lysanderxiii
Member
It order to not clog up another thread, and be admonished again, I'll start my own.
Ball powder was a necessity brought about by the case volume and the energy density of available IMR propellants. In order to meet the velocity and pressure requirements, a certain energy density was required of the propellant. IMR 4475 lots with acceptable energy density had to be cherry picked for use in military ".222 Special" loads. This was fine for small lots required for test and evaluation, but such cherry picking was impractical for orders of upwards of half a billion rounds. This fact was plainly evident by the fact that no approved ammunition manufacturer would submit a bid on FY 64's 5.56mm ammunition requirement.
But, ball powder increased the cyclic rate. Yes, it did. This would have been hashed out had testing been done on the rifle-ammunition system, which is what both Colt and the Army suggested, however the OSD nixed additional testing.
Ultimately the newer heavier buffer design solved the cyclic rate problem. A new buffer was required for other reasons anyway. One, it did not absorb energy as design when dirty or corroded. Two, it caused bolt bounce and failure to fire in full automatic.
(As an aside, IMR 4475 was also used in 7.62mm ammunition, it was found to have excessive pressure variation, and poor temperature stability. In short, it was pretty much a failure as a propellant, that's why you don't see it on the store shelf.)
But, it was dirty and caused cases to stick. No, failures to extract were mainly the result of improper case hardness. If the case is too soft it will not retract after swelling due to the pressure, this can result in stiff extraction to a case stuck hard in the chamber. The first drafts of the 5.56mm ammunition specifications did not specify a case hardness gradient, nor a minimum head hardness requirement, and these values were left to "best commercial practices". .222 Remington, which is what .223 is based on was a bolt action case (name a semi-automatic chambered for .222 Remington in 1959-60), bolt actions are more forgiving in this regard.
But, it was dirty and clogged up the gas tubes. Yes, and no. This was only an issue with one or two lots. And, it took some time to accumulate to the point where it became a problem, 5,000 to 6,000 rounds. Further, Winchester, had studied this issue very early in the M16 development and recommended lot of WC846 made for 5.56mm loading have lower CaCO3 content. This low CaCO3 WC 846 would be spun off as WC 844 a few years later.
In short, WC 846 was the only viable propellant option, and that's why ball powder is still the primary propellant to this day, WC 844 in M193 and M855, an SMP 842 in M855A1. And, for all the stick powder fans out there, yes, the search for an acceptable alternate stick propellant for 5.56mm, IMR 8208 and CMR 170 were developed and accepted, but were never as popular with manufacturers.
Much of this information is in "The Black Rifle, M16 Retrospective", Stevens, B. R. and Ezell, E. C. Additional information comes from: "Bulk Density of Extruded Propellants for Small Caliber Ammunition," "Investigation of Gas Tube Fouling Characteristics of M193 Ball Cartridges in the M16A1 Rifle," "Investigation of Ballistic and Chemical Stability of 7.62mm Ammunition Loaded with WC 846 and IMR 4475 Propellant," "Special Test of 5.56mm Ammunition," "Product Improvement Test of Redesigned Buffer for the M16A1 Rifle."
1) Ball Powder
Ball powder was a necessity brought about by the case volume and the energy density of available IMR propellants. In order to meet the velocity and pressure requirements, a certain energy density was required of the propellant. IMR 4475 lots with acceptable energy density had to be cherry picked for use in military ".222 Special" loads. This was fine for small lots required for test and evaluation, but such cherry picking was impractical for orders of upwards of half a billion rounds. This fact was plainly evident by the fact that no approved ammunition manufacturer would submit a bid on FY 64's 5.56mm ammunition requirement.
But, ball powder increased the cyclic rate. Yes, it did. This would have been hashed out had testing been done on the rifle-ammunition system, which is what both Colt and the Army suggested, however the OSD nixed additional testing.
Ultimately the newer heavier buffer design solved the cyclic rate problem. A new buffer was required for other reasons anyway. One, it did not absorb energy as design when dirty or corroded. Two, it caused bolt bounce and failure to fire in full automatic.
(As an aside, IMR 4475 was also used in 7.62mm ammunition, it was found to have excessive pressure variation, and poor temperature stability. In short, it was pretty much a failure as a propellant, that's why you don't see it on the store shelf.)
But, it was dirty and caused cases to stick. No, failures to extract were mainly the result of improper case hardness. If the case is too soft it will not retract after swelling due to the pressure, this can result in stiff extraction to a case stuck hard in the chamber. The first drafts of the 5.56mm ammunition specifications did not specify a case hardness gradient, nor a minimum head hardness requirement, and these values were left to "best commercial practices". .222 Remington, which is what .223 is based on was a bolt action case (name a semi-automatic chambered for .222 Remington in 1959-60), bolt actions are more forgiving in this regard.
But, it was dirty and clogged up the gas tubes. Yes, and no. This was only an issue with one or two lots. And, it took some time to accumulate to the point where it became a problem, 5,000 to 6,000 rounds. Further, Winchester, had studied this issue very early in the M16 development and recommended lot of WC846 made for 5.56mm loading have lower CaCO3 content. This low CaCO3 WC 846 would be spun off as WC 844 a few years later.
In short, WC 846 was the only viable propellant option, and that's why ball powder is still the primary propellant to this day, WC 844 in M193 and M855, an SMP 842 in M855A1. And, for all the stick powder fans out there, yes, the search for an acceptable alternate stick propellant for 5.56mm, IMR 8208 and CMR 170 were developed and accepted, but were never as popular with manufacturers.
Much of this information is in "The Black Rifle, M16 Retrospective", Stevens, B. R. and Ezell, E. C. Additional information comes from: "Bulk Density of Extruded Propellants for Small Caliber Ammunition," "Investigation of Gas Tube Fouling Characteristics of M193 Ball Cartridges in the M16A1 Rifle," "Investigation of Ballistic and Chemical Stability of 7.62mm Ammunition Loaded with WC 846 and IMR 4475 Propellant," "Special Test of 5.56mm Ammunition," "Product Improvement Test of Redesigned Buffer for the M16A1 Rifle."
