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Posted: 1/16/2026 11:24:20 AM EDT
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Not all weapons are "good" SBRs, but some calibers really do well. What are your favorites? Good: PCCs - handgun rounds typically don't need long barrels for full velocity and stability (9mm, 45 ACP, etc) 300 BLK - due to smallish case and large barrel volume, does fine with shorter barrels .22 LR - Cheap and does well with any barrel length over 5" Okay: .308 - benefits from a longer barrel for velocity reasons 5.56 - lots of unburned powder at shorter barrel lengths, huge fireball, loud Bad: 6.5 Creedmore - needs long barrel for stability and complete powder burn |
Atypical Millennial
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300 BLK. It's the ultimate SBR caliber in my mind. 22LR is a versatile cartridge too but only because we don't have any expectation of ballistic performance. Instead it's a cartridge of fun and convenience. Quiet out of short barrels due to low gas volume, and subsonic velocity even when using supersonic ammo. Then if course you can use particular firearms that really play well into this flexibility and take it a step further, like the Remington Model 24 which cycles on CB Shorts for example. |
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opni 300blk Attached File .22lr Attached File 9mm Attached File Attached File 308 is pretty awesome out of a short barrel though. Sure, it loses some range, but it hits like a sledgehammer. Attached File |
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As far as popular calibers? Big winners (these are all great when your barrel is in single digit inches): 9mm 10mm 45ACP 5.7 22LR 300blk The one foot club. (These perform well as SBR's with 12'ish inch barrels) 7.62x39 6.5G 5.56 6.8spc I'm not sure where 338ARC falls on here. |
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Originally Posted By Daggertt: 308 is pretty awesome out of a short barrel though. Sure, it loses some range, but it hits like a sledgehammer.  It now has an 18" barrel and a flash hider.  |
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Originally Posted By dmk0210: I had an FAL with a cut down barrel and a pinned & welded brake to bring it to 16". I don't know what I was thinking when I decided to do that. With earpro doubled up, you could still feel the blast slap your face and hear it through your teeth. It now has an 18" barrel and a flash hider. |
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Originally Posted By djkest: Not all weapons are "good" SBRs, but some calibers really do well. What are your favorites? Good: PCCs - handgun rounds typically don't need long barrels for full velocity and stability (9mm, 45 ACP, etc) 300 BLK - due to smallish case and large barrel volume, does fine with shorter barrels .22 LR - Cheap and does well with any barrel length over 5" Okay: .308 - benefits from a longer barrel for velocity reasons 5.56 - lots of unburned powder at shorter barrel lengths, huge fireball, loud Bad: 6.5 Creedmore - needs long barrel for stability and complete powder burn Some of this stuff seems like opinion and lore rather than hard data. I'd really like to know what you mean about the 6.5 Creedmoor needing a long barrel for stability? What's a long barrel? Lots of rounds that are similar were used in single shot handguns for years to good effect. 308/7-08/260 in 10-14" barrels. I see a lot of stuff rehashed over and over on here. Example: There are cartridges that are magically more efficient in shorter barrels. Commonly it will be in regards to 308 and that 7.62x39 or 300 Blackout are so much more efficient in shorter barrels that they are almost 308. It's just not true. Now if blast/flash is a huge concern it certainly comes into play but it's just due to case size. A 308 will still trounce a 7.62x39 and 300 Blackout. I just group everything by case size for the most part. Any of the 308ish sized cases including 6.5 Creedmoor 243 etc are going to be similar. 7.62x39. 6.5 Grendel 6 ARC are in another group. |
BikerNut:
Normal people like motorcycles. Real people like motorcycles.
People who don't like motorcycles are just... weird.
Normal people like motorcycles. Real people like motorcycles.
People who don't like motorcycles are just... weird.
