Range Report: AR-Comp & NBT 120

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  • Range Report: AR-Comp & NBT 120

    Though it predictively falls at the slower end of powders appropriate for the 6.5 Grendel, the Alliant AR-Comp powder has the attractive property of being temperature stabilized from -20 to +160 F. It has produced some phenomenal performance in my .300 OSSM, so I thought I'd give it a brief trip to the batter's box. It was assumed to have burn characteristics typical of Varget, but my experience in the .300 puts it between 8208XBR and RL-15. Definitely faster than RL15. Being an extruded powder, the specter of load density looms over it and in practice, it was indeed a limiting factor, much like my experiments with RL15 and Varget in this caliber.

    Search as I may, I have yet to find data that can be plugged into QL, but have had some success starting with RL15 data and increasing the Ba. I started intentionally low in charge none the less and chose NBT 120s because I had some left over from my HBN testing, to use up. From previous tests, that coating costs roughly 5% velocity loss, so figure that into the results. I will probably retest with 123 Amax's just to see if it I can compete with the excellent results that 8208 provide with that bullet. 8202 seemed to be a little fast for the 123 Amax, so perhaps a happy accord can be found with AR-Comp. Fortunately, I didn't have to order the AR-Comp. A philanthropic source provided me with an 8lb jug of it to experiment with across different calibers. I never turn down a fee meal.

    While I did not set out to find any absolute accuracy nodes in order to cover a wide range of charge weights for the limited number of NBT 120s I had on hand, I was nonetheless pleased with the results as they show promise. Range conditions were near ideal as the weather finally broke. I started out at 75 degrees and ended at 79, with low humidity and only a light head-on breeze. The trade-off for having a range 8 minutes from the house is that it is limited to 100 yards on the rifle range.

    The issue of granule size and shape did not lend well to hign density loading, even after vibrating each charge on the variable vibration table to settle them in. You could hear the heal of the NBT moving grains out of the way, but not actually cracking them. I am no fan of compressed loads to the extent that I have a second-hand stethoscope and actually listen closely on experimental loads, for any signs of that. Yeah, I'm weird, but experience has taught me that predictive performance moves out of the linear phase and into non-linear when a load gets compressed. I don't like surprises.

    So, here's a dalliance into AR-Comp



    The 25.5 gr loads were used to sight in a scope change (Nikon Monarch 6-24x50SF) and were all over the place as I dialed in, so they are not included in the following accuracy images.



    There was a little displaceable granule room left in the cases for the 120 NBT and with the right profile bullet, you might be able to get a little more in before it compresses. Going with non-HBN plated bullets will gain you back a little velocity as well. Given that none of the tested loads exhibited any pressure signs or short-strokes, there may be promise for this powder. The real test will be with the 123 Amax's.

    Hoot

  • #2
    Originally posted by Hoot View Post
    Range conditions were near ideal as the weather finally broke. I started out at 75 degrees and ended at 79, with low humidity and only a light head-on breeze.
    Sorry, Hoot, but I never got past this part!!! With Heat Indexes between 105 and 110, we barely make the upper 70's for a nighttime low.

    Now I'll go back and read the whole thread.

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    • #3
      Originally posted by RStewart View Post
      Sorry, Hoot, but I never got past this part!!! With Heat Indexes between 105 and 110, we barely make the upper 70's for a nighttime low.

      Now I'll go back and read the whole thread.
      We, atypically had those kind of miserable conditions for just about the past month. Heat indices got as high as 118 IIRC. People were starting to bicker and bite their hindquarters. A cool front saved us, but then the past few days in the morning, my smell memory which is separate from my cognitive memory has been telling me that we've turned the corner. It usually comes around the 3rd week in July, but this year, everything's slewed a couple of weeks. Crickets aren't chirping yet, so it's more than six weeks until first frost. Could be a warm deer season come November 5th. That's a double-edged sword...

      Hoot

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      • #4
        Originally posted by Hoot View Post
        We, atypically had those kind of miserable conditions for just about the past month. Heat indices got as high as 118 IIRC. People were starting to bicker and bite their hindquarters. A cool front saved us, but then the past few days in the morning, my smell memory which is separate from my cognitive memory has been telling me that we've turned the corner. It usually comes around the 3rd week in July, but this year, everything's slewed a couple of weeks. Crickets aren't chirping yet, so it's more than six weeks until first frost. Could be a warm deer season come November 5th. That's a double-edged sword...

