Originally Posted by Swamplord
What if you were to reduce the diameter of the bullet slightly just in front of the ogive or at the boat tail ? just enough to shorten the bearing surface to an acceptable length
I have done some testing with this on the barnes TSX bullets that showed some promise. What I did was for example, on the 285 gr TSX-TAC bullets, it has 4 bands on the bullet body with obviously 5 relief grooves cut into the side of the bullet to reduce baring surface.
I have taken these bullets and experimented with these bands by removing some of them to see what would happen.
From my experience with 50 cal bore riders I knew that you need a certain amount of body baring surface to get good accuracy so I started at the front of the bands nearest to the ogive of the bullet. I parted off the first one on 20 bullets and did a quick load development to see of this would improve performance at all. I was mearly looking for velocity improvement. Removing one band did not do much compared to the standard bullet. Velocity and pressure using the same standard load stayed pretty much the same.
When I removed two bands, the velocity with standard load dropped by 30 fps.
When I removed three bands, the velocity with standard load dropped by nearly 65 fps.
When I removed all 4 bands, velocity dropped by just under 100 fps with standard load.
Why did the velocity drop, simple, less baring surface made it easier to push the bullet done the bore so there was a drop in pressure which resulted in a drop in velocity with a given load. Its kind of like backing the bullet way off the lands with the same load, this flattens the pressure spike and results in less velocity with a given load.
THAT SAID, this drop in pressure allows the careful reloader to increase the powder charge because the pressure curve of the load is dramatically flattened. As such, it would take more powder to regain the same level of velocity that the original load produced but at the same velocity, the pressure curve would still be significantly flatter with more area under the curve. This means that there is more pressure under the bullet while the bullet is in the bore.
As such, you can often increase powder charges even more and see an improvement in velocity performance with the lower baring surface bullets.
In my testing, I would increase the load by 1 grain at a time (in my 338 Allen Xpress so 1 grain is roughly 1% increase) and load up until i JUST started to see an ejector ring on the case head. I know, not scientifically pure but it works close enough. These were all fired in cases that had had one high pressure firing on them with no ejector ring marks at all.
When loaded to the same visual point based on the ejector rings marks on case head, again just looking for the first hint of a ring, the bullets with one band removed were only 15-20 fps over the standard load.
Bullets with two bands removed allowed close to 50 fps increase.
Bullets with three bands removed were in the 60-70 fps increase range.
Bullets with all four bands removed showed an 80-90 fps increase.
I was a bit suprised to see the velocity gains were slightly off from the velocity drops with the standard loads comparing the number of bands removed but I was still impressed to see the possible increase in velocity. Being able to increase velocity by nearly 100 fps is pretty much as close to a free or CHEAP lunch as you can get.
I machined up 25 bullets with all four bands removed and loaded them up. I had to use somewhat of an odd loading length and the throat had to be long enough so that I could seat the bullet so the base of the bullet body was still in the neck of the case to hold it solidly as the center of the bullet would just fall in the case. Luckily, I had a single shot rifle to test and was able to do this with its long throat set up for the SMK seated to the base of the neck.
At 1000 yards, it was instantly clear that accuracy was VERY poor. Groups could be measured in yards!!!! Was not impressed. Headed back to the shop scratching my head and thats when I remembered many 50 BMG bore riding bullets needing a certain amount of baring surface at the rear of the bullet to shoot accurately.
I machined up another batch of bullets with the front three bands removed and this time they shot MUCH better but still in the 1-2 moa range.
Tested more bullets with only the front two bands removed and these bullets shot to the rifles potential. So in the end, to maintain peak accuracy I was limited to a 50 fps velocity increase. Is it worth it...... Not really to me but it is possible.
Now, I did this testing with the solid Barnes bullets. The Accubond, while it has a thick jacket, its not thick enough to do this type of modifying on without weakening the jacket to the point that you would likely see problems on impact loosing the entire front half of the bullet at best and possibly, in the larger magnums, having bullet failure when the bullet leaves the muzzle. I have seen this alot but thats another story for another time.