500 meter Testing – 3 Heavy 45-caliber Bullets
Today was a beautiful “winter” day south
The focus of today’s testing was to evaluate three, heavy 45-caliber bullets using elevation at the ram line to get a feel for the ballistic efficiency of the bullets. Loads for all three bullets were developed for accuracy as well as a similar MV range, between 1,290 fps and 1,300 fps.
The bullets tested were the Theodore/Brooks “Magic” bullet weighing in at 555 grains, the 575-grain Gunn/NEI Long Range bullet and the 585-grain Lead Zeppelin made by Bernie at Old Western Bullet Molds. All three bullets are excellent choices for Creedmoor, Mid-range or Silhouette. Well, they are a “bit” overkill for silhouette as even the rams fly off the rail like they’ve been hit by a “hay-maker” from these big-boys especially when the bullets are launched in the 1,300 fps range.
The rifle used for the testing was a 45-90 John Bodine Pedersoli. The barrel is 30” long with a 17.7-twist.
The loads for each bullet were:
Magic Bullet (555 grains, grooveless, 1.3940” long): Buffalo Arms 45-90 brass (excellent brass), F150M primer, 60/1000 LDPE wad, White Lightning BPCR Lube (for grooveless bullets), 85.0 grains of Swiss 1.5 powder, compression about 0.140”, MV = 1,296 fps.
Gunn/NEI Long Range Bullet (575 grains, grooved, 1.476” long): Buffalo Arms 45-90 brass (excellent brass), F150M primer, 60/1000 LDPE wad, White Lightning BPCR Lube (for grooveled bullets), 87.0 grains of Swiss 1.5 powder, compression about 0.160”, MV = 1,299 fps.
Lead Zeppelin (585 grains, grooved, 1.497” long): Buffalo Arms 45-90 brass (excellent brass), F150M primer, 60/1000 LDPE wad, White Lightning BPCR Lube (for grooved bullets), 88.0 grains of Swiss 1.5 powder, compression about 0.150”, MV = 1,293 fps.
Below is a picture of the three big, bad boys:
Lead Zeppelin Gunn/NEI Theodore/Brooks
All of the bullets were seated so they were hard into the lands. A damp patch (distilled water) was pushed down the barrel with a nylon brush attached to a flexible rod between shots. The rifle was cleaned after each bullet type was shot for elevation and group and 2 foulers were shot to warm the barrel and create consistent fouling in the barrel. All groups were shot off the sticks. The wind was light, from about 3 MPH up to about 6 MPH with a direction ranging from 9 o’clock to about 11 o’clock. During group shooting no attempt was made to adjust windage. Visibility and sight picture were excellent.
To start the testing 5 rounds were shot to warm the barrel and then 10 rounds were shot at the ram swinger, first with the “Magic” bullet followed by the Gunn/NEI and finally the Lead Zeppelin. As was said above the rifle was cleaned and fouled before each 10-shot string with each bullet.
Below is a picture of the “Magic” bullet group. The left core group has 7 hits, the middle group 2 hits and the far right 1 hit. No windage adjustments were made for the 10-shot string. The horizontal dispersion shows the effects of the wind picking up and letting off from about 3 to 6 MPH from 9 o’clock during the string of fire. This picture clearly shows the accuracy potential of shooting grooveless, barrel-bore-diameter bullets using a simple wiping technique between rounds fired.
