300 PRC Load Test - Unexpected Results

rustyinbend

rustyinbend

GySgt USMC 1976-1992
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Minuteman
    • Dec 9, 2018
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    Bend, Oregon
    #1
    This is just a "Share With The Gang" post ... so ignore if you're not into those kinds of threads ...

    So I've been working hard to settle on a reference load for the 300-PRC barrel on my Barrett MRAD ... something to enter the competition season this spring. My available projectiles are Berger 220 LRHT, and Hornady 225 ELDM. My powders are Accurate MagPro and Hodgdon Retumbo. Ladders gave me good feelings about MagPro at 78.2 grains, and Retumbo at 77.4 grains (Lapua 1x cases and Federal GM215M primers) ... so I loaded 6-round group tests for that 4-way combo. I've been typically getting good and predictable results from MagPro and Bergers in other calibers (300-WM and 338-LM), so I expected those to "win". Not so fast ... data is listed below in the following order:
    1. MagPro & Berger
    2. MagPro & Hornady
    3. Retumbo & Berger
    4. Retumbo & Hornady
    The bottom line here is that the Hornady 225 ELDM's outperformed the Berger 220's across the board, in both powder configurations, by a LOT. I just didn't expect that given how well Berger bullets work for me in other calibers, and given the Hornady's are much easier to find than the Bergers. BTW ... groups tended to favor the Retumbo combinations, with the best (sub-MOA) group coming from the Retumbo-Hornady combination, but the MagPro-Hornady combination also grouped nicely.

    Next test will be to load a dozen each of the two Hornady ELDM configurations, and really mega-concentrate on groups at 100 yards, and then take the winner to our mile-range and see how it performs.

    I guess that's way we test ... eh?

    Data follows:

    1642964022128.png

    1642964038873.png

    1642964054009.png

    1642964069679.png
     
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    #2
    Honestly not sure that the bullet a certain cartridge was designed around performing well in that cartridge is overly surprising. Maybe we tend to exaggerate the differences between bullet makes here a bit. On the other hand, I would not get particularly discouraged about the Bergers. Those are short strings, and especially with the magpro it was really one round. And, of course, we are in the game of shooting targets, not standard deviations! An SD of 12 is never going to hurt you.
     
    #3
    Not discouraged at all about the Bergers ... it's great to have multiple options in these times of supply chain disruption. I've been waiting 6 months for backordered B-220-LRHT, but was able to find as many H-225-ELDM's as I wanted. Groups at 1,000 yards later this week will tell the real story.
     
    #5
    918v said:
    I’m thinking the reason the Hornadys did better is because they have a longer bearing surface and combusted the powder better. Yes? No?
    Click to expand...
    Doesn't appear to be the case, as (a) the boat-tail is the same, and (b) I don't seat into the start of the ogive, and (c) I use the same seating depth for both bullets. I do think the heavier bullet might play better with my twist rate (1:8).
     
    #6
    Hey Rusty,

    Any updates on your progress or updates on your LD?

    Just got my 300 PRC put together. Gonna be testing 230gr A-Tips with 7828ssc and LRT soon because that's what I have to play with at the moment. Optic coming in this week with Rings. I'll post my progress in the 300 prc thread since Retumbo and H1000 are currently unobtanium it be interesting too how these fringe powders do.
     

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    #7
    Andrevius said:
    Hey Rusty,

    Any updates on your progress or updates on your LD?

    Just got my 300 PRC put together. Gonna be testing 230gr A-Tips with 7828ssc and LRT soon because that's what I have to play with at the moment. Optic coming in this week with Rings. I'll post my progress in the 300 prc thread since Retumbo and H1000 are currently unobtanium it be interesting too how these fringe powders do.
    Click to expand...

    If you can get ahold of n570, 230 a-tips and ~80gr = 2850 or so and it shoots very nice with pleasant recoil.
     
    #9
    Andrevius said:
    Hey Rusty,

    Any updates on your progress or updates on your LD?

