ballistics question

Eeyore · Apr 29, 2012

My question involves bullet weight vs. barrel length. Yes, I ran a forum search and didn't find any posts specific to this question.

My CC weapon has a 3" barrel. My OC weapon has a 4.125" barrel. I usually load both with the same brands of 9mm, standard pressure, hollow points. Given that all other factors are equal, I have been loading lighter ammo (115 or 124 grain) in the smaller gun and heavier bullets (147 grain) in the longer gun. This is based on the assumption that a shorter barrel gives the round less time to reach muzzle velocity and a lighter bullet will accelerate more quickly. Therefore, I reason, a light bullet will be faster when it leaves the (short) barrel than a heavier bullet would be, and thus deliver more energy than a heavier bullet. Conversely, a longer barrel gives even a heavy bullet more time to accelerate, so the heavier bullet will deliver more energy.

I found this graph at Ballistics by the Inch (http://www.ballisticsbytheinch.com/megraphs/9mm.html). It's hard to tell because the weights and brands both vary, but it looks like my theory was incorrect. The only "apples to apples" comparison I could make was 124 vs 147 gr HydraShok (almost identical energies from a 3" barrel, but the 124 does better at all other lengths) and the three weights of Corbon +P (where the weights and energies seem to scatter). So what's going on?

That said, I think I have 124 gr Gold Dots in there now, so I seem to be doing all right.....

j4l · Apr 29, 2012

Eeyore said:
My question involves bullet weight vs. barrel length. Yes, I ran a forum search and didn't find any posts specific to this question.

My CC weapon has a 3" barrel. My OC weapon has a 4.125" barrel. I usually load both with the same brands of 9mm, standard pressure, hollow points. Given that all other factors are equal, I have been loading lighter ammo (115 or 124 grain) in the smaller gun and heavier bullets (147 grain) in the longer gun. This is based on the assumption that a shorter barrel gives the round less time to reach muzzle velocity and a lighter bullet will accelerate more quickly. Therefore, I reason, a light bullet will be faster when it leaves the (short) barrel than a heavier bullet would be, and thus deliver more energy than a heavier bullet. Conversely, a longer barrel gives even a heavy bullet more time to accelerate, so the heavier bullet will deliver more energy.

I found this graph at Ballistics by the Inch (http://www.ballisticsbytheinch.com/megraphs/9mm.html). It's hard to tell because the weights and brands both vary, but it looks like my theory was incorrect. The only "apples to apples" comparison I could make was 124 vs 147 gr HydraShok (almost identical energies from a 3" barrel, but the 124 does better at all other lengths) and the three weights of Corbon +P (where the weights and energies seem to scatter). So what's going on?

That said, I think I have 124 gr Gold Dots in there now, so I seem to be doing all right.....

Honestly, I think the 124GDs should be just about right for both.As far as ballistics go.
I doubt you will find all that much difference within only 1 inch or so of barrel-length difference.Maybe 40 -60 fps with the same load in both? If even that much.
It's 9mm, and under 200 grains, so I wouldnt even worry about "energy" levels @ impact, a moot point, at best.
But, given the handicap, 124s should sort of "split the difference" for velocities-vs. 147s.

If you havent tested penetration of your rounds, I'd suggest at least trying to do so, 1st. -Simple and quick, right out in the back yard.- 6 x 1-gallon water jugs end-to-end. With something behind the 6th as a back-stop. Your desired pen. should be around 4-5 jugs,whether expanded, or not.
If you hit the backstop, then expect over-penetrations,of course.

And then there's the JHP via short-barrel thing... in 9mm and .40, JHP really dont often expand anywhere near as much as marketing dept.s and internet forum mythology would like anyone to believe. Even with "modern" "quality" HPs.
The proof is in the pudding, so test it to find out. If you do test, and you get the min. 4 jugs penned, without expansion, then just go ahead and save the $$ and get some good FMJ/TMJ (blazer brass works very well).
If you only get, say, 2-3 jugs penned, then forgot JHP, completely, and go with 147 FMJ/TMJ.

skidmark · Apr 29, 2012

While OCDO is the repository of much good information, it is not the only place where you can learn an answer to your question.

http://www.ballisticsbytheinch.com/ is a great site. You should either pretty much get a straight answer there or be able to use their data and any of the ballistics calculators to plug in your specific data and derive your answer.

stay safe.

dashowdy · Apr 30, 2012

115gr. to 124 I would stick with a longer barrel 4 in. or greater gives the round enough time in the barrel to utilize the expanded gas,but in subcompact barrels there super hot rounds or light rounds while still effective tend to lose more velocity because of the lower weight and increased velocity in shorter barrels due to the loss of time in the barrel. Heavier bullets spend more time in the barrel and effectively utilize gas better than there lighter cousins.

