Firehunter wrote:Texas Sheepdawg wrote:I wouldn’t push them through a Ruger 1:16 twist. Period. Sell them to a handgunner and go buy the XTP mags or something more suitable for the velocities and 1:16 twist RAR.
Could you go into more detail as to why these wouldn't work? I have some that I use with sabots in my muzzleloader and thought about trying them in my RAR.
I'll take a stab at explaining my understanding of this despite never experiencing either phenomena and I'm the guy who early into the 450b, actually tried shooting Berry TMJ bullets out of his 450b to see if he could save a buck! Luckily, I only wound up with a couple of tiny shards embedded in my chronometer. Even then, it wasn't from
centrifugal force. The integrity of the copper foil jackets were compromised fron either seating them into unexpanded case mouths or as they left the muzzle. Most hit the 4ft by 4ft target board at 100 yards but left behind some bits of jacket on the way. When I say most hit, it was nothing resembling a group, not even a pattern. They didn't go puff however, but they were much like FMJ's not hollow points.
Different metals have different shear strengths. IE the point at which they can't hold together due to physical stress. Copper is stronger than lead as you know. 24ga sheet aluminum is stronger than aluminum foil. Another given. When a bullet is launched down a bore, it spins. Yet another given. A spinning object is subject to centrifugal forces trying to tear it apart.
A bullet traveling down a 1:16 (3/4 a revolution per foot) twist barrel at 2225 fps is spinning 3/4 X 2225 revs per sec X 60 sec per minute = 100,000 RPM. That's a lot of centrifugal force being exerted on it. If that bullet was soft, expandable lead, it would probably come apart. Wrapping the sides in a stronger metal (copper) increases its resistance to coming apart. The thicker the copper wrapper, the greater its strength. The regular XTP bullets are designed to expand at nominal handgun velocities. IE somewhere between 1/3 to 1/2 the velocity that the 450b develops. They have a thinner copper jacket than their XTP Mag cousins. Again, I have not had any bullets come apart on me nor seen in person, a hyper velocity rifle round turn into a puff of lead, but I've seen slow motion videos of that happening. Nobody wants their projectiles turning into flechette rounds or rat shot. So, I take it on faith that using the Mag version of the XTP bullet is a better choice.
The second phenomena I have only heard spoken of here, just in the past year, by someone repeating what they read in a credible explanation elsewhere. I think this is what they were alluding to: Upon ignition, at some very short point in time, the bullet leaves the case and runs into the bore which is slightly smaller in diameter. At that point, the bullets has to squeeze down in size to the dimension consistent with allowing it to seal the barrel (obturate) but not so much that it can't still slide down the bore. While it is squeezing down, its forward velocity momentarily slows a little. The pressure behind it is still going up at that point, real fast. Reference to the previous explanation regarding difference in strength. The part of the weaker bullet not already narrower but soon to become so, will squash down, making it fatter and less likely to squeeze through the entrance into the bore. Smokeless powder's energy is a function of pressure. More back pressure, more energy contributing to that pressure will be exerted, up to the limit of the charges total energy content. That's not how smokeless powder is designed to work in practice. Usually during that critical period in time when the pressure is increasing, the bullet is supposed to be moving away from the case, creating more room for the expanding gas, keeping the pressure from going critical mass. Kinda like the reverse of "Chinese Finger Traps", where the harder you pull the harder they hold on. In this case its pushing not pulling. Most of us have seen the images of damage to barrel, bolt or other parts of the receiver when the bullet stops traveling down bore. There, that's my understanding of the butt squash issue. Never seen it in person nor in a video, but it makes sense.
Forgive me if I synopsized these two issues wrong.
I'm a slow composer/typer/editor and hopefully someone else hasn't already "lapped" my reply. It happens more frequently than I care to admit.
Hoot