This topic contains 17 replies, has 1 voice, and was last updated by  Remmie 3 years, 7 months ago.

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  • #27537
     Larry Gibson 
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    Well I have posted numerous groups shot out of Dawn (30×60 XCB cartridge) with the NOE 30 XCB cast bullet at 2900 fps such as this one I shot today.

    Yes it is very nice but there are drawbacks to using that load in CBA matches which may be as few as 40 shots + sighters or as many as 80 shots + sighters. The first problem you have is recoil. Dawn weighs in just under 13 lbs and even at that weight a 164 gr bullet at generates enough recoil that over the long haul shooting from the bench it does get punishing. That means shooter fatigue sets in which reduces position consistency and begins to induce small flinches. With the amount of recoil it is imperative the shoulder tension be consistent If not flyers go high or low. Additionally after 35 – 40 shots fouling will reduce accuracy a bit, not a lot but enough to make you cry when shooting for group or score in a match. Being able to let the barrel cool and clean it may not be feasible in some matches. Better to have a load that can “go the distance” so to speak.

    Thus I went back through my initial test records looking for something else that may give as good accuracy but at a lower velocity. The testing with H4831SC looked very promising with 44.5 gr looking like a good load for further extensive 100 and 200 yard testing. So I loaded up 25 rounds to test; 5 sighters, 10 for group at 100 yards and 10 for group at 200 yards. I did not chronograph today but suspect the velocity to be 2300 – 2400 fps.

    After shooting the above group with the standard 2900 fps I let the barrel cool then ran a wet patch through the bore followed by a couple dry patches, shot 2 foulers which hit low left, moved the scope elevation up 2 moa and shot a .832″ ten shot group. This load was very comfortable to shoot so fatigue should not be that much of a problem in a high shot match. Overlaid on the CBA score target it would have scored 100 with possibly 4 Xs.

    Yesterday while loading those test rounds I scrunched a case mouth on the M-die, my fault I let myself get distracted. I salvaged the case by fixing a punch in the vise, slipping the case mouth over it and tapping scrunch back out gently with a small ball peen hammer. Having recently re read the Houston Warehouse story where in they discussed neck preparation being essential to best accuracy. Thus I loaded it with the same load as the test cartridges planning on, if the test load shot a decent 100 yard group, shooting that defective cartridge to see if accuracy was affected. Can you guess which bullet hole is the defective cartridge’s? A very good lesson learned there; if you have a rifle and load that can tell the differences then such nuances definitely need to be paid attention to. Here’s the “scrunch” inside and outside on that case.

  • #27538
     Larry Gibson 
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    The wind had been running a very mild 0 – 3 mph coming out of 6 o’clock. However, as soon as I put a target up at 200 yards it increased to 3 – 6 mph and was constantly switching back and for the fro 4 to 8 o’clock. It caught me good on one shot. The 9 “good” shots went into 1.837″ at the 200 yards. Comparing the 100 yard .832 group and the 9 shot 1.837 we see very close to excellent linear group expansion. The shot to the right increased it to 3.162″ Overlaid on the CBA target it still would have scored 96 with 3 Xs.

    Next I’m loading up 60 of the same load for a thorough test at 100 and 200 yards shooting three 10 shot groups at 100 yards and three 10 shot groups at 200 yards. If all goes well I’ll be shooting Dawn with this load in the next CBA match at the Been Avery Range in Phoenix on 29 May.

    Larry Gibson

  • #27539
     oldblinddog 
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    Those are fine groups! And a fine rifle! I see winning in your future.

  • #27542
     Sgt. Mike 
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    Which weight class Larry for DAWN you placing her in

  • #27543
     Larry Gibson 
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    Dawn fall’s into “Heavy Rifle ” class.

  • #27545
     Goodsteel 
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    Very interesting about that slightly damaged case neck and the flier Larry. I suspect that our cast bullet loads are much more sensitive to such things than jacketed loads are (amongst other things).
    Some of my rifles put a ding that bad in the necks just by briskly ejecting the brass from the rifle. So the act of ejecting the brass could potentially double the size of the groups. anybody who thinks brass prep and quality is a marginal issue should take a good long look at the implications of what you just demonstrated.
    Bravo sir!

  • #27652
     Kevin S 
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    If a case is damaged like the one you had Larry. After several firings would a case return to a condition equal to the other brass cases?

