Simple question I hope

spacecoast · November 12, 2009, 03:59 PM

In looking at this page - http://reloadammo.com/38loads.htm - I see that the same amount of powder (like 4.8 gr. of HP38) produces velocities of 985 with a lead bullet and 914 with a jacketed bullet, even though both are 125 grain bullets. Why the difference? I am planning to use all jacketed bullets, just want to be sure before I get started.

Ivan · November 12, 2009, 04:13 PM

Jacketed bullets have more friction than lubricated Lead bullets.

- Ivan.

SwampYankee · November 12, 2009, 05:49 PM

AND because there is more friction, jacketed bullets will have higher pressures for the same volume of powder as lead bullets. For this reason, most reloading manuals will give you a jacketed load and a lead load. If you use the high end of a lead load with a jacketed bullet, long term use could cause premature wear on the firearm.

Shoney · November 12, 2009, 06:27 PM

Actually, the lead expands (many incorrectly call that obturation) because of the pressure, to seal off the gasses, as long as the charge is not producing high pressure. Since the copper alloys do not seal the barrel as easily, more gasses escape past the bullet.

**Unclenick** · November 12, 2009, 07:44 PM

The lead upsets or expands to obturate (fill and seal off) the bore. So the bore is what is obturated, and not the bullet.

Regarding velocities, this is gun dependent. We are likely seeing results from a revolver. Owing to the barrel-to-cylinder gap, the higher pressure generated earlier in the jacketed bullet's travel means more gas is blown out of that gap than would be the case with the lead bullet. That reduces acceleration in the latter part of the tube. It would be interesting to try the two in a single-shot pistol and see whether the higher pressure overcomes the higher friction or not? I know rifles actually lose a little velocity when you moly coat bullets to reduce friction (due to the start pressure reduction retarding powder burn and, with it, peak pressure).

November 12, 2009, 03:59 PM	#1
spacecoast Senior Member Join Date: October 14, 2009 Location: Sunshine and Keystone States Posts: 4,461	Simple question I hope In looking at this page - http://reloadammo.com/38loads.htm - I see that the same amount of powder (like 4.8 gr. of HP38) produces velocities of 985 with a lead bullet and 914 with a jacketed bullet, even though both are 125 grain bullets. Why the difference? I am planning to use all jacketed bullets, just want to be sure before I get started.

November 12, 2009, 06:27 PM	#4
Shoney Senior Member Join Date: February 21, 2002 Location: Transplanted from Montana Posts: 2,311	Actually, the lead expands (many incorrectly call that obturation) because of the pressure, to seal off the gasses, as long as the charge is not producing high pressure. Since the copper alloys do not seal the barrel as easily, more gasses escape past the bullet. __________________ I pledge allegiance to the Flag - - -, and to the Republic for which it stands….Our Forefathers were brilliant for giving us a Republic, not a democracy! Do you know the difference??? and WHY?http://www.wallbuilders.com/LIBissue...les.asp?id=111

November 12, 2009, 07:44 PM	#5
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,060	The lead upsets or expands to obturate (fill and seal off) the bore. So the bore is what is obturated, and not the bullet. Regarding velocities, this is gun dependent. We are likely seeing results from a revolver. Owing to the barrel-to-cylinder gap, the higher pressure generated earlier in the jacketed bullet's travel means more gas is blown out of that gap than would be the case with the lead bullet. That reduces acceleration in the latter part of the tube. It would be interesting to try the two in a single-shot pistol and see whether the higher pressure overcomes the higher friction or not? I know rifles actually lose a little velocity when you moly coat bullets to reduce friction (due to the start pressure reduction retarding powder burn and, with it, peak pressure). __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

November 12, 2009, 04:13 PM	#2
Ivan Senior Member Join Date: October 14, 2009 Posts: 141	Jacketed bullets have more friction than lubricated Lead bullets. - Ivan.

November 12, 2009, 05:49 PM	#3
SwampYankee Registration in progress Join Date: November 1, 2008 Location: I can be found on a number of other forums. Posts: 1,333	AND because there is more friction, jacketed bullets will have higher pressures for the same volume of powder as lead bullets. For this reason, most reloading manuals will give you a jacketed load and a lead load. If you use the high end of a lead load with a jacketed bullet, long term use could cause premature wear on the firearm.