We are planning to do carry out a new experiment.

On the effects of a damaged barrel crown on the accuracy of the rifle.

As luck would have it, we have brand new Sako S 491 rifle in 223 Remington, which its owner wishes to change the barrel to a new one chambered for the 223 Ackley.. He agreed to let us loose on his old barrel, and do as we wish with it.

I have already installed a Burris 6-24X scope on it, and will try to develop two loads for our tests.

One with a boat tail bullet and one with a flat base bullet.

Any suggestions on what sort of damage we should do to the crown would be appreciate it.

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saeed@ emirates.net.ae

www.accuratereloading.com

1. See if you can damage the crown in some way with a cleaning rod. Then shoot the rifle to see whether accuracy has been affected.

2. Then take a hammer and drive a stone into the muzzle of the rifle. Then, after seeing that the stone is removed, shoot the rifle to see how accuracy has been affected.

3. Drive a tapered bolt or other metal object into the muzzle. Then remove it and shoot to see how accuracy has been affected.

4. Cut off 1/2 inch of the barrel with a hacksaw and then, without crowning the muzzle, shoot it to see how accuracy has been affected.

Perhaps someone can think of some more intermediate or even greater harmful steps to put the thing through. In any case, the interesting thing will be to shoot it at each stage to see how it has been affected. You will probably want to shoot at least three 5-shot groups after each stage of harming the muzzle so that you can get a good measurement of how much the harm has affected the accuracy of the rifle.

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I would cut it square and crown to start.(Groups)

Then cut the crown again at a 5 degree angle.(Groups)

Then square it again. (Groups)

Then take a diamond hone (or similar) tool and cut a groove deeper at the crown. (Groups)

Then hone down the adjacent land a couple thousandths. (Groups)

Then take a breather - you've earned it!

Don

quote:

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Originally posted by Saeed:
Gentlemen,

We are planning to do carry out a new experiment.

On the effects of a damaged barrel crown on the accuracy of the rifle.

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May I suggest that the change in the point of impact also be recorded.

Of course this is due to the possibility that the crown is damaged on a hunting trip and not noticed until I get home.

JerryO

For example,if we compared a 264 and a 458 the muzzle pressure would be far lower with the 458.

Perhaps this could be duplicated by testing the rifle with some very reduced loads "before" and "after"

Mike

I would suggest that as the test progresses, please take some close-up photos to accompany for results when finished.

The test may be somewhat misleading if the barrel is cut even a little and re-crowned at different stages because that will alter the harmonics of the barrel as you go. But, I will be looking forward to the results like many others.

redleg

To see the effect of "heavy" crowning and without compared to normal would also be interesting.

[This message has been edited by Wachtel (edited 12-30-2001).]

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NRA Life member

A couple of good tests to test the effect of accuracy on a crown involve the release of the bullet and long term wear.

1. Release of the bullet.

With an angled tool, flair a single land. Shoot and note the accuracy. Do the same with another one. Remember to try different bullet types.

2. Long term wear.

Create a flat muzzle, no burrs or chamfers. Shoot >1000 rounds and then perfectly center the barrel and take ultra small facing cuts. This will show the wear movement of the rifling. Then, re-crown properly and note the accuracy change.

When a barrel is recrowned, it will normally have microscopic burrs on the lands. If you re-crown, you'll have to shoot a few to several rounds to clean these off, and let the barrel "settle down".

You are basically looking for a change in variation, and stat tests for that are notoriously weak. In a true 1 MOA gun, 95% of your groups will be between .5" and 1.5". For single, 5 shot groups, any group between those limits is indistinguishable from any other group that is also between the limits. You'll probably have to do 5-10 5 shot groups at each stage of destruction if you want to see smaller differences than that.

You might consider browsing through H. E. Mann's "The Bullets Flight". It's old stuff; lead bullets and black powder, but some of it might be applicable. Mann worked with damaged bullets as opposed to damaged crowns.

Interesting experiment.

