Testing the 30XCB

[popper]

Can't come near to affording a 30/35 XCB to test but I'm a guy who wants to know why it works well. Tim has mentioned the thin/shallow LGs, (I'm thinking the Accurate version), tapered throat section, TC nose (not sure why?) . From an Army (90's) test doc on lead core slump in jacketed 30 cal, well instrumented tests and analysis, I think I see another reason for the better performance - and some proof while testing RD 170 in MG 30/30. Army results were 500# base impulse force provided 300# RADIAL force (which is reduced to 50# when the boolit moves). Part of their claim is this radial force causes (starts?) engraving - not forward motion. Your tapered throat gives good alignment AND directs more of the force wave to the front of the boolit, engraving/creating the bore riding portion. Alloy then only needs to be tough enough to resist skidding from axial force. Guess that is why we get good results with loose bores & jacket ammo.

[oldblinddog]

Your results using the XCB bullet in a 1-in-8" twist would be interesting extra data here.
.....

I'd be very interested in your findings with the XCB projectile in the faster twist, and I'm sure there are others that would feel the same.

I would most certainly like to know. I have .308's in 10 and 12 and .30-06's in 10. From what I have seen, this is a very accurate boolit in any ctg. chamber it is tried in, the limiting factor being the twist/velocity threshold.

[MostlyOnThePaper]

Ooooops

[No_1]

I removed 3 post. Keep on topic folks.

[detox]

Here is the 30XCB next to my new LBT bullet. The 30XCB was designed to work well in most factory chambers. The LBT requires a custom throat (1.5 degree included taper). I hear 2 degree included taper works very well with cast also.


Both bullets were cast using linotype. LBT on left weighs 159 gr. , 30XCB on right 155 gr.

[Hannibal]

Imitation is . . . . well never mind.

[MostlyOnThePaper]

I don't see ANY imitation there. The radius is completely different. The XCB bears a suspicious resemblance to the Lee CTL312-160 with normal lube grooves though...

[MBTcustom]

The main difference with the XCB bullets is that they have a deceivingly short nose, especially after having been engraved. When I was designing them, I separated the part that was supported from the part that was unsupported and designed to the left and right of that point. The part of the bullet from that point back was what it had to be to fit the cartridge and throat. There really was nothing magic there, it was just simply all the support I could give it, and the small lube grooves went right along with that. The part of the bullet from the break forward is where most designs start getting lost in never never land. Mark my words, every thousandth of an inch of bullet nose you extend out there is hurting your chances of HV accuracy. If you give anything for RPM to play with, it will have a ball with it at some point.

The nose you put on a bullet is a compromise between RPM and ballistic coefficient.
For instance, lets assume that the bearing surface is what it is, and we all agree we've taken reasonable precautions to put as much of that bullet in contact with the barrel as possible while keeping the GC inside the neck. Theoretically, once that is finished, the bullet will be a one hole wonder at 25 yards just like a wad cutter (not that anybody would dream of using bullets that look like beer cans in competition.....LOL! the HB wad cutter is one of the most accurate cast bullets there is at low speed.).
Obviously, in the case of a wad cutter, ballistic Coefficient is going to limit your long range accuracy long before RPM gets a crack at it. So you need a nose.
The nose of the bullet will make or break it at HV. The definition of the "nose" of the bullet is anything forward of the area the rifling has control over. The rest of your bullet is trapped, the nose is quite literally "out of control". This is why I designed the XCB bullet to strike a perfect compromise between what I allowed to be out of control to gain BC down range, and what I forced to be under control so that the bullet could complete it's first task which was exiting the barrel with minimal torsional stress in the bullet nose.
This is such a picky part of bullet design that just a very slight difference in nose geometry will make all the difference in the world on paper.
Now, using this criteria, if you look at the aforementioned bullet designs you will see that the XCB stands apart from them. If you cannot see it in by looking, I would encourage you to shoot them side by side from similar alloys and see the effect on paper at HV and at longer range. The XCB might be more different than you think, because even the ogive of the bullet was set at an optimal curve for doing what we are doing with it.

[Bjornb]

Here is the 30XCB next to my new LBT bullet. The 30XCB was designed to work well in most factory chambers. The LBT requires a custom throat (1.5 degree included taper). I hear 2 degree included taper works very well with cast also.


Both bullets were cast using linotype. LBT on left weighs 159 gr. , 30XCB on right 155 gr.

Was the LBT mould cut to your specs or did Veral use your pound cast and cut it specifically to your rifle?

[runfiverun]

Bjorn: it's a lot simpler than that.[really]

and this xcb boolit ain't anywhere near the LEE, I have seen the drawing's for both.
looking at a boolit and making a comparison is gonna be about as far off as your gonna get.
you have to measure and measure and measure, included angles, sloping bands, and tapered nose areas are all going to affect your mechanical fitment in the throat.

B.T.W. just as a note.
Veral's boolit pictured above is more like what I was lobbying for when the XCB boolit was being developed.