    Just got my 300 PRC put together. Gonna be testing 230gr A-Tips with 7828ssc and LRT soon because that's what I have to play with at the moment. Optic coming in this week with Rings. I'll post my progress in the 300 prc thread since Retumbo and H1000 are currently unobtanium it be interesting too how these fringe powders do.
    Click to expand...
    I've got good 300-PRC reference loads now that are shooting accurate and long ... one with MagPro, and one with Retumbo. Both with Hornady 225 ELDM's shooting better than the (unobtainable) Berger 220's. I'm pretty much "done" with load development on this caliber since I have good results, reproducible SD's, tight groups, and everything I need to shoot until this barrel is toasted. It's time to "load and shoot". I've actually been "right place - right time" to get a bunch of Retumbo in the last few weeks. Not quite a "miracle" ... but close. And I already had a ton of MagPro.

    1647957199586.png
     
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    #11
    Choid said:
    Those SDs aren't reasonable for any string long enough to be relevant.
    Click to expand...
    I'm not sure I understand your point. I've used those two load recipes, and reproduced ... not identical ... but certainly very low (single-digit) SD's with dozens of cartridges, and I'm confident this load is delivering accuracy and consistency that I'm happy with. If you're saying the small size of the initial test groups isn't good enough ... I agree ... and I've validated the accuracy and low SD's for both recipes.
     
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    #12
    I'm saying SDs of 2.x aren't reasonable, especially for an 80 grain cartridge. That doesn't mean you shouldn't be happy with the loads, it is just improbable that you are getting these spreads.
     
    #13
    rustyinbend said:
    I'm not sure I understand your point. I've used those two load recipes, and reproduced ... not identical ... but certainly very low (single-digit) SD's with dozens of cartridges, and I'm confident this load is delivering accuracy and consistency that I'm happy with. If you're saying the small size of the initial test groups isn't good enough ... I agree ... and I've validated the accuracy and low SD's for both recipes.
    Click to expand...

    He's saying you didn't fire enough rounds to call out those SD's with statistical confidence. He's right...but it also means your other loads with higher SD's are also going to be even higher if you fire more rounds.
     
    #14
    Sure, with more rounds it's likely and liable to grow, but who all is shooting 20 rounds every time to they reload validate their SC, but if I validate a load with 10 rounds in the beginning and confirm with 5 rounds with each reload and it's close with minimal variation in overall numbers. I'm happy and that is more than sufficient. Whether it's a true SD of 2 or maybe its actually an SD of 5. Single digit SDs will keep me on a Minute of Man and pretty damn close to a minute of angle out to a mile.

    Appreciate your inputs, but not what we're trying evaluate here. If you all have any more insights on atypical powder loadings and bullet combos for 300 prc, I'm excited and all ears.
     
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    #15
    Andrevius said:
    Sure, with more rounds it's likely and liable to grow, but who all is shooting 20 rounds every time to they reload validate their SC, but if I validate a load with 10 rounds in the beginning and confirm with 5 rounds with each reload and it's close with minimal variation in overall numbers. I'm happy and that is more than sufficient. Whether it's a true SD of 2 or maybe its actually an SD of 5. Single digit SDs will keep me on a Minute of Man and pretty damn close to a minute of angle out to a mile.

    Appreciate your inputs, but not what we're trying evaluate here. If you all have any more insights on atypical powder loadings and bullet combos for 300 prc, I'm excited and all ears.
    Click to expand...
    EXACTLY ... well-stated, Sir. If I can get a tight 5-round group and a 3-ish SD during load development, and consistently reproduce single-digit SD's with this load in the subsequent firings ... I'm happy.

    I don't particularly care who is unhappy that I am happy.

    Those that know me here, know that I honestly post my victories ... and my defeats, as well as some bone-head mistakes I've made along the way.
     
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    #17
    Jb343434 said:
    You ever group these at 1000? Especially interested in the magpro load 😉
    Click to expand...
    I went out to verify the loads (Retumbo and MagPro) with one suggested change, and it tanked my results. Well ... "tanked" might be an exaggeration. My Retumbo load went to SD-7.0 and my MagPro load went to SD=11.97. So I've rolled back, and made one small variation in neck tension, and I've got one more test this week to feel good about the load, and then I'll move it out to 1,000 yards. Stay tuned ... (no pun intended).

