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Tuning Re cutting the crown on an air rifle barrel.
- Thread starter Corvid_hunter
- Start date
I did it two times. With a brass ballhead screw.
First time with a battery powered hand drill, all looked great, but turned out I pushed a very thin wire edge inside the muzzle (I realized late that the hand drill may be just a way too heavy tool for this).
I was hoping some 50 shots will clean it....maybe did clean out, but I wasn't really satisfied with the POI grouping.
Next ordered a "manual" hand drill from my grampa's time. Redo the crowning, and..........just perfect.
I did it on all mine FX liners also a Alfa and LW barrels for L2.
First time with a battery powered hand drill, all looked great, but turned out I pushed a very thin wire edge inside the muzzle (I realized late that the hand drill may be just a way too heavy tool for this).
I was hoping some 50 shots will clean it....maybe did clean out, but I wasn't really satisfied with the POI grouping.
Next ordered a "manual" hand drill from my grampa's time. Redo the crowning, and..........just perfect.
I did it on all mine FX liners also a Alfa and LW barrels for L2.
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I did the brass screw method for a LW poly barrel, turned out great.
Thanks for the link Corvid.
Thanks for the link Corvid.
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The brass screw technique works remarkably well. No precision tools needed, just some attention to detail. Well enough that I’ve never had a barrel do worse for having tried.
Many times even barrels from some of the best names in the business will benefit from a little attention. For example just last week I had a Daystate Wolverine that wouldn’t do any better than ¾” to 1” at 50 yards. Dressed the crown and leade and gave the bore a few passes with J-B, and it promptly rewarded me with back to back groups of 0.46” and 0.38”.
Many times even barrels from some of the best names in the business will benefit from a little attention. For example just last week I had a Daystate Wolverine that wouldn’t do any better than ¾” to 1” at 50 yards. Dressed the crown and leade and gave the bore a few passes with J-B, and it promptly rewarded me with back to back groups of 0.46” and 0.38”.
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Great video, thanks. One thing I’d like to add for anyone who going try this at home. If your going use a lathe, please remember to support and center the opposing end of the barrel with a cat’s head or follower of some kind. To ensure the Concentricit he of the barrel over the length of it.
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The crown should be concentric with the bore so the gasses expelled will not give a uneven push on the skirt of the pellet as leaves the bore. (As stated several times in video)
Using a brass screw head will only debur any flashing made at the land and grooves of initial poor machining.
If this is the the case on your barrel then it probably will help, but will not change the concentricity of the crown to bore.
My take he was explaining angle or type of crown didn’t seem to make much difference but making sure the crown was concentric with the bore was very important, he gave examples of this.
Using a brass screw head will only debur any flashing made at the land and grooves of initial poor machining.
If this is the the case on your barrel then it probably will help, but will not change the concentricity of the crown to bore.
My take he was explaining angle or type of crown didn’t seem to make much difference but making sure the crown was concentric with the bore was very important, he gave examples of this.
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OK, I am kind of expert for math and algebra
also couple decades working as ME in production.I am not trying to be in contrast with anybody, only want to separate apples and oranges for folks new to crowning barrels. I am a new as well, but I understand the geometry.
The video explains things if you have a lathe and a Dremmel, still need to do some setups with a cutting blade and that means you need to understand what ya doing exactly. An average lathe operator doesn't do these things regularly or maybe never.
The brass ballhead screw in the other side will self center the sphere to the hole no matter is the bore centered to barrel OD, if you let it sit on its own. As I said earlier I did first time a mistake and second time "self smart".
Both methods can have mild to aggressive errors if you don't understand the process, also both methods can give you fantastic results.
Me in example I have no lathe on my own, yes I could just find one with an expert to work with, but that was an option "B" for me, I did the brass screw method.
Thanks to nervoustrig.
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I just want to acknowledge the brass screw method by itself is insufficient to remedy the issue described in the video. He’s describing a barrel that already has a bevel formed but is not uniform, a lopsided bevel I would say. Obviously if one were to go at it with a brass screw, the result would be an irregular bevel that is simply deeper. So he shows how to do a facing cut to remove the bad bevel, at which point the brass screw method could be used to form a new one.
