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Max Load question

Discussion in 'Ammunition & Reloading' started by rrojohnso, Nov 22, 2011.

  1. rrojohnso

    rrojohnso Vancouver, WA Member

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    Hey guys -

    I am working up loads for my .308. According to the load data from the powder manufacturer (Ramshot), the max load for the bullet is 44.3 grains of powder, to get 2759 fps @ 61,500 psi. I loaded a group of rounds at 41.9 gr, and I am at 2750 fps already! The groups are getting tighter as the rounds get faster.

    Do you think it would be safe to continue to work the load up hotter, or just accept this combo as the best it will get?

    Gun: .308 Win in Rem 700 action, 26" heavy barrel (custom Match grade)
    Load: Winchester Brass, Lrg Rifle Primer, 41.9 gr of TAC powder, Hornady 168gr BTSP, no crimp.
    Temp: 48 deg, clear, dry & cool, 800 feet elevation.

    Thanks guys
     
  2. civilian75

    civilian75 Hillsboro, OR Well-Known Member

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    Most published 308Win data out there has been developed for 22-24in barrel rifles. There is roughly a 100fps gain per each 4in of barrel. So, do not be surprised to be a bit faster than published. I think you have more head room. Keep going up and watch for high pressure signs. My experience with 168gr is hottest is not the most accurate in my rifle.
     
  3. Jamie6.5

    Jamie6.5 Western OR Well-Known Member

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    Watch your primers for signs of flattening and cratering, and be conscious of sticky bolt lift.
    I agree with civilian though, with 26" of barrel you should expect a little velocity gain over published data.
    Just watch for the usual pressure signs.
     
  4. deadshot2

    deadshot2 NW Quadrant WA State Well-Known Member

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    If you aren't getting signs of high pressure like Jamie6.5 pointed out then go ahead and keep working upwards.

    .308 loads seem to work best when the case is full. Keep increasing in .2 gr - .3 gr increments and stop when the group size starts to open up (assuming you haven't reached max yet).

    Your match barrel is not only longer than what most use for published data but may also be optimum in bore diameter and rifling depth for your bullet so speeds could definitely be higher than "spec".

    Before you continue working upwards on this load I would consider first checking the scale for accuracy. The best way is a set of check weights so you can check the accuracy using a weight combo that's close to the actual weight of the desired powder charge.

    Also, check the chronograph. Fire a few factory loads, preferably something like Federal Gold Medal Match, Black Hills Ammo Match, or Hornady Match, which are loaded for consistency at the factory, over the chronograph. Compare your readings with the speed printed on the box. If they "2600 fps" for example, and your chronograph reads higher or lower by a significant amount, just calculate a correction factor from this comparison and apply it to your handloads. On some chronographs a 2%-5% error is not uncommon due to varying lighting conditions, bullet shape, and even muzzle blast "moving" the chrono on it's stand. This can mean anywhere from 50-125 fps error on a round that's supposed to be traveling 2500 fps.
     
  5. civilian75

    civilian75 Hillsboro, OR Well-Known Member

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    Per my Sierra book, 42.0gr of TAC is max under 168SMK, 2.800" OAL, on a 26in bbl Savage12VSS. So, keep an eye for high pressure signs as described above. Go up easy, no more that 0.5gr at a time, preferably less.

    FYI: 42.0gr of RL15 yielding 2600fps on same rifle is Sierra's most accurate load.

    One last thing, controlling OAL can become a critical variable when pushing the envelop. Most 168gr data is for 2.800in OAL. But if bullets are very close to the lands, pressures will be much higher. It might be a good idea you figure how close the bullets are from the lands. If you do not know, google up steps.
     
