The Firing Line Forums - View Single Post - 6mm-06, .25-06, or .25-05 Ackley Improved

Herodotus · January 14, 2001, 12:25 AM

I think Art is on the right trail here.
As I see it, the main problem is that all these cartridges are based on the old 30/06 necked down (270 Win. & 6mm/06) and in addition blown out (25/06 Improved & 243 Catbird??).
Now some people would hold that the original 30/06 is "over bore" to begin with: It holds more powder than is optimal for ideal ignition and the increase in velocity achieved over shorter cases is not proportional to the amount of powder burned.
Being that the original 30 caliber bullet is slightly over bore in this case (not a bad thing in and of itself), the problem gets worse and worse as you neck down to smaller and smaller bullets and in addition blow out the taper for even more capacity. Since the ignition is not ideal to begin with, at some point it gets pretty bad and you begin to eat up barrels pretty bad. It is entirely possible that at some point you begin to loose top fight accuracy because of this after what seems to be absurdly few rounds.
But what do we mean by top flight accuracy? I remember, but cannot reference off the top of my head, reading that one of the bullet manufacturers figured out about how long they could expect a top flight barrel to last for the purposes of accuracy testing of bullet lots. They tested and recorded accuracy data on a couple of well known barrel brands in factory testing of 308 bullets fired in the 308 Win cartridge, a round much praised as being well balanced and definity not "Over Bore". They concluded that accuracy began to be measurably affected after about 4,000 rounds in all the brands. They were getting something like 3/8" five round groups at 100 yds before 4,000 rounds out of their machine rest heavy barrel test rifles and after that things began to open out a bit. Thats accuracy that most of us can only deam about in our more practical rifles, but I would take that as top flight accuracy and about all you can expect with the most efficient of cartridges.
So perhaps 1500 rounds is not too high a price to pay if you must have something that is really hot. And the rifle will still no doubt be quit good and usable long after this peak performance has come and gone. If it gets to be too bad, then you just have to rebarrel the thing, so don't invest in fancy engraved barrels, just good plain ones.

January 14, 2001, 12:25 AM	#5
Herodotus Senior Member Join Date: January 19, 2000 Posts: 743	I think Art is on the right trail here. As I see it, the main problem is that all these cartridges are based on the old 30/06 necked down (270 Win. & 6mm/06) and in addition blown out (25/06 Improved & 243 Catbird??). Now some people would hold that the original 30/06 is "over bore" to begin with: It holds more powder than is optimal for ideal ignition and the increase in velocity achieved over shorter cases is not proportional to the amount of powder burned. Being that the original 30 caliber bullet is slightly over bore in this case (not a bad thing in and of itself), the problem gets worse and worse as you neck down to smaller and smaller bullets and in addition blow out the taper for even more capacity. Since the ignition is not ideal to begin with, at some point it gets pretty bad and you begin to eat up barrels pretty bad. It is entirely possible that at some point you begin to loose top fight accuracy because of this after what seems to be absurdly few rounds. But what do we mean by top flight accuracy? I remember, but cannot reference off the top of my head, reading that one of the bullet manufacturers figured out about how long they could expect a top flight barrel to last for the purposes of accuracy testing of bullet lots. They tested and recorded accuracy data on a couple of well known barrel brands in factory testing of 308 bullets fired in the 308 Win cartridge, a round much praised as being well balanced and definity not "Over Bore". They concluded that accuracy began to be measurably affected after about 4,000 rounds in all the brands. They were getting something like 3/8" five round groups at 100 yds before 4,000 rounds out of their machine rest heavy barrel test rifles and after that things began to open out a bit. Thats accuracy that most of us can only deam about in our more practical rifles, but I would take that as top flight accuracy and about all you can expect with the most efficient of cartridges. So perhaps 1500 rounds is not too high a price to pay if you must have something that is really hot. And the rifle will still no doubt be quit good and usable long after this peak performance has come and gone. If it gets to be too bad, then you just have to rebarrel the thing, so don't invest in fancy engraved barrels, just good plain ones.