    On thing I did figure out is that a good chamfer/debur/brush as a last step ... results in a "huge" improvement in the consistency of seating pressure. Doing this showed me that my pressure variations were self-imposed, and that cleaning up the case neck before priming/charging resulted in a much lighter seating pressure, which caused me to change the bushing and mandrel size to provide a bit more neck tension.

    Going on feel since I have no way of measuring the exact pressure ... but if it feels very consistent while seating bullets, that's new for me and something I "feel" good about.
     
    #18
    Sounds good and I’ll check back, i ran a pressure test yesterday with magpro in 300wm 73.5 to 79.5g no pressure signs other than flat primers on the last load with no excessive bolt lift. Velocities got up to 2937 with the 225 elds with many flat nodes through the test. With retumbo @75g I had a sd of .1 and an es of 0 but it was only 3 shots and Now is impossible to find.
     

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    #19
    My MagPro 300-WM reference load is 78.4gn ... gives me 8.0 SD's and is super-accurate out to a mile with Berger 200.20x projectiles. That's my competition load this year. Average velocity is 2948.
     
    #21
    rustyinbend said:
    This is just a "Share With The Gang" post ... so ignore if you're not into those kinds of threads ...

    So I've been working hard to settle on a reference load for the 300-PRC barrel on my Barrett MRAD ... something to enter the competition season this spring. My available projectiles are Berger 220 LRHT, and Hornady 225 ELDM. My powders are Accurate MagPro and Hodgdon Retumbo. Ladders gave me good feelings about MagPro at 78.2 grains, and Retumbo at 77.4 grains (Lapua 1x cases and Federal GM215M primers) ... so I loaded 6-round group tests for that 4-way combo. I've been typically getting good and predictable results from MagPro and Bergers in other calibers (300-WM and 338-LM), so I expected those to "win". Not so fast ... data is listed below in the following order:
    1. MagPro & Berger
    2. MagPro & Hornady
    3. Retumbo & Berger
    4. Retumbo & Hornady
    The bottom line here is that the Hornady 225 ELDM's outperformed the Berger 220's across the board, in both powder configurations, by a LOT. I just didn't expect that given how well Berger bullets work for me in other calibers, and given the Hornady's are much easier to find than the Bergers. BTW ... groups tended to favor the Retumbo combinations, with the best (sub-MOA) group coming from the Retumbo-Hornady combination, but the MagPro-Hornady combination also grouped nicely.

    Next test will be to load a dozen each of the two Hornady ELDM configurations, and really mega-concentrate on groups at 100 yards, and then take the winner to our mile-range and see how it performs.

    I guess that's way we test ... eh?

    Data follows:

    View attachment 7791563
    View attachment 7791564
    View attachment 7791565
    View attachment 7791566
    Click to expand...
    Sorry, I know this is an old thread but what primer did you use when you did these tests?
     
    #25
    rustyinbend said:
    Nope ... I always use magnum primers in .300's and above (PRC, NM, WM) and always get solid results. And I have "thousands" of the 215's on the shelf.
    Click to expand...

    I see. Yeah, I have the opposite. 1000’s of 210M and few of 215M. I guess it’s time for the range again. You must be shooting these out of a 28” barrel I assume.
     
    #27
    rustyinbend said:
    I have a couple of 26's, and a couple of 28's ... that I use with the 215M's.
    Click to expand...

    I meant when you tested those shots you shown on the thread.

    I have a 26” but with 1:10 twist and I got 2860 fps with 325-eldm using 77.8 of H1000 and 215M. imma try the Retumbo to see if I get squeeze in some more fps with good es/sd. I was also wondering if I can go up on charge weight than what you tested.
     
    #28
    Rockhurr said:
    I meant when you tested those shots you shown on the thread.

    I have a 26” but with 1:10 twist and I got 2860 fps with 325-eldm using 77.8 of H1000 and 215M. imma try the Retumbo to see if I get squeeze in some more fps with good es/sd. I was also wondering if I can go up on charge weight than what you tested.
    Click to expand...
    Here's my current reference load that I shoot out to a mile with great results ... 26" barrel on my Barrett MRAD in 300-PRC.

    1700149658540.png
     
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