Shocked at how much throat erosion

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Alan Griffith, Jan 12, 2008.

  1. Alan Griffith

    Alan Griffith Well-Known Member

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    I started shooting my 30-06 Ackley last November 2007. It's has a 26" SS Lilja barrel. My primer count indicated I've put about 700 rounds through it. I've got a great 180 BT/AB load and am currently working on a 200 AB/PT load for Alaska Brownie/Grizzly/Dall.

    In the process of determing my Partitions distance to the lands, I decided I better see if/how much throat erosion I had. I looked at the original 180 BT/AB data since this is the original bullet I started with. I pulled the original 180 AB from it's primerless case after I remeasured it and compared the measurement w/ the data written on the side of the case. I then ran the same bullet through my process of determing OAL up against the lands. I reseated the bullet to the new OAL and HOLY COW! If I did my measurements and math correctly I've lost .13" in throat. I went back and double checked both the "before" OAL and Length to bearing surface (LtBS), then compared them both to the new OAL and LtBS;----.13"-----.

    Is this normal? I figured I might get .02 to .04" but not a tenth plus.
     
  2. EddieHarren

    EddieHarren Well-Known Member

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    Throat Erosion

    What powder are you using? I experienced severe throat erosion and firecracking in a 7MM Mag. using Reloader 22. Switched to H4831, same velocity, pressure and accuracy, no more erosion or cracking.
     

  3. Varmint Hunter

    Varmint Hunter Well-Known Member

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    I'm not surprised at all. In the off season, I usually recheck all of my rifle throats the same way you did. Many of my rifles have seen .010" of erosion and sometimes more. Think of what 1,000 rounds of any magnum cartridge will do to a throat. Many barrels are "toast" by that time unless treated gingerly. You know - shooting only short strings to allow barrel cooling and careful cleaning using the usual benchrest methods.
     
  4. Alan Griffith

    Alan Griffith Well-Known Member

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    My load is 68.5 gr of Rel 25 for the 180'ers going 2997 fps in Win cases and Fed 210M primers seated .015" off lands.
     
  5. MontanaMarine

    MontanaMarine Well-Known Member

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    I've got about 2400 rounds through my 30-06. Throat has advanced less than .02"

    Barrel is a Douglas stainless steel, #7 contour, 1/10 twist. most of the loads have been moly'd 190-210gr match bullets, under 60-62gr RL22.

    I wonder if the moly shields the metal from some of the effects of heat/pressure?
     
  6. BountyHunter

    BountyHunter Writers Guild

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  7. goodgrouper

    goodgrouper Well-Known Member

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    Shouldn't have been that much erosion but mileage may very. If the barrel was cleaned and not allowed to get too hot, it should have gone 1500 or so before getting rough. My 300 win mag eroded .020" after 1100 rounds. What method are you using to determine the seating depth/throat measurement?
     
  8. 284stak

    284stak Well-Known Member

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    I shoot a 7mm-330 dakota using primarily 140 accubonds, RL-22 and a shilen barrell. Have just over 600 rounds through it and have lost 0.022 to throat erosion. I have heard that the shilen barrels may be softer than others --- but like EddieHarren said, may be the powder also. I adjust my seating depth every 100 rounds to keep up with the erosion.
     
  9. demarpaint

    demarpaint Well-Known Member

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    Good point......I've heard on more than one occasion, although can't prove it, that Moly or Danzac gets into the throat and hardens. This "harder" throat wears less. Just passing info along, I know there are a lot of different opinions on this topic. I use Danzac and find cleaning a lot easier now.

    Frank D
     
  10. Alan Griffith

    Alan Griffith Well-Known Member

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    GG,

    When I first obtained the barrel last October, I had Ian Jensen over at Barnes Bullets (he's no longer with Barnes) chamber, thread, crown and mount it into my Rem 700 action. By November I started shooting. I started with 180 AB's and Rel 25. I fired a couple of bore break-in rounds and took my base measurements. I have a steel rod with two sliding rod stops which can be tightend down via knurled set screws. With a dirty barrel (per Glen Zediker) I use the steel rod to first run it in from the muzzle agaist the face of the bolt, lock the set screw on the rod stop and move the whole afair back about 8". I then gently placed one 180 AB into the chamber and with a fiberglass rod pushed the bullet up against the barrels throat. Working back and forth between the steel rod from the muzzle end and the fiberglass rod from the chamber end and the bullet in the middle, I was able to repeat the procedure, each time tightening down the 2nd steel rod stop. Each time I would take inside measurements between the two rod stops to get my OAL (bullet tip to base of case). I would then seat that same bullet into a primerless case to measure the same OAL. I would then take the Stoney Pt tool to obtain case base to ogive. Both figures were inscribed onto the side of the case for future reference. Now, almost 700 rounds later I take the same exact measurements and come up .13" longer. I thought my first figures were off so I double checked by running the rod measurements again. Both the OAL and base to ogive measurements were, again, .13" difference. I have been known to have drain bammage and make mistakes. I will gladly run the tests again if someone wants me to.
     
