/r/ballistics
Ballistics is the science of the mechanics of projectiles. It is concerned with three separate but related parts: Launching the projectile, that projectile's flight path and the affect the projectile has on what it hits - internal, external and terminal.
The ballistics subreddit is meant to be fairly technically based. Ballistics is focused on the physics involved in launching a projectile and its flight. It doesn't even need to be limited to guns; arrows, missiles and any other projectile can be relevant.
This can seem fairly broad, so I encourage you to think critically about the relevance of your content before you post it, but not feel too hesitant if you're sitting on the fence.
But most of all, enjoy! Ballistics is an exciting field of study not dependant on global location, culture or experience. We're all here to learn and interact, so be friendly and welcoming to those who are less knowledgeable on a certain aspect of ballistics to you.
Check out our wiki.
/r/ballistics
1,894 Subscribers
Is a 10-Year-Old Kevlar Soft Armor Combat Diaper Still Effective?
So, I came across an old Kevlar soft armor combat diaper (yes, really) that’s about 10 years old. It’s been stored indoors, but I have no idea if it’s still effective. I know soft armor has a shelf life, but does Kevlar degrade that much over time?
Would this still offer any real protection, or is it basically just a tactical diaper at this point? Anyone with experience in old ballistic gear, let me know what you think!
Thanks!
16:12 UTC
7.62x39 Question
I know that generally speaking people would say a FMJ round is not a good choice for hunting, not to mention the hate that 7.62x39 gets in the hunting world. However, I have seen many test results with 7.62x39 where the FMJ bullets seem to tumble and actually produce fairly consistent, effective sound channels. So, if this bullet construction will work in war, why not on an animal? I figured that if you were able to get the same tumbling effect in an animal such as a deer then the bullet would be more effective than something like a HP that expanded a lot but didn’t penetrate much. Just wanted to hear y’all’s thoughts on this.
02:12 UTC
Handgun Help
I was researching and have read in lots of places that .38 special is “weaker” than a 9mm due to lower case pressure. If the .38 special has a larger case length, why would more powder not be added to increase pressure, thus increasing velocity. Is the .38 special actually a less powerful round, or just not as fast and volatile? And if it is less powerful, why would someone carry a .38 special revolver anymore?
19:24 UTC
Does a lower expansion threshold for a rifle round mean more effect at close range?
I'm curious about some soft point bullet designs. Some have higher antimony in the lead to make it tougher. Some have more copper than lead making up the slug. I see some of the relatively softer lead bullets expand wider at the same velocities than a tougher bullet would.
My question is, does a faster expanding softpoint translate to more damage at close range than a tougher and slower expanding lead bullet?
17:58 UTC
Which cartridge can break ultra-hard 3/8-inch AR 450 Steel?
21:33 UTC
Opinion
I was diving on the interstate and I heard a loud bang followed by simultaneously a big vibration. No big trucks hauling gravel or rocks. I checked around the car and don’t see holes but I noticed a mark from where I believed it came from. Could this be a ricochet bullet?
05:10 UTC
Which has better stopping power: one big bullet or several small ones?
From what I've read, the #1 determinant of effectively incapacitating a living thing with a firearm is shot placement. That implies to me that a rapid-fire weapon with low recoil would be better at stopping the thing you're shooting at than a large-caliber round (unless it's a car engine or something) because more shots=better chance of hitting something important. However, it's standard to use very large calibers in big game hunting, where stopping power is of special importance, and various militaries have shown a persistent infatuation with larger standard calibers in the name of better stopping power. Why is this?
17:22 UTC
Does the initial explosion of a bullet's powder matter much in the barrel length needed for using it's maximum potential ? (here velocity refers to the power the bullet will have on target)
07:01 UTC
Does pinning a FSB to a barrel affect accuracy?
I wanted to pin a front sight base to a pencil barrel for an AR 15. I called a local gun store to ask if their gunsmith would do it and I was told that pinning a front sight base to a barrel could ruin the “harmonics” of the barrel and that I would be better off buying a pinned barrel from a manufacturer or using a front site base with set screws.
Have any of you experience or seen evidence either way of if pinning a front site base to a barrel will negatively affect it? Is it better to use a gas block with set screws?
I can’t find any front site base online that uses clamping or set screws besides the JP adjustable gas block or some folding front sight base gas blocks which are more pricey than I wanted. I was considering drilling and tapping the front sight block I have (like in this or this video). Do any of you have experience with drilling and tapping a front sight block? Do you have issues with it coming loose? Or is there a simple front sight block with clamps or set screws that I haven’t found yet?
14:17 UTC
Sectional Density Equation Seems Incorrect
I have been digging through all of the fundamental ballistic math and have found a few issues. The one I'm trying to understand presently is regarding sectional density. Why do white papers specific to ballistic account for the area of the bullet as a square as opposed to a circle?
What's consistently listed: SD = Mass / diameter²
Whereas in reality it should be: SD = Mass / pi * radius²
These two equations give different results. For example, if we use a 0.338 with 248gr and do some conversions to get pounds per square inch, we get:
0.03542858lbs / 0.338² = 0.310113266.. psi
0.03542858lbs / pi * ( 0.338 / 2 )² = 0.394848447.. psi
While these may seem relatively close, those decimal values matter. Is the diameter squared just short hand to simplify the process, or does it play a role in correcting further equations?
11:36 UTC
.30 cal. differences
What are the differences in diameter between .300 wm .300 blk 30.06 30.30 etc.?
12:30 UTC
What is most dangerous?
