Severely Overbore Chartidges and short barrel life myths...

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Fiftydriver, Sep 26, 2010.

  1. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    To all, I just spent a few hours this morning getting my personal hunting rifles tuned in and ready to roll for the upcoming hunting season. My personal big game rifles this year will be:

    6mm-06
    95 gr Ballistic Tip @ 3540 fps
    Win M70 push feed
    Lilja #3 contour 1-8 SS barrel, 27" finish length
    Boyds classic sporter laminated stock
    Small PK muzzle brake
    Leupold VX-3 LRT 4.5-14x 40mm with Varmint Hunter Reticle
    Pronghorn hicking rifle
    Weight: 10.5 lbs ready to hunt with

    7mm Allen Magnum
    160 gr Accubond @ 3414 fps
    Rem 700
    Lilja #3 SS 1-9, 26.5" Finish length
    DE 1/2" brake
    HS Precision sporter stock, green with black web
    HS Precision DM system
    Tuned Rem 700 trigger
    Leupold Mk4 FFP 3.5-10x 40mm w/ TMR reticle
    Anything packing rifle
    Weight: 10.0 lbs ready to hunt with

    338 Allen Xpress
    225 gr Accubond @ 3392 fps
    Raptor LRSS
    Lilja Raptor barrel, 1-10 twist, 30" finish
    APS Medium PK brake
    Jewell trigger
    McMillan A-5 w/ adj CP
    HS Precision DM system
    NF NXS 5.5-22x 50mm (soon to be Votrex Razor!!)
    Sit and shoot rifle for ambush hunting
    Weight: 16 lbs ready to hunt with.

    So these are my three babies. The middle child, is the reason I am posting this story. Ya see, she has been around since the spring of 2003 when I first put her together. At that time I developed a load with the 200 gr ULD RBBT from wildcat bullets and did alot of range practice with her. It has never been an EXCEPTIONAL shooter, 3/4 moa give or take. I have many more consistant rifles but I have no rifles that have performed for me in the field like this rifle.

    For the past 3 years, I have been going to put a new barrel on this rifle because its getting extremely long in the tooth. By that I mean I stopped counting at 700 rounds down the barrel and that was three seasons ago. Past that I figured it would go at any time so stopped counting.

    Over the years I have had to switch to several different bullets with complete ballistic work ups and range practice to validate drop chart numbers. First there was the 200 gr ULD, then the 160 gr Accubond, then to the 175 gr SMK and this year I am going back to the 160 gr Accubond.

    The reason is simply that I had a couple situations last fall with the 175 gr SMK that left me wanting for a bit more consistant bullet expansion on soft tissue impacts. The 160 gr AB does not have the ballistic performance but its much better terminally so that is why I went back to that bullet.

    I also decided to use Retumbo with the 160 gr Accubond, something I had never done but I did use that powder with the 175 gr SMK with good results. After a load development session, Retumbo was driving the 160 gr Accubond out at 3414 fps average with ES in the 27 fps range. I have an old drop chart from many years ago and used that and tweaked it a bit for the different velocity average. It only took a few shots to get things on track and then I set up on my steel gong at 880 yards. About the max I have always limited myself to with this rifle on big game. Again, its always been a 3/4 to 1 moa rifle at long range from the start.

    I took four shots at 880 yards. The wind was coming from my 10:30 direction at around 8 mph at the shot. This is the result

    [​IMG]

    Three of the shots went into 3" ctc and all four went into 6" ctc. Things were pretty much right on top of my black aiming point on the gong other then the one shot to the right but all well within where I wanted them for big game hunting.

    I bring up this simply because of all the stories I hear about severely overbored chamberings chewing up throats before you can even get one decent load developed and drop chart tested. Now, there are few combinations out there that will match the 7mm AM as far as being classified as overbore!!!

    the throat on this rifle has some significant heat cracking but I clean it often, always have and most importantly, this barrel has NEVER been over heated. To my best recollection, I have never put more then three shots through this barrel in one string. As such, the barrel still produces fine accuracy, high velocity and its pretty damn easy to clean still.

    So, for those that get scared off choosing an extreme performance chambering, please realize that the life of your barrel greatly depends on how you care for the barrel and how you treat it while shooting. In my opinion, these have much more to do with barrel life then what the rifle is chambered in.

    It is true I do not load this rifle terribly hot. 3414 fps is a good top working load but I can easily hit 3500 fps if I want to and in a full custom rifle with stronger receiver, near 3600 fps with acceptable pressures is easy with the 7mm AM.

    Still, this rifle could not use those loads or take advantage of the ballistic increase created by them simply because I can not shoot the rifle well enough past 1/2 mile to make them worth while.

    3414 fps is roughly 150 fps faster then the 7mm RUM "SHOULD" be loaded to in this barrel length with the 160 gr bullet weight and thats PLENTY for me.

    I have the replacement barrel sitting here and to be honest, I REALLY do want to get this old barrel off and new one on because I have been seeing some good performance with the Berger 180 gr VLD in the Lilja 1-9, 6 groove barrels being able to be pushed to nearly 3400 fps with top loads and so far good accuracy but as long as this old pipe keeps working I will keep her with me hunting.

