I have intently read the last post on bullet runout. Since I have been off work over Christmas vacation, I have had some time to play in the garage a little bit.
First thing I did was to build my own Runout Guage. Built from odds & ends ranging from my fathers dial indicator from the 60's to my son's errector set that I just bought him for Christmas.
Here are Pics of my Runout Guage:
Ok, Don't Laugh, I'm sure there must be a clause against it somewhere on this site!
I started with my older sons old skate board wheel bearings, 5 of them. I happened to have a rod that fit the center of the bearing perfectly. I spaced the 4 bearings with nuts, that also fit the rod just right. This allows the case body to rotate or spin, without moving (better than a v-block in my opinion). The 5th bearing is used as a hard stop for the back of the case.
I then drilled a hole for the Dial Indicator Post (smaller than post dia). Post is press fit into 2 3/4" thick wooden block (left over from front door project)(all rods are press fit into wood). Now I had my guage ready to work. You could spin it by hand but had to be careful to apply steady even pressure on back of case as you rotated it. I improved this by stealing a few components from my youngest sons's errector set. This became the spring loaded pressure arm which presses the case into the roller bearings and angled to apply pressure against the 5th hard stop brg. I can now easily turn the pink wheel to make the bullet rotate in the guage with constant spring pressure.
It works really well, I put the indicator on the bearings to make sure they ran true, and they do!
RESULTS OF CHECKING LOADED CARTRIDGES: "TIR = total indicator reading"
I checked my .270Wby cartridges that I load for my Kirby chambered .270Wby Mag. I found that my bullets were out of round from .0005 (almost perfect) to .006 (worst case).
Some intersting results from testing:
I checked the Neck runout on brand new .270Wby weatherby brass. Most of of the cases were almost perfect with the worst being .0005 TIR. I then put the near perfect cases thru my Forester full length die with expander button removed. What I found surprised me. After coming out of the die, the necks could be misaligned and gave a .001 TIR. But not every time, only some of the time. I tried the 1/4 turn method as you go thru the neck, but still could deform the neck by .001.
I then sorted out the cases that had necks that were no more that .0005 out of round with the case body. I loaded bullets (140 gr. Accubonds) into these cases using a Forester Ultra Micrometer bullet seating die and took measurements. Again I was very surprised. Some of the bullets seated perfectly with no more than .0005 TIR, but others showed as much as .006 TIR.
I contemplated and looked inside the die. Insid the die the it looks like the chamber is designed to fit the case and guide it perfectly. But their is nothing that fits around the bullet to align it to the neck. In other words what ever the wall thickness of your neck (in my case .014 x 2 = .028). So the bullet can flop around .028 within the bullet seater die. Add to it the clearance necessary to allow the spring loaded sleeve to slide and that number increases. Now you may say, doesn't the seater cone center the bullet. Well yes but only to a small degree. The seater cone is designed to be universal to a bunch of different bullet styles and there fore cannot match every bullet perfectly. And even if it did, it is not set in a precision aligned bore. More likely it's designed to float so it can conform to the hole in the neck.
So where do we go from here? [img]/ubbthreads/images/graemlins/crazy.gif[/img]
I tried to seat some bullets with an old RCBS bullet seater and got slightly better concentricity then the Ultra Micrometer Seater Die. Reason = Removal of extra clearance that allows the spring loaded sliding chamber to move.
FROM HERE WE GO TO SEPARATING OUT THE PERFECTLY CONCENTRIC LOADED CARTRIDGES FROM THE OUT OF ROUND CARTRIGES. TAKE THEM TO THE RANGE, TEST FIRE AND RECORD RESULTS:
Rifle's used: .270Wby deep fluted Heavy barrel, by Rock Creek "5R" Smithed by Kirby, in a Bell & Carlson Stock.
Second rifle, .257Wby Action with my old .270Wby 24" stock barrel slapped on in Laser Mark Stock.
Pics of target with orange bulls were shot with Heavy barreled rifle.
1. (no fouling shot) Upper Left, .63" group, TIR=.0005 Load=7828-69.5, 140Accubond
2. Upper Right, .9" group, TIR=.0005
Load=identical to above
3. Lower Left, .56" group, TIR=.004-.005
Load=H1000-72.5, 140 ballistic tip
4. Lower Right, .375" group, TIR=.001
Load=IMR7828-70.2, 135 SMK
CONCLUSION: Meichele is correct, No other sport is frustrating enough!!
It did not seem to make a big difference to accuracy in my case, at least not at 100 yard range.
Now we need to ask why?
Well, what happens when a bullet hits the barrel when it is not perfectly aligned with the bore. Now this is just my theory! The bullet gets shaved or deformed on one side, by the amount that it is out of alignment.
What does this do?: Nothing intitially. The bullet gets squeezed/swaged into the bore (gasses should be sealed behind bullet). Once the bullet leaves the bore, it may now be lighter on one side by the amount shaved off. As the bullet spins it stabilizes as it flies. If however, it is lighter on one side than the other (out of ballance) it may begin to gyrate and it may depart from its original trajectory. This may not be evident at 100 yards, but it may be much more prominent at say 600 yards. Again I am speculating.
Now here is the target from my other .270Wby with 24" barrel:
Here you see that the barrel likes 2 loads a lot better than the other 2 shown.
1. Upper Left, 2.63 group, shot-1=.0005 TIR, shot-2=.002 TIR, shot-3=.006 TIR.
Load=7828-68.5, 150 SST
2. Upper Right, .81 group, shot-1=.002 TIR, shot-2=.002 TIR, shot-3=.005 TIR
Load=7828-68.5, 150 Speer boat tail
3. Lower Left, 1.06 4 shot group, shot-1=.002 TIR, shot-2=.003 TIR, shot-3=.005 TIR, shot-4=.007 TIR
Load=7828-73.5, 140 TSX
4. Lower Right, 2.56 group. This bullets were the exact same bullets with .001 TIR that shot excellent in the other rifle.
Conclusion: Barrel harmonics/powder charge, bullet type & weight may have more to do with accuracey than bullet concentricity. And I'm tired of typing [img]/ubbthreads/images/graemlins/tongue.gif[/img]