Load work up question for 308 in an AR-10?



  • While doing my homework on working up an OCW for my AR-10 in 308 Win using Reloader 15 powder, new Hornady cases, Nosler 175r CC, and CCI 200 primers. I found the max loaded to vary quite a bit in each reloading manual, from a low of 41.4 to a max of 45.0. I used Sierra, Speer, Nosler, Hornady, Lyman, and Alliant. What I did was plug the max loads in spreadsheet and got an average max load of 43.5. My plan is to start at 41.6 and work up in .3 gr steps to 44.3. Anything you guys would do different? Is my plan sound?



  • Sound plan.
    Let your rifle tell you it's max.

    99% of the Lawyers make the rest look bad.

    0


  • Get yourself some different powder. RE15 is extremely temp sensitive. I'm talking like a 100fps swing from winter to summer.

    In a gas gun, you'll want to start a little lower than what you'd think for a bolt gun. You never know how those things are going to behave. You might also find that you'll have to lower the bullet weight to get success in the gasser too, depending on the rifle.

    If you start at 41.6, and go to 44.3... you'll be taking 9 steps. That's a lot of shooting. A much better way to proceed is to run a pressure ladder. Load up single rounds in 1gr increments from safe starting point, to above what you perceive to be max load. So for a varget setup behind a 175SMK, I'd start at about 37gr, and go to 47gr. One round at each charge. Load them one at a time, and fire them one at a time. So load 37gr, shoot it, look for all aspects of pressure. If safe, proceed to 38gr. Continue this until you find a single pressure sign. Once I find a single, I'll load one more increment, pushing to "find" where true max load is. Once I see all pressure signs show up, or significant enough single signs, I'll stop there as the boundary has been identified. A little instinct and a lot of experience counts when looking at pressure.

    Once pressure is found, back a step or two off it, depending on the conditions. If it's very hot out, obviously you can be right up against pressure, knowing that it will only get colder from there. If it's cold, you'll want to be a good margin away from it to account for hotter days. Once that upper limit has been identified, you can do a much more granular OCW near the upper edge with about 5 groups of 3.

    I'll be writing an article on this topic soon, but hopefully that helps for now.



  • @orkan said:

    Get yourself some different powder. RE15 is extremely temp sensitive. I'm talking like a 100fps swing from winter to summer.

    I have never had any problems with the temperature sensitivity of RL-15.
    I don't suppose that has something to do with a mean temperature shift of about 10 degrees from winter to summer?:stuck_out_tongue_closed_eyes:

    99% of the Lawyers make the rest look bad.

    1


  • @ar10shooter
    appears that the low you are starting at is above the max for some of the data you found. I wouldn't start there. As another posted mentioned, ARs are different than bolt guns. They tend to show pressure signs sooner. Verify that all the manuals are listing your exact bullet not just the weight. That may knock some of them out. If there is still a large difference then start well below the max for the lowest max you find. Load 1 or 2 at various increments and look for pressure signs to see what the actual range your rifle can handle and do your ladder tests within that range.



  • a_marks, Welcome aboard!

    Be sure you make it over to the introductions thread to give some background about yourself and your shooting resume. :)

    https://forums.gunhive.com/topic/81/introduce-yourselves/2



  • @orkan

    Ok, I'll do that. Is there anything that shows when someone replies to a thread you posted on? I just randomly found that you sent this.

    Thanks,



  • @a_marks said:

    @orkan

    Ok, I'll do that. Is there anything that shows when someone replies to a thread you posted on? I just randomly found that you sent this.

    Thanks,

    If I quote you, as I did here, it will notify you. :)



  • @orkan said:

    Get yourself some different powder. RE15 is extremely temp sensitive. I'm talking like a 100fps swing from winter to summer.

    I have read that the military had temp issues with RL15 in the 308, but it really did not become an issue til temps were over 100f. I am hoping to find a good accuracy nod before the max load. Living in NC, the temps are now in the upper 60's and low 70's.



  • Going out tomorrow to shoot the OCW for AR-10. It's going to sunny with the highs in the mid 60's.



  • @a_marks said:

    @ar10shooter
    appears that the low you are starting at is above the max for some of the data you found. I wouldn't start there. As another posted mentioned, ARs are different than bolt guns. They tend to show pressure signs sooner. Verify that all the manuals are listing your exact bullet not just the weight. That may knock some of them out. If there is still a large difference then start well below the max for the lowest max you find. Load 1 or 2 at various increments and look for pressure signs to see what the actual range your rifle can handle and do your ladder tests within that range.

    The military loaded RL15 in the M118 match ammo for a long time at 43.1 grains with a 175 SMK.



  • @ar10shooter
    Personally, I look at multiple sources and when I find discrepancies I ensure I'm starting at the low end. And I would certainly start below any published max for my bullet. It is much easier to load a couple rounds to verify than to pull a bunch of bullets or worse have a problem.



  • @ar10shooter said:

    @orkan said:

    Get yourself some different powder. RE15 is extremely temp sensitive. I'm talking like a 100fps swing from winter to summer.

    I have read that the military had temp issues with RL15 in the 308, but it really did not become an issue til temps were over 100f. I am hoping to find a good accuracy nod before the max load. Living in NC, the temps are now in the upper 60's and low 70's.

    You mentioned the military a couple times here. Were you or are you in the military?



  • @orkan said:

    @ar10shooter said:

    @orkan said:

    Get yourself some different powder. RE15 is extremely temp sensitive. I'm talking like a 100fps swing from winter to summer.

    I have read that the military had temp issues with RL15 in the 308, but it really did not become an issue til temps were over 100f. I am hoping to find a good accuracy nod before the max load. Living in NC, the temps are now in the upper 60's and low 70's.

    You mentioned the military a couple times here. Were you or are you in the military?

    Yes, I was USAF.....not a shooter though, shooting is a hobby for me.



  • Excluding the obligatory jab at you from the Army... you certainly should know that military "testing" isn't always what you think it would be. Logic sometimes does not follow.

    RE15's temperature sensitivity is widely documented, and it most certainly affects your load at temperatures beneath 100f. :)


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