Cast vs. jacketed velocities

[RU shooter]

Given the fact that cast bullets are softer and in general have less bearing contact with the barrel than the same weight jacketed bullet . If the loads were with identical weight,bullets and same powder charge, ballpark guesstimate how much faster would the cast bullet be ? Since I don't own a chronograph I just add about 25 or so fps to what's in the manual for jacketed . Sound about right ? Or would it be more ? I'm speaking about calibers that would use similar data like 30/30 32 spl 35 rem and the like.

Tim

[gwpercle]

According to the Lyman #46 : 30-30 winchester
170 grain JFP , 27 grains of 3031 = 1925 fps
170 gr. #31141 LFP , 27 grains of 3031 = 2016 fps
Difference seems to be , in this instance , 91 fps
Wouldn't it just be easier to just use cast boolit data...Lyman puts out some dandy reloading manuals .
Gary

[John Boy]

...fact that cast bullets are softer and in general have less bearing contact with the barrel than the same weight jacketed bullet .

Can't agree with less bearing surface. Ideal mold bullet examples that have substantial bearing surface and will generate excellent obturation in the grooves:

[popper]

My chronyd cast fps are about 100 greater than book jacketed in 30 cal. With ES in the 50s, doesn't make much difference.

[Harter66]

Can't agree with less bearing surface. Ideal mold bullet examples that have substantial bearing surface and will generate excellent obturation in the grooves:

Bearing surface and bearing length are different .

I know that in a 32 Rem using 32 Win data per the data recommendations I exceeded jacketed maximum velocities below start loads with 170-180 gr bullets. Start to max with I4350 is only about 2 gr .
Take this with a grain of salt , as I had 5-6 rifles and a pistol that regularly clocked 200 fps faster than data, several others hit right on data numbers and a second Chrony confirmed the first .

[rugerdude]

My experience has been that cast boolits generally chrony about 100-125 fps faster than jacketed bulIets. The barrel can make a difference as well. Rougher barrels seem to "grab" jacketed bullets more than cast and can really hold velocity back.

[runfiverun]

the lead is slipperier.
it's also softer so when comparing the two your always going to have an increase with the lead boolit.
how much of an increase is pretty hard to predict on a rule of thumb.
it could be 25 fps in a 45 acp.
50 fps in the 44 mag.
or it could be 125 fps in a medium rifle.
or even more depending on the gas volume available to push on the projectile.

[PositiveCaster]

I am glad to hear that no one is saying that cast always has lower pressure than jacketed with the same charge. The data is full of exceptions to that falsehood, simply look on Hodgdon's site, data below. Clearly with equal charge weights the 240 jacketed load would be overpressure under a boolit.

.44 Magnum, 240 grain bullets and 800-X:
Jacketed 14.2 grains = 39,600 CUP
Cast 13.4 grains = 39,600 CUP

Same source, .45-70, 300 grain bullets and Varget:
Jacketed 57.0 grains = 16,300 CUP
Cast 55.0 grains = 20,600 CUP

Please avoid repeating the old lie that to substitute a cast bullet over a jacketed load is always lower pressure.


.

[leadman]

Positive, do we know if the same firearm was used to take both readings? Could be many variables affecting the pressure. I read in a book somewhere that a gas check increased the pressure about 6K psi. IIRC it was in a Handloader magazine.

[OnHoPr]

I am glad to hear that no one is saying that cast always has lower pressure than jacketed with the same charge. The data is full of exceptions to that falsehood, simply look on Hodgdon's site, data below. Clearly with equal charge weights the 240 jacketed load would be overpressure under a boolit.

.44 Magnum, 240 grain bullets and 800-X:
Jacketed 14.2 grains = 39,600 CUP
Cast 13.4 grains = 39,600 CUP

Same source, .45-70, 300 grain bullets and Varget:
Jacketed 57.0 grains = 16,300 CUP
Cast 55.0 grains = 20,600 CUP

Please avoid repeating the old lie that to substitute a cast bullet over a jacketed load is always lower pressure.


.

That's the type of source that I would look for another source/s to check on.