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Jacketed vs. Cast vs. Lead


jschweg

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This is more of a theory question than anything else, I just want to have a better understanding.

Lead/Cast load data requires less powder due to both better sealing/conforming to the barrel and the less effort required to get the bullet going right? Okay, assuming that part is true, let's just say that 3 grains is the max safe lead load for X. For jacketed, it's 4 grains. So if the jacketed bullet is using more powder, and it's harder to get a jacketed bullet moving, wouldn't that create more pressure (not less) on a jacketed load? Why wouldn't 4 grains just blow the gun up?

Secondly, coated bullets are all the rage now, and these coatings are pretty hard (obviously not as hard as a jacket though). As far as the reloading manuals go, everything is assuming uncoated lead or cast, the coatings aren't being taken into consideration yet. One would argue, or maybe not, that coated hard cast bullets are closer to jacketed now than anything else and that starting jacketed loads are fine for coated bullets.

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13 minutes ago, jschweg said:

 

This is more of a theory question than anything else, I just want to have a better understanding.

Lead/Cast load data requires less powder due to both better sealing/conforming to the barrel and the less effort required to get the bullet going right? Okay, assuming that part is true, let's just say that 3 grains is the max safe lead load for X. For jacketed, it's 4 grains. So if the jacketed bullet is using more powder, and it's harder to get a jacketed bullet moving, wouldn't that create more pressure (not less) on a jacketed load? Why wouldn't 4 grains just blow the gun up?

MOSTLY BECAUSE THE BULLET DOESNT SEAL AS TIGHT. SOME PRESSURE BYPASSES THE BULLET THROUGH THE BORE. AND GENERALLY SPEAKING WITH THE TYPICAL POWDERS WE USE THE DIFFERENCE IN LEAD/JACKETED LOAD DATA WON'T BLOW THE GUN UP.

Secondly, coated bullets are all the rage now, and these coatings are pretty hard (obviously not as hard as a jacket though). As far as the reloading manuals go, everything is assuming uncoated lead or cast, the coatings aren't being taken into consideration yet. One would argue, or maybe not, that coated hard cast bullets are closer to jacketed now than anything else and that starting jacketed loads are fine for coated bullets.

COATED BULLETS ARE CLOSER TO LEAD BULLETS THAN THEY ARE JACKETED BULLETS BY A LOT. BUT YOU CAN LOAD QUALITYCOATED BULLETS WITH JACKETED RECIPES AND NOT HURT ANYTHING. MANY OF US USE THEM IN OPEN GUNS WITH NO ISSUES.

Thanks!

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Think friction.

Jacketed highest

Lead & Plated 

Coated lead Least

IMO

 



Yeah, I get that part, but was more not understanding pressures and why a max load for lead might be a mid load for jacketed. Sarge explaining some of the gasses escaping around a jacketed bullet makes sense. Less efficiency with jacketed.

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And as Sarge said, the difference usually isn't a full grain.

In minor 9mm loads the gap is usually 0.2-0.4 grains



Yes, I just randomly picked those numbers out of the air just to represent some sort of difference.

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Please remember that the lead loads, at a lower charge weight, are producing higher pressures. The MAX load for lead goes to the same pressure as the MAX load for jacketed. Never forget the pressure part of the equation.

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2 hours ago, jschweg said:

 


Yeah, I get that part, but was more not understanding pressures and why a max load for lead might be a mid load for jacketed. Sarge explaining some of the gasses escaping around a jacketed bullet makes sense. Less efficiency with jacketed.

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And then throw in variances in different jacketed bullets. Montana Gold bullets are some of the most popular we use, but man oh man are the jackets hard. Probably half a grain difference in the load for them vs BBI in my guns.

THEN, put a slow barrel in a gun and it CAN POSSIBLY get near a one grain bump. But if you are that deep into it hopefully the reloading knowledge base has grown some. I had a Briley barrel for awhile that ran about 173ish with Montana Gold bullets. Put a schuemann in it and PF jumped to about 185. 

It takes lots of testing for each gun you shoot to work up a great load. This is why starting low and working up is important.

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7 hours ago, noylj said:

Please remember that the lead loads, at a lower charge weight, are producing higher pressures. The MAX load for lead goes to the same pressure as the MAX load for jacketed. Never forget the pressure part of the equation.

I think what jschweg is getting at is if it's easier to push a lead bullet down the barrel, why would you reach max pressure with lead at lower charge weights than with jacketed?  Is it because lead gives you a better bullet/barrel seal?  i.e. with jacketed, more gas gets past the bullet in the rifling, so you need more powder/more gas to reach the same pressure?

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2 minutes ago, njl said:

I think what jschweg is getting at is if it's easier to push a lead bullet down the barrel, why would you reach max pressure with lead at lower charge weights than with jacketed?  Is it because lead gives you a better bullet/barrel seal?  i.e. with jacketed, more gas gets past the bullet in the rifling, so you need more powder/more gas to reach the same pressure?

I that's a big part of it.

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I that's a big part of it.


Indeed. Here's some data points...

I've tested a variety through my 5" .40S&W:
- MG 180gr JHP (jacketed .400 diameter) @1.185" needs 5.2gr N320 for 169pf
- Xtreme 180gr HP (plated .400 dia.) @1.185" needs 5.2 N320 as well
- Blue Bullets 180gr RNFP (coated .400 dia.) @1.185" needs only 4.85gr N320 for 168pf
- Acme 180gr RNFP NLG (coated .401 dia.) @1.185" only needs 4.7gr N320 for 167pf.

So, the hardness difference between the jacketed and the plated made no difference in the amount of powder needed. Note that the Xtreme HP's are what they refer to as the thicker plating. Those were the same diameter.

The jump to coated was a reduction of .35gr of N320 for the same nominal diameter.

The jump up to .401 diameter coated is an additional reduction of .15gr of N320.

So, the increased sealing of the coated makes a fairly big difference in the amount of powder needed for the same velocity.
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