11-30-2020, 11:19 PM
I have followed both the Grendel and the SPC since they were introduced. Since the intense rivalry and mud-slinging between the two cartridges has abated somewhat, I thought it might be useful to give a "current day" comparison.
The Grendel has a shorter case and the same overall loaded length, which allow it to use longer, high BC bullets. This gives it the edge when shooting long distance. Both cases hold similar volumes of powder. The Grendel seems to gain relatively more velocity from longer barrels. The SPC has a slightly larger bore diameter and uses slightly higher pressures so it often has slightly higher muzzle velocity given same weight bullet and same length barrels (18" and shorter). In short, the 6.8 SPC and the 6.5 Grendel are pretty close in performance at typical hunting distances (of up to 300 yards or so). For general hunting and plinking, they both work well. The smaller diameter base and thicker walls of the SPC case permit it handle higher pressures before damage to the brass occurs. If my memory serves (not a sure thing), the SPC can be loaded routinely to about 58K psi with good brass life. Bolt life has been a non-issue.
The SPC had much worse teething problems than the Grendel. Remington sent a flawed drawing to SAAMI. First, there is a math error in the SAAMI chamber drawing (numbers transposed on a dimension) for the step-down from the neck to the freebore.* This was exacerbated by errors in a lot of PTG reamers that made this angle closer to 80 degrees than the intended 45. This increased chamber pressure and sometimes even shaved brass from bullets. The SAAMI freebore length is also shorter than what had been used in the prototypes, causing Remington to download its ammo. In the mid-to-late 2000's, a large number of out-of-spec barrels (undersized bore) were produced and this further exacerbated the pressure problems caused by the chamber flaws. These were mostly 1-in-10" twist, 6-groove barrels, so there is myth that only slower twist barrels can be used. Despite this 1-in-10" myth being commonly repeated, many of the barrels currently sold by Bison Armory are chambered in 1-7" to allow them to shoot subsonic loads better. They have no pressure issues.
All of these 6.8 SPC problems have led to several variations of chambers being currently available. All of them are fine with current factory ammo. The first "SPC II" chamber simply lengthened the freebore from the SAAMI 0.059" to 0.100". Later "SPC II" variants fixed the sharp angle problem AND used the longer freebore. These are the chambers that are often used with longer than SAAMI length loads. Several companies have now reduced the freebore to something between SAAMI and SPC II to provide better velocity and accuracy with factory ammo. These include Bison Armory and ARP. ARP barrels tend to be faster than average, possibly due to their increased groove-to-land ratio causing less bullet distortion.**
* the note on the SAAMI drawing says the angle should be 45 degrees, but transposed numbers in the dimensions make it significantly steeper and thus sharper at the beginning of the freebore.
** BTW, although a 50/50 groove-to-land ratio is often seen in the US, a larger ratio is not terribly unusual. For example, my Russian Saiga 7.62x39 has relatively narrow lands and is probably closer to 70/30.
The Grendel has a shorter case and the same overall loaded length, which allow it to use longer, high BC bullets. This gives it the edge when shooting long distance. Both cases hold similar volumes of powder. The Grendel seems to gain relatively more velocity from longer barrels. The SPC has a slightly larger bore diameter and uses slightly higher pressures so it often has slightly higher muzzle velocity given same weight bullet and same length barrels (18" and shorter). In short, the 6.8 SPC and the 6.5 Grendel are pretty close in performance at typical hunting distances (of up to 300 yards or so). For general hunting and plinking, they both work well. The smaller diameter base and thicker walls of the SPC case permit it handle higher pressures before damage to the brass occurs. If my memory serves (not a sure thing), the SPC can be loaded routinely to about 58K psi with good brass life. Bolt life has been a non-issue.
The SPC had much worse teething problems than the Grendel. Remington sent a flawed drawing to SAAMI. First, there is a math error in the SAAMI chamber drawing (numbers transposed on a dimension) for the step-down from the neck to the freebore.* This was exacerbated by errors in a lot of PTG reamers that made this angle closer to 80 degrees than the intended 45. This increased chamber pressure and sometimes even shaved brass from bullets. The SAAMI freebore length is also shorter than what had been used in the prototypes, causing Remington to download its ammo. In the mid-to-late 2000's, a large number of out-of-spec barrels (undersized bore) were produced and this further exacerbated the pressure problems caused by the chamber flaws. These were mostly 1-in-10" twist, 6-groove barrels, so there is myth that only slower twist barrels can be used. Despite this 1-in-10" myth being commonly repeated, many of the barrels currently sold by Bison Armory are chambered in 1-7" to allow them to shoot subsonic loads better. They have no pressure issues.
All of these 6.8 SPC problems have led to several variations of chambers being currently available. All of them are fine with current factory ammo. The first "SPC II" chamber simply lengthened the freebore from the SAAMI 0.059" to 0.100". Later "SPC II" variants fixed the sharp angle problem AND used the longer freebore. These are the chambers that are often used with longer than SAAMI length loads. Several companies have now reduced the freebore to something between SAAMI and SPC II to provide better velocity and accuracy with factory ammo. These include Bison Armory and ARP. ARP barrels tend to be faster than average, possibly due to their increased groove-to-land ratio causing less bullet distortion.**
* the note on the SAAMI drawing says the angle should be 45 degrees, but transposed numbers in the dimensions make it significantly steeper and thus sharper at the beginning of the freebore.
** BTW, although a 50/50 groove-to-land ratio is often seen in the US, a larger ratio is not terribly unusual. For example, my Russian Saiga 7.62x39 has relatively narrow lands and is probably closer to 70/30.