[detox]

Was the LBT mould cut to your specs or did Veral use your pound cast and cut it specifically to your rifle?

I told him my throat reamer specs and he went from there. Veral is a very talkative and intelligent man who has learned lot's from his target shooting customers and on his own. Everyone should buy his book.

Frank's new bullet looks a lot like LBT's original designs (lots of full bearing surface), but has a more streamlined nose.

[detox]

On page 78 of Lyman's Cast Bullet Handbook 4th edition, you will see high velocity (2750-2794fps) loads listed using LBT's lghter weight 100gr bullet (311105). I bet this bullet has a steeper 2 degree included or 1 degree per side taper.

[Bjornb]

Bjorn: it's a lot simpler than that.[really]

and this xcb boolit ain't anywhere near the LEE, I have seen the drawing's for both.
looking at a boolit and making a comparison is gonna be about as far off as your gonna get.
you have to measure and measure and measure, included angles, sloping bands, and tapered nose areas are all going to affect your mechanical fitment in the throat.

B.T.W. just as a note.
Veral's boolit pictured above is more like what I was lobbying for when the XCB boolit was being developed.

I completely agree that looking at 2 bullets side by side doesn't tell much of the story. Reason I asked was that I have heard that Veral Smith wants to make the moulds HIS way or not at all. I own one of his 150 gr moulds; got it from a member here. It had a janky sprue plate, and Tim made a new one. I have hopes for the mould, even though it was specifically cut to fit the first owner's rifle throat. Haven't cast with it yet.

Detox, have you shot Frank's new bullet yet? Did you read the results we got when trying to shoot it? Care to share? How about the LBT? I started this thread because I wanted to share the development of both rifles and bullets involved in the XCB project. Now if there are BETTER designs out there I would certainly like to be made aware of them.

So I'm looking forward to your results with both the ELCO and the LBT; we can talk about bullets until we turn blue in the face but in the end it's the holes in the targets that count.

[Larry Gibson]

The long range rifle range here in Lake Havasu city (Sara Park Range) only goes to 300 yards. Once a month a bunch of us old timers have an informal shoot shooting under "F" Class or HP rules. With F Class and the 300/600 yard F class target is used at 300 yards and you can shoot prone or bench with a front rest. If shooting HP rules (prone unsupported with sling and iron match sights) the 200/600 is used if you want to shoot 200 yards or the 300/600 if you want to shoot 300 yards. I was looking for an "intermediate" load for Dawn or the Palma rifle to use in the F Class at 300 yards. By "intermediate" I mean a load that is still HV but not on the ragged edge which gives a bit of leeway for change in conditions (temperature) or slight variations in the load. I am looking for something in 2400 - 2500 fps range in the Palma rifle or 2650 - 2750 fps in Dawn that will hold the F Class 9 ring at 300 yards.......basically 1.5 moa. Not looking to win as there isn't any "winner" at these shoots. I just wanted to make a good showing with cast bullets is all.

The conditions at the range this morning were good temperature wise at it was 76 when I got there and was only 85 when I was done shooting. However the wind was a bear. It was running a steady 8 - 10 mph and would suddenly gust to 12+ mph. Worse yet was it was switching erratically from 10 to 2 o'clock.

I put a streamer up at 50 yards which helped a bit but I still got caught/surprised by erratic changes I did not catch in time. I tested one load in the Palma .308W rifle today at 100 yards that has always shown promise for such. The load was the 30 XCB bullet cast of linotype/WQ'd, sized .311, lubed with 2500+ and GC'd with uniformed Hornady's loaded over 48 gr of H4831SC in Winchester cases using WLR primers. The cases are well fire formed and were NS'd using a Lee Target Loader. A Lyman .31 M-die is used to give uniform neck tension. I had 15 rounds thus loaded. An additional 5 shots (not shown) of the same load were sighters/foulers loaded with a 311466. I shot all 15 30 XCBs into the same group in one string. I got caught twice by the wind when it shifted very quickly from 10 to 1 or 2 o'clock which bumped both shots to the left. The 13 good shots went into 1.185" but the overall 15 shot group was 1.8". The screened velocity (15' from muzzle using Oehler M35P) was 2426 fps. Computing back to muzzle velocity should give 2440 fps +/- fps.

Attachment 141325


I had previously worked up a load in the 30x60 XCB (Dawn) using the 30 XCB cast of linotype/WQ'd over IMR4895 and it showed promise also. However I wanted to use H4895 because it throws charges more consistently and is an "Extreme" powder and should be less temperature sensitive than the IMR4895. The previous IMR4895 test showed 39, 40 or 41 gr should perform well with in the parameters I was looking for of 2650 - 2750 fps with 1.5 or less moa. Thus I tested those three charges in the formed 30x60 Winchester cases. WLR primers were also used as was a Dacron filler as those powder charges are less than or right at 80% load density.

I did not have any sighters/foulers loaded so the first 2 shots of the 39 gr load may or may not be out of the group. The group was 2.1".

