Moving to Lapua SRP brass from LRP...now what?

Senor_Barney

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  • Jul 25, 2020
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    Due to lack of availability (likely due to existence of Gunbroker) I cannot find any more CCI 200 LRP nor Hornady LRP unprimed brass.

    As a result, I went and bought 500 Lapua SRP brass cases and two bricks of CCI 450s Magnum SRP for my 6.5cm.

    Current load is 42.2gr H4350 at 2790 fps with Berger 140gr and Hornady brass.

    My question is... for those that have made a similar switch...should I expect to be going Up or Down from my current load moving to Lapua SPR brass from Hornady LRP brass? In other words, is there anything about the Lapua brass and the Magnum primers that would require me to back off my load or conversely is there anything that would enable me to go to a higher charge weight comfortably?

    Granted every barrel is different and I'll dedicate some of my valuable components to reconfirm...but I would at least like to hear where other have shaken out after a similar transition.
     

    hdbull

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    Due to lack of availability (likely due to existence of Gunbroker) I cannot find any more CCI 200 LRP nor Hornady LRP unprimed brass.

    As a result, I went and bought 500 Lapua SRP brass cases and two bricks of CCI 450s Magnum SRP for my 6.5cm.

    Current load is 42.2gr H4350 at 2790 fps with Berger 140gr and Hornady brass.

    My question is... for those that have made a similar switch...should I expect to be going Up or Down from my current load moving to Lapua SPR brass from Hornady LRP brass? In other words, is there anything about the Lapua brass and the Magnum primers that would require me to back off my load or conversely is there anything that would enable me to go to a higher charge weight comfortably?

    Granted every barrel is different and I'll dedicate some of my valuable components to reconfirm...but I would at least like to hear where other have shaken out after a similar transition.
    I did somewhat similar from Starline LRP to Lapua SRP and went down with H4350. I probably start a little lower and
    work my way back up if you have no pressure signs to be on the safe side.
     

    salmonhead

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    I also switched at one point and my load data was a mess. Just start over, it will save you time, effort and materials in the end. I had gone from ADG LRP/ CCI BR-2 to Peterson SRP/ Fed 205. It seemed weird to me, but I hit pressure at lower powder charge and lost velocity. Apparently, the pressure curve gets shaped differently. Maybe the magnum smalls will counter act that.
     
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    FatBoy

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    If you don’t have a tight firing pin, expect to see pressure earlier. The 450Ms are outstanding primers, especially with VarGet. If you have a small pin bolt already, I’d drop a few tenths and work back up. Should be fine.

    Also, make sure you measure the loaded neck clearance and the overall length of the Lapua case as compared to your old load. It has a tendency to be thicker than Hornaday, at least in other chamberings. You may need to turn necks or trim length to keep things from spiking.
     
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    davere

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    I suspect the different case volume will affect the load more than the primer, actually - but yeah, just start over. I made a similar move (Hornady to Lapua SRP) a while back, but I also switched powders when I changed brass (was running IMR 4451 due to lack of availability on H4350), so I don't really have any useful data showing what the change was for me.
     

    Senor_Barney

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    If you don’t have a tight firing pin, expect to see pressure earlier. The 450Ms are outstanding primers, especially with VarGet. If you have a small pin bolt already, I’d drop a few tenths and work back up. Should be fine.

    Also, make sure you measure the loaded neck clearance and the overall length of the Lapua case as compared to your old load. It has a tendency to be thicker than Hornaday, at least in other chamberings. You may need to turn necks or trim length to keep things from spiking.
    I was at 42.2gr if H4350. By a few are we talking start at 42gr or do we back down completely to 41.2 and find new nodes?
     

    FatBoy

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    I was at 42.2gr if H4350. By a few are we talking start at 42gr or do we back down completely to 41.2 and find new nodes?

    I’d probably start at least a half grain low. Maybe 5 rounds each working up. Make sure the cases are the same length and have the same neck clearance.
     

    Senor_Barney

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    UPDATE HERE:
    Tested 5 shot strings from 41.6 to 42.4 in 0.1 increments. Flat node from 41.6 to 41.8 and 2782-2785 fps in 52F weather
    SD 3-4
    ES 7-8

    I didnt even bother shooting the 41.9-42.4 strings cuz I'm good with that load right there. This is the same speed as my previous load, but 0.5gr less powder and less than half the SD I had before! Wow, Lapua and SRP....my gawd!

    I didn't test at 300 yet, but fingers crossed this holds up.
     
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    FatBoy

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    UPDATE HERE:
    Tested 5 shot strings from 41.6 to 42.4 in 0.1 increments. Flat node from 41.6 to 41.8 and 2782-2785 fps in 52F weather
    SD 3-4
    ES 7-8

    I didnt even bother shooting the 41.9-42.4 strings cuz I'm good with that load right there. This is the same speed as my previous load, but 0.5gr less powder and less than half the SD I had before! Wow, Lapua and SRP....my gawd!

    I didn't test at 300 yet, but fingers crossed this holds up.

    That’s awesome. I like SRPs. I know Tubbs study with SRP vs LRP in cold weather but the small primers just seem to work, especially with Varget and H4350.
     

    st1650

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    That’s awesome. I like SRPs. I know Tubbs study with SRP vs LRP in cold weather but the small primers just seem to work, especially with Varget and H4350.
    What study ? I’m curious
     

    FatBoy

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    I’ll see if I can find it. Boiling it down, from memory, when it gets cold (below freezing) LRPs are more consistent once you get above 40gr. @DTubb is on here occasionally. Maybe he’ll pop in with refresh some decade old wisdom?

    I have no reason to doubt the results, I just really like SRP cases. 6.5x47, 6Dasher, 6BR. Cold be damned.