Buckshot Willy-
It looks like the experts are sleeping or on vacation, so I'll make an attempt at answering your question. If I write an incorrect answer, perhaps the experts will reply and you and I will both become educated.
Several factors determine whether a particular rate of twist will stabilize a bullet. These include the bullet diameter, length, and weight. A plastic tip may change stability too. Velocity is a very important factor in determining stability; the greater the velocity of a particular bullet from a particular twist, the faster the bullet will spin and so the stability will be greater.
With a 1-turn-in-16-inch twist, almost any conceivable .451 or .452 bullet will be stable at any realistic velocity. In general, longer bullets require a faster rate of twist compared with shorter bullets with the same diameter.
Let's use an extreme example to find whether a 1-turn-in-16-inch twist can stabilize a very long, heavy bullet. The Hornady .458 soft point round nose bullet is 1.365 inches long. If you resize it to 0.452 inches in diameter for use in the 450 Bushmaster, it will become about 1.400 inches long. I don't know what the muzzle velocity of this 500-grain bullet might be from a 450Bushmaster, but let's assume a rather low muzzle velocity of 800 feet-per-second. The bullet
will be stable at this velocity from your barrel with a 1-in-16-inch rate of twist.
All bullets lighter and shorter than this example will also be stable with this rate of twist.
It's possible that very light, very short .452 bullets with a high muzzle velocity might be "overstabilized". With an unbalanced bullet, too much spin can produce in-flight wobble, which can decrease accuracy. With good quality bullets, this is usually an insignificant problem.
My Springfield bolt rifle described elsewhere on this forum has a 1-turn-in-16-inch rate of twist for its barrel. I have found no problems with accuracy that are caused by the twist rate of the barrel.
If you want to explore stability, the website of JBM Ballistics has a helpful interactive calculator for bullet stability that includes rate of twist as a factor. You can use different bullet lengths, calibers, weights, etc. to find whether your bullets are stable for a particular rate of twist and muzzle velocity:
Link to JBM.
Good luck with your project.
--Bob