SLOW Twists and FAST Casts Using CUSTOM Barrels...Results, Please?

[kens]

When you say the boolit is plasticizing, and gas check pops off, how do we know that the nose is NOT falling apart as well?
Consider this: if 1000fps is Mach1 (speed of sound) then 3000fps is traveling at Mach3.
History tells us that supersonic aircraft in the Mach3 category have titanium leading edges to take the heat buildup. Yes, at mach3 the air friction heats things up to the point that heat treated aluminum loses its heat treat.
So then, how do we know whether or not our boolit nose is falling apart at that kind of speed?
If you think about it, all the high speed jacketed bullets have a minimal lead point showing, if any lead at all. The high speed hollow points are usually a hollow copper nose, no lead.

I propose a test of a bullet like a .35rem, .30-30 or soft nose .30carbine (big lead nose) and drive it on up to 3000fps and see if it also falls apart at that speed.

[1johnlb]

Looks like the 30xcb thread is gone.

[Bjornb]

I believe the thread was taken down for Mod review due to extensive trolling by one or two posters. It seems to happen from time to time.

[cainttype]

I hope you're right, Bjornb. There's too much good data contained there to waste.
Perhaps the "High Velocity With Cast" thread could be resurrected by those HV enthusiasts that aren't interested in keeping the "Testing the 30 XCB" thread on track. It would seem too easy a solution, much better than the regular interruptions that have followed the XCB threads.
The efforts you, Larry, and Tim have made to post your test results here on CBs is much appreciated by many.

[Larry Gibson]

When you say the boolit is plasticizing, and gas check pops off, how do we know that the nose is NOT falling apart as well?
...........

We know its the GCs coming off and not the nose melting off because the bullet holes in the target are still round and show no evidence the nose is melting or deforming. We know it's the GCs coming off because it is they who are severely damaging the Skyscreens of which the start screen is 15' from the muzzle. Note in the pictures the severe damage and in some cases perfect 30 caliber holes neatly punched into the face of the Skyscreens. Additionally several GCs thus have been recovered from the inside of the Skyscreens.

Note in the picture of the recovered GC from inside of a Skyscreen how the alloy is soldered to the inside of the GC. That only can happen if the alloy becomes molten at high temperature inside the barrel and the bullet base is still molten or "plasticized" allowing the GC to come off immediately on exit from the muzzle. The velocity of the bullet that lost that GC was 3100+ fps out of the 30x60 XCB (Dawn). The evidence of plasticization as left is how we know. Bjorn B was with me at the range when that GC was recovered from inside a Skyscreen.

Larry Gibson

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[MBTcustom]

That evidence pretty much sums it up.
I find it amazing that a mere GC can produce that much damage. That alone demonstrates the fact that "this little dude was cooking right along at extremely high velocity!!!!"
I've never seen a GC do that before.

[kens]

I have heard that cast boolit can be driven at either high velocity, or, high pressure, but NOT both.
With that in mind, then how can we determine to what pressure/velocity we can drive a boolit before the gas check melts off?

[MBTcustom]

I have heard that cast boolit can be driven at either high velocity, or, high pressure, but NOT both.
With that in mind, then how can we determine to what pressure/velocity we can drive a boolit before the gas check melts off?

Well, seeing as how there is such a deficit of information about shooting cast bullets at HV, the XCB project was started to answer questions just like that.
We shoot. We keep records. We post the results. We keep track of what works and what doesn't. We back up everything with groups posted right up front, every step of the way.
It's new ground.

So far, the trick is finding powders that give a good balance. With the original 30XCB, powders such as Leverevolution, and H414 are pretty good choices (I'm enjoying LvR very much indeed!). I expect Larry is finding slower powders that give satisfactory results.

[Larry Gibson]

I have heard that cast boolit can be driven at either high velocity, or, high pressure, but NOT both.
With that in mind, then how can we determine to what pressure/velocity we can drive a boolit before the gas check melts off?

As usual such statements are an over simplification. The problem in the simplification is what is actually meant by "high velocity" and "high pressure".

Since I measure both velocity and pressure here is what I've found. As with many things involved in shooting it depends on variables. With the 30x60 XCB cartridge using a 30 XCB bullet cast of either #2 alloy or linotype plastization of the bullet alloy at the base of the bullet seems to occur in the 2950 - 3050 fps range. It seems a pretty consistent occurrence above 3050 fps with bullets fired from the cartridge case. Breach seating appears to allow a bit higher velocities to be attained before this "plastization" of the base of the bullet occurs.

The range of psi where plastization occurs in the 45,000 to 54,000 range. The psi where this occurs is not consistent but seems dependent on the time pressure curve of the powder. The powders with the slower time pressure curves seem to cause plasticizing at somewhat lower velocities. This may be due to the longer exposure of heat and pressure to the base of the bullet during the slower time pressure curve(?).

By my definition I am driving cast bullets out of slower twist (14 & 16") rifles at both high velocity (2400 - 2900+ fps) and high pressure (40,000 - 54,000+ psi) and maintaining usable accuracy (2 moa or less) at longer ranges (300+ yards). Thus the above premise of that statement is not correct such as it is with many myths involving the shooting of cast bullets, especially at "high velocity".

As goodsteel points out: "We shoot. We keep records. We post the results. We keep track of what works and what doesn't. We back up everything with groups posted right up front, every step of the way. It's new ground."

It is indeed "new ground". I am not sure I am going to pursue this much further as it is hard on the test equipment which the replacement of can be expensive. It will be interesting to see what results BjornB gets with his 17" twist rifle chambered to the full 30-06 cartridge to XCB chamber specs.