Once the “Magic” bullet group was shot and a picture taken of the swinger, the Gunn/NEI was shot. There was about 1 MOA difference between the “Magic” bullet and the Gunn/NEI bullet with the Gunn/NEI requiring about a 1 MOA increase in elevation. More discussion later to make this an apples-to-apples comparison as the Gunn/NEI is 20 grains heavier and 0.082” longer. The Lead Zeppelin bullet required about 3 more MOA than the “Magic” bullet even though it weighs 30 grains more and is 0.103” longer. Remember, all three bullets were shot at about the same MV. That will also be discussed below as there appeared to be what I’d call “instability” issues with the LZ bullet out of the 18-twist barrel. The LZ group showed what I’d call classic instability in that the wind was having a much larger effect on it compared to the “Magic” and Gunn/NEI bullets. At this point I’d say that the LZ needs a 17 or 16-twist barrel to fully leverage the bullet’s ballistic coefficient potential. Bernie did an excellent job on the brass mold. It is a joy to cast with. Later this year I’ll do some arm twisting to get one of the guys I know that shoots a 16-twist 45-90 to load up the LZ for BC testing and compare the results to the 18-twist in-flight BC. No yaw angle testing has been done at distance with the LZ, but given today’s result that is an interesting proposition that will be leveraged in the future. When the Dr. Robert McCoy stability equations are put to work on the LZ from a Stability Factor standpoint the following is found: Stability Factor = 2.570 @ 1,300 fps. From numerous tests and many rounds down range the LZ probably has a bit too much BC robbing yaw (bullet wobble) for top longrange performance out of an 18-twist barrel. Longer is not always better. That is probably why it required more elevation at the ram line even though it weighs 30 grains more than the Magic bullet and is 1.497” long. The Stability Factor of the 1.4760” long Gunn/NEI is about 2.75 @ 1,300 fps for an 18-twist barrel, still a bit on the low side. For the “Magic” bullet, that is only 1.3940” long, the stability factor is about 3.02. That seems to be about optimum stability for longrange cast bullets launched with BP. If the LZ was shortened to about 1.450” it would probably be an excellent Longrange BPCR bullet for the 45-90’s with 18-twist barrels.
So, given that the Gunn/NEI and “Magic” bullets shot about the same elevation, when launched at the same MV, at the ram line, actually the Gunn/NEI required about 1 more MOA, but let’s just assume both bullets required the same elevation at the ram line for this part of the discussion.
First, from basic drag theory, the drag force exerted on a shape (bullet) is proportional to its length. If the diameters are the same for different length bullets and the nose is the same than the bullet drag of each bullet will be proportional to their length. What that says is that if we have a round-nosed bullet that is 0.75” long and another that is 1.50” long of the same caliber, with the same nose design, the longer, 1.50” long, bullet will have ½ the drag of the shorter bullet. We can use this phenomenon to adjust the longer Gunn/NEI bullet to the shorter “Magic” bullet so we can have an apples-to-apples comparison. We also need to adjust the weight differences due to the fact that the Gunn/NEI weighs 20 grains more.
Since the equation for Ballistic Coefficient is:
BC = Sectional Density / Drag Coefficient
We can adjust the bullets so that the slipperiness of the bullets can be compared with the two differences normalized (bullet weight and length). What is to be investigated is the drag reduction effect of a smooth bullet compared to a grooved bullet. The noses of both bullets are what I’ve come to think are about optimum for Silhouette, Midrange or Longrange shooting when maximizing BC is the objective. Cheating the wind is a very good thing in Silhouette, Midrange and Longrange matches as all that participate in those competitions know painfully well.
So, if we assume that the BC of the two bullets is the same, as they shot similar elevations at the ram line when launched at the same MV’s, we can tease-out the effectiveness of the reduced drag that results from ridding a bullet of grease grooves.
First we need to calculate the sectional density of both bullets:
Sectional Density = Bullet Weight / Caliber Squared
“Magic” bullet = 0.378 lbs per square inch
Gunn/NEI bullet = 0.392 lbs per square inch
The ratio for the sectional densities is:
0.392 / 0.378 = 1.037 (no dimensions)
Next the length ratios must be adjusted as the Gunn/NEI bullet is longer:
1.476 / 1.394 = 1.059 (no dimensions)
From the above we can see, after making adjustments to create an apples-to-apples comparison, the increased ballistic efficiency from removing grease grooves is about 9 to 10 %. The estimate is derived by adding the two above calculated ratios:
3.7% + 5.9 % = 9.6 %
Past testing using the same grooved bullet mold to cast bullets, shoot the grooved bullets at 1,000 yards against the same bullet cast after the grooves were removed from the mold also showed about the same ballistic efficiency increase. Also, since the Gunn/NEI bullet required about 1 MOA more elevation than the “Magic” bullet that would further increase the effects of removing grease grooves to a bit above 10 %. My guess would be a 15% decrease in bullet drag and therefore a 15% increase in BC from removing grease grooves is reasonable estimate.
Certainly these are crude tests, but the effects are clearly evident both from testing done by this BPCR rifle crank and others so afflicted. In the coming months a more sophisticated testing methodology will hopefully be put in place that should place a definitive stamp on how much the BC can be increased by removing grease grooves from BPCR bullets.