I have a .22 air PCP carbine, it shoots 1.3g metal pellets with 21.5 joules of energy
And I have too a .68, it shoots 1.20g rubber ball steel core with 16 joules of energy
My garden is about 10m long
If I have and accident with a animal, human or other livingthing which causes more damage, I usually shoot in my property but I would like to know that if I involuntarily have a wrong shot and it doesn't hit the target ¿What is the most dangerous shot? Thank.
15:30 UTC
Trump Graze Wound Ear - What are ballistics experts saying?
Have any ballistics experts weighed in on the wound yet? Can a bullet from an AR-15 at that distance cause that small of a wound? Wouldn't the spinning of the bullet cause more damage? There have been graze wound photos shared on X and they seem to cause significant damage and none look like anything an ear could survive.
13:47 UTC
Infuriated by this
Could anyone help me understand why half of the articles online define sectional density as mass over diameter squared, and the other half say mass over cross sectional area? Pi is not equal to 4!!! That’s a 27% difference, which is huge. Which quantity is usually used when quoting B.C.s? Thanks!
13:56 UTC
Trajectory question
My in-laed had a bullet come through their kitchen window o the 4th of July and end up hitting the refrigerator, going through the fridge and freezer portion to get stuck in the side. Based on the hole in the screen and the window, as well as the entery hole in the side of the fridge I figured the bullet was angled downward.
My wife is convinced that someone .Just have shot the bullet from right outside the window for it to go into the fridge like that but I think it was likely someone shooting a firearm into the air at an angle and it coming down.
Would a bullet be able to maintain enough velocity to be shot into the air and penetrative through a window and refrigerator like that if it had been shot into the air (say at a 45 degree angle)?
03:39 UTC
This hypothetical cartridge is research for a book i plan to write..
.30 carbine case but 2-5 mm shorter. Projectile is fmj .30 boat tail 165-180 grain. The shorter case and larger mass of the bullet makes the round subsonic ~ 1100 fps. The o/a length is the same as .30 carbine and will feed in its mags. Chamber/slide/ gas chamber would have to be modded but would this work? Be a viable cartridge out to 200+ yards. I know it would get loopy past 125-150 but the improved flight of a traditional rifle vs pistol bullet would help at longer ranges right? Thanks
01:55 UTC
Trajectory question… pertaining to scope zeroing.
I’m brand new to owning a rifle, and will be mounting and zeroing my first scope and rifle in a couple weeks.
I’ve sorta researched the topic, but like many things, everyone’s opinion is different and many have made convincing, if not conflicting, arguments as to why any particular zero is better than _____.
I have a AR-15 with a .223 Wylde chamber, a 16” barrel with a 1:8 twist rifling, and I plan to (or hope to) shoot heavier-grain projectiles loaded to 5.56 NATO spec. The mfg. recommended Hornady Black ammunition because in their testing it performed best. They didn’t exactly explain what “best” meant, but I took it to mean it cycled the rifle more reliably than other ammunition in all circumstances. That said, it seems to me, in my humble opinion, that the Hornady Black ammunition line was meant as a middle-of-the-road / do-it-all cartridge that performed flawlessly in terms of cycling but isn’t exactly a 1MOA precision cartridge.
I’m not expecting to win any PRS matches with the rifle, but I am hoping to squeeze out the finest accuracy I and it can do. My thought is, 62gr is a happy median between the lighter M193 stuff, and the heavy match-grade stuff. But, it’s almost all M855 green-tip and there’s less than a handful of range-friendly FMJ lead-core stuff, so it’s pretty restrictive on ammo selection.
Which leads me to believe that I’ll eventually settle on 62gr, 75gr, or 77gr, but begs the question… which zero is best on my given platform and for whichever cartridge and projectile my rifle performs “best” with?
Is there any way of knowing/predicting? My first thought is to look at the trajectory tables from the ammo mfg. (If available). However, it seems most of them use a 24” test barrel, so the trajectory would be significant different with my 8” shorter barrel, wouldn’t it? For example, if their 24” test barrel provided a trajectory that has the bullet coming up into the line of sight at about 50yrds, then back down into LOS at about 200yrds, that would suggest to start there and trial-error until I got as good a result as I can.
But I wonder if there’s a better way to calculate a particular barrel length and twist rate and projectile to get a good idea ahead if time what zero strategy to adopt.
02:51 UTC
Custom Cartridge Physics Simulator
Does anyone know of any good physics simulators that allow the creation of custom cartridges (projectile weight and caliber, case length, etc.)? I've been working on some worldbuilding for an alt-history universe and I don't want to use a lot of existing modern cartridges like 5.56, 7.62 anything, 5.7, 9x19, etc.
18:55 UTC
Are there any good ballistic dummies that aren't... you know... $2500
16:58 UTC
How does Uranium AP ammo work?
Does someone of u experts know how exactly this "self sharpening" works? I hear it often on thr internet but i cant find infos on under what circumstances it occurs or what alloy this exactly is! All i know is that uranium is soft and i wouldnt use it as AP ammo!
18:18 UTC
Grabovac hill fort Traste weird cupola damage and debris.
Does anyone know what might've caused this damage? Wiki says it was under small-caliber artillery fire and saw little damage, but the debris there says otherwise. Also this cupola damage looks weird.
(some other place)
Sources:
13:09 UTC
Tubular bullets - projectiles of the future in the 19th century?
15:07 UTC
What is the best materials for kevlar and best way to bind them together
What is the best material to lare with kevlar. I heard fiber glass is good and polyethylene fabric are good to lare it with and what would be the best way to bind them all together to make a helmet mold ??????
08:12 UTC
Whats the best type of bullet resistant glass
I want a bullet resistant glass for a helmet visor thats not insanly THICC and can be seen through ealisly
07:32 UTC