Time to argue Crowning as suggested.

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LarryS
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Time to argue Crowning as suggested.

#1 Post by LarryS »

Past threads on crowning may even(probably) make your rifle worse.

If your barrel end is dinged or damaged ANY crowning will help it. But if your barrel is NOT damaged you could easily make the rifle more inaccurate as slightly different size pellets in the same tin are drawn and used...... regardless your recent crowning efforts. My past efforts too, using thread content.

The reason is:

1) Hand crowning be it with a ball bearing, marble, or screw head 'taint gonna work very well folks! because human error enters into it. This error can be isolated to:

a) Unequal pressure at all times at the center of the grinding ball, with variance in side pressure during rotation.

b) Pressure applied to grinding ball will most likely NOT BE IN AXIAL ALIGNMENT WITH THE BORE!. Mere seating the grinding ball over the bore and rotating it can, and WILL, create a crown with unequal flatness to the bore axis UNLESS IT IS GUIDED BY THE BORE ITSELF.

Not important you say?.... I think differently. What determines the variance in pellet grouping out of the tin usually? First answer is seating. Second answer is THE POINT OF LAST PELLET CONTACT WITH THE BORE RIFLING!!!.

A loose pellet doesn't care much, but a tighter pellet does. An even tighter pellet cares a LOT more!.

With an off-axis crown there is a point in the bores circumpherance that extends out more than the rest of the surface. That point or area will deflect a tight pellet more because it is a single point of contact before pellet completely escapes the barrel. Less tight pellets will not be effected as much.... but they WILL be effected. So goes the group..... right down the drain.

The answer I found to all this(and the mouth lathering here) was to find a common item that could be aligned to the bore and used as a crowning tool.

That tool is a common Fence screw.(the VERY hard) black screws with a sharp point. Cut off so that only the Philips head with the nice under curve and a 1 inch section of round shank remain, it will seat well ON the bore face for grinding evenly if it is aligned.

Aligning this tool is simple!. Take a daisy pellet, and with razor carefully separate the skirt from the pellet. Trim skirt down until the hole fits snug over the screw shank. This is your TOOL BUSHING at the bore entry. Now take a Daisy pellet, insuring the shank seats into the untouched pellet and slide it into the bore with the tool end. I greased shank, bushing, and bottoming pellet aforehand. The tool slides easily in or out of the bushing enough to reapply grinding compound or grit to the undercurve of the screw head. The bushing and bottoming pellet prevent the hard grinding tool from making any contact with the rifling during rotation.

Rotation of the tool is easy. A drill with a chucked Philips head driver.

I have another way to insure axial alignment during crowning but it requires a lathe to make the tool. Most folks here do not have a lathe and quite often...... "simpler is better".

Ok.... Lets argue the merits of methods used in crowning. :lol: -LarryS
<P.S. I just shot three Copper Clads into a 1 inch circle at 90 feet.>
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#2 Post by TCooper »

Biohazardman's suggestion:
http://www.network54.com/Realm/CFTech/BioCrown.htm

Here is an old posting of Larry Durham's from the defunct Airgun Letter Forum from January 2000.

Here is a method I read about many years ago in the National Rifleman, and have used to good effect on hundreds of guns since:

I recommend experimenting on inexpensive guns, or even a length of barrel first before recrowning a prized gun. Barrels with recessed crowns cannot be lapped using this method. Guns that cannot shoot round groups are good candidates for recrowning, and I have never seen accuracy get worse as a result of a properly down recrown by this method.

