Zach
Newbie
Introduction
Welcome, gentleman, to Aperture Science. You're here because you're the best, so who's ready to make some science? A topic came up on the Facebook group concerning bullet setback in weapons due to repeated loading of the same cartridge. I decided to throw a little science at the topic and see what sticks. Who says the shotgun effect doesn't work? Those backwater yokel bean counters, that's who.
Catastrophic failure due to setback: http://www.thegunzone.com/glock/setback.html
Equipment
Ammo: 9mm Speer Gold Dot 124gr +P
Gat: Glock 19, Gen 4
Measurin' thang: Ultratech Stainless Steel Digital Calipers
Beer: Sierra Nevada "Beer Camp Hoppy Lager"
Experimental Procedure
A single cartridge was selected from the box of brand new Gold Dot ammunition. The cartridge OAL was initially checked to make sure it was within an acceptable range compared to it's brethren. This single cartridge was then placed into an empty magazine, and then the magazine placed inside the pistol with the slide locked back. The slide then allowed to slingshot forward from full rearward extension. The cartridge was then manually ejected onto a foam pad where it was subsequently picked up and measured with calipers. This process of loading, unloading, and measuring was repeated 62 times to simulate loading the firearm twice a day for a whole 31 day month.
Results
In a brand new box of Gold Dots, the average length was 1.124" with a high of 1.128" and a low of 1.23". This gives me a reasonable idea of the safe range of operation for the cartridge OAL.
Initially the bullet didn't move much. The first ten chamberings only showed a deviation of 0.001" from the initial length. How disappointing. Or not, depending on how you look at it. Things started to pick up later along the line, especially towards the end. The cartridge OAL started at 1.126" and ended at 1.07" for a total change of .054". The OAL of the round only dropped below the shortest factory loaded length after the 19th chambering. The graph below does a much better job of illustrating the state of things than me rambling along.
Total percent change: 4.97%
It was also noticed that the copper jacket around the rim of the hollowpoint began to become increasingly disformed as the experiment proceeded. It's quite obvious that this is due to the hollowpoint riding the feed ramp into the chamber. Wear marks around the rim of the cartridge and the neck of the brass also began to become much more pronounced during the course of the experiment.
Cartridge after 62 chamberings
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Brand new cartridge, 1.127" OAL
Side-by-side new vs. chambered comparison
Conclusions
First and foremost, I need more data. If I were to conduct this experiment again (which I probably will), I'd attempt to source more GD rounds of the same type from different lots in addition to a variety of other 9mm cartridges.
As noted by a member of the Facebook group, variations in manufacturing will lead to some lots having tighter seating, while others less so. Again, I need more data. Albeit tedious, repeating this experiment for a variety of cartridges, even a variety of firearms, would be enlightening. Comparing, for example, bullet setback in a .40 vs a .45 and so on.
Ultimately, repeatedly loading a round from slide lock is a bad idea. Not only will it seat the bullet deeper into the cartridge, it could also adversely alter the performance of the hollowpoint upon striking a target.
We do what we must, because we can, for science.
Welcome, gentleman, to Aperture Science. You're here because you're the best, so who's ready to make some science? A topic came up on the Facebook group concerning bullet setback in weapons due to repeated loading of the same cartridge. I decided to throw a little science at the topic and see what sticks. Who says the shotgun effect doesn't work? Those backwater yokel bean counters, that's who.
Catastrophic failure due to setback: http://www.thegunzone.com/glock/setback.html
Equipment
Ammo: 9mm Speer Gold Dot 124gr +P
Gat: Glock 19, Gen 4
Measurin' thang: Ultratech Stainless Steel Digital Calipers
Beer: Sierra Nevada "Beer Camp Hoppy Lager"
Experimental Procedure
A single cartridge was selected from the box of brand new Gold Dot ammunition. The cartridge OAL was initially checked to make sure it was within an acceptable range compared to it's brethren. This single cartridge was then placed into an empty magazine, and then the magazine placed inside the pistol with the slide locked back. The slide then allowed to slingshot forward from full rearward extension. The cartridge was then manually ejected onto a foam pad where it was subsequently picked up and measured with calipers. This process of loading, unloading, and measuring was repeated 62 times to simulate loading the firearm twice a day for a whole 31 day month.
Results
In a brand new box of Gold Dots, the average length was 1.124" with a high of 1.128" and a low of 1.23". This gives me a reasonable idea of the safe range of operation for the cartridge OAL.
Initially the bullet didn't move much. The first ten chamberings only showed a deviation of 0.001" from the initial length. How disappointing. Or not, depending on how you look at it. Things started to pick up later along the line, especially towards the end. The cartridge OAL started at 1.126" and ended at 1.07" for a total change of .054". The OAL of the round only dropped below the shortest factory loaded length after the 19th chambering. The graph below does a much better job of illustrating the state of things than me rambling along.
Total percent change: 4.97%
It was also noticed that the copper jacket around the rim of the hollowpoint began to become increasingly disformed as the experiment proceeded. It's quite obvious that this is due to the hollowpoint riding the feed ramp into the chamber. Wear marks around the rim of the cartridge and the neck of the brass also began to become much more pronounced during the course of the experiment.
Cartridge after 62 chamberings
Brand new cartridge, 1.127" OAL
Side-by-side new vs. chambered comparison
Conclusions
First and foremost, I need more data. If I were to conduct this experiment again (which I probably will), I'd attempt to source more GD rounds of the same type from different lots in addition to a variety of other 9mm cartridges.
As noted by a member of the Facebook group, variations in manufacturing will lead to some lots having tighter seating, while others less so. Again, I need more data. Albeit tedious, repeating this experiment for a variety of cartridges, even a variety of firearms, would be enlightening. Comparing, for example, bullet setback in a .40 vs a .45 and so on.
Ultimately, repeatedly loading a round from slide lock is a bad idea. Not only will it seat the bullet deeper into the cartridge, it could also adversely alter the performance of the hollowpoint upon striking a target.
We do what we must, because we can, for science.
