Alloy velocity and internal ballistics

Hey all

Been mulling on a thought or two for a while, thought I'd stop theorizing and just ask.

As I understand it, alloys have a velocity limit...softer = slower...in most cases.

Aside from rotational velocities doing weird things to soft alloys, is the limit actually velocity or is it pressure? What got me thinking of it all is the velocity gained with a longer barrel...let's say you're pushing a 150-170 gain boolit from an 06 ...same charge of powder will give you different velocities from a 20 inch barrel vs a 26 inch barrel...the bullet won't know the difference other than being in a barrel longer...the pressure goes way down after the first few inches so is the alloy limit velocity or pressure (I'm guessing it's pressure)

If it's pressure, then different powder burn rates would be important not for velocity limit but max pressure with the charge intended...

My goal is to get boolits working well (accuracy) with lighter loads of faster powders but the faster the powder the higher the pressure and if the alloy limit is pressure based I'll need to work around that carefully to maintain accuracy...

This may be why I've heard higher charges of stuff like unique in 06 is possible but rarely helpful as accuracy starts to decline with higher charges...I'd imagine fast fast powders like red Dot and titegroup would exaggerate this even more.

I have a 26 inch barreled 06...would like to employ it to dispatching whitetail this year with a 165 ranchdog over (probably) 2400 powder....but all this got me thinking about internal ballistics of cast boolits and wanted to check with the sages to get your knowledge

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There are two limits you should be looking at. One is pressure limit, which has absolutely nothing to do with speed. You can have two powders, one accelerating the boolit to 1,100fps, another to 880fps, and yet both subjecting the boolit to the same pressure and requiring the same alloy hardness.

The other is maximum speed it can travel at, which some put at 2150 fps. Above that the lead itself can deform in flight due to nose pressure.

Softer alloy will deform (slump) more easily. Faster powders will be limited to lower velocities than slower powders due to increased deformation caused by higher chamber pressures. If you increase alloy hardness, you can use more of a faster burning powder to obtain a higher velocity without deforming the boolit.

I have been trying to learn about higher speed lead bullets lately. I could be wrong (and quite regularly am) but I think that one of the reasons that having copper jackets allowed a massive increase in velocity was rotational pressure.

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Originally Posted by Traffer

I have been trying to learn about higher speed lead bullets lately. I could be wrong (and quite regularly am) but I think that one of the reasons that having copper jackets allowed a massive increase in velocity was rotational pressure.

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I'd think the same thing too except for the successes of paper patching...I've only dabbled and at low speed but I hear some guys get jacketed velocity from lead bullets with just a paper jacket that comes off at the muzzle

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"Aside from rotational velocities doing weird things to soft alloys, is the limit actually velocity or is it pressure?"

If by "limit" you mean the point of accuracy deterioration when using a bullet such as the165 RD with 2400 powder in a 10" twist 26" barreled 30-06 such as you desire then both velocity and pressure will come into play. The softer the alloy is (assuming a lubed GC'd bullet of ternary alloy) more the accuracy will be affected as the pressure increases because the velocity also increases proportionally. Other variables enter in also such as; the nose pressure on the large meplat of the RD bullet, the quality of the casting, the fit of the bullet to the throat, the lube used, etc.

I suggest, with a ternary alloy such as COWWs + 2% tin and/or mixed 50/50 with lead, that you'll fond the best accuracy with 2400 powder (all other variables being considered) in the 1750 - 1950 fps range. That should be adequate for deer out to 150 yards if the bullet is placed correctly. For usable hunting accuracy, which may be at a bit higher velocity than "best" accuracy, I would suggest working up the load at the maximum range you will shoot a deer and then accept what you believe is the best usable accuracy produce at that range for your purpose.

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Originally Posted by Larry Gibson

"Aside from rotational velocities doing weird things to soft alloys, is the limit actually velocity or is it pressure?"

If by "limit" you mean the point of accuracy deterioration when using a bullet such as the165 RD with 2400 powder in a 10" twist 26" barreled 30-06 such as you desire then both velocity and pressure will come into play. The softer the alloy is (assuming a lubed GC'd bullet of ternary alloy) more the accuracy will be affected as the pressure increases because the velocity also increases proportionally. Other variables enter in also such as; the nose pressure on the large meplat of the RD bullet, the quality of the casting, the fit of the bullet to the throat, the lube used, etc.

I suggest, with a ternary alloy such as COWWs + 2% tin and/or mixed 50/50 with lead, that you'll fond the best accuracy with 2400 powder (all other variables being considered) in the 1750 - 1950 fps range. That should be adequate for deer out to 150 yards if the bullet is placed correctly. For usable hunting accuracy, which may be at a bit higher velocity than "best" accuracy, I would suggest working up the load at the maximum range you will shoot a deer and then accept what you believe is the best usable accuracy produce at that range for your purpose.