Larry Gibson

[popper]

Primarily pressure induced 'heating'. Supposedly 20% of powder energy goes into expanding the barrel, making it 'hot', does the same to the boolit base. Powder burn temp adds some temp but not a lot. I found one GC from 308W, lead left in the GC was silvery - rest of the boolit was gone. The lead crumbled easily. That one cut through 12 ga steel wire & the remains are someplace in a rock pile. Don't believe the pressure thing? FL size a 308 case and feel the temp.

[kens]

Larry quote:
"I am not sure I am going to pursue this much further as it is hard on the test equipment which the replacement of can be expensive."

What is your equipment? Copper crushers? Strain gages?
strain gages should be relatively inexpensive.

[Larry Gibson]

Depends on what you consider "relatively". It is the Skyscreens that get damaged by the errant GCs. I use an Oehler M35P when just chronographing. I use an Oehler M43 PBL when measuring screened velocities, pressures, time/pressure traces and TOF (Time of Flight) muzzle velocity along with other data. The Skyscreens can be somewhat expensive and it totally disrupts a range session when one is shot and is destroyed or misreads. There are 3 Skyscreens required for the M35P and 6 of them for the M43. I have already replaced several of them. The strain gauges do cost money and as they are permanently attached to a test firearm/barrel which also costs money. I currently have 30+ firearm/barrels for various cartridges with strain gauges attached for testing. Additional the M43 and the computer to run it on are not inexpensive nor is the generator and attendant equipment to operate it. I consider my time as valuable also and testing in a scientific manner to get consistent, reliable and reproducible data is not a matter of stepping down range and slapping a Chrony out there.

All of this has been covered by me in the numerous posts/threads I have been giving information on. You might do a search and read some of them for more precise descriptions of the equipment I use and the testing done.

Larry Gibson

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[kens]

are you reading strain gages pressures directly on the laptop?
I work with strain gages but we go through a analog/digital converter before it gets displayed on laptop.
That is quite a good setup you got.

[Larry Gibson]

The Oehler M43 receives the input from the strain gauge and feeds into a program on the computer. The screens, muzzle and down range, also feed into the M43. Data on the load, the test firearm, the physical setup and the current conditions are entered into the computer program. The data from each shot is measured and converted to usable data by the M43 and the computer.

Larry Gibson

[runfiverun]

I just pound them on the table top...
that usually squares them up and bashes them into place good nuff.

[Larry Gibson]

Received a question regarding the "plastization" of the bullet. Question was; "Wouldn't leading of the barrel occur?"

Fact is leading of the barrel did occur. As BjornB can attest after testing the loads (3050 - 3100+ fps) where the GCs were being lost and we had to fix the Skyscreen before testing could continue the accuracy with a standard load in the 2950 fps range that normally give around 1.5 moa accuracy shot poorly with 2.5+ moa accuracy. A normal cleaning of the barrel did not removed the leading as accuracy at the next shooting session was again 2+ moa with proven loads. I used JBs on a patch over an undersized brush to remove the leading and accuracy resumed back to 1.5 moa average for the 2950 fps loads.

Larry Gibson

[kens]

With all this testing can we assume the following as proven results?
1. Slow twist allows us to duplicate Mauser military load velocities using gas checked boolits.
2. Chamber, neck, throat, other tight tolerances allow us to tighten groups at said mauser velocity
3. barrel leading comes from the base of the boolit, not the boolit stripping the rifling, nor the sides of boolit

I am asking these 3 things because of the most common discussion items regarding high velocity cast. Not to be all inclusive here, but to respond to the most common high velocity subjects.
All these 3 things are assuming lube is up to the task, and boolit fits the bore, and quality barrel is used.

Are these a fair assumption of tested results?

[MBTcustom]

Very fair, in my humble opinion. In fact, duplicating 8mm Mauser performance with cast is a very easy thing if a slow twist barrel is used.
2600fps? Totally plug and play, slam dunk, home run.
Heck you don't even need to use Linotype or anything special to get that.
Here's my last range session results using House alloy which is nothing more than COWW carefully balanced with tin to get 95.6/2.2/2.2. BHN of these bullets was 24. Hardly rock hard alloy:

Rifle is a 1909 Argentine rebarreled to shoot 30XCB.
Powder used for these groups was Leverevolution.
Speed was between 2650 and 2700fps
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[Larry Gibson]

kens

Yes, those are fair assumptions considering "8mm Mauser velocities" runs from 2400 to 2950 +/- fps depending on which cartridge and rifle (with attendant barrel length) is used. Certainly the accuracy level of military 8mm (8x57) ammunition can be attained and most often bested with a properly designed and cast bullet in slower twist barrels of equal length.

Shown is what 2975 fps looks out of the 16" twist rifle. This was shot with #2 alloy when the ambient temperature was close to 70 degrees. I have not been able to duplicate that with linotype w/o plastization occurring when the temperature is above 80 degrees. The diamond is .75" on a side.

Larry Gibson

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[kens]

I'm going to respond in 2 posts, and ask you guys to respond in return, if you don't mind.

1. Pressing cast boolit to the 3,000fps class is a tremendous accomplishment. I got a mauser up to 3,000+ but it was a 29" Swede with a little 85gr jacketed pill. To get anywhere near that with a 160gr boolit is just outright awesome. You've gone past bore leading, stripping the lands/grooves, pressures, and all that. You went to the point of melting the gas checks off the shank. That is remarkable.
So now I guess we know the limit of shooting cast……………the limit is melting the gas check off.
All the Mausers models 91, 93, 95, 98 were made for jacketed ammo. You guys have arrived at Mauser velocity with cast. Job well done.