  6. djthemac

    djthemac eugene Member

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    One thing to also consider is winchester brass has a larger case capacity by up to 1-2 grains. As always check for pressure signs as indicated, if you are not seeing any I would continue to load up. This is my recipe

    Winchester Brass
    Varget 44.9 Grain (similar to RL 15, I will swap next month)
    CCI Large Rifle Primer
    Nosler Custom Competition 175 grain BTHP
    O-give 2.293
     
  7. Spitpatch

    Spitpatch Forest Grove, Oregon Well-Known Member

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    I am somewhat concerned, but not surprised with the strategy of exploring the top of the pressure range. Deadshot2 offered some good advice toward this strategy, but do NOT relinquish or fail to explore a lower pressure load in the search for accuracy, if that is the paramount concern. I have been guilty of this "starting near the top" strategy on more occasions than I care to illustrate here, but have been pleasurably surprised when after laying awake thinking of what I might not have tried toward load development, decided to try something considered "pedestrian", and have found it to be far beyond anything at the top of the pressure scale for accuracy.

    I will say this (and I think Deadshot2 mentioned it): a chronograph is one of the very BEST tools we have to measure pressure (sorry guys, all your "head expansion/primer-flattening" techniques are passe'). If your velocities become erratic, or exceed substantially a hot factory load, you are beyond no-man's land. If your bolt-lift is sticky you are dead-man-walking). Any modern gun will take it, take it for a long time, but you are the gambler with no strong hand.

    No guy without a chronograph studiously employed should mess with book max or beyond-book-max loads.
     
    rrojohnso and (deleted member) like this.
  8. orygun

    orygun West Linn Bronze Supporter Bronze Supporter

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    Looking at the Ramshot web site I see a few things that may lead to the discrepancies in velocity you mention.
    #1 You are using a 2" longer barrel. All things equal (which they rarely are in ballistics) that will yield about 50 fps higher.
    #2 They list a Sierra 168gr, not a Hornady 168gr. While it may seem insignificant, that difference in bullets may allow higher FPS or cause higher pressures.
    #3 The acceptable results you show today MAY be a problem when the ambient temp is much higher.

    The web site does not mention which case they used. My experience mimics others here. Winchester cases hold more powder. But to me, that means you should be showing lesser velocity than with a smaller capacity case. Also, my Hornady book is too old to show Ramshot powders, but in the 24" barrel they show nothing faster than 2700fps.

    I can't tell you where I heard it, but I believe that if you are pushing much past factory ammo speeds you are likely pushing past factory pressures. This is something I really pay attention to. I've also seen rifles that would "gobble up" max loads, while others were experiencing sticky bolt lift 2 grains below max.

    All of that dribble aside, if I was doing this, I would repeat the load you are using and load up five rounds each of .5 gr increments. Then I'd shoot them progressively over the chrono. I would stop at the first sign of higher than normal pressures (cratered primers, sticky bolt lift, or heaven forbid, split cases) and would back down a half a grain for further testing. If I saw no signs of excessive pressure by the time I got about 2850, I'd call it quits. That's 150fps faster than my info from Hornady shows and I would stop there!
    Since your rifle shoots smaller groups as the rounds get faster, don't allow yourself to get tricked into pushing too far.
     
  9. orygun

    orygun West Linn Bronze Supporter Bronze Supporter

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    These are good words to live by.:thumbup:
     
  10. Jamie6.5

    Jamie6.5 Western OR Well-Known Member

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    I agree the chrono is a valuable tool in these endeavors.
    But what started this thread is the fact that the OP's chrono already reads high.
    Going by that alone, the OP should back off his loads, when IMO, he's on the right track, and can now zero in on accuracy. (pun intended) And he apparently has room to push it even faster, as long as he has zero high pressure indicators.

    Barrels have a TON to do with velocity. Especially when one is dealing with longer-than-your-average-sporting rifle barrel, like the OP.
    Then there is the issue of fast barrels vs slow barrels. I have seen examples of both, in one case accounting for 150fps difference with the same load.

    There is no doubt that for getting the most from your handloads, the chrono is a must. If for no other reason than developing an ACCURATE drop chart.
    But IMO, it will never be the last word in safe pressures.
    YMMV.
     