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That makes sense...so all the tolerances start to stack at higher "volume" ...like turning up the volume on a singers voice and you start noticing the imperfections...

So concentricity, neck tension, casting imperfections and ect starts to add up at pressure and velocity like volume being turned up...

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Yes, they all start to "stack" at higher pressure/velocity and cause deformation and or misalignment in the bore which translates to imbalance in the bullet [center of form and center of spin not co-axial with center of mass] during flight. During flight the greater the imbalance the greater the centrifugal force acts upon it and the greater the bullets flight departs from center of the line of departure which translates into larger "groups" of loss of precision.

I went to the range today, shooting an NOE 150gr gas checked Spitzer with a 3r profile. I did not chronograph today as there was light rain in Nor CA near the coast. Several shooters were sighting in for the new copper only bullets required by the enviro-nazis of CA. I shot boolits!

I had shot my boolits through the rifle before using the iron sights, no problem. Today, I mounted a long eye relief scope on the Mossberg Scout Rifle and made minor adjustments for elevation and windage but couldn't get any grouping. Weird. Then I decided to shoot a rock on the berm to see where the dirt was flying around the rock. Shot after shot pounded the 4" Rock until it was smaller pieces. I repeatedly hit the smaller pieces until there was gravel. Cool, time to try the paper again.

Again, I couldn't get a group for beans. I had a friend with field glasses spotting for me. He could not believe the repetitive hits on the rock but not on paper. I have decided my boolits love to hit tin cans, rocks, sticks, plastic bullet trays, but refuse to leave a permenant record of their devastating capability on paper. I guess I can live with that. Good day at the range - for paper targets, they survived. The rock, not so much.

Do you think that theoretically a harder metal rod (copper brass etc) in the center of a cast bullet could make the difference? Granting that it could be placed perfectly in the middle. maintaining concentricity of the mass? I have toyed with the idea of swaging a piece of metal into the middle of a bullet like that.

If your goal is to push a cast boolit at typical cast boolit speeds, to dispatch a Deer, then Pressure is the one thing to worry about if you are thinking of using a soft-ish alloy. Click on the link below and scroll down about 1/3 of the way, to "The Approximate Maximum Chamber Pressure For Lead Alloys (PSI)" chart.
http://www.lasc.us/CastBulletNotes.htm

If I were loading the 30 cal RD boolit for 30-06, I'd also suggest the same alloy that Larry Suggested "ternary alloy such as COWWs + 2% tin", which is basically 94-3-3, I mention that because there are other ways to get there if you don't have COWW available. An alloy with a balanced amount of Sn and Sb will be tougher (this is different that hardness). A tough alloy will hold together better (less likely to fragment) and transfer maximum energy to the target.

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Originally Posted by JonB_in_Glencoe

If your goal is to push a cast boolit at typical cast boolit speeds, to dispatch a Deer, then Pressure is the one thing to worry about if you are thinking of using a soft-ish alloy. Click on the link below and scroll down about 1/3 of the way, to "The Approximate Maximum Chamber Pressure For Lead Alloys (PSI)" chart.
http://www.lasc.us/CastBulletNotes.htm

If I were loading the 30 cal RD boolit for 30-06, I'd also suggest the same alloy that Larry Suggested "ternary alloy such as COWWs + 2% tin", which is basically 94-3-3, I mention that because there are other ways to get there if you don't have COWW available. An alloy with a balanced amount of Sn and Sb will be tougher (this is different that hardness). A tough alloy will hold together better (less likely to fragment) and transfer maximum energy to the target.

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Thanks for the guidance here...I'm definitely going tougher vs harder/brittle but after a bit more experimenting going to throw it all out the window and add 12 more factors of complexity on this load ...and paper patch.

Looked at the bullet long and hard and it just looks like a prime candidate so I sized to .3015 and wrapped, lubed, sized to .311 now about to load a set to test a ladder test on Monday....let's see how this goes

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Be careful when sizing a boolit down that much (about .010").
Depending on technique, Sizing a boolit down that much will likely deform it in a undesired way.

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Originally Posted by JonB_in_Glencoe

Be careful when sizing a boolit down that much (about .010").
Depending on technique, Sizing a boolit down that much will likely deform it in a undesired way.

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Thanks, I've got a smooth 50 wrapped up now...will set up 10 loadings of ,5 rounds each to test for accuracy and velocity...I'll try to put together a new extra for expansion testing if I can find some newspaper or phone books to test in

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