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Throat Erosion

Discussion in 'Handloading and Reloading' started by otisrush, Nov 8, 2018.

  1. otisrush

    otisrush Member

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    This is more of a rifle question, but I'm posting it here because I figure we loaders deal and care about throat erosion more than the average rifle shooter. (The gun in question: A Rem 700 SPS Varmint - bull barrel - in .243. It's a target gun only. And I've generally pushed very heavy - i.e. long - bullets through it. I figure they're a bit tougher on the barrel. It gets pretty warm pretty quickly when shooting these heavy bullets.)

    I've kept records of the distance to the lands (over time) for various bullets I load for this gun. (I periodically check the distance and log it....so I can see how throat length has changed over time.)

    Over the last 5 months I've seen what I think is a big erosion: My distance-to-the-lands measurement has grown .030" over 5 months. It's definitely the largest gain I've had in this gun over that kind of timeframe. I have shot a good amount through it in that time - probably 400-500 rounds. Total number of rounds through the gun is on the order of 1,200-1,300. I've read anecdotally .243 barrels tend to get shot out relatively quickly.....1,600-2,000 rounds or so.

    Does anyone have experience for what sort of erosion they've seen in a stock Rem .243 barrel when the barrel was done? I figure this is kind of a long shot (ROFL) question....but I'm wondering if these measurements I'm seeing can be put in a broader context to get a gauge on when this barrel might throw in the towel.

    Right now it's still shooting well. So performance on the range is still strong. I figure that's the ultimate measure: Can it still shoot.

    Any experiences or comments?

    Thanks!

    OR
     
    Last edited: Nov 8, 2018
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  2. cw308

    cw308 Member

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    I'm not shooting a 243 but as you posted your bull barrel heats up quickly , usually the heavier barrels heat up slower but takes longer to cool down . How much time are you taking between shots ? 100 rounds per month doesn't seem that high . Are your groups starting to open up ? What distance are you shooting . Remington's do start out with alot of free bore . On my Rem. 700 LTR 308 barrel had so much leade I couldn't reach the lands . After 4000+ down the barrel I had it completely blueprinted by Accurate Ordnance and installed a Rock Creek M24 5R barrel installed . The barrel has hardly any free bore . How are you checking your wash out ? I use the stripped bolt method , I load one at a time , I removed the heavy ejector plunger spring with a spring from a bic lighter spring , the round layes on the follower so I don't chase my brass or have it hit the floor . Using a stripped bolt with just the housing you get a good feel when the bullet hits the lands . Very repeatable.
     
  3. Slamfire

    Slamfire Member

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    Your barrel life is on the high side, based on my talks with 243 shooters. A barrel is either shooting better, or it is shooting worse. At some point in the future it will stop clustering at distance. My experience with worn 308 barrels was that they still shot well at 300 yards (this was prone with a sling and irons), but they would not cluster at 500/600 yards. That was when the barrel was no longer appropriate for target shooting. That will happen when it happens. You are at the round count point where you ought to be deciding on your next barrel, buying a blank, and to whom you are going to send the action to.

    There was a young man at the range with a 223, he was complaining that the bullets he was using were awful. I think he was using Hornady A-Max bullets, and those are good bullets. His target was at 100 yards and there were keyholing on target, and the group was more of a shot gun pattern. When we got back to the bench, we looked down the tube, and I don't remember if there was any rifling left. My recollection, the barrel was a smooth bore.
     
    Last edited: Nov 8, 2018
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  4. Innovative

    Innovative Member

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    otisrush . . . . .

    Throat erosion depends on several things. I've chambered several rifle barrels and monitored throat erosion. I found that the first 50 rounds can move the throat forward quite a lot. Depending on exactly "where" you measure the bullet contact surface, it can be as much as .070" I recommend using the exact same bullet you intend to shoot for the break-in period. I also recommend using a chamber reamer that considers this early wear. After the break-in period, throat erosion slows way down, and is almost nothing for most shooters to be concerned about. If you establish a good load, you'll notice when accuracy starts to fall off.

    I am also a firm believer in using a good borescope, because you can clearly see when your barrel is not actually clean. At the end of the day, you need to see exactly "where" your barrel needs a bit more cleaning, and every barrel is different. If you want a real tack driver, try to do a "quick clean" of your barrel every 20 to 40 rounds whenever possible. That extends the accuracy life of your barrel more than most shooters would believe.

