Copper vs coated lead pressure/charge

[Flashpoint]

I've been shooting Leatherhead coated 220gr 300blk bullets and was using around 7.2gr of Lil'gun to get me to the 1000-1050 fps range. Well I've decided to shoot some 220gr Hornady Interlock RN I had which is an almost cylindrical bullet that probably has a lot of land bearing surface but I still was amazed that it took a full 2.0 gr more of powder to get these things up to the same velocity range, yes, 9.2 gr. I know copper jackets generate more drag than coated lead but is this amount of charge weight difference commonplace or does it seem excessive?

 

[Bailey Boat]

I would guess common place. Coefficient of friction and bearing surface will play the devil with what we perceive as common sense. Any signs of unburned powder present?? If not, carry on. If there is look at increasing crimp pressure (on the jacketed rounds) to ensure complete combustion.

 

[Slacker]

Sane thing happens with pistol bullets like blues or blacks vs FMJ.

 

[Toprudder]

I don't know if it is what is happening in this case, but sometimes the velocity can be counter intuitive. Pressure is what drives velocity. I have seen situations where a heavier bullet, for the same powder charge, is faster than a lighter bullet. For instance, a 200gn vs 230gn plated bullets (both from Xtreme) and the min charge for a 200gn bullet was in the charge range for a 230gn bullet - the 230gn bullet was faster for the same charge.

Even though the friction of copper should be higher, the coated bullets are probably (should be) slightly larger in diameter than the copper. Where are the bases of the two bullets when seated? Perhaps the coated bullet is seated deeper, which would leave less volume and create more pressure.

Lots of variable here.

 

[11B CIB]

http://blog.westernpowders.com/2014/04/dear-labby-questions-customers-ask-our-ballistics-lab/

Lead Bullet Pressure

Actually it is a general question: All things being equal do lead bullets generate more pressure than jacketed bullets?

Yes, they do. It all comes down to the frictional co-efficient. Gilding metals like copper slide more readily than lead does on a steel surface. You can write your name on a piece of paper using a lead bullet much more readily than you can with a copper one. This tendency to smear, which is why it leaves a track on paper is also why it tends to grab the barrel more quickly and increase pressures. Using jacketed bullet data with a lead bullet of the same weight will result in higher pressures, everything else being equal.

 

[Flashpoint]

http://blog.westernpowders.com/2014/04/dear-labby-questions-customers-ask-our-ballistics-lab/

Lead Bullet Pressure

Actually it is a general question: All things being equal do lead bullets generate more pressure than jacketed bullets?

Yes, they do. It all comes down to the frictional co-efficient. Gilding metals like copper slide more readily than lead does on a steel surface. You can write your name on a piece of paper using a lead bullet much more readily than you can with a copper one. This tendency to smear, which is why it leaves a track on paper is also why it tends to grab the barrel more quickly and increase pressures. Using jacketed bullet data with a lead bullet of the same weight will result in higher pressures, everything else being equal.

This is very surprising since I am experiencing the opposite and have always thought the opposite based on what I thought I had read and heard. It certainly seems like the jacketed bullet is generating more friction, requiring an increased charge and/or pressure to reach the same velocity.

 

[11B CIB]

This is very surprising since I am experiencing the opposite and have always thought the opposite based on what I thought I had read and heard. It certainly seems like the jacketed bullet is generating more friction, requiring an increased charge and/or pressure to reach the same velocity.

The jacketed bullet may create more friction but I don’t know if we can really measure the friction generated by the seal the lead is forming versus the jacket sliding across the rifling but the seal makes a huge difference in the pressure. I’ve always been heard to load lead or plated bullets at lower charges than the FMJ counter parts

 

[Beef15]

Lead/coated obturate and seal the bore better and faster.

Less blowby alows a smaller volume of gas to the same/more work.

You run into the same type thing when you compare traditional lead core jacketed bullets to all copper.

Sent from my SM-G360V using Tapatalk

 

[Flashpoint]

The jacketed bullet may create more friction but I don’t know if we can really measure the friction generated by the seal the lead is forming versus the jacket sliding across the rifling but the seal makes a huge difference in the pressure. I’ve always been heard to load lead or plated bullets at lower charges than the FMJ counter parts

I always heard the same but had heard it was due to the lead being slicker and not requiring as much pressure, instead of what you're saying that the lead generates a better seal, able to generate the same pressure with less powder. Both support the "less powder with lead" rule though.

 

[Toprudder]

It isn't "use more powder to reach the same velocity", it is "use more powder to reach the same pressure". The pressure is the limiting factor. If there is less friction, there will be less pressure, so more powder can be used before reaching the pressure limit.

 

[John]

I've always gotten a little higher velocity with a properly sized lubed, cast bullet than a jacketed one of the same weight with the same charge.

YMMV.