Supplies:
(1) brass, roundheaded screw with a head about 4-6mm dia.
(1 gram) very fine lapping compound (I use JB Bore Paste, but Toothpaste can work too).
(1)magnifying glass, 4-10X
(1)Drillmotor or drillpress
(5) airgun pellets

Procedure:
1. Insert an airgun pellet into the muzzle and push it in with a pencil to a depth of 4mm.
2. Chuck the brass screw in the drillmotor or press chuck, setting the rpm at the slowest speed if possible.
3. "Charge" (gob some on) the screwhead with lapping compound.
4. Very lightly engage the screwhead against the crown area of the muzzle and start the motor.
5. Using a rocking, rotating motion, lap the crown until a slight ball-shaped depression is lapped into the crown. Rotate the barrel 90 degrees every few seconds during the lapping process, all the while "rockin" the screw head or barrel to maintain the round shape of the screwhead and distribute the lapping action across the entire screwhead surface.
6. Check your progress every 50-60 seconds by wiping the crown clean and examining the edges of the rifling lands where the meet the lapped crown surface. When there is a perfectly even, sharp margin on every land and groove as it meets the crowned surface you are done. If it becomes obvious the original crown is so deep and ragged the lapping is not effective the barrel must be carefully filed or machined back to eliminate all or most of the original crown before lapping (only expert metalworkers should perform this phase).
7. Push the pellet out of the bore from the breech end and clean the barrel (from the breech of course).
8. Testfire ... it is not uncommon for the Zero to shift, this is nearly always a sign the original crown was bad, and accuracy will improve.
ld
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#3 Post by jezX »

i hate to read post on recrowning ,i can't think of why a person would do this with a drill , i'm sure if you took the barrel to a machinest and asked for a recrown and even if you had to tell them what to do it would turn out better then a drill job . and cost less then $15 . it take me about 1 minute to recrown a barrel .
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#4 Post by TCooper »

I think most of the "recrowing" you hear about on the forums is done on the Cr2240 pistols with various barrel lengths. Shooters seem to enjoy tinkering with these low priced pistols and they seem to like independance. From what I have read, the results often seem be more than adequate for this pistol. The Custom 2240 that I tested had a 12" barrel that was chopped&crowned by a Crosman hobbysmith. It averaged 3/8" groups (5 shots) at 10 metres (41 group average). With favoured pellets it would average .32" for 5 shots (4 group average). The report is on my web site.

A lot of Chinese airgun tinkerers also enjoy independance and seem to report reasonable results from home hobbysmith crown jobs.

I have to admit that I have never tried crowning an airgun or firearm.

Todd
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#5 Post by webstien »

as much as id love to have a machinist recrown for me I wouldn't know what to tell him if he didnt know. IE. what angle to cut, how deep, etc. Add to the fact that I dont know where to find machinists.
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Cadeau
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#6 Post by Cadeau »

Larry , I like your idea and it make more sense then trying to recrown free handed with a marble or a screw . But I think I see one flaw. I think a better bushing needs to be found. Lead being soft, will distort from the shank as the drill turns the screw head and that small amount of run out may be enough to throw off a perfect recrowning. In a perfect world we could use a tiny brass bushing but some may argue that it may hurt the rifling. Maybe two or three pellet bushings and lots of slippery lub may extend the wear out and keep the tool running true.
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#7 Post by TCooper »

A good gunsmith is also a machinist. They will definitely know how to cut a crown. They will often give you an option as to different crown types.

We have two gunsmtihs in the small city where I live. Both have lathes, milling machines, large drill presses, drilling jigs, etc. One shop also has hot bluing tanks, plexi-glass bead blasting box, and table sander. It's an expensive profession if a 'smith is set up for rebarrelling, chambering, bead blasting, bluing, etc. The amounts of tools, gun parts, and related products can also add up to big bucks.

Todd
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#8 Post by webstien »

TCooper wrote:A good gunsmith is also a machinist. They will definitely know how to cut a crown. They will often give you an option as to different crown types.

We have two gunsmtihs in the small city where I live. Both have lathes, milling machines, large drill presses, drilling jigs, etc. One shop also has hot bluing tanks, plexi-glass bead blasting box, and table sander. It's an expensive profession if a 'smith is set up for rebarrelling, chambering, bead blasting, bluing, etc. The amounts of tools, gun parts, and related products can also add up to big bucks.