  11. orygun

    orygun West Linn Bronze Supporter Bronze Supporter

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    Jamie, you're right about a lot of things here. But he stated he's getting smaller groups as the velocity increases. (although with no comment about pressure signs) What would you do then?
     
  12. Jamie6.5

    Jamie6.5 Western OR Well-Known Member

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    Assuming I KNOW the gun is in good condition.
    As long as accuracy isn't suffering, and especially if it's improving, I'll keep going up in charge weight until:
    1)I start to see primers getting flat, or new ones are loose, or going in too easy.(this usually comes before Sticky Bolt Lift, but if SBL comes first STOP! and back it down)
    2)Groups start getting larger, and I am at the max or already above.
    3)ES and SD start moving towards the extreme, IOW, velocities start getting erratic/inconsistent with a given load. (Of course this almost always causes precision to deteriorate)

    As long as groups are getting smaller, and velocity spreads aren't opening up, I will even put up with primers a *little* on the flat side.
    As long as the cases aren't showing signs of developing loose primer pockets that is. Short case life is just as important as any other consideration, and THE BEST INDICATOR that your loads are too hot. Especially if you aren't FL resizing every time. "Over" resizing shortens case life regardless of the load, by work-hardening the brass.

    I can make a 30-06 shoot like a .300Win Mag if I don't care about tossing cases after 1 or 2 reloads, because they won't hold a primer. That doesn't mean I should. And I wouldn't/won't.

    Ambient temps need to be considered when up around the max though too. A load worked up this time of year needs to be watched closely when it's being shot in summer, when temps are 50+* warmer.
    When I sit down at the bench during load development, I am usually looking for a load that shoots with the best compromise between fast and precise (small groups). That means I may need to give up a little one way or the other. I will not give up 250fps to gain 1/4" smaller groups.
    I will give up <150 or so for 1/2" though.

    Again, YMMV, everyone's standards are different. I know people that consider speed uber-alle. I know others that want bug-hole groups out of every rifle they own.
    They are NEVER able to shoot the same loads.
     
  13. Spitpatch

    Spitpatch Forest Grove, Oregon Well-Known Member

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    Ambient temperature is rightly illustrated by Jamie as an important factor when dancing on the head of the pin that is maximum loads. Another factor (for the same reason) that is important is the consideration toward repeated fire (3-4 shots at game in quick succession). In this scenario, chamber temps can skyrocket to the point where a seemingly safe load on the bench becomes the grim reaper (hopefully only for the gun).

    I will once again state that primer flattening is among the POOREST indicators of pressure (along with its timeworn partner, head expansion). Too many variables can cause it to happen early at low pressure, or not occur at all at extreme pressure. This subject has more detailed treatment elswhere if researched, especially recently when actual pressure is now more easily measured by those not in a laboratory. The "Fast" or "Slow" barrel theory has also been shown to be more directly related to pressure: BECAUSE: higher velocity is produced by higher pressure. No getting around it.
     
  14. deadshot2

    deadshot2 NW Quadrant WA State Well-Known Member

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    I agree with almost everything you said in your post with only one exception. Unfortunately primer flattening is not high on my list of indicators, especially if using winchester primers. Every manufacturer's primer cups flatten differently due to the variations in the materials used by each. I've found that Winchester primers can be absolutely flat in my Lapua .308 cases while, using exactly the same load, CCI's and Wolf or Tula primers still have a substantial radius on their edges when fired.

    As for cratering, be sure to note the condition of the bolt face before condemning a load as to high a pressure. Some rifle manufacturers will allow larger firing pin channels than others thus allowing primer flow at lower pressures giving a false "cratering" of the primer. My Remington has the firing pin channel chamfered at the bolt face. Drove me nuts as starting loads showed cratering. When I took a close look it's a case where someone took a countersink tool to the opening and put a chamfer on the sharp edge. My WWII vintage 1903 with A-4 bolt has a tight firing pin and "square" edge on the firing pin channel. If I see cratering with this rifle I pull down the remaining rounds in the test.

