What 3000 fps looks like.
Here’s what 3000+ fpslooks like:bigsmyl2:
The original accuracy/velocity criteria for the 16” twist with the 30 XCB bullet was 2 moa or less 10 shot groups at 100 yards at 2800 – 2900+ fps while maintaining linear dispersion to 300 yards.With my 30x60 XCB rifle, Dawn, objective criteria was met within the first 100 rounds tested.It was observed that the 30x60 cartridge in Dawn might be capable of 3100+ fps and maintain accuracy.
However, since it was taking a measured (Oehler M43 PBL) 48,000 – 52,000 psi to accomplish that thequestion that comes up is; will #2 or linotype alloy hold up to that pressure and acceleration?Initial testing with 3 difference powders resulted in poor accuracy although the 3100 fps goal was attained.As I previously reported the problem was some of the GCs were coming off the bullet immediately on muzzle exit.No doubt about this exists as the heavily damaged chronograph screens give adequate testimony.
It was a given if we pushed the ternary alloyed cast bullet hard enough and fast enough plastization of the bullet would begin.Plastization (the alloy begins to get soft transforming from a solid to a semi solid state) is caused by pressure and heat.The place where the pressure is highest and probably where the largest heat transfer occurs is the base of the bullet…..exactly where the GC is.If the base of the bullet plasticizes then the GC crimp has nothing to hold onto and would readily come off.It was believed this was what was happening in the 2950 fps+ velocity.I’ve been working on solving a problem the last several weeks but realized that at some point the ternary alloyed cast bullet could be pushed only so hard and maintain accuracy.
One of the 1stthings noted with the use of linotype alloy was the very good fill out and minimal shrinkage.The linotype bullets drop outof the NOE 30 XCB mould just a tudge (only a couple ten thousandths) under .311which is about .0005 - .0008 larger than with #2 alloy.This meant the GC shank also was a bit larger in diameter.Noting that when the Hornady GCs were seated using a .311 H&I die and the Lyman GC seater in a 450 Lubrasizer the crimping portion of the GC was scraping part of the shank forward.To correct this goodsteel made me one of his GC uniforming tools with swaged the Hornady GC to a proper slip fit over the GC shank.The uniformed GCs then were a perfect fit on the 30 XCB bullets.
I had recently cast some 30 XCBs (about 5 days ago)and since they were WQ’d they were ready for use.I weight sorted them into .1 gr variation lots (see my post on that in the Consistency Thread).I selected some of the sorted bullets of equal weight and GC’d them with the uniformed GCs.They were then sized and lubed (Lars 2500+)in the 311 H&I die.I honed a Lee.309 push through sizer to size the linotype 30 XCBs at .310 to fit the throat diameter of the 30x60 chamber throat.
A previous test with LeveRevolution powder showed 3000 – 3100 fps with 49 and 50 gr.The pressure was 51,000 and 56,700psi(M43).Accuracy was poor due to the GCs coming off as evidences by a 5.3 and 8.4” ten shot groups.The velocity for the 49 gr load was 3025 fps and for the 50 gr load it was 3103 fps.
Last night I loaded 10 shot test strings of 49, 49.5 and 50 gr LvR. A 1/3 gr Dacron filler was used. The .310 sized linotype alloy 30 XCB s were loaded.
I was able to slip off to the range today around noon.It was a paltry 80 degrees with a mild 2 -3 mph wind coming out of 6 o’clock.I fired 2 foulers into the berm and then fired the 3 ten shot test strings back to back.I let the barrel cool about 2 minutes between shots.I did not set up the M43 or the M35P chronographs as I already had the data from 49 and 50 gr loads tested previously.My estimated velocities are based on that previous test.
The 1st groupwas the 49 gr load which went into 1.65”.That should have been close to or just above 3000 fps. The diamond measures .75 on a side.
Attachment 134528
The next ten shot was with 49.5 gr and it went into a very nice and consistent 1.25” group.The velocity should be around 3050 fps for that load. Now that's what we're looking for:bigsmyl2:
Attachment 134529
The last group did not fare well and it was obvious the GCs of several of the bullets were shed and the bullets were unbalanced.The velocity should have been about 3100 fps.As we see here it doesn’t matter how well we make and load the bullets if we push them too hard.It is how balanced they come out the barrel that matters.In this case the bullets were unbalanced and the loss of accuracy shows that.As ballisticians such as Rinker and Litz note the unbalanced bullet is adversely affected in flight by the centrifugal force created by the RPM.Here we find, at 3100fps the RPM to be 139,500…….right at the top end of the RPM Threshold…..fathom that.
Attachment 134530
I would say that right about 3100 fps is about as far as we can push a ternary alloyed .30 caliber bullet. At that velocity and pressure it is obvious some pretty bad things happen to the bullet during acceleration. That means no matter how perfect we get the bullet into the barrel it's just not going to come out perfect (as in balanced) and it crosses the RPM threshold and accuracy goes south. At this point in my testing I will see what the 49.5 gr load can do out at longer range, perhaps to 600 yards. I then will do some testing with the breach seating tool goodsteel made for Dawn. Perhaps with breach seated bullets we can push above 3100 fps before crossing the RPM threshold....given the experience Bjorn had with his 14" twist Bertha in 30x57 XCB more could be possible in the 16" twist of Dawn with the 30x60 XCB. We shall see, the experimenting and testing continues.
Larry Gibson