure increases to a very high peak before the bullet’s travel down the bore abates this pressure spike. This is called peak pressure and is measured in pounds per square inch (p.s.i.).
It is important to note that both firearms and ammunition manufacturers keep peak pressure in mind for design and production while the Sporting Arms and Manufacturers Institute (SAAMI) governs the safe operating pressures for each within a reasonable margin of error. So, the bullet set-back I experienced here not only caused the weapon to jam, it changed the internal dimensions of the cartridge by reducing the volume of space available within the cartridge case and pressing the base of the projectile into the propellant… thus compacting the propellant and potentially increasing the peak pressure beyond SAAMI specifications if I had fired this ammunition. In more simple terms, this could have caused the gun to explode if I had shot the cartridge.
I have never personally experienced a catastrophic firearm failure or “kaboom,” but there is plenty of evidence of this phenomena in Gun Store Lore, on the ranges, and across the internet. Remember, under normal circumstances, the pressure internal to the firearm quickly peaks while the firearm construction contains this pressure and translates it into projectile forward motion. In extreme circumstances, if the pressure exceeds the metallurgy or construction of the firearm, the pressure must go “somewhere” and it will follow the path of least resistance. This path of least resistance could be the seam between the chamber and the slide or any other metallurgical imperfections (cracks or weak spots in the firearm).
I was lucky enough to learn,or re-learn, something in this process without injuring my self, damaging a firearm, or having a gun malfunction when I needed it the most. So, I’m sharing this with the hope that you learn something and can avoid the same.
- Choose the correct ammunition for your personal defense firearm. While my choice of personal defense ammunition was perfectly acceptable for one handgun in which it functioned well for years, it is clearly not acceptable for the new platform. (note, the 185 grain jacketed hollow points are great rounds and the Sig P227 is a tremendous handgun, but the two do not work well together in this case).
- Routinely test your firearm/ammunition combination. It is important to routinely test the function of your personal defense handgun and ammunition combination to ensure 100% reliability, reinforce basic skills, and build confidence in the platform.
- Exercise your magazines, rotate your ammunition stock, and inspect your cartridges. It is important to routinely unload and clean your personal defense handgun and magazines… and be aware of the potential bullet set-back caused by repeatedly chambering the same cartridge.
- Don’t become complacent. Even though I’m on the range training or competing many days a month, I had become comfortable in my routine and was veering toward complacency with my personal defense firearm and ammunition. Don’t just focus on the “fun” aspects of training, focus on all of the fundamentals.
Do you have any stories of lessons learned that would benefit our readership? If you do, sound-off below or shoot me an email at HHall@aegisacademy.com
Stay safe and shoot straight!
– Howard Hall