Finishing A New Barrel Blank ?

I’m all ears!, thinking of buying a barrel or two “used” for a little experimental work?

I'm no barrel expert but have finished quite a few. Still learning myself. I grind my own cutting tool to cut the inside oring groove. A dremel with a cut off wheel and a bench grinder will give you a quality HSS tool for cheap. A tapered pin reamer will make cutting the leade much easier. They run about $20-30 each and give you a nice transition. You could also cut out in the lathe but I think a reamer gives the best finish. I like to profile the barrel, drill the transfer port, cut the leade, cut the oring groove, thread the end and cut the crown in that order. I feel it goes the fastest that way. 

Manual or cnc lathe? 

Thammer

if you don’t mind sharing your techniques how do you cut the crown? I’ve seen a lot of methods posted, from brass screws with grinding compound to tool-post grinders on a lathe, with angles from zero to whatever you get when the brass screw wears down.

The crown angle is unimportant, within reason. I mean if you were trying to form a deep crown with a grinding technique (e.g. stone or brass screw with abrasive), there is a greater probability the grind will gradually develop a bias to one side or the other, meaning you lose perpendicularity with the bore. That's no good. But for any typical shallow angle or a simple square crown, none has a decided advantage over the other in terms of accuracy potential.

For most DIYers, what you're likely to be doing is making sure there is no burr remaining at the end of the rifling from whatever method was used to cut the barrel. So for example you could take a dull hacksaw and cut the barrel to length, and then file the end square with a coarse double-cut file and a machinist's square. The end of the barrel would be rough looking and there would be micro burrs (or worse) at the ends of the lands and grooves. Then finish up the task by applying a subtle bevel with the brass screw technique to remove said burrs and you'd have a barrel with equal capacity for accuracy as one done with finer tools.

Or if you're doing it on a lathe, be sure you're precisely centered on the bore (e.g. 4-jaw chuck or spider) and the bore is axial to the lathe, and the cutter is supremely sharp. In other words a freshly sharpened HSS cutter will generally be better than carbide. If any doubt about those things, the brass screw method is always an option. Don't knock it. No matter the method, attention to detail is the most important tool for achieving a successful result.

Case in point, I have a lathe and use it for every barrel preparation step except the crown. I prefer the result I get from the brass screw approach:

Do you leave freebore or try to start the projectile close to the rifling?

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My goal is always to have the projectile seated neatly into the rifling when the bolt is closed. In most cases that means wiping out the rifling to just past the barrel port.

What angle you taper the leade?

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Kinda depends. A straight reamed leade does best to ensure the projectile is chambered as close to perfectly axial to the bore as possible. In that case you just need to break the sharp leading edge of the rifling so the pellet (or slug) can ease gently into the rifling. So rather than the lands cutting into the pellet and damaging it, they instead swage or displace lead. A regimen of wet sanding with a dowel or a rubberized abrasive bit (e.g. Cratex point or equivalent) will do the trick.

However a tapered leade can be beneficial in some cases, particularly to help alleviate harder chambering for slugs given the much larger bearing surface compared to pellets. Of course this also applies a taper to the leading edge of the rifling so not much secondary sanding is required. Like Troy said, a tapered pin reamer is the tool for the job. Get one with a maximum diameter slightly over what you need, then mark it at the diameter you need and grind off the portion behind it.

Are you using an off the shelf micro boring bar or grinding your own?

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I only use the aforementioned straight reamers or tapered pin reamers for doing leades. For O-ring grooves, I've ground my own HSS and used purchased cutters. Usually grind it for the one-off type of jobs and use a purchased carbide cutter for the more frequent tasks.

I’ve done quite a few barrels but I had a bit of a head start. I treated my powder burners like we do our PCP’s now. I just don’t own a stock gun. I spent so much time at my gunsmiths that I finally just started working with him. I was younger and my life was far more complex then so I didn’t absorb what I should have but it gave me a head start. You want more info than I’m willing to type because there are so many variables. What I can say about a crown is when shooting slugs with a silencer, I have 3 different crowns I try before I give up on the best accuracy out of a particular barrel/projectile combo. Crown and angle can be important. Don’t dismiss it. With Airguns and slugs, for the time being, we all are still learning. I personally cut my chamber/leade for one projectile. The last TJ I did I cut the leade for a 32gr slug. It gave me room if the 32 didn’t work to cut again for a 34gr. When I cut for the 34gr I found it wasn’t better so I had to build an adjustable probe for my RTI to seat the 32gr to get it to work again. Then there was mag clearance issues. Like I said, too many variables for a post. Barrel building instructions are for a book. Or at least a manual. 

Please don't mix up airguns and firearms. These are different animals.

I don’t think the angle makes much of a different, but whatever cut is made has to be done square to the bore. (not the OD of the barrel) 


My understanding is if it’s cut out of square, the escaping air will shift the pellet as it exits the barrel. Because one side is vented before the other. 

Believe what you want. When you start building barrels for airguns shooting slugs battling dirty air you can come up with your own conclusions.

I went through school as a science major so I'll stick with what I know on that part. I'm grateful for everyone's contributions whether I use them or not. Everyone should gather all the information they're able on a subject of interest then use what they can. 

I know I come off like an ass in text sometimes but it's not my intention. I believe being honest and direct shows you really care.

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Nah your fine….you have your ideas 

I was mostly surprised to find argument against a squarely cut crown. Seems every knowledgeably gun smith I’ve ever dealt with puts value on it.

just a week ago I got my raw back from Allan zasadyn….he seems to put great value on properly cut breech and crown.

It ensures that the whole circumference of the pellet leaves the barrel at the same time, otherwise the pellet tip or yawn 

There is almost zero science when it comes to modern mass produced airguns shooting slugs. So there is not much science to show a book worm. Keep an open mind and that’s how we move forward. Know it all’s keep guys in the know from sharing important findings. If you’re shooting pellets, things are pretty simple. There is just more wiggle room with them.

There is almost zero science when it comes to modern mass produced airguns shooting slugs. So there is not much science to show a book worm. Keep an open mind and that’s how we move forward. Know it all’s keep guys in the know from sharing important findings. If you’re shooting pellets, things are pretty simple. There is just more wiggle room with them.

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I think there is science involved…but it can’t be used because guns aren’t being properly reproduced. 
not to much mention ppl are trying to shoot slugs out of choked barrels.

thomas air makes a slug gun….I would guess that gun it produced and reproduced down to a science. 

I went through school as a science major so I'll stick with what I know on that part. I'm grateful for everyone's contributions whether I use them or not. Everyone should gather all the information they're able on a subject of interest then use what they can. 

I know I come off like an ass in text sometimes but it's not my intention. I believe being honest and direct shows you really care.

Click to expand...

Nah your fine….you have your ideas 

I was mostly surprised to find argument against a squarely cut crown. Seems every knowledgeably gun smith I’ve ever dealt with puts value on it.

just a week ago I got my raw back from Allan zasadyn….he seems to put great value on properly cut breech and crown

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Absolutely. You ever wonder why some guns seem to be slug friendly when other top quality guns are not? It all starts with the leade. I believe some manufacturers have a very forgiving lead cut in their guns. Their process lends itself to being able to successfully shoot both projectiles.