Tuning Crowning your barrel

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357cal

357cal

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Jul 7, 2022
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Would just like to know how many of you have crown your own barrel or barrels? as soon as my orders come in i will be doing so on my Airforce Texan .308 and AEA big bore challenger 357,
Essential Tools & Supplies for Barrel Crowning
1. Brass Self-Centering Lap (Brownells)

.30 cal: Brownells Brass Lap – .30 Caliber

.357 cal: Brownells Brass Lap – .38/.357 Caliber

Price: ~$13–15 each

These are bore-piloted and self-centering—perfect for my Texan and Challenger.

2. Lapping Compound

M*CARBO 180 Grit Silicon Carbide Compound

Price: ~$10

Comes with a small brass lap too (45°), but i will mainly use the compound with your Brownells laps.

3. Drill (Cordless or Low-Speed

4. Cleaning Supplies

Cotton patches, Q-tips, and a bore plug (tight patch or foam earplug) to keep compound out of the barrel.

5. Vise with Soft Jaws

Compound: ~$10
 
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357cal said:
Would just like to know how many of you have crown your own barrel or barrels?
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giphy1[1].gif
 
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The only time I've done such a thing was when there was a problem. Probably every other cheapo airgun that I've had suffered a burr or some such imperfection in the crown area. All were resolved by the brass domed screw head trick, just twirling it between my fingers while rotating the barrel (the whole gun) so that there is no set orientation of the barrel.
A Diana 250 I have (cheap springer) wasn't as accurate as I would expect, and I noticed the muzzle end felt a little funny when I'd push a pellet through. Not really a choke but gritty. So I lopped 2 inches off the barrel, thinking that I certainly couldn't make it worse. I just marked with a pen and used the hacksaw, which didn't even follow the pen marks. Then I filed away to even it out, eyeballing the "flushness" of the new muzzle, and finished with fine sandpaper. It ended up more rounded than squared off. Then I hand twirled drill bits at the bore opening to cut in a little crown, just a couple millimeters. I turned the barrel around while I twirled so that the angle or curve or blunderbuss or whatever the new shape was of the crown, was at least similar all the way around. Then I did the domed screw trick but with fine sandpaper over the screw head to remove any burrs, and cleaned the barrel. In the end it shot a lot better, so I was happy, but under a magnifier it looks like... nothing because the plastic front sight covers the scars.

But I wouldn't do such a thing to a perfectly good crown from the factory.
 
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357cal said:
Would just like to know how many of you have crown your own barrel or barrels? as soon as my orders come in i will be doing so on my Airforce Texan .308 and AEA big bore challenger 357,
Essential Tools & Supplies for Barrel Crowning
1. Brass Self-Centering Lap (Brownells)

.30 cal: Brownells Brass Lap – .30 Caliber

.357 cal: Brownells Brass Lap – .38/.357 Caliber

Price: ~$13–15 each

These are bore-piloted and self-centering—perfect for my Texan and Challenger.

2. Lapping Compound

M*CARBO 180 Grit Silicon Carbide Compound

Price: ~$10

Comes with a small brass lap too (45°), but i will mainly use the compound with your Brownells laps.

3. Drill (Cordless or Low-Speed

4. Cleaning Supplies

Cotton patches, Q-tips, and a bore plug (tight patch or foam earplug) to keep compound out of the barrel.

5. Vise with Soft Jaws

Compound: ~$10
Click to expand...
I'd order the tool from brownells with the guide tip and not use a cordless drill. I just crowned a few crosmans last week in the lathe and I've done pb.... In a lathe.
 
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The main idea of crowning is to make it so the gases exit evenly around the projectile. As long as that happens, the "shape" of the crown, whether round, flat, tapered, doesn't seem to matter much. I've used different crowns on both rifles and hanguns. Another thing to consider is how to "shield" the crown from damage, For example the "target crown" on some barrels is a counter-bore, so if the edge of the barrel is nicked, it doesn't touch or affect the crown. I've taken the time to crown/recrown hunting rifle barrels for customers only to watch them place them in their trucks barrel nose down on a dirt-covered floor board. I wonder why the accuracy diminishes over time!
 
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I have a very old, but in good condition Jet 1024 lathe. Of course I have done a fair amount of gunsmithing in the past (still do some, but mostly retired), so needed a decent lathe and other shop machinery and tools. (I'm also a retired automation engineer.) An important thing about a metal working lathe is the size of the spindle bore (hole through the spindle) to allow barrels to go into and/or through the the spindle. Mine only has a 1-1/16" bore which limits the barrels I can work on. Also, the swing and length; mine is a 1024 which means it can handle a 10" diameter part by 24" long "between centers." There are a multitude of foreign made lathes, both new and used, on the market. Just do a search. Also, "How to Run a Lathe" by South Bend Lathe Works is an inexpensive repro book that is still available and a good reference.
 
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I do know some tuners that often recrown Airgun barrels even if it doesn’t look like it needs to be done and it often make a difference. I wish I had the equipment to do it the right way. I was taught a poor man’s way for FX barrels but it’s not something that would give me an 11 degree crown. It’s only if it’s totally destroyed somehow. Unfortunately my experience buying customs powder burner barrels and mounting them to actions, but first scoping them and seeing the quality and comparing that to a high end Airgun then barrels do not even compare. Airgun barrels are absolutely crap in comparison MOST of the time. You spend $2500 on a semi-custom powder burner you’re going to get a pretty well done barrel, not so in the case of an Airgun and that’s a s shame. Really is a weak link in the Airgun build for most manufacturer.
 
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Showme said:
Many posts refer to a lathe. I'm curious as what is the lathe of choice. I use a Powermatic for my woodturning but don't have experience with metal lathe's.
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I have a little chinesium cd210v metal lathe (was $600) it's not a great lathe but it works when you get the right tooling. 3 jaw for basic, 4 jaw for accurate and to hold my er32 collet block. I tend to use collets because I can indicate the 4 jaw true and just stick barrels in collets when I need to.
 
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Before-

187 RS.JPG


1960s vintage Crosman 187 Co2 rifle.


And after-

187 Titles.jpg


Converted into a world-beating Field Target pistol, capturing three National Champion and three State Champion titles (to date). Tools used to chop and recrown the barrel were a hacksaw, sander, grinder (with buffing wheel), and a rotary tool with tapered (rubber) polishing bits.


Another (before)-

Sniper bipod.jpg


.22 Brocock Sniper XR.


And after-

Sniper convertible.jpg


Turned pistol/carbine convertible with the same tools and techniques.


Yet another-

Bro Rif and Pis.jpg


Brocock Bantam HiLite rifle and pistol-conversion. Same tools and techniques.

All shoot as well or better in pistol-conversion form than they did in original rifle form.

.

.
 
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nervoustrig said:
One guy’s opinion on crowning…I use the lathe for the facing cut in preparation for crowning but I prefer the brass screw approach for actually forming the crown. By using an abrasive and a light touch, I can better ensure no burr is left behind.

View attachment 571147
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Nicely done! I happened to have an 11* chamfer tool in my empire of dirt that works well enough for crosman stuff. I like your method too.
 
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