260 Remington in long action R700

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  • DavidA

    The Master of Disaster
    Dec 6, 2013
    371
    Annapolis
    So I have three Remage R700 rifle one in 270 win with a 1-8 twist barrel. One 284 win 1-8 twist and one 338 win Mag. So I am buying a Black Hole Weaponry 26” barrel that I can switch out with one of the Standard .473 long actions. I know I could do 6.5 x 55 Swede or a 6.5-06 . I get it. I just have a two LR308’s in 260 Rem and they shout great. I just wanted to pull 260 Rem over to a bolt gun, as I have all the match dies and components already for 260 Rem. The object is to load the bolt gun rounds as long as I can to get the best performance out of the cartridge. My calculations say I should be able to load Hornady 147 gr RLD M bullets to a COAL of 3.05” +/-. So beyond SAMMI by a ways. Any hoot I have enquired Columbia River Arms about what the free-bore is on the readers they are using and to see if they will match them to dummy rounds if I send them. No answer yet. But if they will not what are my options to extend the free bore to match the intent of my rifle? Also while I have read that feeding may not be a problem, what modifications if any do you think will be required to magazine. Magpul bottom metal with their 10 round magazines.


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    dedan

    Member
    Dec 5, 2011
    26
    delaware
    most rem 700's, 260, 7-o8, are on short actions. longer bullet you might feed it single shot. also, if you do 260, barrel should be 1x8, to shoot heaver bullets. remington 260 barrels are 1x8 1/2, not great for heavy bullets....dan
     

    DavidA

    The Master of Disaster
    Dec 6, 2013
    371
    Annapolis
    If you do have feeding issues, which I doubt, a single stack detachable mag setup should take care if that. There are a few to choose from. Magpul would not be my first choice.

    Long 260 had been done. I suggest checking out 6mmbr.com

    http://forum.accurateshooter.com/threads/260-remington-long-range-load-development.3831912/

    Thanks I figured it should feed in a single stack no problems. Just waiting for the gremlins to come out since I am not not building a standard configuration. FYI got hold of Columbia River Arms (manufacturer of BHW barrels) The have a SAMMI chanber reamer and a Bore Rider reamer as well, So I just have to tell them how much beyond SAMMI do I want to extend the throat. Good news! Figuring it out with bullets will talk some research. Ill be checking out that atrticle now. Thanks
     

    DavidA

    The Master of Disaster
    Dec 6, 2013
    371
    Annapolis
    That is a good point. You can’t add throat back in. So of course this got me thinking. So it called for a spreadsheet to analyze SAMMI spec chamber dimensions and where different bullet would be at the lands. So based upon SAMMI chambers specs, a Hornady 147 gr ELD M will HITT the lands at a COAL of 2.916” bases upon my 260 new unfired brass 2.025. It comes down to a .553 case intrusion. Optimum intrusion is roughly .400. In a SAMMI chamber free bore is .1185 and the lead is .0859 so total throat is .2044. So if you pushed it out .15 you would have a COAL of 3.066 to lands and a case intrusion of .3894. If you set back 10 thousandths back .01 you would have intrusion of .3994. Dam near perfect. So I went on the compare other long heavy bullets with a extended .15 bore total throat of .3544

    Berger 153.5 Hybrid target calculated out to 3.1176 COAL at lands with .4204 intrusion.

    Nosler 140 RDF calculated out to 3.078 COAL .3659 intrusion. bearing surface in knock in this case is a littler short.

    Berger 156 Elite Hunter calculated to 3.1326” with intrusion of .4034.

    Sierra 150 SMK calculated 3.1376” with intrusion of .3734.

    All of the above would work to the lands but this is the max length load with bullets at lands. Chances are I will not jam lands as they erode the throat faster. So if I go back 10 thousandths these will be fine extending the throat .15 from SAMMI. I do want to preserve some dimensional spacing though for chasing the lands as the throat moves. So I am thinking .12 or .13 extension. With the above bullets at lands COAL range 3.036 to 3.107. I could push it to a .15 extension but that is max today. Any hoot. Here is link to the spreadsheet if you have any interest. With Reloader 26 I am thinking 2850 fps with 150 SMK bullets . That’s would place it supersonic to 1800 yds at sea level. with a 10 degree cross wind at sea level and 200 yds zero. at 1,000 yds 7.0 mil drop , 1.39 mil drift.

    https://1drv.ms/x/s!Am5F-6DkWN6fgaIc8Bk86zsoivhThw


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