If your goal is efficient use of a short barrel, yes, the shorter the bullet the faster it accelerates (assuming you make a powder loading with that in mind) 350 legend does it even better, but at the sacrifice of performance past ~200-250 meters.
Follow along:
The acceleration of a projectile is a function of the pressure on the base of the projectile divided by it's mass. If the area of the projectile (read: the diameter) goes up faster than the mass of the projectile (in this case: the length, because bullets are made of lead and copper they don't vary greatly in density) the acceleration is greater. This assumes that the pressure doesn't change, which is pretty reasonable because cartridges have max pressures.
So wider, shorter bullets accelerate faster than longer thinner bullets, given a limited chamber pressure.
a 123 grain x39 bullet has a sectional density of .183, a 110 grain bullet has an SD of .166 and .196 at 130 grain (highest weight my reloading manual goes to)
5.56 has a sectional density of .196 at 69 grains and .219 at 77 >3x as much weight
Maybe subsonics, but I'm not going to imply that you think that subsonic 5.56 is a good idea.
homie all I care about is when I pull the trigger and it goes booms! What bullets are better and what ones are not? Its simple stuff a no scinece needed
It depends on the application and bullet construction. 7n6 has an air pocket/steel 'clacker' that causes the bullet to tumble and fragment upon impact. 5.56 relies on velocity to achieve it's fragmentation effect. In the real world there are many instances where 5.56 performs well out of shorter barrels. Bullet weight plays a role as well, heavier bullets etc.
300 BLK and 7.62x39 rely on mass to do their damage. It doesn't need to get to a certain speed, it just fhwacks into the target and does it's thing, provided shot placement is on point.
>Is it true that 7.62x39 and 300blk are better than 5.56 and 5.45 for SBRs?
They would perform better, yes, as they use heavier projectiles and can thus make up some for the loss of velocity. .300BLK outright gets a full burn from a relatively short barrel, so you don't actually get much benefit from going past a certain length.
>If so, why do Russians use AKS74U and not AKMSU?
Standardizing on one cartridge. But also, they actually don't, the AKS-74u is not used very widely because the range and ballistic performance has been found to be lacking (mind, this gun has an even shorter barrel than something really short like the American Mk.18 carbine). It does get issued sort of, but not very widely, all the regular grunts and doorkickers usually prefer an AK-74M or AKS-74 because it has much better range and terminal ballistics (and also doesn't have as an obnoxiously loud and concussive report which is almost worse for people standing next to you).
IIRC the people who get issued the AKS-74u the most often are helicopter pilots, ergo people who don't get involved in infantry combat unless something has gone really wrong.
Perhaps he meant a hypothetical one, there does exist short 7.62mm AKs which would basically fit that description, even if the Red Army/Russian Army themselves never adopted anything of that spec or with that designation.
>why do Russians use AKS74U and not AKMSU
Besides the obvious that AKMSU doesn't exist (AK-104 is an approximation), the soviet union wanted to get behind a single caliber for all infantry rifles and LMG's for simplified logistics.
Never mind the fact it made the AKS-74U a pile of shit.
Yeah because (in very simple terms) heavier bullets can use their momentum to somewhat make up for what's lost in muzzle velocity and spin for accuracy and effective range, greater mass means more inertia throwing the bullet down range.
>Why does AKS-74U use 5.45?
Because by the time the Soviets decided they wanted a PDW, the AK-74 was already in service and the future of logistics and they didn't want to complicate things by keeping 7.62x39mm in stock. As it's a defensive weapon for vehicle crews, ballistics outside of 200m probably wasn't the main concern compared to keeping it small and incurring no burden on logistics.
The gun was intended to be used by vehicle crews or other people whose primary task wasn’t to fight with a rifle, so the lighter cartridge, already part of the normal infantry logistics chain makes sense in spite of worse performance, though some special forces would use it later. When the Russians made the Groza, which was more of a special use weapon for combat (and intended to replace the 74u among certain forces), they did make a variant in 7.62 but didn’t pursue the 5.45 one very far, likely due to a higher emphasis on performance.
Is 7.62x39mm or 5.45x39mm the better round? The reason I ask is even Russia cannot make up their fricking mind and deploys both rounds. They also seem to perform the same against a soft target unlike 5.56.
Do they even still use the AKS-74U? I was under the impression the invention of 9x39 and guns that fire it means it pretty much isn't anything more than a legacy weapon.
They basically never used the aks-74u for much beyond photo ops and some very limited security/Leo tasks if we're excluding people who were never expected to shoot their gun.
There's been a number of Afghan memoirs published where they directly point out it's trash but they liked it for photos.
I think the AK-105 has mostly took over its role, but there’s probably still some of them floating around. 9x39 is mostly superior than 5.45 out of short barrels and at closer range, but 5.45 is just easier to deal with logistically, and most people who need a smaller, handier weapon (barring special forces) probably don’t care as much about the performance of their gun.
If your goal is efficient use of a short barrel, yes, the shorter the bullet the faster it accelerates (assuming you make a powder loading with that in mind) 350 legend does it even better, but at the sacrifice of performance past ~200-250 meters.
What the frick am I reading
Follow along:
The acceleration of a projectile is a function of the pressure on the base of the projectile divided by it's mass. If the area of the projectile (read: the diameter) goes up faster than the mass of the projectile (in this case: the length, because bullets are made of lead and copper they don't vary greatly in density) the acceleration is greater. This assumes that the pressure doesn't change, which is pretty reasonable because cartridges have max pressures.
So wider, shorter bullets accelerate faster than longer thinner bullets, given a limited chamber pressure.