  • #27658
     Larry Gibson 
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    Kevin S;n6612 wrote: If a case is damaged like the one you had Larry. After several firings would a case return to a condition equal to the other brass cases?

    I do not know, but we shall see. I plan on continuing to test that case and see if it ever returns to an “accurate” status.

    Larry Gibson

  • #27667
     chutesnreloads 
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    A good question Kevin.I’m curious about that too.

  • #27727
     Sgt. Mike 
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    Correct me if I’m speaking outta school here Larry but DAWN thus far has never fired a jacketed bullet since the 1-16″ barrel went in.
    And Barrel wear (throat wear actually) has been barely noticeable. Best of Luck in your weight class.

  • #27733
     oldblinddog 
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    Do you have a chamber drawing or, alternatively, would you mind describing the 30×60 XCB cartridge again? I know you did over at CBF, but would be nice to have that here as well. Thanks.

  • #27740
     Remmie 
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    Larry, I was wondering if you could post your techniques for brass prep. Obviously what you are doing works extremely well and maybe we could identify short comings in our methods. Thanks, Jack

  • #27747
     Larry Gibson 
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    Sgt. Mike;n6693 wrote: Correct me if I’m speaking outta school here Larry but DAWN thus far has never fired a jacketed bullet since the 1-16″ barrel went in.
    And Barrel wear (throat wear actually) has been barely noticeable. Best of Luck in your weight class.

    Actually just about a year ago at round count 1201 I shot 5 jacketed bullets through Dawn. They were the jacketed that have been through her. I was just curious to see how the Nosler 125 Ballistic tip would do. These are a bit long for the 16″ twist and at 2900 fps the Sg was in the low 1.3s. I just used a max load for the .308W with that bullet using IMR4895. The five shots went into .61 which I though was close enough. I’ve considered trying the Sierra 130 gr MKs but other than that I’ve not had any interest in shooting any other jacketed through Dawn.

    When unfired I measured the distance from bolt face to the leade at 2.473″. At 1010 rounds it was still 2.473″. Just last week at 1681 rounds the measurement was still 2.473″> I can see no measurable throat erosion so far.

    Larry Gibson

  • #27748
     Larry Gibson 
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    oldblinddog;n6699 wrote: Do you have a chamber drawing or, alternatively, would you mind describing the 30×60 XCB cartridge again? I know you did over at CBF, but would be nice to have that here as well. Thanks.

    I only have a hard copy of the 30 XCB. I tried scanning it but it didn’t come out to clear. I’m sure Tim can post a drawing?

    The 30 XCB cartridge is a very refined end product of an original idea I had many years back; to simply shorten standard 30-06 dies creating a cartridge with just a grain or two more than the .308W having the ’06 length neck and the body taper to feed through Mauser actions (M91 thru M98s), particularly those with the shorter actions, with out any feed rail or other magazine modifications. I simplified the length by making the cartridge a 30×57. This was done so 30-06 case could be formed or more simply to use 8×57 cases. Standard 30-06 dies could simply be shortened negating the need for custom dies. A standard 30-06 or, preferably, a match reamer with a tighter neck could be used to just short chamber the barrel for the shortened case. A 12 or 14″ twist barrel of 26″ or longer was also part of the concept. If the standard M98 action with a 3.3″ magazine was used then the chamber could be deepened simply by running the reamer in deeper until the size of the desired cartridge was met up through the 30-06 length. Tim called me after I began the RPM Threshold thread and posts on CBF as I was already pushing 2600 fps with the .308W using a Lyman 311466 in a 14″ Palma rifle. Contrary to the super mod on CBF those RPM Threshold threads were very productive and led the way to the 30 XCB cartridge and the 30 XCB NOE bullet.

    Tim took the concept of the 30×57 and using 3 formed cases I sent him he had a very precise reamer made and he named it, with my blessing, the 30 XCB to differentiate it from my 30×57. At the same time we cogitated on the 30 XCB bullet and the throat of the 30 XCB cartridge was made to fit the bullet. Turned out to be a perfect marriage. Tim made several 30 XCB rifles including Bjorn who did extensive load work initially with it. At the same time I was doing extensive shooting and pressure testing of the 30 XCB bullet at high velocity in my Palma .308W rifle. Based on Bjorn’s and my results I determined the case capacity of both the 30 XCB (30×57) and the .308W were about 3 -4 gr short in capacity for the projected 2800 – 2900+ fps with consistent sub 2 moa accuracy that was linear in group dispersion to 300 – 400+ yards that I believed was possible with a cast bullet of ternary alloy. Thus I ordered a Broughton 3 groove barrel 32″ long with a Palma contour and had them send it to Tim. I then sent Tim a CZ24 M98 action to install it on. I also sent 3 formed cases for a bit longer case than the 30 XCB that increased the case capacity 4 gr of AA4350 powder for time to run the 30 XCB reamer in a tad deeper than the 30×57……..Tim worked his magic and the 30×60 XCB was born.

