Leading and velocity


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eldon519
November 29, 2010, 11:01 AM
Is leading really a function of velocity or is it simply attributed to velocity because that is the only thing most people have any ability (if that) to measure (vs pressure)?

Take .38 Special for instance. If you shop around, reviews of bullets for the popular FBI load 158 gr SWCHP+P from Remington, Speer, Hornady, etc tend to mention in the review that they'll lead the barrel around 1100-1200+ fps. I certainly believe that in a 2-3" revolver where you'd be pushing it pretty hard (.357 load probably), but what about in something like a 1984 Marlin? I'd imagine the .38 FBI load would achieve velocities on that order out of the longer barrel, but the pressure ought to be the same or similar. Would this load be likely to start leading the Marlin just because of the longer barrel and surpassing that velocity threshold, even though it's still just a .38+P load?

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CraigC
November 29, 2010, 11:44 AM
No .38Spl load, even +P will produce 1100-1200fps with a 158gr SWCHP. You're talking .38-44 velocities and enough pressure to grenade many a .38Spl. IMHO, swaged bullets should not be pushed much beyond 800fps to avoid leading. So the velocity you'll get out of a rifle will lead the bore and quick. Trust me. ;)

If Speer still makes their half jacketed SWCHP, that would be a viable option for the velocities you're talking about. Otherwise, you need a good cast bullet, which will do fine at those velocities.

kaferhaus
November 29, 2010, 11:51 AM
Gas cutting is one of the primary causes of lead fouling. That's why rifle bullets usually have "gas checks" installed on the base of the bullet.

Velocity does equal more leading as the coefficient of friction increases with the increase in speed..... in other words more drag pulls more lead off the bullet.

Usually a hard cast, gas checked bullet will not lead badly if velocities are kept under 2000fps. they will still lead....just not as bad.

Barrel condition also has a lot to do with how fast a barrel lead fouls.... hand lapped custom barrels hardly lead at all... Factory barrels on the other hand are a different story..

fecmech
November 29, 2010, 12:00 PM
Leading comes in many forms. There is gas cutting which is generally due to bullets being undersize for the throat or barrel. The high pressure gas escapes past the bullet melting the sides and depositing the molten lead in the barrel. There is stripping where the acceleration of the bullet against the rifling exceeds the strength of the lead and shears leaving lead behind. There is lube failure which is as the name implies allows the lead to gall into the rifling. You also can have rough or pitted bores and forcing cones(revolvers) that cause leading.
Generally speaking if the bullet is slightly larger than throat or groove size and wears a good lube there will be little or no leading. The FBI load that you mention will run about 1100 fps out of a rifle. I shoot a similar load out of my .357 lever gun with an almost pure lead bullet at 1120 fps with no leading and excellent accuracy. The only way you will know if commercial bullets will lead your Marlin is to try them. If they do then I would try lubing them with Lee liquid alox which may help. I would guess though that if you stay with +P loadings you will be ok in your rifle. Full power mag loadings will require you to start casting or find commercial cast that works for you.

Walkalong
November 29, 2010, 12:13 PM
Leading comes from not matching the bullet size to the bore (or throats in a revolver), or from excess velocity that the alloys strength cannot handle (bullet skids in the bore, alloy can not hold the rifling), or from a bullet that is too hard for the pressure. (won't bump up to seal the throats/bore) Sometimes you can have a bullet harder than needed if the fit is tight enough. Revolvers with throats smaller than the bore will lead pretty much no matter what. (Ream throats to .001/.0015 over bore size)

Jesse Heywood
November 29, 2010, 12:42 PM
As you can see, everyone has their opinion on this. Most of them are correct, but have caveats. So here is my attempt at an explanation.

First, the correct size bullet is needed. Without the proper fit, the bullet cannot expand to seal the bore. In a revolver, matching the cylinder bore is where to begin.

Second, the proper amount of lubricant needs to be applied. I usually tumble lube lead bullets with Rooster Jack.

Finally, all other factors are dependent on pressure. That includes expansion to fill the bore, velocity of the bullet and friction created. Hardness of the bullet will determine how much the base swells to fill the bore.

More can be learned on the MBC website. http://www.missouribullet.com/technical.php

Steve C
November 29, 2010, 12:54 PM
A note on velocity from a rifle. I load 158gr LSWC & LSWCHP's in.38 spl to +P level using 4.7grs ow W231 (Winchester Data) and it duplicates the factory published ballistics of Winchesters .38 spl +P 158 gr LHP of around 890 fps from a 4" revolver. From my Timberwolf carbine the velocity was 1,101 fps average with a hard cast bullet but would be fast enough that you'd likely get leading from a soft bullet.

243winxb
November 29, 2010, 01:42 PM
Would this load be likely to start leading the Marlin just because of the longer barrel and surpassing that velocity threshold, even though it's still just a .38+P load? If we do a quick study of 38/pistol & 357mag/rifle loads on the Hodgdon website, you will notice pressure to be about the same (16,200 to 15,550 cup) with HS6 powder. A pistol 7.7"bbl w/6.3gr = 1010fps. A rifle/18.5bbl w/7.0gr=1222fps. So, if we get leading there might be 2 reasons. :confused: 1. The cast bullet has run out of lube. 2. The barrel is rough, causing more heat buildup or drag, stripping the bullets. This is with an alloy of the correct hardness, along with correct bullet diameter. the popular FBI load 158 gr SWCHP+P from Remington, Speer, Hornady, etc These factory bullets are swaged and may lead the barrels in pistol or rifle. As you see, we still dont have an answer. :D Shooting them in the firearm is the only way to know for sure. :)

murf
December 2, 2010, 03:20 PM
if the manufacturer says the bullet will lead past a certain velocity, i would believe the manufacturer. the only way to find out is to shoot the load through your particular rifle and see if that is the case.

murf

rcmodel
December 2, 2010, 03:29 PM
158 gr SWCHP+P from Remington, Speer, Hornady, etc are all using soft lead swaged bullets to insure expansion at .38 Spl velocity.

Soft lead has an upper velocity limit in that it will strip out of the rifling at the beginning of rotation far easier then a Hard-cast lead bullet, or a jacketed bullet.

I would say if it makes it into the rifling in a carbine and gets up to full RPM, it would lead no worse in a carbine then a handgun, assuming it carries enough lube to keep it lubed in the longer barrel.

Some of those loads you mentioned do not use grease grooves filled with grease, only knurling with a dry-lube applied.

rc

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