Can a bullet slow down before leaving barrel?

In fact, my "scribbling" says just that. If there's a "positive" net force you have positive acceleration. If there's a "negative" net force the opposite is true. Centuries of data confirm my conclusion

See "1st and 2nd Law of Thermodynamics"

Perpetual motion machines are impossible outside an isolated system (for which there are none), and thus the same for a bullet traveling down a rifled bore indefinitely.

Gas leaks, friction, volume of space gas resides in expanding as bullet moves further away from explosion, etc. all lead to decay of force/energy acting on projectile.

Bayourambler said:

So may variables..

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Haha that we can all agree on

Olon said:

As requested

Edit: conclusion state 3 should say insufficient, not sufficient and I apologize for reusing lowercase a. in F=ma it's acceleration and everywhere else it's the area of the back of the bullet.

That's for a bullet that's flat in the back as a curved one would involve more work and not add anything to the model.

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That's not data. Data would show when the powder has burned 100% and the velocity of the bullet in the barrel before and after that point, showing that the speed of the bullet decreases immediately after the powder has burned 100%.

fxvr5 said:

That's not data. Data would show when the powder has burned 100% and the velocity of the bullet in the barrel before and after that point, showing that the speed of the bullet decreases immediately after the powder has burned 100%.

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I don't have the data, I'm just showing that the principles behind it indicate that there's a possibility.

It's a constant balance between forces acting on the bullet from both sides, leaning one way or the other. The pressure is a time rate while the opposing forces are relatively constant/negligible suggesting that there very likely is a point at which the bullet could begin to slow.

Not meaning to get anyone all fired up. Didn't know that classifying myself as a "physics nerd" and demonstrating my reasoning would cause such contention. If you disagree that's fine but no need for the sarcastic jabs. I fell for it too.

This is The High Road, after all, and that sort of nonsense is something we all should leave out.

A low pressure, large diameter round in a long/ for caliber barrel, say 45/70 would be a good candidate to test.
Lower starting pressure, and more volume inside the barrel behind the bullet as it accelerates

Olon said:

Haha that we can all agree on

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But there's also two undeniable facts.
1. squibs occour that end up with a bullet loged in the barrel therefore bullets obviously can accelerate and decelerate in the barrel.

2. Pressure at the muzzle can easily be calculated and is lower the longer the barrel is yet almost universally longer barrels produce more velocity.

Several people have already posted the right answers. Yes, it is possible. But it is not common with typical barrel length/cartridge combinations. Total gas volume along with barrel friction are the big variables.

If we imagine a barrel 12 feet long, a lot of small-gas-volume pistol cartridges wouldn't exit the barrel.

jmorris said:

For 9mm it looks like it’s about 17” for the loads they tested, they were slowing in the 18” barrel.

http://www.ballisticsbytheinch.com/9luger.html

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And it might happen even sooner with a 147 grain pill with a lot of bearing surface, especially over a small charge of fast powder.

It is possible to create a hose so long, you cannot blow through it. You won’t find one at Home Depot, however. So it goes...

Longer barrels will only yield more velocity If the pressure doesn't drop below what it takes to accelerate the bullet though. Therefore Slower powder. A pistol caliber with faster burn rate will be slower out of a 100 inch barrel than out of a 10 inch barrel. There will be a point where it stops gaining velocity depending on burn rate/ psi/ friction then after that it has to slow down. Take a PVC pipe and make a potato gun with hairspray and a gas grill ignitor , keep adding 2 foot sections and eventually the potato gets stuck.( I was a inquisitive child with too many scraps and opportunities to build and screw stuff up) . Or grab a straw and make a spitball, it will shoot. Now go get your waterhose and do the same, same principle........Anyway Eventually the bullet to barrel friction will over come the declining pressure. No PhD required.
In "normal"guns in the real world, the barrel lengths will usually be chose by what gives best velocity/accuracy. Obviously some choose being compact over velocity though. But no one is going to make a barrel that is unwieldy and gives less fps than a more usable (and cheaper to manufacture) counterpart. You can find barrels that are questionably short (18 inch 300 mag?) But in rifle calibers you will likely not find them too long but I don't know. In pistol calibers you certainly can. A 24 inch 44 magnum will be slower than an 14 inch with any ammo intended for a pistol. Handloads could be tailored to it though.

It's for illustration purposes.

But I think the answer is no, in rifle calibers they won't waste their time, money, and materials to make an unwieldy rifle longer than optimal
In pistol calibers, yes there are examples of barrels too long for standard ammunition a 30 inch barreled 44 magnum will be traveling slower than an 18 inch one.