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Originally Posted By ALASKANFIRE: Some of this stuff seems like opinion and lore rather than hard data. I'd really like to know what you mean about the 6.5 Creedmoor needing a long barrel for stability? What's a long barrel? Lots of rounds that are similar were used in single shot handguns for years to good effect. 308/7-08/260 in 10-14" barrels. I see a lot of stuff rehashed over and over on here. Example: There are cartridges that are magically more efficient in shorter barrels. Commonly it will be in regards to 308 and that 7.62x39 or 300 Blackout are so much more efficient in shorter barrels that they are almost 308. It's just not true. Now if blast/flash is a huge concern it certainly comes into play but it's just due to case size. A 308 will still trounce a 7.62x39 and 300 Blackout. I just group everything by case size for the most part. Any of the 308ish sized cases including 6.5 Creedmoor 243 etc are going to be similar. 7.62x39. 6.5 Grendel 6 ARC are in another group. But you're right about 308 vs 762x39 etc I don't remember the specific numbers, but a 12.5" 308 slings 123gr projectiles much faster than a 16" AK or heavier bullets like 150gr about the same velocity as a 123gr from a 16" AK for much more energy either way. The energy numbers overlap around 8". So an 8" 308 and an 8" x39 are providing about the same ft lbs of energy. In anything longer than 8", 308 comes out on top in terms of energy. |
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Originally Posted By Daggertt: I haven't seen anyone say that in this thread. But you're right about 308 vs 762x39 etc I don't remember the specific numbers, but a 12.5" 308 slings 123gr projectiles much faster than a 16" AK or heavier bullets like 150gr about the same velocity as a 123gr from a 16" AK for much more energy either way. The energy numbers overlap around 8". So an 8" 308 and an 8" x39 are providing about the same ft lbs of energy. In anything longer than 8", 308 comes out on top in terms of energy. Originally Posted By Daggertt: Originally Posted By ALASKANFIRE: Some of this stuff seems like opinion and lore rather than hard data. I'd really like to know what you mean about the 6.5 Creedmoor needing a long barrel for stability? What's a long barrel? Lots of rounds that are similar were used in single shot handguns for years to good effect. 308/7-08/260 in 10-14" barrels. I see a lot of stuff rehashed over and over on here. Example: There are cartridges that are magically more efficient in shorter barrels. Commonly it will be in regards to 308 and that 7.62x39 or 300 Blackout are so much more efficient in shorter barrels that they are almost 308. It's just not true. Now if blast/flash is a huge concern it certainly comes into play but it's just due to case size. A 308 will still trounce a 7.62x39 and 300 Blackout. I just group everything by case size for the most part. Any of the 308ish sized cases including 6.5 Creedmoor 243 etc are going to be similar. 7.62x39. 6.5 Grendel 6 ARC are in another group. But you're right about 308 vs 762x39 etc I don't remember the specific numbers, but a 12.5" 308 slings 123gr projectiles much faster than a 16" AK or heavier bullets like 150gr about the same velocity as a 123gr from a 16" AK for much more energy either way. The energy numbers overlap around 8". So an 8" 308 and an 8" x39 are providing about the same ft lbs of energy. In anything longer than 8", 308 comes out on top in terms of energy. Yeah I don't think I've seen much 8" 308 data. I wish there was more mainstream testing of barrels down to super short lengths. I was actually hoping we'd see some real numbers if Sig started selling that little MCX they were teasing. I think it was the Raptor or something like that. I'd like to see some 14.5" 6.5 numbers now that those are becoming a thing. I think that would be a perfect all around for me. |
BikerNut:
Normal people like motorcycles. Real people like motorcycles.
People who don't like motorcycles are just... weird.
Normal people like motorcycles. Real people like motorcycles.
People who don't like motorcycles are just... weird.
