Rifle Ballistics on SBR and Performance

S

stonewall50

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So I am wondering what y'all can tell me about how shortening the barrel of a rifle impacts the velocity and energy of the round, as well as accuracy. And for sake of discussion we will keep this close: under 100 yards. And I'm wondering about the 223/5.56 vs other rounds.

What I am basically wondering: is there a round that "outperforms" the .223 (more fps delivered accurately...just has advantages) within the range discussed? Not really wondering about abilities beyond 100. Just inside. I love learning about the finer points of ballistics inside little boxes like this. :)
 
Generally you'll loose 25-50 fps of velocity per inch you loose. A 16 inch 5.56 shooting M193 is cruising along in the neighborhood of 3000 fps
Once you go to 12 inches you will be going around 2850 fps and 10 inches you'll be roughly 2690 fps.

http://www.thetruthaboutguns.com/2013/07/jim-barrett/comparing-sbr-calibers-5-56-223-versus-300-blk/

This is a great article comparing the effectiveness of the 300 AAC blackout in SBRs compared to the 5.56/223 rounds in short barrels.

A 10 inch 300 AAC blackout shooting 110g Barnes has the same energy as a 16 inch rifle firing M193, and a 16 inch blackout firing a 110 Barnes has equivalent amount of energy to a 24 inch rifle firing M193.

Accuracy wise, a shorter barrel will generally be more stiffer than a longer barrel of the same diameter. This could potentially increase accuracy because of less "barrel whip" because of the shorter barrel. That's one way people look at it, but I believe the quality of the barrel and how it's machined will affect accuracy 10x more than the length will.
 
Greg500sw said:
Generally you'll loose 25-50 fps of velocity per inch you loose. A 16 inch 5.56 shooting M193 is cruising along in the neighborhood of 3000 fps
Once you go to 12 inches you will be going around 2850 fps and 10 inches you'll be roughly 2690 fps.

http://www.thetruthaboutguns.com/2013/07/jim-barrett/comparing-sbr-calibers-5-56-223-versus-300-blk/

This is a great article comparing the effectiveness of the 300 AAC blackout in SBRs compared to the 5.56/223 rounds in short barrels.

A 10 inch 300 AAC blackout shooting 110g Barnes has the same energy as a 16 inch rifle firing M193, and a 16 inch blackout firing a 110 Barnes has equivalent amount of energy to a 24 inch rifle firing M193.

Accuracy wise, a shorter barrel will generally be more stiffer than a longer barrel of the same diameter. This could potentially increase accuracy because of less "barrel whip" because of the shorter barrel. That's one way people look at it, but I believe the quality of the barrel and how it's machined will affect accuracy 10x more than the length will.
Click to expand...


So we aren't talking about an extreme loss in fps, and so I can only assume in F=ma it won't be much energy then.
 
Under 100 yards it doesn't matter. The extra 100fps or so from a longer barrel starts to have an advantage at longer ranges. Forget energy numbers. All that really matters is bullet penetration and expansion. All else being equal LONG bullets penetrate better than short bullets. A 60+ gr 223 bullet is quite long in relation to it's diameter and will penetrate much deeper than a 110 gr 308 bullet which is a short stubby bullet with poor flight characteristics.

Speed at impact determines bullet expansion. Most bullets need around 1800 fps to expand. If they impact at slower speeds they may not expand.

Bullet shape determines bullet speed down range. Lots of poorly designed bullets start out very fast, but slow down very fast. Don't pay attention to muzzle velocity. Look at the speed at 100, 200, yards etc. Many bullets start out 300-400 fps faster, but are slower down range.

A short barreled 223 still has plenty of speed to make it very effective within 100 yards. A longer barrel would help maintain that 1800 fps threshold a little farther down range.
 
jmr40 said:
Under 100 yards it doesn't matter. The extra 100fps or so from a longer barrel starts to have an advantage at longer ranges. Forget energy numbers. All that really matters is bullet penetration and expansion. All else being equal LONG bullets penetrate better than short bullets. A 60+ gr 223 bullet is quite long in relation to it's diameter and will penetrate much deeper than a 110 gr 308 bullet which is a short stubby bullet with poor flight characteristics.



Speed at impact determines bullet expansion. Most bullets need around 1800 fps to expand. If they impact at slower speeds they may not expand.



Bullet shape determines bullet speed down range. Lots of poorly designed bullets start out very fast, but slow down very fast. Don't pay attention to muzzle velocity. Look at the speed at 100, 200, yards etc. Many bullets start out 300-400 fps faster, but are slower down range.



