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Larry Gibson
I’ve just completed a test of the NOE 30 XCB bullet in 10” and 12” rifles. Was it a complete test? No. Did I seek the best accuracy? No. What I did was push the XCB to high velocity while maintaining acceptable accuracy where most all other cast bullets lose accuracy. Before we get into the test results let me explain the test parameters.
The rifles: the 10” twist rifle is a M1909 Argentine made M98 action with a 24” Adams & Bennet barrel having a 10” twist and chambered in .308W. The barreled action is bedded in a wood sporter stock (Churchill Arms, England). The action has not been trued. The chamber was finish reamed to minimum headspace with a Clymer M118 Match reamer. The rifle shoots right around 1 moa (10 shot groups) with selected match loads using 168 or 175 Sierra MKs. The rifle has an old original Weaver K-10 scope on it.
The 12” twist rifle is a M70 Heavy Varmint rifle with a 26” factory barrel on it. It has been pillar bedded and a rail put in the fore end for a hand stop. It is a very accurate rifle and shoots ½ moa with 175 MKs. I’ve “cleaned the 600 yard line several times with it and the 1000 yard line a couple. For testing it has a Redfield Ultimate 4×12 scope on it.
The 30 XCBs were cast of Lyman #2 alloy and WQ’d out of the 4 cavity aluminum NOE mould. The BHN runs 22 – 24. They drop at .3105. The bullets were visually inspected and any visible defect rejected the bullet. The visually passed bullets were then weight sorted to +/- .1 gr. Hornady GCs were crimped on using a .311 H&I die in a Lyman 450 with the GC seater used. They were then light lubed with a spray lanolin lube and pushed through a Lee .311 sizer to fully crimp the GC on. The GC’d bullets were then lubed in the .311 H&I in the 450 lubrasizer and lubed with 2500+ lube. Fully dressed the bullets weighed 164.7 gr.
Cases were match prepped LC Match. Primers were WLRs. Cases were fire formed and neck sized with a Redding Bushing die to give just a slip fit over the NOE M die expander (a very neat tool BTW) for Lee case mouth expander die.
Already knowing which powders gave the best high velocity accuracy with the Lyman 311466 and the LBT 30-160-SP bullets in both rifles I chose to use the same powders under the NOE 30 XCB bullet. That would give a good comparison. Thinking the NOE 30 XCB should withstand a bit higher acceleration each powder was loaded over the point where the Lyman and LBTs went over the RPM Threshold and lost accuracy.
That brings up “accuracy”. The objective of this test and the other XCB tests was to push to the highest velocity possible while maintaining 2 moa or less accuracy with linear expansion at 200 and 300 yards or further for 10 shot groups. Why 2 moa? Because that is the useable accuracy criteria those of us running these tests chose. The 2 moa criteria has been the high power standard for many years. You can kill deer, coyotes and such all day long with a 2 moa rifle. Some have a hard time with “useable” and seem to grasp “reasonable” as a good measure. The two mean the same. That criteria was chosen because the primary objective is high velocity with accuracy. Once we find out the upper end of velocity with one set of components that maintain 2 moa or less then we can tweak the load and components for best accuracy, if we want to.
All velocities (muzzle) were measured with the Oehler M43 PBL. For each shot the screened velocity was recorded along with a “proof”, a pressure trace was recorded and the peak pressure and associated Area and Rise of the pressure were recorded. The averages of velocity and the pressures along with their SD & ES were computed. The screened velocity was converted to muzzle velocity. On the data sheet for each test string I traced the bullet holes, measured group size (ctc) for record and computed the RPM. Most of the test strings are of 10 shots but 3 have 9 shots (out of 20 test strings). I also tracked each shots location on the target and numbered each bullet hole on the data sheet accordingly. This gives a very clear understanding of what is happening during the internal ballistic phase. This test produced 20 data sheets (both rifles) so I will not post them all. I will post the pertinent ones that show the top end capabilities of the NOE 30 XCB as tested in each rifle.
For those enamored with 5 shot groups it is interesting to note that in tracking the shots on target in 7 of the 20 test groups the first 5 shots went into less than 1 moa (1 in the 10” twist and 6 in the 12” twist). Thus, based on 5 shot groups, we could claim that 35% of our groups were “sub moa” and thus our loads were. However in doing that we would only be fooling ourselves.
I have often stated the RPM Threshold (120,000 – 140,000 RPM) is not a “limit” but could be pushed up. I have said two of the prerogatives for doing so is to use a slower burning powder to slow the acceleration rate and to use a properly designed cast bullet of appropriate alloy to with stand that acceleration rate. The NOE 30 XCB bullet was design expressly for high velocity. It is succeeding exceedingly well at 2600 – 2800+ fps in 14” twist barrels. Let us see how well it does at higher velocity and RPM in the 10 and 12” twist rifles.
The 10” twist rifle (24” barrel) results;
I chose two powders to test under the NOE 30 XCB bullet in the .308W rifle with 10” twist; RL19 and RL22. Both of those powders gave the best accuracy out of this rifle with the Lyman 311466 and LBT 30-160-SP cast bullets. Both of those bullets began going over the RPM Threshold at about 2300 fps/165,000 RPM with RL19 and about 2350 fps/169,000 RPM with RL22. Note how both of those bullets and powders have pushed up the RPM Threshold over the incorrectly assumed “limit” of 140,000 RPM. Both of those bullets held under 2 moa accuracy with linear expansion at 200 yards. Thus with that baseline to measure against I loaded test strings of 38, 40, 42, 44 and 46 gr of each powder to test the NOE 30 XCB bullet.