    To date, this rifle has 17 big game kills at ranges from 385 yards to 845 yards and has never missed a big game animal I have pointed it at!!!

    By conventional wisdom, this barrel should be worth nothing more then a paperweight by now but it just goes to show if you take care of a barrel and especially do not over heat the bore, you will get much longer barrel life they you would expect with a chambering such as this. I hear all the time that you can not practice with one of these rifles to become proficent with it. Again, BULL. Once I get my load, which generally takes 20-25 rounds total, You can verify a drop chart in another 20-25 rounds and then its simply a matter of taking the rifle out from time to time to practice on targets of opportunity just as you would big game hunting. 10 rounds a summer is plenty once you get the drop chart figured out. NO NEED at all to run 100s of rounds down the bore.

    In fact, Now that I have this load developed, I will take water filled milk jugs out and set them up at ranges from 300 to 1000 yards and shoot one shot at each. Actual rounds down the bore will be very limited and as such, barrel life will be greatly increased.

    The key here, get away from load development as soon as you can, never shoot on paper once your zeroed. Tinkeritis is a bad thing. Many will develope load after load trying to find that magical load that offers sub 1/2 moa groups, single digit extreme spreads when in reality, they could likely take any load they try out in the field and have a load that would shoot better then they can shoot the rifle at long range from field conditions. I am saying this about myself.

    I know this because this old 3/4 to 1 moa rifle has NEVER let me down in the field even though many would say its not accurate enough for big game hunting at long range.

    So for those that are scared away from extreme performance chamberings, do not believe alot of the hype you hear about them being barrel eaters, thats greatly dependant on you, not the chambering.

    Good hunting and shooting to all this season, be safe and have fun.
     
  2. J E Custom

    J E Custom Well-Known Member

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    +1

    A very good post worth thinking about.

    J E CUSTOM
     

  3. pyroducksx3

    pyroducksx3 Well-Known Member

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    You said you use only 20-25 rounds on average to figure out your best load. I understand this is probably a new thread all together but could you explain the reloading method you use. I have heard of the ladder testing method but maybe what you do is different. I have gone through way to many rounds trying to get that load just right. I appreciate all the knowledge you share here, thank you
     
  4. Mikecr

    Mikecr Well-Known Member

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    I agree that a hunting barrel's life should be high, no matter the cartridge. This, because we should be highly focused on cold bore accuracy rather than grouping. Even a 220swift could last a lifetime of actual hunting.

    Barrel life has always been subject to performance expectations though. I recently polled BR shooters about their current 6PPC barrel life expectations. This is by no stretch a barrel burner, and if used strictly for hunting, would probably last 100yrs. A link:
    Barrel life of 6PPC?
    Now these guys have to toss a barrel by 0.1moa of performance slip. But even at the pressures and timing they punish these barrels with, they would never have to toss one if 3/4 to 1moa was acceptable.

    Personally, I would toss or set-back a hunting barrel once exceeding 1/2moa of cold bore accuracy at 500. That would be the point where it's just no use to me, as I hunt groundhogs.
    So I get more out of my barrels than BR shooters, but less than you.
    As implied in another thread, there is rarely anything in shooting that applies across the board.
     
  5. Oliveralan

    Oliveralan Well-Known Member

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    Excellent read! I totaly agree.
     
  6. ICANHITHIMMAN

    ICANHITHIMMAN Well-Known Member

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    Nice post but I need the rifle pic.
     
  7. geargrinder

    geargrinder Well-Known Member

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    So, is the 224 Allen Mag going to be based on the RUM or 338 Lapua?:D

    Great explanation, thanks.
     
  8. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Pyroducksx3,

    Are you ready for this.... My load development will be scorned by most but her goes.

    Start at a know safe starting point, in the case of my 7mm AM with 160 gr AB I started at 92.0 gr of retumbo and worked up to 97.0 gr. One round each, adding one grain to each load on the way up. I shot these over a chrono graph behind the shop into my bullet trap, no paper, no groups, nothing, shoot and write down velocity and most importantly watch for any increase in effort needed to open the bolt on firing.

    There were no pressure signs at 97.0 gr so I increased one more grain to 98.0 gr Retumbo which clocked 3507 fps and there was a noticable increase in the bolt lift so 97.0 gr was then considered my max working load in that rifle with this componant combo.

    Then I look at the velocity numbers and see if anything stands out. In this case it did. I gained good velocity until I hit 95.0 gr of powder which had an actual chrono velocity of 3411 fps for that one shot. After that, the velocity increases flatlined even though there were no pressure signs until I reached 98.0 gr. THis tells me that with this powder, in this bore diameter and behind this bullet, 95.0 gr is the max that I can burn relatively effectively in this barrel length.

    So, I take the 95.0 gr load, load 5 rounds and shoot them over the chrono and record the velocities. If they show less then 40 fps spread for all five shots fired, I am at that point done with load development and onto long range testing. At this point I have 12 rounds down the barrel!!!

