357 mag, cast vs jacketed, velocities differences

S

Shadow9mm

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So i tested some 357 mag loads out of my 6in gp100 the other day. 2 identical loads except for the bullets. But i got significantly different velocities.

Starline 357 mag brass
13.5g H110
Winchester small rifle primers.

Hornady 180g xtp .357 diameter
Home cast 185g gas checked wide flat nose, sized .359

10 rounds fired each
180g xtp, avg 1025, sd 58.69, es 185
185g cast, avg 1234, sd 35.92 es 94

Sd and es were rather poor in both cases as well. All the charges were weighed.

I understand my lead bullets fit the throats better. I am just astounded by the 200fps gain.
 
So am I. That's a lot.

I was waiting to read something in the order of 50 or 75 fps.

Scratching my head over here.
 
Just curious, what is your pistol's bore diameter?

Lead is softer (and lubricated) than a copper jacket. Even though the lead is oversize compared to the jacketed (and hopefully the bore) it is softer and I don't think the force needed to squeeze it a bit and for the rifling to dig in is as much as the force needed by a jacketed bullet.

Therefore, with equal amount of "push" I would expect the lead bullet to go a bit faster. 200fps is unusual, but its what you got so, obviously is possible.

DO exactly the same thing in a different gun and I expect you would get a different result (fps between the lead and jacketed slugs).

I have seen 100fps difference firing the same (jacketed) ammo between 3 different guns with the same barrel length. Also rare to be that much, but not unheard of.
 
I slugged it a while back, believe it was .3575 if i remember correctly. The cylinder throats were all pretty even. I did not slug them, but they would all pass a .358 bullet with a gentle push and a .359 did not want to pass. .357 would drop through.
 
I assume the cast bullets, because of their lube grooves, are longer and sit deeper in the case, which will raise pressure. Also, lead bullets can upset more easily to seal the chamber and bore, and they can upset to start filling the forcing cone, raising pressure a bit as they are forced into it. It seems to me Skeeter Skelton commented that lead bullets always ran at higher pressures in revolvers shooting near upper load limits.
 
Therefore, with equal amount of "push" I would expect the lead bullet to go a bit faster

Now, the other side of the coin. IF, as Uncle Nick states lead bullets raise the pressure, then the amount of "push" from the pressure is not the same. So, I would think that, once the bullet gets moving the acceleration rate, determined by the bullet's resistance moving down the barrel and the amount of pressure pushing it will be different between lead sized .002" over and jacketed sized to what your bore is.. (to the nearest thousandth)

My current theory is that while cast raises pressure and so takes more to get it moving, once it does, it slides down the barrel easier than jacketed does. This MAY account for the higher final velocity.
How much, I can't say.

you might try experimenting with your cast slugs, size some of them the same .457" as the jacketed and see what that does to your velocities. (might have an adverse effect on their accuracy, but would show you how the size variable plays a part)
 
Unclenick said:
I assume the cast bullets, because of their lube grooves, are longer and sit deeper in the case, which will raise pressure. Also, lead bullets can upset more easily to seal the chamber and bore, and they can upset to start filling the forcing cone, raising pressure a bit as they are forced into it. It seems to me Skeeter Skelton commented that lead bullets always ran at higher pressures in revolvers shooting near upper load limits.
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I didnt measure, but the cast bullets are longer. However when compared against the crimp groove there is a tad bit less in the case with my cast bullets.

The other thing i have considered is that while i applied equal crimp pressure to both, the xtp has a cannelure, not a groove to roll the crimp into. Which i would expect to cause the bullet to be released at a lower starting pressure.
 
That would be easy to test. Make up a few rounds with no crimp and fire them singly to see what the chronograph says.

Also, while they work at short distances most of the time, if you are using an optical chronograph, they can sometimes produce remarkably consistent chronograph errors due to a little bit of non-bullet ejecta passing the bullet and triggering the start screen too soon for a false low reading, or actually pass the bullet after the start screen trips to trigger the stop screen too soon, giving a false high reading (less common). Odd stuff, but happens. For that reason, I always default the SAAMI standard distance of 15' for the midpoint of an optical chronograph, then see if the readings are the same out there.
 
I typically set my chrono out 15ft whenever i do rifle work. However for handgun work i do 6ft and have never had an issue. I will re-test and see if that charges anything.
 
H110 only really performs well when you can get good ignition and good initial powder burn.

As your jacketed bullet starts to move, it probably has very little friction resistance with the throat and you a probably getting a lot of gas leakage past the bullet until it leaves the cylinder.

It sound like your cast bullet is starting out a little bigger in diameter. This plus some upset is giving it much higher friction and a much better gas seal before it leaves the cylinder.

These two items above are combining to give you "reasonably good ignition and initial burn" for the cast. With jacketed, you load is in the region where the H110 is just not igniting and/or burning nearly as well.
 
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I would offer the primers are causing your awful SD and ES. There is a great article in the current Handloader about primers. There are dimensional, thickness, and burn differences between rifle and pistol primers. My own experience with cast versus jacketed is similar. Cast is always faster in equal loads.
 
GeauxTide said:
I would offer the primers are causing your awful SD and ES. There is a great article in the current Handloader about primers. There are dimensional, thickness, and burn differences between rifle and pistol primers. My own experience with cast versus jacketed is similar. Cast is always faster in equal loads.
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Unfortunately all i have is small rifle and small rifle magnum. Amd i am rather hesitsnt to put a small rifke magnim in a et7 mag case. Small rifke should be more than enough to get the job done. It is used in 350 legend with the larger case and larger powder charges of h110
 
P Flados said:
H110 only really performs well when you can get good ignition and good initial powder burn.

As your jacketed bullet starts to move, it probably has very little friction resistance with the throat and you a probably getting a lot of gas leakage past the bullet until it leaves the cylinder.

It sound like your cast bullet is starting out a little bigger in diameter. This plus some upset is giving it much higher friction and a much better gas seal before it leaves the cylinder.

These two items above are combining to give you "reasonably good ignition and initial burn" for the cast. With jacketed, you load is in the region where the H110 is just not igniting and/or burning nearly as well.
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After checking a few more sources i found data from sierra up to 15 grains of h110. I suspect it may just need a touch more case fill. Gonna work up towards that next outing.
 
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