Very surprising Larry. Thanks for posting. Lots to think about.
I can't wait for the new barrels to arrive!
With results like these, long range hunting with cast bullets could be a very tangible reality. It's real hard to pull the trigger on a deer a long ways off, if the consistency of your load is balanced on the tip of a needle, but these results of yours show very consistent and usable hunting accuracy (even the "sub standard" ones).
Very exciting!
Precision in the wrong place is only a placebo.
Range trip again Sunday. After a surprising cold snap (below 40), it was warming up nicely.
Due to a marathon fire forming session for my XCB rifle (340 cases) that I described over on the HV thread, I had been struggling with some serious barrel leading (even though I was bragging at the time that there was NO leading), and not until Larry advised me to shoot a few backwards seated jacketed bullets (.311 dia.) did I get a handle on the leading problem. 2 range trips with cr@ppy groups were wasted, and I even thought there was a shooter problem!
Here are some sample groups with known accurate loads and a barrel full of lead:
Anyway, I needed to get my confidence back, and I loaded up some strings with both old and new cases (not mixed), to see if they would perform differently. I had formed the second batch very differently that the first; the newer brass had been fire formed with undersize bullets with the goal being to get the necks ironed out completely (without the shade of the old 30-06 shoulder) before being turned.
After shooting 10 rounds with a moderate load, to condition the clean barrel (White Label 2700+ lube and NOE 165 XCB bullets were used), I shot these 2 groups:
I was happy with the results, since it showed that the leading was most likely all gone.
Finally I shot 3 strings with jacketed, again to see if the new brass would behave much differently from the old.
Yep, I threw 2 out of 30. I am mostly posting these groups as a shameless plug for my good friend Tim Malcolm AKA Goodsteel, who builds insanely accurate rifles and is also one hell of a good guy.
It was a good day at the range.
VERY nicely done, Sir! And I couldn't agree more.Originally Posted by Bjornb
+2
Those are amazing 10 shot groups!
Super nice at those speeds with cast. Right on time too as i was going to pick up some 760 to try in my whelen or h414. I've kept up with a lot of this but i know i've missed some of what's been tried. Have you tried the h414 in your rifle? Some say they are the same powder but i used to have both on hand and seem to remember a difference in appearance? Seemed like the 760 was darker so it may just be a difference in coating or i may not be remembering it right....been a few years. Glad you got the leading thing figured out....things like that can run you nuts till you find out for sure what's going on. Hoping i can ease the speed up a bit with one of those powders in my 1/14 twist whelen. Again very good shooting!!
That's how Tim's rifles shoot.
This was the last of my W760 and I picked up some H414 recently. I poured them into 2 plastic cups and compared them side by side. Visually I could detect no difference.
Excellent shooting Bjorn. That really is a fantastic rifle.
Thank you all for the kind words!
Precision in the wrong place is only a placebo.
Good post, Bjornb. The minor leading issue and post-cleaning groups clearly demonstrate a common problem that might be easily overlooked when pushing the limits of any load combination... I have more than a few toys I might have bragged on with 3 MOA groups at over 2800 fps with cast! lol
Although I'm generally well served with much less speed using cast, I have toyed with breathing new life into a hunter-benchrest type rifle that hasn't seen use in years. It's chambered in 308x48 and twisted 1-14.
I have considered rechambering it's 24" barrel to 308 Win in the past. I have a sporter style stock in hand and would lean towards fluting the barrel for a little weight reduction... Not there, yet, but thinking about it more often.
I thought groups like that come from pulling the trigger then trying to see the boolits fly through the air in the spotting scope.
With the Weaver T36 scope no spotter is needed!I thought groups like that come from pulling the trigger then trying to see the boolits fly through the air in the spotting scope.
The information I give in post #16 in http://castboolits.gunloads.com/show...-at-long-range is still correct and applicable to why several of us have migrated to 14 and 16" twists with more such longer barreled slower twist rifles being built. The results from shooting these with cast bullets at 2600 - 2900+ fps while maintaining 1.5 moa and less speaks for itself.
Obviously the information in the Accurate Bulletin demonstrates that the effects of RPM is an important consideration. Most of the ballistic world understands this. What being actually demonstrated in this thread documents that understanding.