Robert

First of all, I suggest mounting the scope with some brand of quick release rings so that the scope can be removed for some of the tests so that scope damage will not result and not be the source of inaccuracy. My choice would be Leupold QR rings and bases -- they allow the scope to be removed and reinstalled with no change in zero point.

Here are some more suggestions for things that could be done with the barrel of the gun (after each of these, the rifle should be shot for several 5-shot groups for accuracy tests):

a. I've read the claim here many times that improper cleaning ruins barrels. I'm not convinced that those claims are true. So I suggest a concerted effort to ruin the crown of the barrel through rough or improper cleaning.

b. For another test, I suggest dropping the rifle (scope removed) muzzle-first onto a concrete walkway from a height of 3 to 6 feet (one to two meters).

c. Run the muzzle into mud containing sand and stones, and then shake only some of it off, so that some sand and possibly even some small stones remain in the barrel (but not plugging the barrel so that the barrel isn't actually obstructed).

d. (Maybe this should be one of the earlier stages). Put some fabric or thread into the muzzle, such as might happen if the gun were in a case that "sheds" and it were not examined after removing it from the case.

e. Rig up a sling that allows the rifle to swing back and forth like a pendulum, and have the muzzle of the rifle hit into a heavy steel plate for a number of swings. This would be designed to duplicate what could happen to a rifle that rides in a rifle rest in a vehicle for a long time.

f. Figure out how to have the barrel rust inside -- but only at the last 4 to 6 inches at the muzzle -- and then shoot it with the rust in it.

[This message has been edited by LE270 (edited 12-31-2001).]

-Cut or file crown un-evenly.

-Rust in last 1 inch of barrel and shoot.

-Damage one land at muzzle and see effect.

Note change in point of impact with these destructions.

Saad

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"The greatest griefs are those we cause ourselves"
-Sophicles-

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"The greatest griefs are those we cause ourselves"
-Sophicles-

Remove the rifling on the last inch of barrel, see what it does.

Like Shikaree said, an uneven-crown test will be neat.

Gosh...all the things you can do to an unwanted barrel.

quote:

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Originally posted by redleg155:
I would suggest that as the test progresses, please take some close-up photos to accompany for results when finished.

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I agree strongly with this suggestion.

You might also take videos of the processes of successive stages of damaging the thing.

[This message has been edited by LE270 (edited 01-01-2002).]

It is like the old saying goes: "Give an old lady an inch, and she wants a foot!"

My intention was to see what effect what we classify as normal damage to the crown might do.

Like damage from cleaning and dropping the rifle, rust and so on.

Walter is due back in 5 days time, he is the perfect candidate to ruin this barrel. In the meantime, I will develop a good load for it while I have the workshop to myself without him being around to offer his usual helpful hints!

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saeed@ emirates.net.ae

www.accuratereloading.com

It can be out of square with the bore. (Angled) or it can have material eccentrically removed OR it can have barrel material intruding in on it.

The NRA, Aberdeen Proving grounds and most gun writers, living and dead, have done all these various test and published the results, but its still fun.

I had a bench gun that needed the crown freshened so I messed it up some first.

A center punch mark .100 from a land will throw bullets away from it but still a good group.

A damaged (removed) land corner made bigger round groups. The amount of damage it took to tell a definite difference in groug size (from .3s ), could not be seen with the naked eye. This explains group creep in button rifled barrels, I think.

I've never bothered with an angled crown since the only way it can happen on a lathe is by having an eccentric bore and since almost 100% of ALL factory bores *are* eccentric and they do OK. Unless the angle is severe, the only effect is an off center group.

I cut all target crowns with hand lapped corners and forget about it.

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Welcome to Saeeds site.

Again, we find ourselves on the same side of the fence. The law of averages continues to work

Crowns are like telescopes. A lot can be wrong and no one would ever notice in the field. In fact some people would not even notice on a target.

Do you think if all else is equal, that a cartridge with lower muzzle pressure would show less change from muzzle damage.

I had not thought of that until Saeeds post and my post above.

Mike