It’s not that far off course, crestoncowboy summed it up nicely without any math or scientific jargon.

Longer barrels will only yield more velocity If the pressure doesn't drop below what it takes to accelerate the bullet...

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If pressure does drop below what it takes to accelerate the bullet, they start to slow down...that’s it.

Take another look at the link I posted on the last page.



The gains in velocity from the addition of 2” in barrel length slow a lot even to just 18” OAL, would have been nice if they went out to 30” though.

Yeah,
I take overly sophisticated orders from eggheads with no common sense nor ability to perform rudimentary tasks (upper level management) and translate them to normal people who cant comprehend fancy nerd speak but can perform tasks and function in society (blue collar workers) , for my living. I'm the middle man.

Bayourambler said:

In my mind this handload tweaking is all about burning just the right amount of powder for the setup we are working on..

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What is the purpose of this pursuit? Trying to achieve some theoretical goal? And the benefit of this is what?

Bayourambler said:

Simply put. I guess its darn near impossible to gauge whether a bullet is slowing down 2" from the muzzle.

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You can but it’s a destructive test, doing it the way BBTI does it.

FWIW really long barrels are used by some as a form of sound moderation. You only see them in shotguns because a wad has much less resistance going down the barrel than a lead much less jacketed bullet.

Some clams of noise emissions under 80 dB with just a longer barrel, less gas. At some point it exiting would sound like popping to cork on a whiskey bottle.



Talk about sight radius!

I am not a scientist. I'm just a redneck that has been loading and shooting all his life but I can tell you this from experience. I had loaded up some xTreme plated 158gr THP (which I'll never buy again) but they were loaded with 3.0gr of bullseye which was what I was loading with 158gr SWC for my girlfriend to shoot starting out. Loaded these for cleaner shooting. They shot fine out of a 2 and 3" revolver. Shot pretty much to poa at 15 -20 yards. Shot the same load in a 6" Model 686 and they would stick in the barrel at least 75 percent of the time. Now I'm not stating I'm that smart and I have 2 ex wives that will vouch for how stupid I am but if a bullet shoots fine in a 2 inch gun and sticks in a 6 inch gun then it has to slow down going down the barrel. Now I'm sure there are a lot of variables at play here such as barrel diameter and diameter of bullet. But I would think that the tighter the bullet is in the barrel the more chance it would have to decelerate going down the tube. That to me seems to be whey you can get different chronograph reading on the same bullet fired out of 2 different guns with same length barrel.
Maybe I'm looking a this question not scientific enough but it sure makes sense to me that a bullet could slow down at some point going down the barrel when the peak pressure starts dropping

I think thoes taste just like lion but after you eat them you’ll be stuffed...

Bayourambler said:

All you reloading scientists listen up!! I was just wondering if anyone could answer this question. Is it possible for a bullet to actually start slowing down by the time it exits the muzzle? If you were loading a minimal charge of one of the faster powders reccomend out of a longer rifle barrel, is it possible to loose acceleration if the powder is all burnt while the bullet is traveling down the barrel? You can imagine how much force it takes to hurl a bullet through the rifling. It probably sounds like a dumb question to more experienced reloaders, but I am fairly new and curious if it can happen. I ask this because if this were true, you could load in a tiny window that would give you random slow velocities if you were right on the edge of full powder burn. Reload gurus, enlighten me on powder burn and delta v.

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The effect is well enough known so as to be a feature in Quickload. Get a copy and bench experiment to your heart's content.



Here is what 300 BLK looks like in a 24" barrel - subsonic 168 grain:

I can even make it slow down and STOP halfway down the barrel.
The only thing I can't design . . is making it back up.







CAUTION: The chart/post includes load data generated by calculation in QuickLOAD software based on a particular powder lot, the assumption the primer is as mild as possible, and assumptions about component, chamber and gun geometry that may not correspond well to what you have. Such data should be approached by working up from published starting loads. USE THIS DATA AT YOUR OWN RISK. Neither the writer, The High Road, nor the staff of THR, nor QuickLOAD's author nor its distributor assume any liability for any damage or injury resulting from use of this information or information derived from it.

MEHavey said:

View attachment 820546

I can even make it slow down and STOP halfway down the barrel.
The only thing I can't design . . is making it back up.

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The joke's on you. That is one of several 168 grain subsonic loads I shoot. Nothing has been changed except the barrel length to more plainly see the effect.