    The five cartridge shown are, from left to right; the .308 CBC (a shortened .308W with an ’06 length neck), the .308W, the 30×57, the 30×60 (my first rough formed case) and the 30-06. They all have a 30 XCB bullet seated.

    Larry Gibson

  • #27750
     Larry Gibson 
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    Remmie;n6710 wrote: Larry, I was wondering if you could post your techniques for brass prep. Obviously what you are doing works extremely well and maybe we could identify short comings in our methods. Thanks, Jack

    For really accurate loads I use cases of one lot. For the 30×60 I form the cases using virgin Winchester 30-06 cases. I’ve done 3 lots of 100 each and keep them separate in MTM 50 round boxes. I also track the number of times fired and keep each lot separate.

    I’ll address my brass prep after the cases are initially formed. The formed case receive a final trim to length with a Forster case trimmer and are cleaned. The cleaned cases are then FL sized again in the shortened RCBS FL 30-06 die. The necks are then outside neck turned with the outside neck turning attachment for the Forster case trimmer. The XCB chamber neck runs .337 so I turn the necks for and outer diameter of .336 with a .310 sized XCB bullet seated. That gives .0005 neck clearance around the cartridge neck. The case mouth is lightly chamfered inside and out with a Lyman tool. The flash holes are then uniformed and deburred with the Lyman tool for that job. That’s about all the initial case prep I do.

    After the cases are fired I clean them in an old Thumbler rotary tumbler using long grained rice with a bit of Frankford Arsenals case cleaner in it. I neck size the cleaned cases with a shortened Redding ’06 bushing die with a .333 bushing. The press used is a Forster COAX. I put a very small swipe of lanolin on the necks for sizing and wipe it off immediately with an old T-shirt. I then clean the primer pockets and inspect each case for debris in the case or flash hole. I then use a Lyman .30 M-die which is a snug fit inside the case necks and flares the case mouth just enough so the bullets starts into the case to the depth of the GC. This keeps the necks very concentric and provides .002 – .003 neck tension on the .310 sized 30 XCB bullets. I seat the primers using an RCBS bench priming tool. The powder charges are thrown using a Lyman 55 powder thrower. The bullets are started into the case and then seated in a standard shortened RCBS 30-06 seating die in the Forster COAX press. I had intended on using a Bonanza Benchrest Micrometer seating die but found I would have had to honed the bullet guide out for the .310 diameter bullets and I didn’t want to do that. Also shortening the seating collet probably would have been a problem. I tried the standard seater and found it worked just fine and produces very concentric cartridges. Yes, I do spin test for concentricity with usually 5 – 8 randomly selected cartridges and find they are all consistently very uniform (under .003 run out with .000 to .0015 being the norm). I also seat the bullets to an OAL so the bullet is slight seated into the leade.

    Here’s some freshly formed cases.

    Larry Gibson

  • #27751
     Sgt. Mike 
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    Larry Gibson;n6717 wrote:

    Actually just about a year ago at round count 1201 I shot 5 jacketed bullets through Dawn. They were the jacketed that have been through her. I was just curious to see how the Nosler 125 Ballistic tip would do. These are a bit long for the 16″ twist and at 2900 fps the Sg was in the low 1.3s. I just used a max load for the .308W with that bullet using IMR4895. The five shots went into .61 which I though was close enough. I’ve considered trying the Sierra 130 gr MKs but other than that I’ve not had any interest in shooting any other jacketed through Dawn.

    When unfired I measured the distance from bolt face to the leade at 2.473″. At 1010 rounds it was still 2.473″. Just last week at 1681 rounds the measurement was still 2.473″> I can see no measurable throat erosion so far.

    Larry Gibson

    Yeah, there are some whom claim how abrasive the alloys that are selected are on the bore just wanted to dispell that falsehood.

  • #27753
     oldblinddog 
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    Thanks for the write up. This picture tells the tale.

  • #27767
     Remmie 
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    Thanks Larry, I see several things that will improve my brass prep.

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