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The importance of the crown on a rifle?

Discussion in 'Rifle Country' started by Mark-Smith, Dec 17, 2010.

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  1. Mark-Smith

    Mark-Smith Member

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    There seems to be a lot of emphasis on the crown of a rifle - what exactly does it do?

    As long as the rifling down the length of the barrel is accurate, what effect does the last tiny bit have on the bullet?
     
  2. WNTFW

    WNTFW Member

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    Because the crown is the last part of the rifle to affect accuracy as the bullet leaves the muzzle. A bullet can be pushed off center by an uneven crown or crown with damage. The high pressure gas has to vent to evenly. Incidently a defect on the base of a bullet can be more detrimental to accuracy than damage to the tip.
     
  3. Mark-Smith

    Mark-Smith Member

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    Is there any reason the rifling just doesn't get gradually wider until it won't touch the bullet? Or would it just ricochet down the barrel if it was built like that?
     
  4. taliv

    taliv Moderator

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    mark, think about what the very high pressure gas would do if the bullet didn't seal it
     
  5. BrocLuno

    BrocLuno Member

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    The crown is the last thing the bullet and gas sees. What ever it does, is what the bullet will react to. An old barrel with so-so rifling, pits and wear will still shoot OK if the crown is good. First thing to get tuned when you are looking for accuracy is a crown job. Fixes more problems than most any other piece of work.

    Target & bench rest crowns used to be about 11 degrees. Field crowns were rounded, but usually at 45 degrees where they left the rifling. Modern accurate factory guns often come with a flat recessed crown. If you have enough metal, that's what I'd put one a rifle if I were recrowning :)
     
  6. J.Boyette

    J.Boyette Member

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    The gas behind the bullet moves 5x's faster then the bullet does, this is how you keep the pressure up to speed up the bullet as it travels down the barrel. Also this is how a gas operated rifle works.

    Gas is faster then the bullet.

    now, if the crown is not evenly cut, right at the time the bullet exits the barrel, if the gas flows faster in one direction, it will move the bullet in the other direction. Dependent on how bad this uneven part is, the bullet could tumble right off the exit.

    This is called jump. The jump is measured by how well the crown is cut.
     
  7. Mark-Smith

    Mark-Smith Member

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    Ahhh - interesting stuff! So what's the right way to cut a crown? Perfectly flat? Counter-sunk?
     
  8. Mr_Pale_Horse

    Mr_Pale_Horse Member

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    11 degrees for a target crown
     
  9. OYE

    OYE Member

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    All the above is good info. We would add that the other end of the barrel is just as important. If the bullet starts in wobbly, it's going to come out wobbly. Some of the articles on Lilja Barrels website may be of interest. Of course every factory has different views on what a crown should look like. There's a whole lot of "same hole" barrels out there with what most consider to be hunting crowns. The crown of the shootist may
    be of equal concern.
     
  10. Freedom_fighter_in_IL

    Freedom_fighter_in_IL Member

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    All of my "long range" weapons have an 11* crown. All my normal duty hunting weapons have a rounded 45* "hunters" crown. There is a good reason for that. Your muzzle can get a little bit "abused" in the field under rough hunting conditions and the typical "rounded" type crown, while not as efficient as an 11* sharp cut, is more resilient and will hold up under such stress. I am not saying that you should use your muzzle for a walking stick, but it is much stronger and more than efficient enough for hunters needs.
     
  11. AStone

    AStone Member

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    This is a fascinating thread.

    I've wondered about crowns for a long time.
    I knew they were important, but never really understood the details of why.

    This makes sense.

    JB's post #6 nailed it for me.
     
    Last edited: Dec 18, 2010
  12. JDMorris

    JDMorris Member

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    I have heard of people in the Military having a crown cover that they yank off last minute to shoot if needed and it can be shot though in a bind.
    I want one.
     
  13. Picher

    Picher Member

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    I just put a piece of electrician's tape across the muzzle when hunting. It not only protects the crown somewhat, but keeps dirt, snow, and rain out of the barrel. Air in the barrel ahead of the bullet blows the tape away before the bullet reaches it, so there's no variation in bullet impact.

    The crown isn't the only part of the bore that's critical. The last inch of bore is the second most important part. Rifles that are cleaned from the muzzle end, (especially those with micro-groove rifling), can be worn by the grit that accumulates on the cleaning rod. I liken it to a Remington Rod Saw, but to a much lesser degree. Perfectly straight, polished stainless steel rods, wiped after every patch or brush sroke will cause less wear than softer rods. It's not the rod, but what sticks to it that will cause the problems. Primer grit, especially when mixed with metal fouling, can stick to coated or soft metal rods.