A short barreled 223 still has plenty of speed to make it very effective within 100 yards. A longer barrel would help maintain that 1800 fps threshold a little farther down range.
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A question about this though: isn't the amount of energy delivered an important factor in determine effectiveness? Penetration will only matter as long as it is still within the target. Once it exits, no more damage is done. But energy determines wound channel size. So shouldn't that be relevant inside 100? Or am I wrong?
 
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I don't think energy matters quite as much in the same bullet profile. EDIT (if it is by a minor abount, obviously if we are talking within 100 yards and different barrel lengths) Bullet construction matters more in how the bullet will react in the target.

For instance a bullet with the same velocity and weight will have the same energy whether it is a hollowpoint or an fmj. Now if your talking a significant amount of energy, then sure. It all depends on how it's transfered. As someone stated before and sbr in 300 Blackout will have more energy than an sbr in 5.56. They also act differently in a medium.
 
So we aren't talking about an extreme loss in fps, and so I can only assume in F=ma it won't be much energy then.
Click to expand...

Wrong equation. Energy goes as velocity squared. When going from a 18" to a 10" barrel with .223 rem (depending on powder and bullet) the velocity loss can be from 250 to 600 fps. This can be a loss of energy of as much as 40%. With a shorter barrel, some .223 bullets may not expand (if that matters to you) and therefore expend substantially less energy passing through soft targets.

Accuracy improves with a shorter barrel.

With a 300BO, the losses in velocity are less, and a much lower percentage. Thus the energy loss is much less. Since most 300BO rounds use a faster powder, they also lose less for that reason. A sub-sonic round of 300BO from a short 10" barrel has less on target energy (about 1/2) than a .223 from an 18" barrel. A 110 grain supersonic round from a 300BO with a 10" barrel has about 30% more energy than a typical .223 round from an 18" barrel. Granted they will all have different terminal ballistics.
 
.223 shooting a 55 gr. Remington UMC will have a MV of 2616 FPS. And a ME of around 815 FPE, those are ballistics out of a 10 inch barrel.

.300 BO shooting 115 gr. Remington UMC will have 2100 fps MV. And 1124 FPE MV. That is out of a 9 inch barrel.

Out of a SBR, I would take the .300 BO as it performs very well and looses very little ballistics per inch.

But it depends on what distance you will be shooting at also, but if your getting a SBR I hope it's not for too much long range shooting as it defeats the purpose of a SBR.
 
.300 blackout was designed to perform well in short barrels (and with suppressors in subsonic). It will generally perform better out of SBRs, within a few hundred yards than a 55 or 62 grain .223 out of a similar barrel.

That said, if you want to go past about 300yds, .300blk is going to start dropping a lot faster than the average .223. (velocity differences are a primary factor for flight path)
 
For the short range needed that the OP states I would take a .300 BO any day for 100 yards or under like the OP states. The Blackout will drop a lot more at long ranges than a 5.56, but for 100 yards or less I would take a Blackout over a 5.56.
I have a Blackout and have cleanly taken game out to 280 yards with it with only taking one shot and the animal dropping in its tracks. I haven't been presented with a shot past 280 yards, but I would take a shot out to a little over 300 yards with it on a coyote or hog.
 
If you're just playing, it doesn't make much diff but it's sort of disconcerting if you find your SBR .223 is turning out velocities below .222 Rem(22-24") and even down close to .22 Hornet from a 20-22" rifle.
Under 100 yards the velocities are still adequate to initiate expansion of most soft point bullets.
 
The difference, under 100 yards, is practically negligible when compared to the real important stuff like getting good hits.

Sbr that sucker and practice!
 
"I have a Blackout and have cleanly taken game out to 280 yards with it with only taking one shot and the animal dropping in its tracks. I haven't been presented with a shot past 280 yards, but I would take a shot out to a little over 300 yards with it on a coyote or hog."

Wow, that's quite a statement. I need to find me some of those magic bullets.
 
I was using Remington Hog Hammer 130 gr. bullet. It was just a coyote trotting but I nailed him in the neck.

Also Ive taken a 300 lbs. boar which was at a dead run 260 yards off. He was running broadside so I squeezed off a shot and hit him in his lower spine. He went head over heels upon impact but he was not dead, just paralyzed in his back legs so I still had to finish him off at very close range with my Glock 20. I was also using Remington Hog Hammer 130 grains with him.

It doesn't take magic to make those shots, it just takes being familiar with your bullet trajectory and being comfortable with a particular gun or guns to make those shots.
 
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