The wind really caught me a couple times on the 40 gr load test with switching strong gusts. The 8 good shots went into 1.35" but the 2 left shots where the wind caught me make the overall group 1.95".

Attachment 141326


I buckled down with the 41 gr load and really paid attention to the wind streamer but it's hard to concentrate on two things (the streamer and aiming/shooting) at the same time. I managed to put all 10 of those shots into 1.35" though.

Attachment 141327


Next is to load up 20 shots each of the .308W load for the Palma rifle and 20 each of the 40 and 41 gr loads for the 30x60 XCB and test them at 300 yards.

Larry Gibson

[Bjornb]

; we can talk about bullets until we turn blue in the face but in the end it's the holes in the targets that count.

Man, I actually had to quote myself!

If somebody has a better cast bullet design that consistently gives results such as these it would certainly be a treat to see it in print. Great shooting Larry.

[detox]

Detox, have you shot Frank's new bullet yet? Did you read the results we got when trying to shoot it? Care to share? How about the LBT? I started this thread because I wanted to share the development of both rifles and bullets involved in the XCB project. Now if there are BETTER designs out there I would certainly like to be made aware of them.

So I'm looking forward to your results with both the ELCO and the LBT; we can talk about bullets until we turn blue in the face but in the end it's the holes in the targets that count.

I am waiting for a short chambered barrel to arrive so that I can try the new LBT bullet. Both of my 308 have longer throats that are .300 and .600" long. The Accurate bullet on far right was instantly shooting very impressive groups when I first tried it.

I plan on taper bumping Franks bullet and trying different alloys. So far it has shot just as inconsistently as the 30XCB.

[Bjornb]

So far it has shot just as inconsistently as the 30XCB.

I looked back through this thread, but couldn't find any inconsistent shooting with the XCB bullet posted. Not trying to bust your chops here, but it would be very educational if you would post the details of shooting sessions where you found inconsistencies. The thread is named "Testing the XCB", so your testing of the bullet, complete with results, would be very much appreciated.

[detox]

Bjornb, I think a good cast bullet should shoot under one MOA consistently. So far I have not seen that with these precision chambered 30XCB rifles. You are welcome to use my throater (.310 x 1.5 included angle) and matching bullets to see groups improve. Just be careful not to cut throat too deep. Both the Accurate and LBT molds should work great in the 30XCB. I know for a fact the Accurate 200gr bullet did very well in my rifle .

[Larry Gibson]

Detox

"I think a good cast bullet should shoot under one MOA consistently."

A more precise criteria of your expectations would be appreciated. Expressive language without definition, especially without posted targets actually shot and associated data with such, is meaningless. Let me explain; numerous times I have shot 10 shot groups at 100 yards with the XCB bullet out of 2 different rifles at 2400 - 2900+ fps and have mentioned the first 5 shots went into less than 1 moa. I have also given the groups sizes for such in this and several other threads. Thus if you are comparing your 5 shot groups or even 10 shot groups to the posted 10 shot groups we've shown at lower than these actually tested higher velocities is the comparison valid?

Also some of us are still using the original criteria for the 30 XCB cartridge and 30 XCB bullet in 14" twist rifles which still concerns HV above 2400 fps to 2700+ fps holding 2 moa accuracy with linear dispersion to at least 300 yards. With the 14" twist .308W and the 16" twist 30x60 cartridge I am mostly concerned with 10 shot group accuracy of the same 2 moa holding linear accuracy to 300+ yards also. Thus if you are talking just "moa accuracy" of 5 or even 10 shots at less than those velocities (you've not said what velocities you are shooting at) is your comparison valid to what we are doing with accuracy and high velocity? If so could you please provide the groups and associated data so we may further understand?

Additionally I might add that there have been numerous threads over the past several years bespeaking volumes of we "think" should be on this topic of HV cast bullet shooting. Thus in reading the beginnings of this thread started by Bjorn and in particular his last post, #761, it appears to me Bjorn wants to keep this thread going not about what we "think" but about what we actually "do" in "Testing the 30 XCB" by "posting the results with complete details". I could be wrong on that but it's the impression I get. I've no problem with testing the 30 XCB at lower velocities or in comparison with other bullets. If you find "inconsistencies" with the XCB bullet we sure would like to see them with the associated test and load data? I'm not trying to "bust your chops" here either, just trying to explain what we are looking for.

Larry Gibson

[MBTcustom]

Hey, I'm willing.
Heres some nice three shot groups I just fired moments ago with the XCB bullet cast of House alloy, water dropped, lubed with 2700+, and a standard Hornady GC.
I was bored with these loads anyway. Figured I'd burn them up to make Detox happy.
These are three shot groups fired at a 100 yard target. Speed was 2650fps chronographed.
Attachment 141571
Attachment 141573
Attachment 141575
Attachment 141576

That was fun.
I'm going to reload now and get back to the purpose of this thread.