DAMAGED BULLET ACCURACY
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- Last Post 01 February 2018
Winchester M54. 30WCF, 30X Lyman STS
The load is:
314299 "No Dot", GC Alox lube, WLP, 12.5/AA#9, LOA 2.845"
"Perfect" bullets, Hard, cast 2/3/07, 199.4-200.2 gr., sized .309"
- 1/2 grain bullets, same as above but 1/2 grain filed off as shown
-.2 grain bullets, cast 3/9/07, 194.7-195.0 grains, sized .312"
On Wednesday, May 16, 2007 I shot these test "filed-side" bullets at 100 yards, 2 foulers and 2 5-shot groups per 15 minute relay, alternating between the 3 test loads. Groups measured to the nearest .025" with a plastic ruler with .1" increments.
I repeated the tests on 5/23/07 and 6/20/07. Here is a table showing the results of the tests:
PERFECT FILED .2 GR. FILED .5 GR.
5/16/07 1.400 2.200 .950
5/16/07 1.500 1.350 2.750
5/16/07 1.950 1.200 1.175
5/16/07 1.475 1.950 3.150
5/16/07 1.825 1.275 2.500
AVERAGE 1.630 1.595 2.105
5/23/07 1.300 .900 1.750
5/23/07 1.700 1.750 1.300
5/23/07 2.000 1.300 1.250
5/23/07 2.100 2.150 2.050
5/23/07 1.800 2.050 1.150
AVERAGE 1.780 1.630 1.500
6/20/07 1.450 1.900 2.400
6/20/07 1.950 1.975 2.050
6/20/07 1.450 1.750 2.450
6/20/07 2.350 1.350 2.425
6/20/07 1.750 2.800 1.250
AVERAGE 1.790 1.955 2.115
GRAND
AVERAGE 1.733 1.727 1.907
Group sizes were measured with a plastic ruler graduated in tenths of an inch.
Resolution of group size was to .025" increments. All three-place decimals were formatted for consistency and ease of reading.
These three sets of groups were shot on three different days under three different sets of conditions.
If the grand averages are an indication of the process, then there is no "real" difference in group size for groups shot with "perfect" bullets and bullets with .2 grain round-filed off; and there may not be a "real" difference in groups shot with perfect bullets and bullets with .5 grain round-filed off.
In order to confirm that there is a difference in accuracy between "perfect" and ".5 grain" bullets, with 90% confidence, 28 groups with each bullet would be required. For 95% confidence, 47 groups, each, would be required. Now these groups should be shot with bullets, powder, etc. from the same lots, under the same conditions. I'm not going to do it, and suggest that the results of this test can be summarized as follows:
"In gun/load/etc. systems with capability to shoot 100 yard groups averaging 1.75" or greater, filed grooves on the sides of the bullets of up to .5 grain simulating holes only slightly increase average group size."
Note: A lead sphere .05" in diameter weighs .2 grains, .a 07" diameter sphere weighs .5 grains. These are pretty big holes or bubbles to imagine in the bullets.
Attached Files
DAMAGED 22 RIMFIRE BULLETS
Here’s a picture of 22 RF bullets with .3 grain filed off.
Cartridges were prepared with .1 and .3 grains filed off with a triangular file.
On 6/27/2007, Model 12/15 BSA Martini, Lyman STS 30X, 50 yards, windy and starting to rain in fits.
Perfect, .1 grain filed, .3 grains filed ammunition.
This gun, like the rest, loves Eley Match ammunition.
I was going to file some Eley Match Red Box, I had the file in one hand and the first cartridge in the other, but a force stronger than I, (and I am enormously strong), kept me from touching that Eley cartridge with the file.
I was able to file the PMC Match Rifle, this ammunition works well in this gun.
Group sizes, leaded edge to leaded edge - .244", all in " (pp)
Perfect -.1 gr. -.3 gr.
.433 . 473 .353
.382 .564 .324
.439 1.294 .394
.419 .732 .546
.547 .443 .910
Avg. Avg. Avg.
.444 .699 .505
Attached Files
"In gun/load/etc. systems with capability to shoot 100 yard groups averaging 1.75" or greater, filed grooves on the sides of the bullets of up to .5 grain simulating holes only slightly increase average group size."
I concur if the velocity/RPM of the load is held to the lower end as the test load.
