Barrel Crown Discussion

[celltech]

Maybe this is the wrong section for this post, but I don't really see a gunsmithing thread...

I just got my 3rd Cabelas 12FV as a project gun that I intend on cutting the barrel down. So I have been looking at a lot of DIY barrel crowning articles. There seems to be numerous ways to do it ranging from using a shell reaming tool to a brass screw/marble/oversize bullet and polishing compound.

I was also just reading a thread in the 110-series section on a guy who has a burr on his new rifle crown and there was a recommendation on how to remove it. This made me look at my rifles and sure enough my 12FV .22-250 seems to be less than perfect :mad: It already shoots MOA and I wonder if it would tighten up if I worked on it.

Ok, so where is this going. I would love to talk barrel crowning and experiences y'all have had on either having someone do it or you DIYers and what steps you followed. Is the profile really that important? Do you have to have a <insert degree angle here> on the business end? Is it just more important to have a clean cut and transition, no matter if the angle is fixed or rounded?

Do you think that most every factory rifle could benefit from sort of polishing/honing to get that last little bit of accuracy? Maybe this is more important than bedding the action?

Thanks for your thoughts!!

[joeb33050]

With an M11 22" Sporter bbl, hacksaw to ~ 16.5", file the muzzle ~ flat, chamfer the bore with an RCBS 'cricket", the case mouth chamfer tool. This gives me a bbl that goes on my Striker and rifle actions legally. On 11/3/17, five 100 yard 5-shot groups from the Striker averaged .860". I've cut maybe a dozen barrels this way, accuracy seems to improve. On an M10 rifle back in June this M11 bbl averaged .808" for 12 100 yard 5-shot groups.
joe b.

[celltech]

With an M11 22" Sporter bbl, hacksaw to ~ 16.5", file the muzzle ~ flat, chamfer the bore with an RCBS 'cricket", the case mouth chamfer tool. This gives me a bbl that goes on my Striker and rifle actions legally. On 11/3/17, five 100 yard 5-shot groups from the Striker averaged .860". I've cut maybe a dozen barrels this way, accuracy seems to improve. On an M10 rifle back in June this M11 bbl averaged .808" for 12 100 yard 5-shot groups.
joe b.

Have you ever tried, or felt the need, to take it even further and lap the crown with some sort of brass screw/cone/plug and compound?

[foxx]

The crown needs to be clean and consistent so the gases escape in a uniform pattern around the front of the muzzle so as to not push the bullet off center. It does not matter what angle it's cut at. Unless the crown is damaged, there's no need to mess with it. Ranking the importance of a good crown over other factors such the "need for action bedding" is dependent on the degree of the need of the other factors. i.e. how badly damaged is the crown? How badly is the action being stressed by binding? in my mind, if the crown is damaged, fix it. If it isn't damaged, leave it alone. Lapping or polishing a good crown won't make it better, and 99.9% of the barrels from most any source come from the factory good enough. Damage occurs from poor cleaning practices and misuse/abuse.

[joeb33050]

Have you ever tried, or felt the need, to take it even further and lap the crown with some sort of brass screw/cone/plug and compound?
I used to lap with a big brass screw head and valve grind paste or others, even JB. In a hand-cranked drill. The cricket seems to work fine, so I gave that up.
Some report using a Lee case trimmer with a small-enough mandrel down the barrel. My .22 mandrels won't go in the bore, but the cricket works, so I haven't bothered.
It seems that the muzzle can be cut on a bias, and accuracy doesn't suffer. The muzzle not 90degrees from the bore. This goes back to Dr. Mann.
I suspect rumor and "I think it's so" have prevailed for years.
joe b.

[clm2112]

I'm probably going to offend and commit an act of heresy here... but my opinion is that the perfect muzzle crown is not as important as it is made out to be. I've done a lot of barrels for M1 Garands and M1 Carbines that have shot well. That is using 90 degree crowns, 11 degree crowns, and even radius crowns (folks who want the barrel crowned the same way Springfield did it for looks.) As a mark of professionalism, you do want a crown that looks nice and doesn't have any stray bits of metal hanging out. But in terms of accuracy, what matters most is that the bullet leaves the barrel the same way every time. Even a minor defect will effect every bullet launched from the barrel in the same way, so it really doesn't detract from the overall accuracy of the barrel. However, the closer you get to a crown perfectly square to the bore and uniform in contour, the better your chances of having a barrel that will shoot a wide range of different loads accurately.

I usually use little squares of sandpaper on my finger tip to touch the crown while it is still spinning in the lathe. Working my way up from 220 grit up to 1200 grit with a few drops of cutting oil. Again, the only goal is to remove any stray bits of metal that the cutter raised when forming the crown. It also makes a pattern on the muzzle that looks pleasing and polished out.

[m12lrs]

an interesting article on the importance of the barrel crown. Now i don't want my crown damaged but...

https://www.longrangehunting.com/articles/the-over-rated-crown.670/

[bsekf]

Why in heck did I read that!!!!! Another excuse gone!!!!! I am a great believer in "shorter is better". So have cut several barrels and the accuracy improved. Theory..... it is easier to cut a 20 inch straight hole than it is a 30 inch straight hole. And a 20 inch pipe doesn't flex as much as a 30 inch pipe. But, I figured a good muzzle crown was essential. New crown $100, hacksaw blade and a brass screw, maybe $5.

Bill

[clm2112]

Good article.... yeah, I found myself cringing when he took a carbide burr to the rifling... but hey, all in the name of scientific inquiry.

It goes to what I was saying. Every barrel deforms the bullets... it squeezes them down, presses rifling marks into the jackets, and scrapes the heck out of the jacket with every defect and machining mark in the bore. But what matters is that it will mangle and kick all the bullet the same way. So the mangled chunk of metal that emerges from the bore is going to fly the same way as the one before it. Gross defects may cause shifts in point of aim/point of impact between wildly different loads, but so long as every bullet is getting the same abuse, accuracy is still possible, even if the bullet is no longer even close to the shape the manufacturer intended.

That said, it is always nice to eliminate variables whenever possible. So it is still worthwhile to have a decent crown on the barrel, just to cross it off the list of variables.

There is also a psychological aspect to this... something that looks right to the shooter inspires confidence in the shot. If the crown looks right, then the shooter stops worrying about it and focuses attention elsewhere, like actually executing the shot well. I liken it to folks who fixate on the fit of the upper and lower receiver in an AR-15. A tight fit doesn't do anything to help the accuracy of the rifle, but it helps the shooter feel better about the rifle. You can pound the X ring with a AR that rattles just as efficiently as with one that is tight... all you have to do is get past the feel of the thing rattling and focus on the shot you are about to make.