Bullet Diameter vs Velocity

TN Shooter · Friday at 8:14 PM

If 2 bullets have the same weight but different diameters, does one have a higher velocity over the other? For example: 6ARC vs 6.5 Grendel or 22CM vs 6CM or 6CM vs 6.5CM. I think I read somewhere that the larger diameter bullet would have a higher velocity assuming all other variables were equal (barrel length, charge weight, etc.). Can someone help explain this?

spife7980 · Friday at 9:55 PM

The larger diameter offers more surface area upon with the pressure/force can act and so it accelerates more rapidly than an equivalent weight bullet in a smaller diameter.

Macht · Friday at 10:36 PM

Force = Pressure X Area. Assuming identical pressure curves, the larger diameter bullet is being acted on by a larger force.

Keep in mind that for identical case volumes the larger diameter bullet will require a faster burning powder to achieve that identical pressure curve (more bore volume for the same amount of bullet movement).

Zemplar · Friday at 10:46 PM

Being pedantic, the OP asked about velocity, not acceleration. Also, the more surface area, the higher the drag.

What are we trying to solve?

Besides, I have yet to encounter all other variables being equal.

ma smith · Friday at 11:05 PM

Drag, it slows you down.

spife7980 · 2025-02-01T07:57:24-0500

Zemplar said:
Being pedantic, the OP asked about velocity, not acceleration. Also, the more surface area, the higher the drag.

What are we trying to solve?

Besides, I have yet to encounter all other variables being equal.

You didn’t really think this comment through if your argument is that more acceleration won’t result in velocity.

Aftermath · 2025-02-01T08:08:26-0500

If 2 projectiles leave their barrels at the same velocity, they are flying through the air at the same velocity at that moment regardless of diameter or weight or mass or sectional density or coefficient of drag or direction of fire or any other factor you might dream up.

Aftermath · 2025-02-01T08:13:49-0500

spife7980 said:
You didn’t really think this comment through if your argument is that more acceleration won’t result in velocity.

Think about that for a minute...
A VW Beetle accelerates slowly to a final velocity of 80 mph in 60 seconds.
A Ford Pinto accelerates faster to that final velocity of 80 mph in 30 seconds.
What is the velocity of each vehicle?

salks · 2025-02-01T08:15:58-0500

I have noticed a significant difference in velocity between bullets in .44mag. A bullet that is .001 larger will have a higher velocity with all other things being pretty much the same.

Aftermath · 2025-02-01T08:16:35-0500

TN Shooter said:
If 2 bullets have the same weight but different diameters, does one have a higher velocity over the other? For example: 6ARC vs 6.5 Grendel or 22CM vs 6CM or 6CM vs 6.5CM. I think I read somewhere that the larger diameter bullet would have a higher velocity assuming all other variables were equal (barrel length, charge weight, etc.). Can someone help explain this?

The question is not well formulated. Think this through and ask a better question.

TN Shooter · 2025-02-01T08:53:05-0500

Aftermath said:
The question is not well formulated. Think this through and ask a better question.

I suppose I should have left out the “all other variables” part of my post. All I’m wondering is how velocity compares between 80gr ELD (22 CM) and 80gr ELD-VT (6CM).

So assuming the same barrel lengths, do lighter bullets (thinking of ELD-VT)in 6.5 Grendel, 6 CM, and 6.5 CM tend to have a higher velocity than the same or similar weight bullets in 6ARC, 22 CM, and 6 CM respectively?

spife7980 · 2025-02-01T09:01:24-0500

Aftermath said:
Think about that for a minute...
A VW Beetle accelerates slowly to a final velocity of 80 mph in 60 seconds.
A Ford Pinto accelerates faster to that final velocity of 80 mph in 30 seconds.
What is the velocity of each vehicle?

And you expect the one that hit it quicker to just flatline its acceleration?

Rio Precision Gunworks · 2025-02-01T09:07:53-0500

Aftermath said:
Think about that for a minute...
A VW Beetle accelerates slowly to a final velocity of 80 mph in 60 seconds.
A Ford Pinto accelerates faster to that final velocity of 80 mph in 30 seconds.
What is the velocity of each vehicle?

This is a terrible example to compare to bullet velocity and acceleration for too many reasons worth listing.

