It is beginning to be a puzzle as to why folks are so quick to identify the capability to shoot specials from magnum chambers as a benefit. It can't be that they don't know, so it must be that they don't care. If that's the case, then so be it---case closed.
There is no question specials can be fired from magnum chambers---if the shooter is not concerned with accuracy. But then we have the conundrum of why shoot if you don't care about accuracy? Or you reckon maybe there's an accuracy which is "close enough"? That'd be pretty sad.
By way of review for any neophytes in the crowd, the longer the throat the less the accuracy. Shooting specials in a magnum adds what---1/10" to the throat? If that doesn't sound like enough to hurt, figure it as a percentage increase. Then factor in the bullet scraper you've introduced into the equation. It's sitting in the magnum's chamber 1/10" ahead of the special's case mouth. One can only imagine what that's doing to the bullet as it passes by---and one can only wonder about the effect on accuracy.
If you want to know, get a Ransom machine rest---and get answers. But fair warning: Once you use a machine rest you're going to find out just how well your guns shoot. Then comes the problem of figuring out how come you can't even come close. It's a great motivator----or it'll drive you nuts!!
Ralph Tremaine