View Single Post
Old January 3, 2013, 06:56 PM   #65
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 3,878
Mythbustin some points, applauding others on Rainbow Demon's post. . . . .
Quote:
A great barrel in a suitable chambering will do you no good if the ammo isn't suited to the purpose. Bullet design being the first factor. Low drag bullets, boat tails in particular, allow the bullet to remain supersonic all the way to the target, this avoids transonic buffering or at least minimizes its affect, and reduces affect of cross winds. Flat base bullets may (be) and often are, more accurate at closer ranges (600 yards or less) than a boat tail of the same weight.
Applause, but with conditionss.

Any bullet fired fast enough will remain supersonic through 1000 yards. Boattailed ones of the same diameter, fundamental shape, construction and weight can do so with a bit less muzzle velocity.

Quote:
On the other hand. The old timers of pre WW1 did some excellent long range shooting with long heavy flat based round nosed bullets that most wouldn't consider suited to the purpose these days, and at rather modest velocities barely breaking 2K fps at the muzzle.
Applause, but more conditions.

The 40 to 45 caliber long black powder cartridges were popular in the late 1800's, but so were the .303 and .30-40 Krag in early Palma matches; both won their share of the medals. But the Palma match targets were huge; 3-foot square bullseye was worth 5 points and 10 feet wide overall. It was later changed to a round bullseye but still 36 inches, the 4 ring at 54 inches, the 3 point 72 inch square had 2 point 24 inch by 72 inch “wings” on each side. With the decreased wind drift of the 173-gr. FMJBT bullet, the 2-point rings were removed making targets only 6-feet wide enabling more firing points on a given range. And the 173's better accuracy caused so many unbreakable ties a tie-breaker ring, a 20" V ring was put inside the 36" 5 ring. This military “C” target was the NRA long range target until the early 1970's when changed to a 10 inch X ring, 20 inch 10 ring, 30 inch 9 ring, 44 inch bullseye 8 ring.... due to the increased numbers of unbreakable ties caused by .308's and .30-.338's used in long range matches.

Quote:
The 168 gr .30-06 AP bullet was considered pretty darn accurate at any range. The core was boat tailed but enclosed in a copper alloy cap seated in the base so it was effectively a flat base bullet, the steel core and copper plug did make this bullet much longer for its weight than other bullets in its class.
Applause...

Before the 30 caliber AP, tests at Daytona Beach (small arms ammo, not racing cars, but the same beach) in the 19-teens showed a new 30 caliber bullet was great at the longer ranges for accuracy and machine gun fire; it was a 173-gr. FMJBT bullet that went through a few shape changes. Standardized in the mid 1920 as the 30 caliber M1 bullet. Same bullet was used in match ammo starting in 1922 made by 2 or 3 arsenals and did very well indeed. The 1924 ammunition was one of the most accurate match cartridges ever made, giving a 600-yard mean radius of only 2.26 inches, a record that would last until 1962.

After WWII when the NRA and DCM resumed service rifle matches, military teams used good lots of 30 caliber AP ammo for competition. It shot more accurate at all ranges than the 150-gr. M2 ball bullet. However, some lots of AP were pretty bad; their steel cores were way off center. 30 caliber match ammo production with the 173-gr. FMJBT bullet did not resume until the late 1950's. Meanwhile, commercial match ammo from Winchester and Remington with 180, 190 and 200 grain boattail bullets were giving the arsenal match ammo a run for its money.

Quote:
There are boat loads of suitable actions out there, if properly set up. My friend liked to "blue print" actions. Major work done was in using a diamond coated wheel mounted in a bushing that mimicked the barrel shank, my friend used actual cut off barrel shanks from shot out barrels, to true up the locking lug seats in the receiver ring. The bolt lugs were then hand smoked and stoned for equal bearing and lapped in place. First proof round then finished up the mating of those surfaces. This seldom required removal of more than one thousandth of an inch from either surface, not enough to compromise a properly carburized layer.
Moderate mythbusting. . .

Most blueprinting of actions is a waste of time. But some folks believe it has to be done if best accuracy’s the objective. None of that total blueprinting’s been able to better what a pre-‘64 Win. 70 action, sloppy bolt fit and all, that only had its face squared up with the barrel tenon threads, bolt face squared up the the tenon thread axis and bolt lugs lapped to full contact. Many modern actions may equal it, but none’s bettered it as far as I know. As long as the action's parts are back in the same position for every shot, tight fit and near zero tolerance ain't needed.

Quote:
There are a number of factors governing flight of the bullet, which are seldom noticed at shorter ranges. Spin Drift is an example. The bullet spins at very nearly the same rpm at one thousand yards as it did at the muzzle, but because velocity has now fallen off greatly the effect of spin drift increases the further out the target.
Applause and mythbusting. . .

Yes, bullets have spin drift. But that doesn’t effect their accuracy. If the group’s 1 MOA to the right of the vertical bore axis, big deal; adjust your sights. Same thing if a constant wind’s blowing the group 2 MOA to the left; correct for it and shoot.

Quote:
A prime example of this effect is the .30-06 fired from the 1903 Springfield. A little understood phenomena was discovered. When the bullet left the muzzle there was a very slight but measurable jump to the left of the bore line. Since the Springfield rifling has a right hand twist spin drift worked to off set this jump by guiding the bullet ever so gently to the right.
Bullet path and bore line converged at around 600 yards, after which spindrift guided the bullet more and more to the right of the bore line. So spin drift had only a beneficial affect up to six hundred yards.
Probably mythbusting. . . .

I’ve never heard of a bullet jumping to the left caused by the rifling twist. And it's not traveled far enough for any spin drift to change its course. It’ll jump to the right if the heavy side of the bullet is at its top as the bullet exits; centrifugal forces work this way. They’ll go to the left if that heavy parts at the bottom on exit.

The .30-06's 173-gr. FMJBT bullet drifts about 8 inches at 1000 yards. So if the rifle’s zeroed at 600 yards, the bullets will be left of the LOS a few inches at about 400 yards and a few inches to the right at 1000 yards. Therefore the beneficial affect is good way past 600 yards. Doesn’t it apply if the bullets also to the right of the LOS?

Quote:
I believe the slight jump to the left was due to less support on the right hand side of the receiver due to the clearance for ejection to the right. This sort of flex is far more noticable with bolt actions that have rear lock up, usually cured by a front sight base off set to the left. When rear lock up and left hand twist are combined, with muzzle jump (bullet throw) and spin drift working together to send the bullet to the left of the bore line, as with the Lee Enfields, the off set of the front sight base is very noticeable. So I'd suggest only right hand twist barrels, unless you are using a lefthand action with ejection to the left.
More mythbusting. . .

This is news to me. Never heard of such a thing. But Creighton Audette proved some years ago that out of square case heads caused horizontal shot dispersion moreso than vertical with bolt actions with locking lugs in the vertical axis when in battery.

.303 SMLE’s and Metfords rear locking actions were such that they caused more barrel whip vertically than horizontally. Which is why they were favorites for long range matches. Slower bullets left when the bore axis was at a higher angle than faster ones that left at lower angles. At ranges past 600 yards, that compensated for the 80 fps muzzle velocity spread that cordite-loaded ammo had. This was proved over a hundred years ago.
__________________
US Navy Distinguished Marksman Badge 153
Former USA Palma Team Member
NRA High Power Long Range High Master
NRA Smallbore Prone Master

Last edited by Bart B.; January 3, 2013 at 07:46 PM.
Bart B. is offline  
 
Page generated in 0.05441 seconds with 7 queries