"Accelerators in 30-06
Question:
You make a good argument, but I have my doubts. The accuracy problem with Accelerators may be due to the twist rate of the rifles, or just a flaw in the design, I don’t know. But I can’t see how the shock wave would have anything to do with it. If what you are saying is true, hyper-velocity varmint cartridges would be useless, as they would be too inaccurate to hit a small target at any long range. A friend has a 40XB in 220 Swift that will put 5 rounds into a dime sized group at 100 yards. The 220 Swift has essentially the same ballistics as the 30-06 Accelerator (actually the 220 is a little slower). I have a .17 Remington that shoots about .7 MOA, with 4100 fps. My .17 has 45% the mass, and the same velocity as the ‘06, BTW, the use for a bullet like this coming out of a high power rifle at such high speeds is hammering small targets a long way away, like prairie dogs, ground squirrels, crows, etc. I agree completely with your assessment of what happens when you shoot one of these in brush, the bullet goes to pieces, which is what they are supposed to do (varmints aren’t very thick). The results to a squirrel can be pretty spectacular. They also shoot very flat. My .17, zeroed at 50 yds, is 1.3" high at 150 yds, dead on at 250, and zeroed at 50 yards, will be dead on at 150, and almost 10" low at 300. As I understand it the shock wave is only an issue when the projectile slows below the speed of sound, which is why most match grade 22lr ammo is subsonic. Anyone else have any ideas? Tom — "Quemadmoeum gladius neminem occidit, occidentis telum est." ("A sword is never a killer, it’s a tool in the killer’s hands.") –Lucius Annaeus Seneca "the Younger" (ca. 4 BC-65 AD)
I don’t claim to be an expert on the subject but I do have some relative knowledge I may be able to add to this. A bullet traveling at 4000fps is also moving at 2,727 mile per hour. Since I believe the sound limit at sea level is around 727 miles per hour this is also mach 3.7 plus. The fact that the previous writer said the bullets hit 7 inches higher than where his heavier ones hit (assuming no changes made to his scope’ aimpoint) is not surprising. It is normal. The ballistic trajectory for a much lighter bullet moving faster is going to be higher than the heavier bullet moving slower for which the scope has already been "sighted in" for. The real issue here in regards to a serious lack of accuracy is the shock wave. A bullet moving close to mach 4 is going to have a hell of a shock wave. The less mass that the bullet has, the less it will be able to hold this shockwave stable. Changes in the slightest amount at all of any of the following will cause severe changes in rate of deceleration and possiblly induce tumbling: Pressure changes in the barrel such as from powder build up from the previous round. Exact amount of grains of powder. Air pressure changes due to wind, or temperature. Exact diameter and roundness of each bullet. The smaller the bullet mass the less it can sustain holding the shockwave the bullet is creating at high speeds. You have here the combination of a low mass bullet with a very high speed, i.e., a ridiculously high shock wave coming out of the muzzle. I am not surprised that the bullet does not hold tight groupings because anything that disturbs the shockwave can cause the bullet to start to wobble or tumble. This does not even cover the rate of spin from the riflings also being much higher and therefore having a higher rate of deviation one from another due to the slightest little deviation in actual surface contact. Nor does it cover that the 30-06 rifle barrel with the rifling twist rate it was given was never designed to cover such an extreme change from the original group of bullet types in a much heavier and slower weight range. I cannot say that I see much use for a bullet like this coming out of a high power rifle at such high speeds. Using it to hunt with in the brush may meet with very unpredictable results, Just hitting a leaf could cause it to tumble and shred itself and anything in front of it. This was a problem with the M16 in Vietnam. An 0.223 caliber 40 grain round coming out at 2800 to 3200fps hitting the foliage turned into a shredder instead of staying an accurate ballistic projectile. It often (but not always) ripped up the foliage and did not put a hole into the intended target a short distance behind the foliage. Reference "The Gun Digest Book of Assault Weapons", 3rd edition, The highest velocity I see in my "shooters bible" for normal bullets, not an accelerator round is 3140fps. This is 2142mph or mach 2.95. The mass to mach number ratio will be much higher of course as this is with 125 grain bullet instead of only 55. Using this simply as a relative scale the accelerator round has a 14.7 mass to mach number. The 125 grain bullet has 42.4 mass to mach number ratio. You will never see this printed in this manner. But a bullet moving at supersonic speeds has to obey those same laws of physics that rockets and missiles do, just on a much smaller scale. Maintaining flight accuracy and holding the shockwave stable around the bullet are not easy things to do. It certainly doesn’t get any easier trying to approach mach 4 with such a small projectile in thick air. Just my 2 cents worth.