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Originally Posted By ALASKANFIRE: Some of this stuff seems like opinion and lore rather than hard data. I'd really like to know what you mean about the 6.5 Creedmoor needing a long barrel for stability? What's a long barrel? Lots of rounds that are similar were used in single shot handguns for years to good effect. 308/7-08/260 in 10-14" barrels. I see a lot of stuff rehashed over and over on here. Example: There are cartridges that are magically more efficient in shorter barrels. Commonly it will be in regards to 308 and that 7.62x39 or 300 Blackout are so much more efficient in shorter barrels that they are almost 308. It's just not true. Now if blast/flash is a huge concern it certainly comes into play but it's just due to case size. A 308 will still trounce a 7.62x39 and 300 Blackout. I just group everything by case size for the most part. Any of the 308ish sized cases including 6.5 Creedmoor 243 etc are going to be similar. 7.62x39. 6.5 Grendel 6 ARC are in another group. I did not see a comment here that said 300blk/7.62x39 so much more efficient in shorter barrels that they are almost 308. I do think 300blk and 7.62x39 are more efficient in shorter barrels than 308. That does not make them more powerful, but power and efficiency are two different things. It comes down to case capacity and powder type where faster burning powders = better efficiency in shorter barrels. As for capacity, more powder usually equals more power, but the shorter the barrel, the less bore volume there is to make efficient use of those hot gasses created by that additional powder. Some of that additional powder ends up as muzzle blast, concussion and accelerated parts wear, hence the efficiency loss. An 8" 308 will certainly have more power than an 8" 300blk, but I would stand on an 8" 300blk being more efficient than an 8" 308. I think that is where what makes a "good SBR" could become subjective. |
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Originally Posted By panthermark: I did not see a comment here that said 300blk/7.62x39 so much more efficient in shorter barrels that they are almost 308. I do think 300blk and 7.62x39 are more efficient in shorter barrels than 308. That does not make them more powerful, but power and efficiency are two different things. It comes down to case capacity and powder type where faster burning powders = better efficiency in shorter barrels. As for capacity, more powder usually equals more power, but the shorter the barrel, the less bore volume there is to make efficient use of those hot gasses created by that additional powder. Some of that additional powder ends up as muzzle blast, concussion and accelerated parts wear, hence the efficiency loss. An 8" 308 will certainly have more power than an 8" 300blk, but I would stand on an 8" 300blk being more efficient than an 8" 308. I think that is where what makes a "good SBR" could become subjective. Originally Posted By panthermark: Originally Posted By ALASKANFIRE: Some of this stuff seems like opinion and lore rather than hard data. I'd really like to know what you mean about the 6.5 Creedmoor needing a long barrel for stability? What's a long barrel? Lots of rounds that are similar were used in single shot handguns for years to good effect. 308/7-08/260 in 10-14" barrels. I see a lot of stuff rehashed over and over on here. Example: There are cartridges that are magically more efficient in shorter barrels. Commonly it will be in regards to 308 and that 7.62x39 or 300 Blackout are so much more efficient in shorter barrels that they are almost 308. It's just not true. Now if blast/flash is a huge concern it certainly comes into play but it's just due to case size. A 308 will still trounce a 7.62x39 and 300 Blackout. I just group everything by case size for the most part. Any of the 308ish sized cases including 6.5 Creedmoor 243 etc are going to be similar. 7.62x39. 6.5 Grendel 6 ARC are in another group. I did not see a comment here that said 300blk/7.62x39 so much more efficient in shorter barrels that they are almost 308. I do think 300blk and 7.62x39 are more efficient in shorter barrels than 308. That does not make them more powerful, but power and efficiency are two different things. It comes down to case capacity and powder type where faster burning powders = better efficiency in shorter barrels. As for capacity, more powder usually equals more power, but the shorter the barrel, the less bore volume there is to make efficient use of those hot gasses created by that additional powder. Some of that additional powder ends up as muzzle blast, concussion and accelerated parts wear, hence the efficiency loss. An 8" 308 will certainly have more power than an 8" 300blk, but I would stand on an 8" 300blk being more efficient than an 8" 308. I think that is where what makes a "good SBR" could become subjective. So what data can I look at to show me more efficient? My point is that I don't really understand what that means. If I am looking at 12" barrel data between two different rounds how do I know what's more efficient? With something like a car efficiency is easy to establish ie 25mpg vs 30 mpg but in this context I don't really get it. |
BikerNut:
Normal people like motorcycles. Real people like motorcycles.
People who don't like motorcycles are just... weird.
Normal people like motorcycles. Real people like motorcycles.
