Maximum velocity

rmorris3006 · #1 10-19-2014, 01:29 PM

I hand load 38 special. My powder is 7625. My bullet weight is 158Gr. I noticed in my load book that MEI Cast bullets loaded with 4.2 grs. have a velocity of 894 fps @16,100 psi and jacketed bullets loaded 4.5 grs have a velocity of 825 fps @ 16,300 psi. My question is how can a jacketed bullet loaded with more powder travel slower than lead loaded with less powder? Notice that PSI is higher on the jacketed

PALADIN85020 · #2 10-19-2014, 01:40 PM

Quote:

Originally Posted by rmorris3006

I hand load 38 special. My powder is 7625. My bullet weight is 158Gr. I noticed in my load book that MEI Cast bullets loaded with 4.2 grs. have a velocity of 894 fps @16,100 psi and jacketed bullets loaded 4.5 grs have a velocity of 825 fps @ 16,300 psi. My question is how can a jacketed bullet loaded with more powder travel slower than lead loaded with less powder? Notice that PSI is higher on the jacketed

I would imagine that the coefficient of friction would have a lot to do with it. Cast and lubed lead bullets "skate" down the bore, and jacketed bullets would require more force to overcome their higher friction.

John

JBnTx · #3 10-19-2014, 02:30 PM

Quote:

Originally Posted by PALADIN85020

... Cast and lubed lead bullets "skate" down the bore, and jacketed bullets would require more force to overcome their higher friction.

John

Are you sure about that?

Fishinfool · #4 10-19-2014, 02:45 PM

A cast bullet is simply softer than a jacketed bullet, and offers less resistance when going down the bore. That is why it is usually safe to use max jacketed loads with cast, but not the other way around. Its common to tap a lead slug down a bore to measure bore diameter. Try doing that with a jacketed slug.

Larry

rwsmith · #5 10-19-2014, 03:00 PM

It is much harder to push a jacketed bullet down a bore than a lead bullet. More powder to get equal velocity. However a jacketed bullet can attain high velocity without leading the barrel AS LONG AS allowable pressures are not exceeded.

David R · #6 10-19-2014, 04:25 PM

In the low pressure calibers, it looks like a loss of 75 fps going from lead to jacketed. Look at 44 special for the same affect

Sent from my KFTT using Tapatalk HD

RIDE-RED 350r · #7 10-19-2014, 05:05 PM

I agree with Paladin..

Ever recover a bullet?? Notice the grooves cut in the sides of the bullet from the rifling in the barrel. They are remarkably deep. Copper is a fair bit harder than lead. It's going to take more of a push to send that jacketed bullet down the bore than it does for lead. This is also what leads to copper and lead fouling. Some of the bullet material transfers to the bore on it's way out.

venomballistics · #8 10-19-2014, 06:21 PM

Quote:

Originally Posted by rmorris3006

I hand load 38 special. My powder is 7625. My bullet weight is 158Gr. I noticed in my load book that MEI Cast bullets loaded with 4.2 grs. have a velocity of 894 fps @16,100 psi and jacketed bullets loaded 4.5 grs have a velocity of 825 fps @ 16,300 psi. My question is how can a jacketed bullet loaded with more powder travel slower than lead loaded with less powder? Notice that PSI is higher on the jacketed

try shoving a 358 wax slug through your bore ...
then try shoving a 357 JHP through your bore.
betting the JHP takes just a little more effort.

Therein lies the answer

scooter123 · #9 10-19-2014, 10:16 PM

As noted the difference is due to differing coefficients of friction.

As someone who is truly a fan of SR7625 I have to say that it's a superb powder for low recoil loads in a semi auto caliber. But it is a poor choice in the 38 special. As for why, try the following experiment. First, point your muzzle down, tap lightly on the cylinder, then slowly bring the revolver level and fire a shot. Then point the barrel straight up, tap lightly on the cylinder, then slowly bring the revolver level and fire a shot. Once you notice the huge difference in recoil you will understand why it's not a good choice in any revolver caliber.