Rio Precision Gunworks · 2025-02-01T09:09:53-0500

spife7980 said:
And you expect the one that hit it quicker to just flatline its acceleration?

In his example sure......

He just failed to realize bullets don't have brakes and/or the ability to reduce combustion whenever they want.

Supersubes · 2025-02-01T09:41:41-0500

TN Shooter said:
I suppose I should have left out the “all other variables” part of my post. All I’m wondering is how velocity compares between 80gr ELD (22 CM) and 80gr ELD-VT (6CM).

So assuming the same barrel lengths, do lighter bullets (thinking of ELD-VT)in 6.5 Grendel, 6 CM, and 6.5 CM tend to have a higher velocity than the same or similar weight bullets in 6ARC, 22 CM, and 6 CM respectively?

Generally, yes. You can see this play out in the loading data as well. For a wider window of bore size with identical cases, check out data for the .243 win, 260 rem, 7-08 rem, .308 win.

Mike Casselton · 2025-02-01T10:07:09-0500

Aftermath said:
Think about that for a minute...
A VW Beetle accelerates slowly to a final velocity of 80 mph in 60 seconds.
A Ford Pinto accelerates faster to that final velocity of 80 mph in 30 seconds.
What is the velocity of each vehicle?

That depends on the location of the unit measuring velocity.
Is it at speed or at a place before final speed is reached?

Since your question asked for velocity, then it's 80mph. If one was to measure in meters per second, feet per second, furlongs per second or even skittles per second, all of it can be mathed out, knowing the 80mph velocity.

Acceleration rate is a different animal. Look at the cheetah and the pronghorn antelope. Both can reach 50 mph with ease. Their acceleration rates probably differ. Also, the pronghorn can maintain the 50mph for a much longer time.
It's got a much better BC...

Mean_Man · 2025-02-01T10:07:35-0500

One, er two words, bore rider. I think Barnes or Berger one makes some... the main body of the projectile rides on the lands and has bands or a fatter portion at the rear that engages the rifling. Less contact, less friction, and for solid copper's especially since they have more friction typically than lead core jacketed designs, that's a good thing, helps keep pressures for similar weight lead core projectiles and solid coppers more close if everything else was equal (like the powder charge and projectile weight) and MAY make them faster than their lead core counter parts? I'd wager makes them faster than their solid copper cousins that have a lot more engagement area for sure.

Mike Casselton · 2025-02-01T10:10:08-0500

salks said:
I have noticed a significant difference in velocity between bullets in .44mag. A bullet that is .001 larger will have a higher velocity with all other things being pretty much the same.

That's because the larger diameter bullet, with all other things being equal will generate a different and higher pressure curve.

Aftermath · 2025-02-01T10:24:08-0500

Mike Casselton said:
That depends on the location of the unit measuring velocity.
Is it at speed or at a place before final speed is reached?

Since your question asked for velocity, then it's 80mph. If one was to measure in meters per second, feet per second, furlongs per second or even skittles per second, all of it can be mathed out, knowing the 80mph velocity.

Acceleration rate is a different animal. Look at the cheetah and the pronghorn antelope. Both can reach 50 mph with ease. Their acceleration rates probably differ. Also, the pronghorn can maintain the 50mph for a much longer time.
It's got a much better BC...

There is but one question to be answered and it is a very simple answer without any convoluted and irrelevant wanderings.

Aftermath · 2025-02-01T10:27:35-0500

Rio Precision Gunworks said:
This is a terrible example to compare to bullet velocity and acceleration for too many reasons worth listing.

Name a few.
The point being made, and it is 100% relevant, is that velocity is independent of how it was achieved or how soon it was achieved or where it was achieved or what is traveling at that velocity.
Sure...go ahead and add in other shit like atmospherics and whatever but the fact remains.

Mike Casselton · 2025-02-01T10:28:45-0500

TN Shooter said:
I suppose I should have left out the “all other variables” part of my post. All I’m wondering is how velocity compares between 80gr ELD (22 CM) and 80gr ELD-VT (6CM).

So assuming the same barrel lengths, do lighter bullets (thinking of ELD-VT)in 6.5 Grendel, 6 CM, and 6.5 CM tend to have a higher velocity than the same or similar weight bullets in 6ARC, 22 CM, and 6 CM respectively?

