fitting bullet diameter to cylinder throat/bore

[Black Jaque Janaviac]

I'm quite new to revolvers.  I recently purchased a Ruger Blackhawk.

I've been having fun trying to develop a few loads for it, and have been running into problems along the way.

One thing that puzzles me is I shot a few 158 grain bullets testing out a lube.  One group was with unsized bullets, the other group was with sized bullets.

Is there any reason the sized bullets should perform better than the unsized bullets?  I always thought that the larger bullets would seal the bore better and produce better accuracy.  I was suprised to see a tighter group with the sized bullets.

The cylinder throats seem to be around .358 or .359 should they be bigger?  Or smaller?

What should the bullet diameter be if the throats are .358 and the groove diameter is .357?

[KN]

The only throat problems I'm aware of with ruger is in their 45 colt calibers. A 358 throat should be fine in a 38/357 caliber pistol. As far as accuracy with one bullet verses another, most firearms will shoot different bullets with varying results. You just need to find the best ones for your gun.  KN

[unspellable]

In a perfect world the chamber throat diameter of a 357 revolver would be .358 and the barrel groove diameter would be .357.  The critical point is that the groove diameter should be .001 smaller than the throat.  Cast bullets should be .001 larger than the groove diameter or the same as throat diameter.

Of course, it's not a perfect world and the above relationships often get lost.

Over sized bullets will be less accurate because the rather abrupt sizing operation as they go through the throat and forcing cone is not as neat and tidy as doing it with sizing dies.

A few years ago Dan Wesson ran an estensive research project to determine best throat diameter, forcing cone angle, etc.  An obvious thing to want to know, but nobody else bothered to run any experiments in the last 100 years.

[44 Man]

I once owned an engraved Dakota Colt clone in .45colt/.45acp.  Beautiful little gun with full coverage engraving.  The colt cylinder had throats measuring .458 to .460 and a .451" barrel.  Needless to say, it shot horrible, averaging about 15" groups (patterns?) at 15 yards.  The acp cylinder was correctly dimensioned and shot into 2".  I was able to get the groups down to about 5" using .458 unsized bullets.  I had brain fade and sold it.  Should have rebored the acp cylinder to .45 colt and kept the gun.  Too soon old, too late smart!  44 Man

[unspellable]

44 man,

You have given me an idea!  I have a Blackhawk in 45 Colt / 45 ACP.  I should take measurements and give a little thought to boring out the 45 ACP cylinder.  I have been bemoaning the over sized chambers one typically finds in a 45 Colt.

By the way, I occasionally get up your way.  Probably Easter weekend next trip.

[Glanceblamm]

Have recently got a copy of Veral Smith's book, Jacketed preformance with Cast bullets.
Is very interesting reading and Veral covers everything quite well and has goes into great detail on measurements.