The 38 gr load of RL19 gave 1938 fps, 139,536 RPM at 28,100 psi(M43). The group size for 9 rounds was 1.2” (I excluded the 1st shot out of the cold clean barrel which always drops low out of the group). Shots 2 through 6 went into .85”. The ES was 146 indicating that RL19 does not ignite and burn efficiently at this pressure. A dacron filler probably would have helped that but no filler was used.
The 40 gr load of RL19 gave 2075 fps, 149,400 RPM at 31,100 psi(M43). The group size was 1.5”. The ES immediately tightened up to where it should be. In fact this test strings ES or 37 fps and SD of 11 fps were excellent.
The 42 gr load of RL19 gave 2194 fps, 157,968 RPM at 35,000 psi(M43). The group size was 1.65”
The 44 gr load of RL19 gave 2313 fps, 166,536 RPM at 38,900 psi(M43). The group size was 1.55”. Again an excellent ES of 30 fps with the SD at 9 FPS. The Pressure ES was 1,200 psi with an SD of 400 psi which is excellent and demonstrating excellent ignition and uniform burn.
The 46 gr load of RL19 gave 2434 fps, 175,248 RPM at 43,700 psi(M43). As with the much slower 14” twist rifle I am finding the psi of 41,000+ to be very hard on cast bullets of this alloy. We see while the group size is 1.9” there are 2 and probably 3 flyers telling us that this load is exceeding the RPM Threshold or, at least those 3 shots were. Dropping the load to 45 gr would probably give close to 2400 fps at 41,000 or less psi and still give us the 1.5 +/- accuracy level we’ve achieved with the other loads. That is a 100 fps +/- increase over the Lyman 311466 and the LBT 30-160-FN bullets in this rifle with RL19. That is indicating the NOE 30 XCB bullet is indeed holding up better under the high rate of acceleration and RPM generated in this 10” twist rifle.
Larry Gibson
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Replies
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suemunger
Thanks Larry for all your work, and thank you Dr. Owl Creek for making me aware of this forum. I have some catching up to do reading wise.
This Summer I had the opportunity to buy a rifle from the estate of an old High Power shooter. It features a pre-64 Model 70 NM action set up as a single shot in a home made stock with an adjustable cheek piece. It has a heavy stainless Douglass 2XX barrel in .308 with a 1/10 twist. It has a Weaver K-15 scope on it. I got it so cheap I couldn’t resist. I have too many hobbies and right now is ice fishing season, but your work with the 10 twist has certainly fired me up.
What little work I have done with the rifle shows me it is set up tight. In order to shoot .310″ bullets I had to lightly neck turn the brass or else I experienced difficulty chambering. I recently got a .309″ push through sizer and that may help.
Come Spring I think I’ll give this rifle the attention it deserves. Larry, do you believe the 30 XCB bullet would prove useful for sub 1,800 fps use, and do you have any thoughts on powders that would provide a gentler push yet still burn efficiently at the pressures involved at those lower velocities?Duke
sgt.mike
patrickharrington
Oh, a perhaps the biggest difficulty. Just how does a person go about buying a 30-165-fn-xcb mould anyway? Is this an in inventory item, or was it a group buy mould no longer available?
Duke
You are in Luck, looks like one left
http://noebulletmolds.com/NV/product_info.php?cPath=30&products_id=915&osCsid=196q2kf7ogocfci1on8bua90d7Oh, a perhaps the biggest difficulty. Just how does a person go about buying a 30-165-fn-xcb mould anyway? Is this an in inventory item, or was it a group buy mould no longer available?
Duke
You are in Luck, looks like one left
http://noebulletmolds.com/NV/product_info.php?cPath=30&products_id=915&osCsid=196q2kf7ogocfci1on8bua90d7LOL if nothing else call AL, and get on the next time he does a run on them. Probably won’t be as long a wait as you think. No where near like a two to three year wait on some Mihec mold group buys.
Larry, do you believe the 30 XCB bullet would prove useful for sub 1,800 fps use, and do you have any thoughts on powders that would provide a gentler push yet still burn efficiently at the pressures involved at those lower velocities?
Duke
I’m sure the 30 XCB bullet will prove excellent at the lower velocity end. The usual suspects from 2400 up through 4895 should burn efficiently in the 1800 -+ fps range. I plan on testing the 30 XCB thoroughly from 1700 – 2200 fps with several of those powders in my 12″ twist .308W M70 Target rifle when I get the chance. However, given the 30 XCB chambered rifles already around with faster twists they may have solid information before I do.
Larry Gibson
ianharris
The AM 31-190X is a tack driver at lower velocities, I would expect the same from the 311-165 NOE bullet, particularly in ’06/XCB throats which match the nose angle pretty much exactly unless they are worn to the usual “worn throat” configuration, which is different. The “nose bump” crowd has been doing this for nearly a hundred years and it does work well provided you get things like seating depth, alloy type, and powder charge correct to make the system work. Each static fitment technique has its own set of loading parameters for optimal results, for example if the alloy is “too soft” and/or the pressure rise is too rapid, AND the bullet is seated to fully contact the throat, base riveting and alloy extrusion into the area in front of the case mouth will result. Giving the bullet a “run” at the throat will cure this, but introduces high probability for misalignment which defeats the purpose angle-matching in all but the tightest of chamber neck situations.
Gear
timknowles
suemunger
sgt.mike
patrickharrington
ianharris
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