I'm gonna go out on a limb here and just say it.

Stop worrying about all of this velocity stuff. A difference of 50fps doesn't make much difference in the real world.

A bullet diameter by itself doesn't make for more or less velocity. It is all dependant on the brass, the primer, the powder, the barrel and even the outside temperature.

With that said, if you could duplicate everything down to the barrel length, powder charge, and velocity per inch of barrel length, then yes, the 224 diameter bullet will go faster, simply because it generates more pressure in the smaller bore.

I have an experiment for you that will help you understand how this works.
Swing by your nearest Burger King AND McDonalds.
Grab a straw from each place.
Note the McD straw is larger in diameter. That's your 6mm barrel.
The BK straw is your 224 barrel.

Now, take two good strips of napkin, identical in size. Make a tight fitting spitwad from each of them and place it into their respective straws.

Huff and puff and blow that 6mm Micky Ds spitwad.
Now, pick up the 224 BK spitwad and do the same thing.

Note the difference in back pressure generated from each straw/spitwad combo.

Both spitwads should have gone out at the same velocity, but they didn't. The BK, higher backpressure spitwad represents what it takes to make the two spitwad bullets accelerate to their maximum velocity.
You didn't use more lung capacity. You didn't huff and puff longer. You simply needed more pressure to get the spitwad out of the straw.
You felt the difference in your cheeks.
Your cheeks represent the piezoelectric transducer the measures pressure in the chamber and down the barrel until the bullet exits.

It's simple physics

Aftermath · 2025-02-01T10:29:23-0500

TN Shooter said:
I suppose I should have left out the “all other variables” part of my post. All I’m wondering is how velocity compares between 80gr ELD (22 CM) and 80gr ELD-VT (6CM).

So assuming the same barrel lengths, do lighter bullets (thinking of ELD-VT)in 6.5 Grendel, 6 CM, and 6.5 CM tend to have a higher velocity than the same or similar weight bullets in 6ARC, 22 CM, and 6 CM respectively?

Again...not well formulated or maybe you do not understand that 2750 fps with an 80 gr ELD is the same 2750 fps with an 80 gr ELD-VT

Mike Casselton · 2025-02-01T10:31:46-0500

Aftermath said:
There is but one question to be answered and it is a very simple answer without any convoluted and irrelevant wanderings.

Look, the entire premise of this thread is a time waster.
Your question on velocity of two vehicles was no less convoluted and equally irrelevant.
I love answering silly questions with equally (or worse) silly answers.
You don't have to read them.

Aftermath · 2025-02-01T10:34:03-0500

spife7980 said:
And you expect the one that hit it quicker to just flatline its acceleration?

Aftermath said:
Think about that for a minute...
A VW Beetle accelerates slowly to a final velocity of 80 mph in 60 seconds.
A Ford Pinto accelerates faster to that final velocity of 80 mph in 30 seconds.
What is the velocity of each vehicle?

Supersubes · 2025-02-01T13:15:31-0500

Aftermath said:
Again...not well formulated or maybe you do not understand that 2750 fps with an 80 gr ELD is the same 2750 fps with an 80 gr ELD-VT

I agree his question isn't super clear, but you can see where’s he’s going. You changed his question. His question isnt what will these bullets do at the same speed as one another. Its will a 80 vt in a 6cm be faster than the 80 eld in a 22 cm. A bunch of variables aside, the simple answer is yes. To what degree depends on the variables of course.

XLR308 · 2025-02-01T13:21:54-0500

Mike Casselton said:
That depends on the location of the unit measuring velocity.
Is it at speed or at a place before final speed is reached?

Since your question asked for velocity, then it's 80mph. If one was to measure in meters per second, feet per second, furlongs per second or even skittles per second, all of it can be mathed out, knowing the 80mph velocity.

Acceleration rate is a different animal. Look at the cheetah and the pronghorn antelope. Both can reach 50 mph with ease. Their acceleration rates probably differ. Also, the pronghorn can maintain the 50mph for a much longer time.
It's got a much better BC...

Because the Pronghorn is made in Merica damnit and the lazy ass cheetah is african.