People who don't like motorcycles are just... weird.
|
Originally Posted By ALASKANFIRE: So what data can I look at to show me more efficient? My point is that I don't really understand what that means. If I am looking at 12" barrel data between two different rounds how do I know what's more efficient? With something like a car efficiency is easy to establish ie 25mpg vs 30 mpg but in this context I don't really get it. I don't think there is a singular table easily available to show that data since there are a lot of variables. The terms that get thrown around for this are "Cartridge Efficiency" and sometimes "Ballistic Efficiency" (although I think the latter can have other meanings in terms of BC) . But they all boil down to the same criteria. Energy (weight/velocity) produced based on powder charge and bore volume, taking into account (more subjective criteria) recoil, muzzle blast, barrel life, throat erosion ect. Here are some good articles on it: https://bulletin.accurateshooter.com/2015/10/cartridge-efficiency-basics-from-the-usamu/ https://www.harvestyourown.ca/articles/what-is-rifle-cartridge-efficiency/ https://www.rifleshootermag.com/editorial/the-truth-about-ballistic-efficiency/83495 Here are some old articles I remember looking at on .308 by barrel length where they basically shot 308 from 28" down to 6" and measured velocity. The conclusion is the article https://rifleshooter.com/2014/12/308-winchester-7-62x51mm-nato-barrel-length-versus-velocity-28-to-16-5/ https://rifleshooter.com/2016/02/308-winchester-7-62x51mm-nato-short-barrel-length-and-velocity-a-six-inch-308-bolt-gun/ Since we are talking SBR's, the barrels are getting shorter (how short is a different question). The bigger the initial powder charge, the less efficient it will become as the bore volume (barrel length in this case) decreases. If we were talking 24" barrels, than the opposite would apply for 300blk vs .308. No one would lug around a 24" 300blk to get so little power out of it relative to .308. The efficiency (energy created by powder charge vs bore volume) for 300blk would be way too low to be worth it. Recoil, blast, and such are easier to handle out of a 24" .308 compared to an 8" .308. |
Moderate-Length Barrel Evangelist
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Originally Posted By ALASKANFIRE: So what data can I look at to show me more efficient? My point is that I don't really understand what that means. If I am looking at 12" barrel data between two different rounds how do I know what's more efficient? With something like a car efficiency is easy to establish ie 25mpg vs 30 mpg but in this context I don't really get it. Mostly just impression of unpleasantness or signature. 300 BLK doesn’t just lose less velocity per inch than .308, it also gains less. In other words, it gives up less because it has less to give up. But it probably isn’t as insanely loud and flashy in a SBR of equal length. Similarly, as sectional density (bullet mass per caliber) goes up within the same cartridge, there is a smaller penalty for chopping the barrel, and less to be gained by going longer. It’s actually pretty exaggerated how much less per inch BLK loses. It’s not like the curve turns negative at 5” or whatever silly length. Not too hard to envision why BLK is never more powerful than .308…most cartridges from 9mm to .308 will get pretty similar in velocity at 3”, but not all will reach 3,000fps. And not all would be considered reasonable at 3”. To some reloaders, “efficiency” is defined as an efficient use of their ammo resources. You know, why shoot a coyote with a .308 when you can do it with a fraction of the powder using a .22 K-Hornet. I think that is a reasonable definition, as long as it is economically efficient, also. If you already have the .308, just shoot the coyote with that, regardless of barrel length, powder burn percentage, or the pennies of difference per shot. For most, it’s a vague term used to justify sales, purchases, or opinions. I think that’s what you’re seeing. This ramble isn’t directed at you; I think we agree. Just nerding out a bit. |