7.62x39 is not shorter than 5.56 or 5.45. it's nearly triple the weight as well.
a 123 grain x39 bullet has a sectional density of .183, a 110 grain bullet has an SD of .166 and .196 at 130 grain (highest weight my reloading manual goes to)
5.56 has a sectional density of .196 at 69 grains and .219 at 77
>3x as much weight
Maybe subsonics, but I'm not going to imply that you think that subsonic 5.56 is a good idea.
homie all I care about is when I pull the trigger and it goes booms! What bullets are better and what ones are not? Its simple stuff a no scinece needed
there is it, the most confidently wrong post ive ever seen on this site
They allow for a shorter barrel but they do not tumble as much so it depends on what you mean by better
Because it doesn't make sense to have 2 different calibers logistically
Depends how SB your R is.
7.62x39 and 300blk perform very well out short barrels like 12.5 and shorter. They have mean punch to it, but won't tumble as much tho
It depends on the application and bullet construction. 7n6 has an air pocket/steel 'clacker' that causes the bullet to tumble and fragment upon impact. 5.56 relies on velocity to achieve it's fragmentation effect. In the real world there are many instances where 5.56 performs well out of shorter barrels. Bullet weight plays a role as well, heavier bullets etc.
300 BLK and 7.62x39 rely on mass to do their damage. It doesn't need to get to a certain speed, it just fhwacks into the target and does it's thing, provided shot placement is on point.
Ammunition/parts commonality with the current main service rifle.
>If so, why do Russians use AKS74U and not AKMSU?
because the AKMSU doesn't exist? learn some shit you dumbass
>Is it true that 7.62x39 and 300blk are better than 5.56 and 5.45 for SBRs?
They would perform better, yes, as they use heavier projectiles and can thus make up some for the loss of velocity. .300BLK outright gets a full burn from a relatively short barrel, so you don't actually get much benefit from going past a certain length.
>If so, why do Russians use AKS74U and not AKMSU?
Standardizing on one cartridge. But also, they actually don't, the AKS-74u is not used very widely because the range and ballistic performance has been found to be lacking (mind, this gun has an even shorter barrel than something really short like the American Mk.18 carbine). It does get issued sort of, but not very widely, all the regular grunts and doorkickers usually prefer an AK-74M or AKS-74 because it has much better range and terminal ballistics (and also doesn't have as an obnoxiously loud and concussive report which is almost worse for people standing next to you).
IIRC the people who get issued the AKS-74u the most often are helicopter pilots, ergo people who don't get involved in infantry combat unless something has gone really wrong.
Perhaps he meant a hypothetical one, there does exist short 7.62mm AKs which would basically fit that description, even if the Red Army/Russian Army themselves never adopted anything of that spec or with that designation.
Learn some shit dumbass. Wasn't made by Russia but it does exist.
those rounds are better for short barrels, but short barrels are better for being a homosexual
>why do russians use x
who cares
what's the dwell time on that
>why do Russians use AKS74U and not AKMSU
Besides the obvious that AKMSU doesn't exist (AK-104 is an approximation), the soviet union wanted to get behind a single caliber for all infantry rifles and LMG's for simplified logistics.
Never mind the fact it made the AKS-74U a pile of shit.
Yeah because (in very simple terms) heavier bullets can use their momentum to somewhat make up for what's lost in muzzle velocity and spin for accuracy and effective range, greater mass means more inertia throwing the bullet down range.
>Why does AKS-74U use 5.45?
Because by the time the Soviets decided they wanted a PDW, the AK-74 was already in service and the future of logistics and they didn't want to complicate things by keeping 7.62x39mm in stock. As it's a defensive weapon for vehicle crews, ballistics outside of 200m probably wasn't the main concern compared to keeping it small and incurring no burden on logistics.
The gun was intended to be used by vehicle crews or other people whose primary task wasn’t to fight with a rifle, so the lighter cartridge, already part of the normal infantry logistics chain makes sense in spite of worse performance, though some special forces would use it later. When the Russians made the Groza, which was more of a special use weapon for combat (and intended to replace the 74u among certain forces), they did make a variant in 7.62 but didn’t pursue the 5.45 one very far, likely due to a higher emphasis on performance.
I think the main Groza variant uses 9x39mm for greater penetration in a subsonic round at PDW ranges.
The 7.62 model is adopted by some groups, it has benefits like better range than 9x39, cheaper price and higher capacity.
i like the 74u bc its a sick gun from stalker and more aesthetic than a full size ak
It's a cool gun, but a full-sized milled AK is a thing of beauty.
I remember hearing some Russian dudes didn't like the shorter one.
Is 7.62x39mm or 5.45x39mm the better round? The reason I ask is even Russia cannot make up their fricking mind and deploys both rounds. They also seem to perform the same against a soft target unlike 5.56.
Out of a long barrel 5.45 is definitely better unless subsonic.
Do they even still use the AKS-74U? I was under the impression the invention of 9x39 and guns that fire it means it pretty much isn't anything more than a legacy weapon.
They basically never used the aks-74u for much beyond photo ops and some very limited security/Leo tasks if we're excluding people who were never expected to shoot their gun.
There's been a number of Afghan memoirs published where they directly point out it's trash but they liked it for photos.
I think the AK-105 has mostly took over its role, but there’s probably still some of them floating around. 9x39 is mostly superior than 5.45 out of short barrels and at closer range, but 5.45 is just easier to deal with logistically, and most people who need a smaller, handier weapon (barring special forces) probably don’t care as much about the performance of their gun.
You cant improve perfection.