    If your barrel is fired quickly enough to keep it hot (like prairie dog shooters do), that will shorten your barrel life quicker than anything. I have a few AR-15s (.223 Rem) that still shoot 3/4 MOA groups after well over 3000 rounds.
     
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  5. MrMagumba

    MrMagumba Member

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    I have a 20 year old Rem 700 VLS (Varmit laminated stock with the target barrel) in 260 that ate the throat at a rate of .001 per 12 rounds as I tried to find a load it liked. Never found a good load after trying a few tweaks like a trigger job, recrown, bigger scope. Never got under 1/2" 5 shot at 100yd. (That was a couple times-otherwise mostly 1" and occasional 3/4"). I'm just calling it a bad factory barrel now with .148 longer throat than new. A mix of hot and cool loads searching for that 1/4" group. Not sure what to do with it now. Nice looking gun :)
    Just one experience for you.
     
  6. 243winxb

    243winxb Member

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    New 243 , Rem 40x single shot , 1976 to 1994 no log kept. 1994 to 2018- 1090 rounds fired using IMR powders. 68 to 90 gr mostly. Not a competition rifle, mostly occasionally target shooting. Used for woodchuck, crows and turkey shoots.

    This is what i go by.

    Last time out, 8 groups of 5 shots each @100 yds average .568" All 8 loads different using 2 bullets and 2 powders. Not great, but ok.

    Not enough 88/90 gr Berger bullet shank is left in the case neck , now, when touching the rifling. Never did like a jam or contact with the rifling.
     
    Last edited: Nov 9, 2018
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  7. 243winxb

    243winxb Member

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    There is less barrel wear, if the front of the bullet seals the bore before the bullet base leaves the case mouth. Less hot gas blowing by the bullet on firing.
    The 55 gr bullets would be the worst. But it depends on when the neck expands at the time of firing and if it fully expands. Place a bullet into a fired case neck as a test.

    Just how i see it. No proof or testing done.
     
  8. Cemetery21

    Cemetery21 Member

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    I used to figure 1400 rounds on a 22-250 prairie dog rifle. It would still group at 1400, but the velocity was down (I didn't change bullet seating depth for the erosion). So, set the barrel back and shoot another 1400 rounds. Repeat.
    A buddy finally burned up a VSSF .223 barrel after several years of prairie dogs (he did abuse it with long strings and little cleaning). It grouped well up until the end, it just lost a lot of velocity. When it went wild, it was all at once. He was hitting dogs one minute and missing by 3' the next. Borescope showed about 6" of dried pond mud looking cracks according to the guy that rebarreled it.
     
  9. otisrush

    otisrush Member

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    Wow.....really fascinating experiences and perspectives above. Lots to think about.

    Although I called this a "target gun" - I was focusing more on the aspect that "it's not a hunting gun". But in the world of non-hunting guns I'm not really chasing groups per se. I use it mostly to shoot steel silhouettes out to 500m. I use the heavier bullets because they'll consistently knock down the 500m steel rams. I've tinkered around with it at 1,000 yds.....but nothing involving competing.

    Very interesting perspective from 243winxb re bullet sealing the bore before the bullet base leaves the case. One new variable in this 5 month window where I've seen increased erosion is I started shooting a 70gr Sierra MatchKing bullet.....which happens to be quite short. Up until that point I was shooting Berger 105gr and 115gr target bullets basically exclusively. That short 70gr may have put more stress on the rifling than the longer/heavier bullets were.

    I figured this day was coming. (In reality "that day" hasn't arrived yet, as the gun still shoots well.) The real point of this post was just the relative surprise of the amount of recent erosion. I knew I'd need to be rebarreling it at some point. To that end I'd say I'm *strongly* considering rebarreling it in 6.5 CM. I know that's a really popular cartridge now. But I need to decide whether I want to keep it as a .243......or go to a caliber that might be a little more consistent at 1,000 yds.

    Thanks all! I really appreciate it!

    OR
     
  10. Nature Boy

    Nature Boy Member

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    I read that double base powders, like the VV 500 series, really accelerate throat erosion. It's because of that that I don't use them, therefore, I have no first hand experience with them.

    It could be true, or I may just be perpetuating a half-truth or a pure myth. Such is the nature of the internet.
     
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