Gunsmithing burr on crown??

[operator1]

Just got finished recutting the the crown on my .308 and noticed a small burr on the inside of the bore. I used a sharp HSS toolbit and cut from the inside out taking .001-.002 cuts.
Will the burr be shot off in a couple rounds? How do you guys finish the crown?

 

[AXEMAN]

Re: burr on crown??

ok can i be the first to say i thought this had something to do with drinking crown royal outside in the snow... its been that kind of day. im also going to guess polishing compound of some sort on the burr

 

[jbell]

Re: burr on crown??

No, do not attempt to polish it,the best course of action is if its a very small burr just on the end of a land or grove is to shoot it. It should come out. But the only way to properly remove it is to cut the crown agan. Polishing it will only allow you to potentially lap a reverse taper to your bore this is BAD.

 

[operator1]

Re: burr on crown??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jbell</div><div class="ubbcode-body">No, do not attempt to polish it,the best course of action is if its a very small burr just on the end of a land or grove is to shoot it. It should come out. But the only way to properly remove it is to cut the crown agan. Polishing it will only allow you to potentially lap a reverse taper to your bore this is BAD.</div></div>

I made several cuts and got the damn burr everytime. I don't ever recall having this problem before.

 

[wnroscoe]

Re: burr on crown??

During the final few passes, take very light cuts with a very slow feed by hand, .0005" and less at 600-800 rpm with a sharp tool. Use a Q-Tip and drag it from the ID of the bore across the crown. If cut right, there should be no burr.

 

[bohem]

Re: burr on crown??

Last pass should be from the bore to the OD and you won't create a burr at the end of the cut at the bore interface.

 

[Keith Johns]

Re: burr on crown??

So do you(anyone) prefer to make the final crown cut with a charp tool, a piloted chamferer from brownells, or a polishing stone/lapping tool like mentioned?

I can see how the polishing tools (like those brass balls you spin in a drill with lapping compound in it) could push the bur the wrong way, into the bore kinda.

The 45 degree chamfering tool that uses a brass pilot seems good. Anyone try these? If you face off the barrel scquare to the bore, and chamfer with one of these, how could it not be a good crown after firing a few bullets past it.


And lastly, making the final(and every) cut with a sharp tool. Cant rememember if Carbide of HSS is prefered for this cut. But I'm just refering to putting that last little 45 degree touch on the actually crown.

 

[wnroscoe]

Re: burr on crown??

AZ, for a chatter free and stellar surface finish all cuts should be made via the single point method with a sharp tool. Proper tool alignment (just below center), speed and feed are essential.

I use HSS / Rex95 that is ground for the purpose. Carbide works good too.

 

[operator1]

Re: burr on crown??

Well, I recut the crown taking .0005 cuts from the bore to the OD. Still had a slight burr. I decided to put it back together and fire it. 2 shots burr is gone and the crown is smooth as a babys ass.

 

[Long_Action]

Re: burr on crown??

maybe your cutting tool was too high in the lathe. Next time try to drop the tool down off center or try more relief under the cutting edge.

 

[wnroscoe]

Re: burr on crown??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: operator1</div><div class="ubbcode-body">Well, I recut the crown taking .0005 cuts from the bore to the OD. Still had a slight burr. I decided to put it back together and fire it. 2 shots burr is gone and the crown is smooth as a babys ass. </div></div>

Burr's gone and smooth finish is all that matters. Sharp tools, light cuts and proper tool relationship to the work piece and proper speed / feed will solve 99% of machining problems.

Tool cutting tips should be slightly below center of work piece for best results and finish.