Todd
Thats the problem, I dont think we have any airgunsmiths in montreal... maybe If I took the barrel with me to a few gunshops maybe one of them could help me out....
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#9 Post by airbuddy3 »

I have used a roundhead brass screw in the manner very similar to what Todd discribed.. quoting Larry Durham , and it works really well .
The nature of the round head makes the screw self centering , and because its a soft brass it will be very forgiving dureing the grinding process , it takes quite a bit of work , and with inspections dureing the progress ..you will be amazed at how good the results are.
I have not had to recrown a HW or Diana ( yet) OR a CZ ( they have rescessed crowns ) But the Chineese guns often come with a poor crown , or with a burr at the crown , sometimes they will shoot really well ..and the crown just looks ill defined ..and I will clean it up and put a good crown .

Frank
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#10 Post by DoctorFrankengun »

Why bother with a crown? Don't most high end target rifles just have the muzzle machined flat?

I'm not trying to be a smart buttock. A fellow came to my shop the other day that has some high end target rifles. They are all machined flat across the muzzles.
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#11 Post by jezX »

all barrels should be set in about 1/32'' .this will keep the end from getting messed up . i do 1/16 for all my guns ,just easier to not worry about if you bump it . can't hurt to do a small inset .
Charles/NM
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#12 Post by Charles/NM »

Target barrels are often machined flat because any small amount of off center bore will not affect the exit of the bullet/pellet. When I machine new crowns on barrels in my lathe I turn a small amount of flat crown that is usually set in a deeper pocket to protect it from dings. If the bore is perfectly centered, and a good many are not, I cut a 11 to 13 degree crown. That angle seems to work as well as a flat crown and provides some small measure of ding protection. The only use the brass ball with polishing compound has in my shop is for lightly champhering the newly cut crown to remove any burrs. A burr in a barrel's muzzle is more detrimental to accuracy than a slightly off center crown. I usually use a cone shaped Cratex abrasive rod for burr removal in the lathe. I reshape the Cratex rod for each barrel job. I run the lathe in forward and reverse to deburr the bore in both sides of the lands and grooves.
It's easier to show someone how to cut a good crown and deburr it than it is to describe it in words.
Having had a lathe for 35 years it's hard to imagine getting along without one. Mine is a Craftsman/Atlas 12" swing, 48" long bed. Bought it new in 1971. I chose the long bed so I could profile rifle barrels.
Charles in New Mexico, USA
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#13 Post by DoctorFrankengun »

Charles/NM wrote:Target barrels are often machined flat because any small amount of off center bore will not affect the exit of the bullet/pellet. When I machine new crowns on barrels in my lathe I turn a small amount of flat crown that is usually set in a deeper pocket to protect it from dings. If the bore is perfectly centered, and a good many are not, I cut a 11 to 13 degree crown. That angle seems to work as well as a flat crown and provides some small measure of ding protection. The only use the brass ball with polishing compound has in my shop is for lightly champhering the newly cut crown to remove any burrs. A burr in a barrel's muzzle is more detrimental to accuracy than a slightly off center crown. I usually use a cone shaped Cratex abrasive rod for burr removal in the lathe. I reshape the Cratex rod for each barrel job. I run the lathe in forward and reverse to deburr the bore in both sides of the lands and grooves.
It's easier to show someone how to cut a good crown and deburr it than it is to describe it in words.
Having had a lathe for 35 years it's hard to imagine getting along without one. Mine is a Craftsman/Atlas 12" swing, 48" long bed. Bought it new in 1971. I chose the long bed so I could profile rifle barrels.
Thanks for the explanation Charles. I am a home shop machinist but I have a lot to learn about guns.
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#14 Post by LarryS »

Cadeau, I like that. multiple bushings would indeed extend accuracy time of the tools alignment.

Top Gun, The rocking motion with rotation, plus rotation of barrel in your reference source is designed to minimize human error in bore axis alignment during crowning.

My thoughts were designed to do two things. Allow me the independance* (*cheap-o), and still get the job done easily at home with minimal error. Incidently, the under-curve of that hard screw has nearly an exponential curve. I do believe it will reach recessed pre-crowned barrels that are .22 calib.

JezX, The gunsmiths & machinist here in California won't even put their coffe cup down to pick up $15.00

In General I am learning something here.... No crown at all?, Flat bores?,
MMmmmm...........most interesting...... :shock: -LarryS
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