Response:
I forget to save the posting, but I have seen some messages fly back and forth about the lack of accuracy of 55 grain bullets with a 30-06 shell behind it. The post’er said something about the bullet moving a 4000fps and being seven inches high compared to his normal hunting round bullets and having 6 inch groups??? I don’t claim to be an expert on the subject but I do have some relative knowledge I may be able to add to this. A bullet traveling at 4000fps is also moving at 2,727 mile per hour. Since I believe the sound limit at sea level is around 727 miles per hour this is also mach 3.7 plus. The fact that the previous writer said the bullets hit 7 inches higher than where his heavier ones hit (assuming no changes made to his scope’ aimpoint) is not surprising. It is normal. The ballistic trajectory for a much lighter bullet moving faster is going to be higher than the heavier bullet moving slower for which the scope has already been "sighted in" for. The real issue here in regards to a serious lack of accuracy is the shock wave. A bullet moving close to mach 4 is going to have a hell of a shock wave. The less mass that the bullet has, the less it will be able to hold this shockwave stable. Changes in the slightest amount at all of any of the following will cause severe changes in rate of deceleration and possiblly induce tumbling: Pressure changes in the barrel such as from powder build up from the previous round. Exact amount of grains of powder. Air pressure changes due to wind, or temperature. Exact diameter and roundness of each bullet. The smaller the bullet mass the less it can sustain holding the shockwave the bullet is creating at high speeds. You have here the combination of a low mass bullet with a very high speed, i.e., a ridiculously high shock wave coming out of the muzzle. I am not surprised that the bullet does not hold tight groupings because anything that disturbs the shockwave can cause the bullet to start to wobble or tumble. This does not even cover the rate of spin from the riflings also being much higher and therefore having a higher rate of deviation one from another due to the slightest little deviation in actual surface contact. Nor does it cover that the 30-06 rifle barrel with the rifling twist rate it was given was never designed to cover such an extreme change from the original group of bullet types in a much heavier and slower weight range. I cannot say that I see much use for a bullet like this coming out of a high power rifle at such high speeds. Using it to hunt with in the brush may meet with very unpredictable results, Just hitting a leaf could cause it to tumble and shred itself and anything in front of it. This was a problem with the M16 in Vietnam. An 0.223 caliber 40 grain round coming out at 2800 to 3200fps hitting the foliage turned into a shredder instead of staying an accurate ballistic projectile. It often (but not always) ripped up the foliage and did not put a hole into the intended target a short distance behind the foliage. Reference "The Gun Digest Book of Assault Weapons", 3rd edition, The highest velocity I see in my "shooters bible" for normal bullets, not an accelerator round is 3140fps. This is 2142mph or mach 2.95. The mass to mach number ratio will be much higher of course as this is with 125 grain bullet instead of only 55. Using this simply as a relative scale the accelerator round has a 14.7 mass to mach number. The 125 grain bullet has 42.4 mass to mach number ratio. You will never see this printed in this manner. But a bullet moving at supersonic speeds has to obey those same laws of physics that rockets and missiles do, just on a much smaller scale. Maintaining flight accuracy and holding the shockwave stable around the bullet are not easy things to do. It certainly doesn’t get any easier trying to approach mach 4 with such a small projectile in thick air. Just my 2 cents worth.
