I’d love to hear your feedback and answer any questions!
It's unfortunate that everything related to firearms is now viewed as political. There are just so many interesting things unique to thos subject matter that inquisitive and mechanically inclined people, like those on HN, are missing out on.
I'm just here to learn and share. Hopefully this will help towards breaking down some negative stereotypes about a fun an interesting hobby!
I suspect what you saw was the sudden release of the couple of pounds of rearward trigger pressure causing the gun to move forward shortly before the pressure buildup and recoil drove it backwards. That would swamp any small recoil associated with the firing pin.
It may require faster data acquisition, so I hope that folks will contribute to the accelerometer project that I open-sourced to make that possible!
Just before the trigger releases, you are pulling back with 1 lb of force on the trigger, and to maintain aim, are pushing forward with 1 lb of force on the butt (likely with your shoulder). When the trigger releases, suddenly there is no more force being applied by your trigger finger, but the same amount being applied by your shoulder. In response, the gun starts moving forward. It keeps moving until the trigger bottoms out and the force from your finger stops the forward progress, or until the recoil from the acceleration of the bullet begins.
I'm not sure he's right, but I think this is what he's saying, and I think it fits what you measured. I am confused though how the gun can move forward in the "preloaded" case. Isn't the gun already pushed forward as far as it can go against something incompressible? If so, how does it accelerate forward?
1. Interference with the rifle barrel
2. Interference with the shell casing (is there a measure of how tight a shell fits the bullet that changes the velocity / is more interference fit good?)
3. do slight variations in diameter or weight matter more?
It looks like youre measuring muzzle velocity with a device mounted to the barrel. If that's true, i suspect it almost entirely negates the difference you are looking for because the rifle recoiling adds perceived muzzle velocity that the target (and the rest of us) do not experience.
That said, I'm more interested in the truth than who is right or wrong. I've open sourced all of my data and want others to try this experiment for themselves and share their results rather than rely on me as a source-of-truth!
It really does mean that my poor accuracy with a large caliber handgun is from flinching. I sort of thought it was from being unable to control the recoil but it sounds like that has no bearing on where the bullet is heading, and so I guess I'm just flinching in anticipation.
Btw, where do you live that you have a 300yd range? I'm jealous. Here near Chicago (well, NW Indiana) I mostly make do with small indoor ranges and a .22 rifle which is typically allowed, but would love to get into shooting larger calibers longer distances.
When I shoot my revolver, I will load empty shells in a couple random spots, spin it, and close it. This immediately exposes any flinching or anticipating I'm doing. I squeeze the trigger, the gun moves slightly downward and no round is fired.
Do that a couple times and you learn to remain neutral pretty quick.
It's not as easy on a magazine-loaded pistol. I imagine you'd need to get some purpose-made dead rounds. And the randomization is harder.
I live in Oregon and am fortunate enough to be within 40 miles of an amazing club where I can shoot out to 600 yards every week with an awesome group of people! For what it's worth, you can (and should) drive out to Ohio for the National Matches at Camp Perry in the summer. It's on your way to Cedar Point ;)
It may also be how how you're pulling/squeezing the trigger. That's the problem I have, and consequently I am far more accurate with revolvers when using single action trigger pulls (hammer already cocked back, so the trigger pull is very short and crisp.)
Indeed. Outstanding work :)
> I'm a little surprised that the bullet has left the barrel before the rifle recoils, but I guess that makes sense with the differences in mass.
That puzzles me too. I mean, once the bullet has left the barrel, what force could be accelerating the rifle?
Two possibilities came to mind. One was ongoing gas expansion, but that seems unlikely, because the chamber pressure is small after 2.5 msec.
The other is something mechanical about the rifle. Could the barrel stretch, as the bullet is exiting? And then contract afterward? Or maybe some elasticity in the attachment of the barrel?
The PRB covers the role of propellant gases in recoil, and measures effectiveness of muzzle brakes. He talks about 20%-50% reduction in recoil with muzzle brakes. And that implies that gas expansion from the muzzle accounts for at least 50% of recoil.
Even so, some additional measurements might be useful. It'd be interesting to know, at sub-msec sampling rates, the velocity of gas leaving the muzzle. And if there's still appreciable unexplained recoil: 1) the length of the barrel; 2) the displacement of the barrel from the stock; and 3) the diameter of the barrel, measured at maybe 4-5 points from the chamber to the muzzle.