Larry Gibson
Most of John Ardito's CBA records were fired in .308x1.5" with 200 grain bullet seated out and held by the GC only, with a caseful of RL7, using 14" twist Hart barrels on a sleeved 40XB action. Bullets were tapered in a bump die cut with the same throater used to do the barrel. He used monotype alloy and the old RCBS green lube, sequentially reloading the same case over and over again, no sizing the brass, just decapping, cleaning the primer pocket, repriming, filling the case full of powder in a rice bowl, striking it off with a card, starting the bullet with his fingers and seating it about 1/8" into the case using a Wilson type seater in an arbor press. Mold was one he cut himself which resembled 311299 before bumping.
The ENEMY is listening.
HE wants to know what YOU know.
Keep it to yourself.
Off topic alert!
For those who have been running cast full tilt, have you hade the barrels scoped? Is throat erosion similar to running full tilt jacketed?
No barrel has returned to the shop for inspection yet, except the original barrel on BjornBs Bertha rifle.
Bjorn can give a figure on how many shots had gone through that barrel.
I did take the opportunity to scope that barrel before borrowing it to build the Felix rifle, and the wear at that point was minimal. Had I seen this barrel unaware, and assuming it had been shot only with jacketed, I would have assumed it had less than 100 rounds through it.
The fine tooling marks left by the reamer were wiped out and the edges of the rifling in the throat were smooth like the rest of the barrel.
No flame scoring (this happens rather quickly with jacketed and looks like fine scratches extending from the chamber to the end of the throat.)
No gator belly at all.
It looked smooth and clean.
Thats all the help I can give at this time.
Precision in the wrong place is only a placebo.
Thanks, Tim!! I am very much interested in throat wear and overall barrel life running full tilt cast as you all are doing. If you recall, my slow powder, low-ish pressure, experiment with jacketed IRT barrel life did not turn out as I expected.
Back on topic now!
Love Life
I am planning on only using "full tilt" cast bullet loads in Dawn, my 30x60. I am recording every shot through the barrel. I should have a very good idea of the accuracy life of the barrel. I don't have a bore scope but am measuring the throat for erosion.
Larry Gibson
I'm all over it LL. As soon as I get a barrel back, I'll scope it out.
However, I once had a conversation with Larry Gibson and he had some experience in that regard that he may share here.
All I know is that not one single person has sent me back a barrel for a setback, and I've been doing this for a number of years at this point.
Remember the recipe for a burnout:
Fast twist
heavy bullets
Slow powder
Overbore cartridge
High pressure
As cast bullet shooters, with the 30XCB we only meet one of those criteria because nearly all of them would be detrimental to accuracy with cast lead. Also, it's not the bullet composition/hardness that burns out the barrel, it's the chemical reaction under pressure that does it. Therefore, I would speculate that if the burnout rate is identical for cast vs. jacketed, based on pressure, bullet weight, twist rate, and cartridge design, it would take about 6000 rounds before any measurable negative effect could even be detected, and we are a long way from seeing that from any of the shooters here.
Near as I can tell, the average cast bullet shooter involved in these projects shoots about 1500 rounds per year if he's really ambitious. Ie: get comfortable because this could take a while!
The average 308 requires about 3000-4000 rounds to burn it out with pressure in the 50,000psi range and a 1-10 twist rate. (That's match grade accuracy where your .5MOA turns into 1MOA). So reduce the pressure, slow the twist rate, use a softer bullet that generates less back pressure, and open your accuracy requirements to 1-2 MOA, and your barrel life is looking really really good for a long period of time.
I'm hoping to get the chance to scope one of these barrels after several thousand shots have been fired, but given the above prediction, lets just say I'm not holding my breath.
Precision in the wrong place is only a placebo.
popper
Wondering where you got those "stability factors"? What formula was used?
Larry Gibson
Here’s what 3000+ fpslooks like
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
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
Last edited by Larry Gibson; 03-19-2015 at 11:37 PM.
Posting Permissions
| BP | Bronze Point | IMR | Improved Military Rifle | PTD | Pointed |
| BR | Bench Rest | M | Magnum | RN | Round Nose |
| BT | Boat Tail | PL | Power-Lokt | SP | Soft Point |
| C | Compressed Charge | PR | Primer | SPCL | Soft Point "Core-Lokt" |
| HP | Hollow Point | PSPCL | Pointed Soft Point "Core Lokt" | C.O.L. | Cartridge Overall Length |
| PSP | Pointed Soft Point | Spz | Spitzer Point | SBT | Spitzer Boat Tail |
| LRN | Lead Round Nose | LWC | Lead Wad Cutter | LSWC | Lead Semi Wad Cutter |
| GC | Gas Check |
Reply With Quote