    If this was a totally unproven load combo, I would then load up 12 test loads with this exact load and head out to my long range shooting area. I would find a very small(sub 1/4 moa in size) target rock which there are hundreds of them where I shoot, set up at a range that I consider at least the max I would use this specific rifle for in the field.

    It generally takes 3 shots or so to get point of impact very close to point of aim. At this point, I let the barrel cool and if alone, set up my video camera with its 72x optical zoom. I am not looking to hit the target rock. I only want a very small aiming point for a quality hold and then I use the camera to record where each shot lands. I will shoot a shot every 4-5 minutes, recording each shots impact. That way I can get back home, and review the tape. Watching impacts on video tells you 10 times what you see through the scope. What often appears as a solid center hit through the scope is seldom that when you see it through a high powered video camera.

    I now have roughly 25 shots down the barrel and when I watch the video I am looking for two things. Group consistancy and size and also making sure there is no vertical stringing. If shooting in good conditions, you will rarely see much more then 1 moa of horizontal stringing, even in a lightweight rifle as long as its mechanically sound. The vertical stringing tells you what your velocity consistancy is.

    Books have been written on the topic of Low extreme spreads but I doubt many that read about this and try to get ES numbers into the single digits have ever tried to tell the difference between a 40 fps ES and an 8 fps ES at 1/2 mile shooting from field positions. If you can tell the difference your a MUCH better shot then I am and there are many that are. For me however, it means nothing. As long as I see consistant shot impacts I am satisfied.

    At that point, my total load development is done.

    Developing a drop chart can also be done very quickly. Generally in less then 5 shots, at least to get it close. Once you have a rifle zeroed at your desired range. Mine is 250 yard zero because I do not dial up for each shot, I use a ballistic reticle for hold over and I do not want to have to use up my reticals MOA with a 100 yard zero. Plus, anything from 0 to 400 yards is just point and shoot with most of my wildcats.

    With your known zero, then you need to pick out and test at at least three other ranges. For an 880 yard max range I would test at 400, 600 and 880 yards. Take one or two shots at each range, record your drops and if they impact off point of aim, record by how much in moas. Generally, if your BC is close, are your off, you will be consistantly off. For example, if your on at 250, 1 moa low at 400 you will generally continue to be low at 600 and 800.

    Once you get this data and correct for the drop adjustment with either a tweak of your ballistic data or a scope adjustment, you will be pretty damn well set with your drop.

    All you need now is to continue to test it at various ranges to confirm drop at all the different ranges. You will also learn that things will vary slightly from day to day. If you hunt in the same general area and conditions, it will generally not be enough to even notice big game hunting but because of this, you want your drop chart to be as accurate as possible for the majority of shooting conditons you will be hunting in and that is just done by testing the drop chart at various ranges.

    That does not mean you need to take alot of shots. You could take your rifle out with you every time you shoot, set up each session at a different range, take one shot, record the data and be done and over the summer you will have a wealth of ballistic drop data and probably only have 15-20 rounds down the barrel.

    Like I said, extremely simple.

    I do not use the ladder test. I have never been lacking with the loads I have developed using this method and I have yet to have a load not produce at least 3/4 moa which is what this rifle does. Most of my heavier rifles are WELL under 1/2 moa using this method.

    Now if your shooting a factory rifle, ladder tests can be more valuable because their vibration patterns can be pretty wild. In a properly machined and assembled custom rifle, you will not see as dramatic of vibration patterns as you would in a factory rifle for the most part.

    Hope this helps some. For those that are already biting their lip on this post, I apologize but it works and works well.
     
  9. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Mikecr,

    I would agree, for chuck size critters, you would need to hold slightly better moa but the group I placed on the gong would have killed any chuck around here at that range except perhaps the single shot that landed a bit to the right.

    For hunting anything the size of a yote or larger, More then enough accuracy out of a light rifle.
     
  10. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    ICANHITHIMMAN,

    This is about the only pic I have of the rifle. Took this 146" 5x5 whitetail three years ago at 470 yards.


    [​IMG]
     
  11. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Geargrinder,

    I worked with my 224 Allen Magnum which was based on a 270 WSM necked down and fireformed to the Allen Magnum shoulder and body design.

    The problem was that we do not have any 22 cal bullets that were heavy enough to make this case capacity work well and those that were heavy enough (100 and 107 gr ULD RBBTs customs) could not survive the launch speeds over 3100 fps...... Unfortunately the 224 AM could easily drive these bullets to 3450 fps!!!

    Then the lighter bullets that would handle the RPMs did not have enough bullet weight to get efficent powder ignition. Until we get a 100-110 gr 22 cal bullet that will handle what the 224 AM can produce, it will be moth balled.
     
  12. ICANHITHIMMAN

    ICANHITHIMMAN Well-Known Member

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    Good info thanks again for the pic. Whats the barrel profile?
     
  13. meatyrem

    meatyrem Well-Known Member

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    Ok. I have a 7 RUM. I am curious as to what a 7mm AM is? How was it developed? What is the comparison between the two? What is the 7 AM case based on? Just curious, thanks.
     
  14. meatyrem

    meatyrem Well-Known Member

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    Have you tried US869? Or just Retumbo?