Because steel is, after all, notoriously elastic. And the barrel may be attached to the stock in a way that smears out recoil. Also, the rifle may have other recoil-management features that reduce recoil, and smear it out. It's bolt-action, so there's no blowback, and I don't see a muzzle brake, but ???
Also consider that multiple bits of the gun are mechanically attached to each other. It looks like the accelerometer is attached to the barrel, whereas the majority of the rearward forces before bullet leaves the barrel is acting on the bolt. Even as a bolt action, there's plently of interesting mechanical interfaces to absorb energy and movement before transferring to the barrel.
Well not 100%.
That's why it's important to hold a rifle in a position where it will kick back in a straight trajectory.
1. Bazooka-like barrel open on both ends with identical bullets shooting out each end. I would say that each bullet got approximately half the energy.
2. Fixed barrel, hard mounted, no recoil movement. Bullet should get about double the energy of (1). If you imagine the expanding gas between the bullets of (1) but then change it to operate in half the volume (split down the middle), the pressure would be double but not quite since combustion rates may differ.
3. Barrel with very long throw, very low spring force. Bullet gets most of energy, peak recoil force is low.
But always true:
- Newton's third law: For every action, there is an equal and opposite reaction.
- Conservation of momentum: p = m v
considering impulses: F t = m = p / v, p = F t / m
That said, you're spot on with your equations, though there are a few others I'll cover as well!
I've heard that before, but this is the first time I've seen actual data. Nice work!
The presentation of the information was well done, I'd say.
It's very nearly a proper paper, if you ask me.
Thanks for sharing!
I especially enjoyed the pictures of the arduino and gear setup.
You can also do some meta-analysis with all of the high speed video on YouTube. Get something like Tracker to watch the barrel displacement while the bullet is travelling down the barrel. This video from SmarterEveryDay  provides some good examples.
I've watched tons of these vids and my basic observation is that there is some motion while the bullet is in the barrel, but as soon as it leaves you basically are left with a rocket trying to launch into the shoulder of the shooter. Even at high frame rates there's a perceivable increase in rearward acceleration once the gases start escaping.
Looking forward to future articles! Particularly with the improved accelerometer, it feels like there's a story in the gaps. I'm sure you've got plenty of ideas when you start a blog with that name, but here are a few I've been mulling about while chasing a lawnmower around the yard (some of these may be tired stories for folks into match shooting).
- Benefit of powder sorting for uniform and/or even distribution of grain size/weight (maybe via sieve or some kind of scattering method?)
- Benefit of tip conditioning in terminal ballistics (e.g. precision shaping/polishing)
- Building a press + strain gauge to push bullets through barrel to characterize impact of variations in diameter/length on energy required to make the trip.
Last bit of spam from me. I did take a quick peek at the data. It looks like the area under curve measurement more closely correlates with velocity than peak pressure, but not by much. Not sure what the data column on the left represents in the PTC file.
The one extra thing I can think of so far is that the recoil reduces the effective length of the barrel by the distance it has moved by the time the bullet exits the muzzle, but again that seems too small an effect (~0.2 millifeet, four orders of magnitude less than the barrel length?)
It does bring up a good point though, which I'll cover in the article where I deep-dive into the physics: Knowing the acceleration of the rifle, I should be able to calculate how far it has moved in the same amount of time it took for the bullet to leave.
Thanks for taking the time to read it, and for your feedback!
Edit: forgot about the powder which as hot gas is subjected to pretty much the same acceleration as the bullet. With the powder being about 2-4x bullet mass it makes the rifle only 150x-300x heavier than the [bullet+powder] and that brings us to the 20-10ft/s of the rifle recoil speed, ie the article claim pretty closely matches the theory.
Not all the gas reaches the bullet speed. We might guess that it averages half that, but that is assuming, I think, a uniform density and complete gasification of the charge (though with regard to the latter, is there a reason for there being a larger charge than that?)
This argument also suggests that the recoil firing blanks would be a substantial fraction of the recoil with a live round, which is not how I recall it.
I suppose I could just break out the screens and find out, but it's nice to argue over beers.