        Hoot
        It must be nice to have 4 seasons. Here we have 2- rake and mow!

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        • #5
          Originally posted by RStewart View Post
          It must be nice to have 4 seasons. Here we have 2- rake and mow!
          Here in New Mexico the two seasons are DRY and BURN.

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          • #6
            Originally posted by davidj View Post
            Here in New Mexico the two seasons are DRY and BURN.
            Nice! I like that.

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            • #7
              Hoot,

              That's a great range report. I like the excel format and your detailed description of your load development with this powder and the 120 NBT's. What barrel length were you pushing those through?

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              • #8
                Originally posted by LRRPF52 View Post
                Hoot,

                That's a great range report. I like the excel format and your detailed description of your load development with this powder and the 120 NBT's. What barrel length were you pushing those through?
                Wish I could blame it on a 16" carbine barrel, but it is a 24".

                Historically, I get faster velocity for the same charge from the 123 Amax than the 120 NBT, so lets hope that remains the case. You know, that just made me look back a few pages here at my NBT 120 HBN and 8208 Range Report and lo and behold. I'm getting faster non-pressure indicating velocities with the AR-Comp at 27 and 27.5gr charges. Things are looking better already!

                Unfortunately, we are closing our 8 bench rifle range this coming Saturday to pull off the superstructure for replacement the following Saturday, assuming we stay on schedule. A lot depends upon whether the volunteer carpenters and the lumber yard come through as promised. So, if I'm going to make a timely move, it'll have to be one day this week after work, before I have to pick up the wife from the Park-N-Ride. We can't afford to drive both the vehicles alone anymore. My aging F150 with it's 5.4L is a guzzler. Reliable, but a guzzler.

                Hoot
                Last edited by Guest; 08-09-2011, 03:24 PM.

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                • #9
                  I'm planning a followup visit to the range Wednesday, to try the Amax 123 with this powder. FWIW, I have an email into ATK for either a canned powder file thast imports directly into QuickLoad, or a list of parameter values that I can use to create the file myself. Not sure if they'll share that kind of information yet or not. Time will tell. In the mean time, they do have some caliber specific recipes for this powder and in both the .223 and .308, it really outdistances some of the common powders I use for those calibers in terms of velocity, assuming we can get the same results as they published, at home. I have been reverse engineering those recipes into QuickLoad and playing with the choice of powder and the Ba to get similar results. In the case of their published .308 recipes, it looks like Vihtavuori N530 with the Ba bumped approximately 1-2%, achieves the same results with the heavier bullets say in the 168gr and up. How that correlates to the grendel, remains to be seen. They have a smaller set of recipes for the .243, which may be a closer approximation. That's my next check after I iterate out the .308 loads, then I'll see which more closely approximates the tweak necessary to predict Grendel performance.

                  Hoot

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                  • #10
                    Originally posted by Hoot View Post
                    ...snip... I have an email into ATK for either a canned powder file that imports directly into QuickLoad, or a list of parameter values that I can use to create the file myself. Not sure if they'll share that kind of information yet or not. Time will tell...snip
                    Hoot
                    According to Ben Amonette at ATK, one of the Engineers has been in contact with the author of QuickLoad regarding the powder data. He advised me to check wherever QuickLoad's author puts updated or new powder files for download.

                    Anyone know the FTP or Web site that QuickLoad's author maintains for doing that?

                    Hoot

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                    • #11
                      Originally posted by Hoot View Post
                      According to Ben Amonette at ATK, one of the Engineers has been in contact with the author of QuickLoad regarding the powder data. He advised me to check wherever QuickLoad's author puts updated or new powder files for download.

                      Anyone know the FTP or Web site that QuickLoad's author maintains for doing that?

                      Hoot
                      Apparently ATK was jerking me around as Ed at Neconos said that Hartmut has not told him of having gotten any new powder information from ATK.

                      Perhaps one day...

                      I did order some Amax 140s on sale at Midway to give a try anyway. If they don't work out in the Grendel, I can load them for my .260 Remington instead.

                      Hoot

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                      • #12
                        Hoot,

                        Did you ever give those 140's a go? I am thinking on buying a can of this powder to run behind my 139 gr Scenars and 142 gr SMK's.

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