  11. Rimfire

    Rimfire Well-Known Member

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    Allen

    I had the same problem one time and found that the new batch of NBT's varied 15 thou from the old batch / position of ogive/ distance from ogive to tip.

    I save a bullet from my first measurement and put it in a film can along with data. When I got out the original bullet used to check oal everything was still the same. Called Nosler and they said it was within specs. The new batch shot the same just had to set them the same 10 thou off.

    It's hard to say for sure without the original bullet, does it still shoot the same?
     
  12. goodgrouper

    goodgrouper Well-Known Member

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    I'm trying to imagine what your tool looks like and how it works. It sounds something like the Stoney point tool without the threaded brass on the end? I have never found that tool to work well enough. In my tool, there is an easy .010" worth of slop in the materials and fit which is enough to render it useless when dealing in thousandths.

    The best method is still the low tech magic marker on the bullet method. Of course, you have to have an original bullet left to keep re-checking. Just my 2 cents.
     
  13. Steve Shelp

    Steve Shelp Well-Known Member

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    Alan,
    I'm one of the guys that posted on the benchrestcentral.com post that Bountyhunter put up a link to. I keep very close track of my rifles on this. Two posters here have already pointed out a very important detail and one of the big disadvantages of using the steel rod and 2 stop method. You need to use the exact same bullet everytime. The tips do vary form lot to lot. But let me state that I don't think this accounts for all of your .130" of erosion taking the bullet variation into account. That is excessive for a 30-06 even an improved version. So did you use the same bullet to measure the throat erosion now as when it was new?

    I always take a bullet when I get a new style and put it asside in my loading bench organizer. It one of those metal cabinets with several small plastic drawers in it. One drawer is set aside jsut for these "benchmark" bullets and I use them for checking seating depth and checking neck clearance on neck turned brass. That is it. when I'm done with them they go back into this drawer. Keep in mind I shoot several widlcats and use custom bullets for 90% of my shooting time. If your talking about a hunting rifle then maybe I would suggest keeping 1 benchmark bullet in your reloading die case might be a good idea. Especially seeing how you are only using 2 different bullet style in the BTs and ABs.
    As for the method I use to measure this. I use the Stoney Point device on a set of calipers that gives me a OAL reference dimension. And I use the majic marker also to clearly see the engraving to begin with. I seat a bullet in a dummy case and keep adjusting back until the land engravings go away. When I'm close I use 0000 steel wool to polish the bullet and a jewelers loupe to watch the engraving pattern. This is the very simplified version. But you get the jist of it. This method is also a good way to see if the throat is burning out evenly also. Remove your ejector when using this method or simply use a neck sized only casing to help cut down on the off-center issue.


    On the issue of certain powders causing more erosion: I use a lot of Allaint Reloader and Hodgdon slow burning powder in several widlcats and haven't seen any evidence yet to support one wears out a barrel more then the other. I think what the one poster saw in his 7mm Mag after switching powders and slowed the erosion down was the thruth. But it probably wasn't caused by switching powders. I would have to say it was the non-linear erosion that was discussed in the post on BRCentral.com. Throats will wear fast in the beginning then slow down after all the nice sharp edges of the chambering reamer burnoff rather easily. This is a repeatable pattern for any caliber.
    I think the best analogy I can think of is when you throw a book into a fire. The edges of the pages catch pretty easy, but then it takes forever for the whole book to burn up. Sometime you can sift through a firepit and find centers of pages that are readable that were totlaly engulfed in flames just hours ago. Same scenario to me.

    Steve
     
    Last edited: Jan 13, 2008
  14. EddieHarren

    EddieHarren Well-Known Member

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    Barrel Erosion

    Steve, just to clarify, after the initial firecracking and erosion, on several barrels in 7mm Mag, the barrels were toast. Once the barrels were replaced, and the powder was changed to H4831, we saw no more firecracking or excessive erosion. The barrels, that originally showed the erosion, would no longer perform to the standards, that were required of these rifles. Examination of previous take-off barrels, before we started using R22, showed no excessive erosion or fire cracking, even after 1500 rds. The barrels, same manufacturer, that were used with the R22 propellant, showed excessive erosion in as little as 450 rds.
    The ammo, used by this agency, is loaded by an outside contractor, who must keep pressure, velocity and accuracy within very tight tolerences.