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Originally Posted By 1168RGR: Mostly just impression of unpleasantness or signature. 300 BLK doesn’t just lose less velocity per inch than .308, it also gains less. In other words, it gives up less because it has less to give up. But it probably isn’t as insanely loud and flashy in a SBR of equal length. Similarly, as sectional density (bullet mass per caliber) goes up within the same cartridge, there is a smaller penalty for chopping the barrel, and less to be gained by going longer. It’s actually pretty exaggerated how much less per inch BLK loses. It’s not like the curve turns negative at 5” or whatever silly length. Not too hard to envision why BLK is never more powerful than .308…most cartridges from 9mm to .308 will get pretty similar in velocity at 3”, but not all will reach 3,000fps. And not all would be considered reasonable at 3”. To some reloaders, “efficiency” is defined as an efficient use of their ammo resources. You know, why shoot a coyote with a .308 when you can do it with a fraction of the powder using a .22 K-Hornet. I think that is a reasonable definition, as long as it is economically efficient, also. If you already have the .308, just shoot the coyote with that, regardless of barrel length, powder burn percentage, or the pennies of difference per shot. For most, it’s a vague term used to justify sales, purchases, or opinions. I think that’s what you’re seeing. This ramble isn’t directed at you; I think we agree. Just nerding out a bit. Originally Posted By 1168RGR: Mostly just impression of unpleasantness or signature. 300 BLK doesn’t just lose less velocity per inch than .308, it also gains less. In other words, it gives up less because it has less to give up. But it probably isn’t as insanely loud and flashy in a SBR of equal length. Similarly, as sectional density (bullet mass per caliber) goes up within the same cartridge, there is a smaller penalty for chopping the barrel, and less to be gained by going longer. It’s actually pretty exaggerated how much less per inch BLK loses. It’s not like the curve turns negative at 5” or whatever silly length. Not too hard to envision why BLK is never more powerful than .308…most cartridges from 9mm to .308 will get pretty similar in velocity at 3”, but not all will reach 3,000fps. And not all would be considered reasonable at 3”. To some reloaders, “efficiency” is defined as an efficient use of their ammo resources. You know, why shoot a coyote with a .308 when you can do it with a fraction of the powder using a .22 K-Hornet. I think that is a reasonable definition, as long as it is economically efficient, also. If you already have the .308, just shoot the coyote with that, regardless of barrel length, powder burn percentage, or the pennies of difference per shot. For most, it’s a vague term used to justify sales, purchases, or opinions. I think that’s what you’re seeing. This ramble isn’t directed at you; I think we agree. Just nerding out a bit. I had responded to that post earlier. The first link I provided was the United States Army Marksmanship Unit's weekly article on advice for hand-loaders. https://bulletin.accurateshooter.com/2015/10/cartridge-efficiency-basics-from-the-usamu/ The definition they provide was: Efficient cartridges make excellent use of their available powder and case/bore capacity. They yield good ballistic performance with relatively little recoil and throat erosion. Later in that article they reference comment from a Lapua Staffer. Cartridge Efficiency and Energy — Another Perspective Lapua staffer Kevin Thomas explains that efficiency can be evaluated in terms of energy: “Cartridge efficiency is pretty straight forward — energy in vs. energy out. Most modern single-based propellants run around 178-215 ft/lbs of energy per grain. These figures give the energy potential that you’re loading into the rifle. The resulting kinetic energy transferred to the bullet will give you the efficiency of the round. Most cases operate at around 20-25% efficiency. This is just another way to evaluate the potential of a given cartridge. There’s a big difference between this and simply looking at max velocities produced by various cartridges.” The objective parts are simple. "x" amount of energy (ft.lbs) / "y" amount of Powder (gr) = energy per grain. The more energy per grain, the more efficient it is, so to speak. The subjective parts like muzzle blast, shooter fatigue from weight/recoil, function, and accelerated parts wear are harder to quantify. Since this an SBR topic, there is an additional objective factor that can be included. Barrel length. The subjective part is that no specific barrel length was defined, and "good SBR" is also a subjective measurement. Something "good" at 14.5" may or may not be "good" at 10.5", and that may or may not be "good" at 7.5", but all are SBR's. I'll add in the 2024 burn rate chart, which will help objectively quantify the responses. As I mentioned earlier, powder type matters.  300blk uses powders that range from basically 65-74. Lil'Gun, H110, 296, 4227, 1680 and CFEBLK are all common. (Several of these are common for both .357 and .44 Magnum) 7.62x39 uses powders that often range from 77-85. 5.56 has a large range that could go from 79-123, although I think a lot sit in the 80-90's. .308 has a huge range as well. Roughly 99-130 Outside of Varget (113), 6.5 Creedmoor often uses powders in the 130's (well, Reloader 26 is 160) while 6.5 Grendel is roughly 91-118. Objectively, faster burning rifle powders are typically better suited for shorter rifle barrels since bore volume is reduced. How the subjective parts are balanced is the tough part. (Think 300 WinMag or 6.5 Creedmoor out of a 10" barrel. Plenty of power, but is that a "good" SBR that is efficiently using its slow burning powder charge?) |