So usually when I pick a defensive load, which in 9mm is always 147gr. regardless, 180gr. in 40, I like heavy for caliber for two reasons, recoil control and penetration, when it comes down to it how many rounds I can put down range and the ability of those rounds to penetrate through enough to hit a vital area are the most important thing. Expansion is great but most rounds actually dont expand because the human body is not made up like a ballistic block it has cavities and bones and is just not uniform enough to give expansion everytime.

j4l · Apr 30, 2012

dashowdy said:
115gr. to 124 I would stick with a longer barrel 4 in. or greater gives the round enough time in the barrel to utilize the expanded gas,but in subcompact barrels there super hot rounds or light rounds while still effective tend to lose more velocity because of the lower weight and increased velocity in shorter barrels due to the loss of time in the barrel. Heavier bullets spend more time in the barrel and effectively utilize gas better than there lighter cousins.

So usually when I pick a defensive load, which in 9mm is always 147gr. regardless, 180gr. in 40, I like heavy for caliber for two reasons, recoil control and penetration, when it comes down to it how many rounds I can put down range and the ability of those rounds to penetrate through enough to hit a vital area are the most important thing. Expansion is great but most rounds actually dont expand because the human body is not made up like a ballistic block it has cavities and bones and is just not uniform enough to give expansion everytime.

^bingo.
Personally, I consider anything less than 200 grains to be... spitballs. For much of the reasons above. Gel is one thing- real world/clothed, human bodies of wildly-variable weights, sizes, muscle:fat contents. etc.. something else entirely.-Not to mention any intermediate materials between you and the target.
Go for the heaviest rounds of your load, when possible.
For my primary (loaded in pistol) mag, I split the difference in JHP/TMJ. with alternating shots of each. (1st round is Gold Dot, 2nd TMJ, etc). Spare/reload mag is all hardball.

Michigander · May 1, 2012

The way it was explained to me by a detective who is a career gun nut is that 124 grain + P offers the perfect combination of penetration and expansion in just about any common handgun barrel, whereas going to a significantly heavier bullet will slow the velocity enough to give you similar performance to a .38 special, the .38 being less desirable.

I've wet pack (wet phone book) tested some high velocity 124 grain JHPs, putting items in front of them such as coats folded over several times, wood, drywall, and a car door, and believe me, they work. We're talking about a round pushing nearly twice the case pressure of a .45 ACP, and with a good SD load those 124 grains out of a 3 inch barrel should still be doing well over 1000 FPS. A 4" should be at 1,200 or better. Unless you need the gun for penetrating large animals skulls, I would think you'll have no problems with either gun going with a hot loaded 124 grain round.

dashowdy · May 1, 2012

j4l said:
^bingo.
Personally, I consider anything less than 200 grains to be... spitballs. For much of the reasons above. Gel is one thing- real world/clothed, human bodies of wildly-variable weights, sizes, muscle:fat contents. etc.. something else entirely.-Not to mention any intermediate materials between you and the target.
Go for the heaviest rounds of your load, when possible.
For my primary (loaded in pistol) mag, I split the difference in JHP/TMJ. with alternating shots of each. (1st round is Gold Dot, 2nd TMJ, etc). Spare/reload mag is all hardball.

9mm and 40 s&w are still more widely used today than 45 acp which is what I assume you are talking about. If 9mm or 40 are spit wads then why do law enforcement continue to use them to this day, Because when it comes down to it terminal ballistics are exactly the same for the premier self defense loads in each caliber. They all penetrate about 12 to 16 inches and expand around .75 of an inch. Dallas pd still uses 9mm 147 gr. ranger t-series, which is what I carry, and have had excellent stoppage results with it. By no means am I saying one is better than the other each has there advantages and drawbacks whether it be capacity, stopping power( which is a myth), or cost of training, each is a respectable defense caliber as long as you do your part and stoke it with premium bullets.

ballistics question

Eeyore

Regular Member

j4l

Regular Member

skidmark

Campaign Veteran

dashowdy

Regular Member

j4l

Regular Member

Michigander

Regular Member

dashowdy

Regular Member