    Bolt-actions are cleaned from the breech end and rods should just clear the muzzle, to minimize wear at that critical location. Brushes should be removed at the muzzle and never dragged back across the crown. For that reason, I grind off most of the threads on my brushes, so a quick twist removes them after they clear the muzzle.

    Hunters who shoot once a year and shoot a deer, then clean again will probably never wear out a bore. Hunters bores usually rust/pit from lack of cleaning and protection. Hoppe's #9 bore cleaner is not adequate protection. I use Break-Free after cleaning with other products, but it also cleans quite well.
     
  14. ranger335v

    ranger335v Member

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    "a lot of emphasis on the crown of a rifle - what exactly does it do?"

    If it's perfect it does nothing. It's the imperfections that cause problems.
     
  15. AStone

    AStone Member

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    Wow, I gotta say again, this is a great thread. So many questions I've had for a long time being addressed here.

    Picher, that's a really useful description and tips.
     
  16. JDMorris

    JDMorris Member

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    I'm now going to use electrical tape over my muzzle, And I have been cleaning it wrong and Might need a recrown because I have bulled the brush back through the gun, Do ya'll think I need a Re crown I have some Tiny tiny scratches but nothing seriously bad.
     
  17. kis2

    kis2 Member

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    probably not if they are just little scratches JDM, just change the way you clean it now, as long as the accuracy is where it was.

    but that's why serious shooters keep a log book as well. any decrease in accuracy for any reason (example: tiny scratches building on top of each other over a few hundred cleanings) would be noticed.
     
  18. JDMorris

    JDMorris Member

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    I have a bit over 200 rounds in my .308, I'm going to start a logbook once I get all the dang copper out of it so next time I go shooting it will.
     
  19. OYE

    OYE Member

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    I'm in the duct tape over the muzzle crowd. Mainly to keep mud out of the bore from
    an unplanned mis-step. I've yet to ruin a bore, throat or crown, from cleaning one with any type of cleaning rod. We would be in the crowd that thinks the chamber end (throat), rifling, last couple of inches of the bore, and the crown, are all of equal importance. Personally I'm not aggressive enough with a cleaning rod ( of any kind ) to abraid a throat or crown
    more so than the 10th bullet traveling down a fouled bore. If anyone is, I suggest you take all the above advice and tone it down a bit. Cheers
     
  20. Float Pilot

    Float Pilot Member

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    Asking about which type of crown and to what degree should it be cut is like asking if a Ford truck is better than a Dodge or Chevy. You will get several answers.

    If I can get the photos to stick, these are before and after photos of shot groups taken with the crappy Ruger factory crown and what happened after I re-crowned the stainless muzzle with a radius bowl shaped crown.
     

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  21. Mark-Smith

    Mark-Smith Member

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    If that's from the crown alone being changed... That's impressive!
     
  22. Freedom_fighter_in_IL

    Freedom_fighter_in_IL Member

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    Mark, I have seen MANY times where a crown job improved a weapon by 60%. You would be SHOCKED at just how much a little "out of whack" crown can affect a bullet at range.
     
  23. GURU1911

    GURU1911 Member

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    Having 30 years experience smithing on a couple of hundred rifles (.22lr to .300 mags), auto pistols, & revolvers of assorted calibers, i have personally witnessed some really crappy muzzle crowns even on high $$$$$ brand new firearms, that i started recrowning everything i personally own in my collection.

    99% of my customers requested recrown work on their rifles & handguns after seeing what a precision difference it made in my personal firearms. I have a target dated 1997, where i personally witnessed my friend david, shoot a 3-shot group from the bench with his 7mm magnum savage & the group measured .212" ctc with federal premium ammo !!!!!

    So remember-----protect the crown at all costs
     
  24. Picher

    Picher Member

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    Guys, if crowning was the only change in the Ruger, it would be dramatic, however, he also fully-floated the barrel and glass-bedded it, so it's impossible to tell what did the trick, but it's probably a combination of all three.

    That brings me to a suggestion. When you want to determine what is wrong with any gun, change only one thing at a time and test shoot exactly the same way as before. How else can you determine what the problem was?

    It also helps to bring another rifle to the range both times and shoot it without any changes to rifle, load, or rest. That's the only way to determine whether it's the rifle, the conditions, or you.
     
  25. OYE

    OYE Member

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    " Guys, if crowning was the only change in the Ruger, it would be dramatic, however, he also fully-floated the barrel and glass-bedded it, so it's impossible to tell what did the trick, but it's probably a combination of all three."

    Golly, I would have never guessed that from looking at that target !!!!!
     
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