Model 10P Crown Issue

[Russmerle]

I bout this 10P-SR a couple years ago and she's been a great shooter. I've just noticed, however, that the crown is rough. There is a noticeable edge if you scrape your fingernail along the muzzle at the bore. Feeling from inside the bore to outside, the muzzle it is smooth. Going from outside the muzzle to in, the crown is rough and seems to have burs. I ran a Qtip over it and nothing stuck but she's still rough.

Though she shoots 1/2 to 1 MOA, should I lap the crown? None of my other rifles feel like this at the muzzle.
See pic, thanks

russ

http://i.imgur.com/Uy5lzkb.jpg

[GaCop]

Lapping it won't hurt if done right and will give you the added peace of mind. Go for it.

[darkker]

Though she shoots 1/2 to 1 MOA, should I lap the crown?

Russ,
Read your question again, and consider what you are asking.

You are asking if, for the sake of beauty, you should mess with a good shooting rifles crown.

If you aren't happy with the accuracy, then do something about it. If you are happy with the accuracy, then keep your fingers of the muzzle, and go shooting.:cool:

[foxx]

^^^ +1

If building a rifle, I would not INTENTIONALLY rough-up a crown the way yours is, but if it shoots, it shoots. What no one knows for certain is if the rough outside edges of that crown are what is causing the good accuracy. It's unlikely to be a contributing factor, but it's not something you can replace or reverse if you mess with it and it and then find out it doesn't shoot as well after smoothing it out. These factory barrels have a lot of "flaws" such as tool marks in the bore, yet most of them shoot very well. I guess the common, accepted wisdom is you want a clean, smooth, crisp crown so as to allow the gasses to escape in an even, unmolested fashion when the bullet leaves the barrel. The truth is, though, what you REALLY want is for the bullet and gases to exit the barrel in a way that allows the bullet to travel in a consistent path towards the target. For all we know, in this case, those rough edges are making up for some other unknown flaw deeper in the barrel. If it were mine, I would leave it alone. If I had a few good barrels sitting around (more accurate than this one) just waiting to be used and this one had a 10% chance of showing improvement by cleaning up the crown, I guess I would do so. But I would also have to believe that I was a good enough shooter to discern the difference when done. I am not, so I would not take that chance.

Now, if someone much more knowledgeable than me said cleaning up the crown could NOT possibly have a NEGATIVE affect on it's accuracy, then I would go for it. (That SOMEONE just might be GAcop)

Perhaps I have done nothing more than simply reiterate the premise of your question. :)

[Russmerle]

I'll hold off until the accuracy falls off then. I'm sure the crown will eventually be a problem as bad as it is compared to my other rifles. Brass screw head and lapping compound should do the trick when the time comes.

[DanSavage]

I had one like that ,, I never did mess with it, but maybe it's hard carbon?

[jonbearman]

It looks like a cleaning rod was banging around while cleaning. If so clean from the breech and get a dewey cleaning rod and a bore guide. I would have that crown done right if it were mine. it looks awful rough to me. Take a q-tip and put it in the bore and then drag it lightly across the crown. If it catches or removes any cotton then the crown is in sorry shape.

[Ol' BW]

I'd say if it ain't broke don't fix it. As discussed previously the theory is a smooth crown makes for a smooth transition with gasses flowing in a uniform pattern around the bullet as it exits. In reality how pretty the crown looks has nothing to do with how the gas escapes. I would say the sharp transition would still make the gasses escape in a uniform pattern as long as the crown is square with the bore and bullet path. IMHO, Unless the accuracy was a problem I'd leave it alone, YMMV.

BW

[Russmerle]

It looks like a cleaning rod was banging around while cleaning. If so clean from the breech and get a dewey cleaning rod and a bore guide. I would have that crown done right if it were mine. it looks awful rough to me. Take a q-tip and put it in the bore and then drag it lightly across the crown. If it catches or removes any cotton then the crown is in sorry shape.

I did the Q-tip test and nothing stuck. It wasn't a cleaning rod. I clean from breach and never let the jag come all the way out or I just use a snake... It's had to of been like this. I'd never noticed it since it shoots so good. The "rifleman" in me wants to fix it but everybody has a good point. One shouldn't let the crown stay buggered up but I shouldnt mess up a good shooter...

im perplexed. Lol

[foxx]

^^^ Shouldn't have ever looked at it that closely! :)

It would bother me, too.

[Russmerle]

^^^ Shouldn't have ever looked at it that closely! :)

Got that right foxx... it's gonna bug me now lol

[Russmerle]

Problem solved! Used a handheld drill, round headed bolt and some 220 grit lapping compound. I put the bolt in the drill chuck round head facing out, dipped it in lapping compound and used circular motion ensuring the bolt head found center bore and lapped a little bit at a time. The muzzle passes a qutip test and also looks good! Took her to the range and had great results though she shoots about the same as before. Lol

BEFORE:
http://i.imgur.com/Uy5lzkb.jpg
AFTER:
http://i.imgur.com/LQkBEhr.jpg
RESULTS:
http://i.imgur.com/yFHJWhq.jpg

Two three shot groups. Had to adjust after first one but they were 1/2 MOA and .8 MOA respectively. These were SMK GMM 175s but also shot some surplus ammo groups and scored just I've MOA with those too!! Fweeeeuuuuw! I thought for sure I was going to be displeased after my lapping venture but I'm happy with the results.

[m12lrs]

Now I am not advocating this but it is interesting

The Overrated Crown

http://www.longrangehunting.com/articles/rifle-crown-1.php

[Russmerle]

Now I am not advocating this but it is interesting

The Overrated Crown

http://www.longrangehunting.com/articles/rifle-crown-1.php

Thats a good read. So hard to believe he didn't believe it himself. I bet the first two rounds knocked the burrs off caused by the carbide tip. That's a lot of info too. Worth bookmarking