    Speed is important for accuracy at longer ranges. For me, developing a load for 100 yard "group size", I could care less about the speed. There is no doubt that the bullet will remain supersonic when arrives at the target. Likewise for 200 yard ranges. Only time I start worrying at all about speed starts at 300 yards and beyond. I don't want the bullet to transition from supersonic to transonic speeds where it is subject to the collapsing shock wave. This phenomena can begin to occur at approximately Mach 1.2 and continues down to Mach .8. Assuming standard atmospheric conditions, this occurs when a bullet drops below approximately 1400 fps. For a 168 gr .308 bullet, leaving the muzzle at 2600 fps, it will reach this speed at approx. 750 yards. Downloading can cause this to occur at far lower speeds so it's something to watch for if you're really trying to "reach out and touch something".
     
  15. orygun

    orygun West Linn Bronze Supporter Bronze Supporter

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    Sounds like we're all pretty much on the same page here. (Not trying to get an "atta-boy" for myself.) I am not a newbie at this, but there are a lot of people that I can learn from. I appreciate others that have offered up their experience here, as I'm sure the OP does. Thanks.
    To back up Deadshot, I have been using Winchester primers for a while and have noticed they get flat at pretty low pressures.
     
  16. Jamie6.5

    Jamie6.5 Western OR Well-Known Member

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    Then how does one account for the wide variations in velocity from the same load/case/bullet/primer out of two different rifles of the same brand and barrel length?
    A well worn barrel with a long throat may allow another 100-200fps over a short throat barrel that has very few rounds through it, and is on the tight side of the groove diameter spec.
    There is waaayy more to internal ballistics than just to say that "more pressure equals more velocity."

    That is enough of an oversimplification to keep anyone 3 grains and/or 300fps below max loads.

    Not to mention that sometimes excess pressure doesn't result in more velocity, especially between guns. My .270 may show extreme pressure signs when it's still 100fps slower than my hunting partner's, when his doesn't show any excess pressure signs with the same components/loads.
    I won't push it to catch up.
    But that's just me.

    YMMV
     
  17. Jamie6.5

    Jamie6.5 Western OR Well-Known Member

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    I have to agree with both of you as well.
    I believe that's why Lee doesn't want Winchesters used in their 1st gen auto prime too.
     
  18. deadshot2

    deadshot2 NW Quadrant WA State Well-Known Member

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    I thought Lee had issues with Federal primers, not Winchesters?
     
  19. Jamie6.5

    Jamie6.5 Western OR Well-Known Member

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    Could be deadshot. It's never stopped me anyway. The only primers I've never loaded through my AP have been Tula and Wolf. Only because I've never owned any.
    But then again, I am not under the misconception that an Auto-Prime is a vice either. Additional resistance always begets additional inspection, and often results in a component being disposed of.
    It just isn't worth it.

    But then again, I've always done my best to be cognizant of the risks I take, and I've never sued anyone.
    Even when I knew a problem developed that wasn't my doing. A risk is just that,... A risk.
     
  20. deadshot2

    deadshot2 NW Quadrant WA State Well-Known Member

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    Several of the BR Shooters at my Club have purchased the new Lee AP's and wish they hadn't. I guess Lee figures that an inverted or "sideways" primer is safer than one installed properly. They new little "gate" mechanism seems to produce more cocked or inverted primers than the old ones. I'm keeping my old AP as it's showing no signs of giving out any time soon. Over 30 years so far with the same tool.

    As for continuing to "crush" when resistance is felt, I follow your method. Any resistance means stop and look. It's always amazed me the number of people that complain about breaking parts on their progressive presses when it's clear that they just kept on pushing on the handle after the "warning". Makes me wonder how they treat their firearms.