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That burn rate chart is largely irrelevant for this discussion. The powder that gives best velocity in a 20” barrel for a given cartridge and projectile will likely do the same in a 10” one. For example, with 5.56, CFE223 and BLC2 give top velocities in both long and short barrels with 62gr projectiles, as I have tested. Doesn’t necessarily make them the best (though I like them). And some powders will only give slower velocities, as I have also tested in similar barrel lengths. Because most burn happens in the first few inches. Sure, different powders have different suitability levels for different cartridges, but you can’t reasonably make a decision like “I want a 9” Bbl, so that means I need to use H335, so that puts me into X, Y, or Z chamberings”. If that were the case, we’d all be using Bullseye-suitable cartridges in our SBRs. I’m not knocking that, and I favor pistol cartridges in pistol-length Bbls. But 5.56, Grendel, or .308 kicks the crap out of them in most performance measurements. As a sidenote, I’ve also found that chart to not work as expected for predicting flash, either. |
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Originally Posted By 1168RGR: That burn rate chart is largely irrelevant for this discussion. The powder that gives best velocity in a 20” barrel for a given cartridge and projectile will likely do the same in a 10” one. For example, with 5.56, CFE223 and BLC2 give top velocities in both long and short barrels with 62gr projectiles, as I have tested. Doesn’t necessarily make them the best (though I like them). And some powders will only give slower velocities, as I have also tested in similar barrel lengths. Because most burn happens in the first few inches. Sure, different powders have different suitability levels for different cartridges, but you can’t reasonably make a decision like “I want a 9” Bbl, so that means I need to use H335, so that puts me into X, Y, or Z chamberings”. If that were the case, we’d all be using Bullseye-suitable cartridges in our SBRs. I’m not knocking that, and I favor pistol cartridges in pistol-length Bbls. But 5.56, Grendel, or .308 kicks the crap out of them in most performance measurements. As a sidenote, I’ve also found that chart to not work as expected for predicting flash, either. But we are not changing powders based on barrel length. Those are already the powders native the cartridges, and those cartridges are already "optimized" at specific barrel lengths (or range). We are taking those cartridges, with those powders, and reducing the barrel lengths under 16 inches. That is where the cartridge efficiency (both objective and subjective) comes into play in regards to SBR's, although without a specific barrel length, it is a moving target. Cartridge Efficiency isn't raw power, it is power per grain, while trying to incorporate subjective factors. An 8" 308 might have +40% more energy at the muzzle than an 8" 300blk, but that 308 uses twice as much powder for +40% more energy and who knows how much increased muzzle blast and parts wear. That much "slower burning" powder in that little of barrel loses a lot of its native efficiency. A 16" .308 will have over 70% more energy than a 16" 300blk. As the barrel length (bore volume) increase, that 308 is making more efficient use of its larger and slower burning powder charge. For this discussion, it is the reason why many won't go shorter than 10.3" (11.5" actually seems to be new hotness) in 5.56, or shorter than 12" in Grendel, or shorter than 13" (many not going shorter than 16") in .308. There was a recent thread in GD asking that question. https://www.ar15.com/forums/General/Where-is-the-sweet-spot-the-point-of-diminishing-returns-on-a-short-308-barrel-/5-2833905/?page=2 But again, the list differs if we are talking about a 14" SBR vs a 7" SBR. It is also hard to quantify how much blast is too much blast or the action being to harsh since it would be a very subjective question. |
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