The .2 gr damage falls within that ES and is thus fairly inconsequential as your test shows. However, since the "perfect" bullets have a .9 gr ES in weight and the .5 gr filed off portion weighs less than or is about equal to that ES we do see larger groups. Not much larger given the closeness of the "damage" to the ES of the "perfect" bullets but enough to make a point.
If we are seeking to improve accuracy for CBA matches lets look at the groups sizes in that context. Given CBA matches are shot for score and group size (matches I shoot in are mostly just for score) the "perfect" bullet loads accuracy is hardly competitive at all in BR competition.
Assuming wind and humidity no worse than when the test was done the "perfect" bullet group average shows only 7 groups barely 9 ring capable on the CBA score target. Eight of the 15 groups would be only 7 and 8 ring capable. Of the 15 groups with the .5 defect only 2 groups would be 9 ring capable and the other 13 groups are only 6 to 8 ring capable.
Since many here rely on statistical analysis of CBA stats for "proof" and the question seemingly is "why isn't accuracy improving in CBA competition" it seems to me assuming the "real" results from this test are very misleading.
Better testing would be taking "perfect" bullets of one weight and then comparing the purposely damaged bullets accuracy against those. I believe that is what I was asked to do? Also looking at CBA stats I see the velocities are more into the 1600 - 1900 fps range out of 10" twist barrels primarily. That increased velocity/RPM over the test here increases the adverse affect on accuracy any imbalance/defect/damage will have. As the velocity increases so does the centrifugal force which is what act upon and thus causes the inaccuracy with unbalanced bullets. That means any imbalance with have a greater adverse affect on accuracy.
I also find it rather disconcerting in studying CBA match results to find,with the availability of chronographs the last 20+ years, that "estimated" velocities are accepted in CBA matches, especially regional and national matches.
Frankly joeb, if we accept your assumption/opinon that a .5 gr imbalance "only slightly increase average group size" and thus choose to ignore that consequence is it no wonder we aren't improving accuracy?
My purpose for this post is to only assist us in understanding what is really happening and how we may improve accuracy instead of just accepting what always has been.
LMG
Concealment is not cover.........
Attached Files
Maybe I'll look for another M54, made in 1928, that might shoot better. Bill McGraw has it now. Watcha got here is DATA, and summary/opinion. I'm sure we all have opinions. I'd be happy to have other summary/opinion based on this, or any, data.
Chronographs and estimated velocities. My magnetospeed chronograph is showing s.d. unlike most I saw or have read about. I'm beginning to think that just maybe the skyscreen chronograph may not tell the truth about s.d.
(The Standard Deviation and Extreme Spread are both estimates of Standard Deviation; E.S. is normally called "Range". Range is frequently used by the Quality Assurance guys. And SAAMI.)
joe b.
F.T.!
Attached Files
As the velocity increases so does the centrifugal force which is what act upon and thus causes the inaccuracy with unbalanced bullets.
Ya gotta stop talking about "centrifugal" force, Larry; it doesn't exist!
joe b.
F.T.!
Attached Files
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Bullets do not typically follow a straight line to the target. Rotational forces are in effect that keep the bullet off a straight axis of flight. These rotational effects are diagrammed below:
-
Yaw refers to the rotation of the nose of the bullet away from the line of flight. Precession refers to rotation of the bullet around the center of mass. Nutation refers to small circular movement at the bullet tip. Yaw and precession decrease as the distance of the bullet from the barrel increases.
I have yet to discover exactly why any of these take place, 100% of the time.
Attached Files
Ya gotta stop talking about "centrifugal" force, Larry; it doesn't exist!
Well that answers that........! Silly me for reading all those science books on physics and ballistics........and believing them.........my bad.
LMG
Concealment is not cover.........
Attached Files
This dummy on the side lines would like to know if the center of the groups changed for each of the 3 bullet groupings???? Or were they all about the same point of impact?????????
Attached Files
technically joeb is correct in that "" centrifugal "' force does not exist . consider that once free of the barrel, the offset mass in our unbalanced bullet does not continue to accelerate outward ... thus no force in that direction ...
but as in many things that get us through life, we know what centrifugal force means .... we also know what ft means ... ( g ) ... both are an result of not understanding how things really work . ( g ) ...
ken maga
Attached Files
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