The importance of the crown on a rifle?


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Mark-Smith
December 17, 2010, 10:12 PM
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?

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WNTFW
December 17, 2010, 10:19 PM
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.

Mark-Smith
December 17, 2010, 10:26 PM
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?

taliv
December 17, 2010, 10:30 PM
mark, think about what the very high pressure gas would do if the bullet didn't seal it

BrocLuno
December 17, 2010, 10:40 PM
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 :)

J.Boyette
December 17, 2010, 10:57 PM
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.

Mark-Smith
December 18, 2010, 12:03 AM
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.

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

Mr_Pale_Horse
December 18, 2010, 12:27 AM
11 degrees for a target crown

OYE
December 18, 2010, 01:06 AM
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.

Freedom_fighter_in_IL
December 18, 2010, 01:11 AM
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.

Nematocyst
December 18, 2010, 01:13 AM
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.

JDMorris
December 18, 2010, 01:40 AM
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.

Picher
December 18, 2010, 06:22 AM
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.

ranger335v
December 18, 2010, 11:00 AM
"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.

Nematocyst
December 18, 2010, 04:39 PM
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.

JDMorris
December 18, 2010, 04:45 PM
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.

kis2
December 18, 2010, 05:06 PM
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.

JDMorris
December 18, 2010, 05:12 PM
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.

OYE
December 18, 2010, 05:21 PM
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

Float Pilot
December 18, 2010, 07:27 PM
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.

Mark-Smith
December 18, 2010, 07:41 PM
what happened after I re-crowned the stainless muzzle with a radius bowl shaped crown.

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

Freedom_fighter_in_IL
December 18, 2010, 08:00 PM
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.

GURU1911
December 18, 2010, 09:02 PM
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

Picher
December 18, 2010, 10:14 PM
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.

OYE
December 18, 2010, 11:11 PM
" 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 !!!!!

Float Pilot
December 18, 2010, 11:15 PM
Picher:

You are right, I mistakenly picked out a later photo which showed even more improvement from a partial action bed and a free floating. I did it in stages, but not all of my old photos are in my newer computer. Often using another shooter just to make sure the improvements or set-back were not just me and my old eyeballs.

This should be the correct photo showing after the re-crown alone. Using the same load as the first, which at the time was the only load that would shoot worth a darn in this rifle....Unfortunately that bullet, at those speeds flew apart when hitting moose.

Also I have attached a photo of how the rifle now shoots. It now has a full action glass bed and a full channel barrel bed. The action has been smoothed up, sights have been added and so on....
That load is with a 275 grain Barnes old stock. It will do pretty much the same thing now with Swift 280 grain bullets.

Freedom_fighter_in_IL
December 18, 2010, 11:35 PM
Well float, not to be picky, but you are shoing 220 grain speer fp verses 275 barnes SP. COULD be just your barrel likes those 275gr barns better

Float Pilot
December 19, 2010, 12:22 AM
Yes you are being picky.
I posted before crown, after crown and after crown & partial bedding with the 220s. They just happen to be on two pages.
I guess I should have stopped there...

The, just for kicks, photo of the group with 275s just shows that a crappy Ruger can (at times) be made to shoot well, with lots of work.
I do not have any pics of how the 275s used to shoot before I worked on the rifle, because it was so bad that it was scary. The photo of the horrible group of 220s on the first page was the BEST group that this rifle could fire when it came out of the box.
A real stinker from the factory, but it now does pretty well as a hunting / protection rifle.

Now I have to wander out to the shop and figure out why a 300 Win Mag is shooting bizarre groups.

Freedom_fighter_in_IL
December 19, 2010, 12:27 AM
Ah ok. I was confused for a moment there (Like thats hard to do anyway)

OYE
December 19, 2010, 12:30 AM
Did you use a crowning tool on that Ruger ( if so what kind ), or did you remove the barrel and use the lathe?

Ruger GP100 fan
December 19, 2010, 12:39 AM
When re-crowning a barrel,what is done to the bore/rifling? Wouldn't something have to be done to eliminate burrs and such left over from machining the crown?

Float Pilot
December 19, 2010, 02:45 AM
Back from the shop..The front scope mount was loose on a M-700. Now I have to sit and watch a movie with the wife...

OYE: http://www.mansonreamers.com/
He really makes some nice stuff.

I also have about 80% of an old oddball set from Germany that came in a walnut box. I have no idea who made them, but they are super hard. They cut barrel steel like butter.

RugerGP100: When done right you do not have any burrs or chatter marks. (caused by bouncing the reamer) There is a smooth caliber specific guide that fits into the bore that centers the reamers. Of course you polish for a final finish.

Offfhand
December 19, 2010, 12:59 PM
Post fro above;

"When re-crowning a barrel,what is done to the bore/rifling? Wouldn't something have to be done to eliminate burrs and such left over from machining the crown?"

Indeed so, which is why a gunsmith who specializes in accuracy will spend almost as much time finishing the crown as cutting the chamber. Then carefully inspecting it with a magnifying glass for burrs, etc. I know a number of serious target shooters, myself included, who own lathes mainly for the purpose doing their own crown jobs and recrowning when necessary.

Ruger GP100 fan
December 19, 2010, 11:22 PM
Thanks. My Ruger GP100 6" SS came with chatter where the crown meets the rifling. I can't hit a darn thing with it. If it was yours would you send it back to Ruger? Or is it as simple as this seems to make it? iIn another video he cuts a few inches off of a rifle barrel and it does not appear that he's too careful about the cut being exactly perpendicular to the barrel. If how the gas pressures exit the barrel are critical to achieve accuracy,why such a relaxed mindset as to whether or not they begin exiting equally around the full circumference of the barrel? I'd think that using a hand file wouldn't even get you close to a cut that's exactly 90* to the barrel.

http://www.youtube.com/watch?v=OorpZlG28fI&feature=related

http://www.youtube.com/watch?v=b43odFm0mrI&feature=related

Ruger GP100 fan
December 23, 2010, 03:30 AM
Does the barrel above need a good smith?

GURU1911
December 23, 2010, 06:56 PM
Mr. Gp100---guru1911 here for you !!!

If that is an actual photo of the crown on your revolver, it needs some serious metallic surgery. Wished you lived nearby so i could correct that crown for you. Cost to cut, lap, & polish to a sparkling finish would cost $50.00.

When i figure out how to post photos on this forum, i will send you some photos of my work---30 years of practice sure helps.

Ruger GP100 fan
December 23, 2010, 07:28 PM
Thanks for your response,GURU1911. Does it look like the condition would cause accuracy problems? I bought the gun new last spring.

Dookie
December 23, 2010, 10:36 PM
A trick that might help, as the crown looks rough but even, is to polish it. Get some bore paste, about 10 bucks for a small container, it lasts a long time, get a BRASS screw that fits nicely into the crown. Chuck the screw into a hi speed screw gun, coat the screw with bore paste and be liberal about it. Use the round end of the screw to polish the crown. The brass and bore paste will not hurt it. I have done this to a few rifles and have always had good results when the crown is not damaged.

Ruger GP100 fan
December 26, 2010, 02:10 PM
Thanks

WinchesterAA
December 28, 2010, 12:45 AM
So what is the effect of a flash hider on a crowned muzzle?

If you enjoyed reading about "The importance of the crown on a rifle?" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!