BTW in his particular case, the facing cut could have been skipped, to just spend a little more time grinding with the Dremel wheel. But to use the brass screw method, the starting point needs to be a freshly faced off muzzle. Some guys have succeeded with nothing but a file, a machinist’s square, a keen eye, and patience. Before I had a lathe, I rigged up a support scaffold on my drill press to support the muzzle, then spin it up and gently kiss the surface with an emery wheel. Not as tedious as using a file and a little more precise. Something similar can be accomplished with a hand drill.
For the record, I still prefer to establish the bevel with the brass screw method rather than a HSS or carbide cutter.
BTW in his particular case, the facing cut could have been skipped, to just spend a little more time grinding with the Dremel wheel. But to use the brass screw method, the starting point needs to be a freshly faced off muzzle. Some guys have succeeded with nothing but a file, a machinist’s square, a keen eye, and patience. Before I had a lathe, I rigged up a support scaffold on my drill press to support the muzzle, then spin it up and gently kiss the surface with an emery wheel. Not as tedious as using a file and a little more precise. Something similar can be accomplished with a hand drill.
For the record, I still prefer to establish the bevel with the brass screw method rather than a HSS or carbide cutter.
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you also want to make sure you use the right size Brass screw head, too big and it doesn't bevel enough, too small and it bevels too much, for .22 I use a #8, and for .25 I use a #10.
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If the end of your actual barrel is protected and you clean with a patchworm or the like there is no reason to cut a crown. Just square the barrel end to the rifling and be sure there are no burrs. No cut you make can improve accuracy beyond that. Why do extra work that serves no purpose.
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I agree there is no need for a recessed crown except to afford some protection to an otherwise exposed end. However I have an admittedly pedantic point to raise, which is that crowning is any operation that establishes the finished state of the end of the rifling. Even if it is nothing more than a simple 90° facing cut that will get no further treatment of any kind, the result is still a crown. The trick is getting a supremely burr-free result from even the sharpest of cutters which is why it is usually necessary to follow up with an abrasive of some kind.
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We're on the same page. I think the chamfer he put on after the grinding operation was totally unnecessary. I think it would've been perfect with just the grind. I'll start doing mine that way. The concave looks nice and covers all bases.
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Agreed, the chamfering bit has the potential to reintroduce a burr that the abrasive wheel had just removed.
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Often the crown getting receded like that is to protect it from getting damaged when the muzzle gets bumped. Probably not a huge pcp thing….but it’s very real in firearms and work related application like farm ranch where firearms get thrown around in in vehicles and bush…as they are very much tools of the trade.
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Most people with nice expensive airguns don't toss them around or use them as a hammer. For those that do those things a quadruple angle deep recessed crown may be in order.......... as well as a hard had with chin strap. I think 99% of PCPs have a shroud or moderator covering the muzzle. In the USA anyway.
This post is meant to be funny and not to offend people who use their expensive airgun as a pogo stick.
This post is meant to be funny and not to offend people who use their expensive airgun as a pogo stick.
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I center the bore up in my lathe then cut an 11 degree crown. I would do my pcp barrel the same way. in a production setting that takes too much time. Most production shops would use a crowning tool with an pilot that fits the bore. In theory it will cut a square crown to the bore and has no setup time. I am surprised FX or whoever makes the liners for them dont use a cutting tool with a pilot. If the bores dimensions are not consistent liner to liner then a cutter and pilot doesnt work as well.
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Rule One, know a little about what you're doing before doing anything. If a crown needs "recutting", then more than a brass screw and drill is needed. If the original machine work just needs a little cleaning up, then the process described may help. If the crown needs machine work, the typical owner would be well advised to find a gunsmith. It requires only basic machining capability, but more than a brass screw and drill.
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Pellet guns must be more forgiving of their crowns. I’ve seen some ugly crowns shoot pretty well. Now on my slug barrels, my crowns are razor sharp. No chamfering or anything that risks absolute concentricity.
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