Aftermath · 2025-02-01T15:23:03-0500

Supersubes said:
I agree his question isn't super clear, but you can see where’s he’s going. You changed his question. His question isnt what will these bullets do at the same speed as one another. Its will a 80 vt in a 6cm be faster than the 80 eld in a 22 cm. A bunch of variables aside, the simple answer is yes. To what degree depends on the variables of course.

Negative. I did NOT change his question to be what either bullet or Pinto or fucking freight train will DO at some given velocity.

"A bunch of variables aside" that is maybe the most misunderstood part of what he is asking.
Can a 6CM shoot the same weight bullet faster than a 22CM? Yes.
Can a 6CM shoot the same weight bullet the same velocity as a 22CM? Yes.
Can a 6CM shoot the same weight bullet with less velocity than a 22CM? Yes.

Supersubes · 2025-02-01T15:37:00-0500

Aftermath said:
Can a 6CM shoot the same weight bullet faster than a 22CM? Yes.
Can a 6CM shoot the same weight bullet the same velocity as a 22CM? Yes.
Can a 6CM shoot the same weight bullet with less velocity than a 22CM? Yes.

You're not following, at all. His question is very simple, and has been stated and restated by me and other posters above.

Here, i’ll try another way. He’s asking how bore area affects velocity. Thats it, nothing more.

Aftermath · 2025-02-01T15:46:27-0500

Supersubes said:
You're not following, at all. His question is very simple, and has been stated and restated by me and other posters above.

Here, i’ll try another way. He’s asking how bore area affects velocity. Thats it, nothing more.

Negative, it's not simply the bore, as that would include length and twist. His question, as faulty as it is posed, is only concerned with DIAMETER. THAT's it...nothing more.

And the most correct and extremely simple answer to the question as to whether a small diameter will shoot faster or slower than a larger diameter, using the same lot of powder and charge weight, the same primer...all else being equal, is, simply, MAYBE.

Supersubes · 2025-02-01T15:58:14-0500

Aftermath said:
Negative, it's not simply the bore, as that would include length and twist. His question, as faulty as it is posed, is only concerned with DIAMETER. THAT's it...nothing more.

And the most correct and extremely simple answer to the question as to whether a small diameter will shoot faster or slower than a larger diameter, using the same lot of powder and charge weight, the same primer...all else being equal, is, simply, MAYBE.

He’s asking how one variable affects velocity, thats it. He notes bullet diameter. We say bore area in the context of the question. No need to keep saying there are other variables, the OP has already demonstrated he understands there are many other variables.

Aftermath · 2025-02-01T16:43:02-0500

Supersubes said:
He’s asking how one variable affects velocity, thats it. He notes bullet diameter. We say bore area in the context of the question. No need to keep saying there are other variables, the OP has already demonstrated he understands there are many other variables.

If you look back, go ahead, go look, I am the one that has repeatedly said there are not other variables.

Here, let's figure out how to calculate velocity....
Measure the distance traveled then divide by the amount of time it took to travel that distance.
THAT'S IT!! Nothing more.
No BC, no twist rate, no diameter...it doesn't even matter what the object is (car, bullet, bulldozer) nor how it came to be traveling that distance in that amount of time. Not part of the equation, are they?
Simple, really.

XLR308 · 2025-02-01T16:54:15-0500

Compare the 30BR to the 308win and your theory in blown out the door.

Supersubes · 2025-02-01T17:01:34-0500

Aftermath said:
If you look back, go ahead, go look, I am the one that has repeatedly said there are not other variables.

Here, let's figure out how to calculate velocity....
Measure the distance traveled then divide by the amount of time it took to travel that distance.
THAT'S IT!! Nothing more.
No BC, no twist rate, no diameter...it doesn't even matter what the object is (car, bullet, bulldozer) nor how it came to be traveling that distance in that amount of time. Not part of the equation, are they?
Simple, really.

Go back a read the Op’s question, he’s not asking about the measurement of velocity. How can you have missed this so many times?

Aftermath · 2025-02-01T17:02:13-0500

Supersubes said:
Go back a read the Op’s question, he’s not asking about the measurement of velocity. How can you have missed this so many times?

View attachment 8606630

You truly might be a fucking idiot

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