Jacketed bullet vs. lead velocity question

[Ruger45LC]

In reading some good articles on reloading the .45 Colt, I have a question. At Ruger level pressures I've heard that cast bullets give better velocity than jacketed bullets. Why is this, given the diameter is the same .452"?

On a related note, for my Glock 23 (barsto barrel) I've always heard to not push hard lead bullets very fast, at least not as fast as jacketed bullets. This seems to contradict what is said about the .45 Colt. I know they're different cartridges, but why is lead better in one and "worse" in another? Could it be a pressure issue for the Glock 23? What about leading? Seems the the slower the lead is traveling the more it would lead the barrel. Thanks guys.

[J.D.B.]

Lead bullets are generally sized .001 larger than their jacketed counterparts. The accuracy of a bullet is dependant upon a number of things, including how well the fired bullet fills the barrel, rate of twist, hardness of the lead alloy, quality of lube, etc. Leading usually occurs at higher velocities (pressures) for lead bullets because they are softer than a jacketed bullet. Jacketed bullets were developed, in part, for higher velocities. Generally, the harder the lead alloy, the faster they can be pushed, within limits. The (Speer) rule of thumb is to keep lead bullet velocities below 1000fps for minimal leading of the barrel. Your .45 Colt round started out as a lead bullet over a black powder charge operating at far less pressure than a G23 in .40 S&W. These two animals are VERY different and really don't compare for this example. The .40 S&W fires almost exclusively jacketed bullets while .45 Colt is almost exclusively a lead shooter in it's natural habitat.
Josh

[Leftoverdj]

Cast bullets will normally give a little higher velocity than jacketed at the same pressures because of lesser friction. The .45 Colt operates at pressures well within the capabilities of lead bullets.

The .40 S&W operates at far higher pressures, and jacketed bullets can use every bit of that pressure. Plain base cast bullets can't so the charge has to be reduced to what they will tolerate.

I don't shoot the .40 S&W, but I do shoot several cartridges which operate at that pressure level. Gas checked, moderately hard cast bullets perform perfectly. Getting an appropriate mould and checks might be a problem, but I would expect an experienced caster to be able to match jacketed bullets. The gain is probably too slight to be worth the effort, though.

The Speer limit of 1000 fps is a slightly different story. The Speer bullets are swaged from nearly pure lead and have a thin coat of lubricant. The pressure limits on those bullets are much more severe than on the much harder and more generously lubed cast bullets. IMHO, 1000 fps is being generous to those bullets although they are extremely accurate within their pressure range.

[Ben Shepherd]

With the same pressure levels lead will give more velocity due to less friction in the bore.

However-
Due to the increased friction of a jacketed slug vs. cast, the same powder charge DOES NOT give the same pressure level for a given slug weight. Make sense?

[joshua]

I think your factory Glock barrel has polygonal rifling instead of the standard type. Factory Glock 40 barrels and lead loads are bad combinations due to association of KABOOM effect. Most USPSA shooters or large volume shooters are often the shooters that encounters it. The polygonal rifling is not conducive to shooting lead shooting due to severe leading of the barrel. Common sense usually comes into play here that when your barrel is severely leaded it will increase friction/pressure due to the bullet leade shortened by lead fouling. Depending on how high the pressure is, I've seen a Glock that had case head separation to bulge/split barrels. josh