Barrel Crown
- Thread starter Louis.J
- Start date
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j mckinnie
Guest
no comment lol ha ha
When I noticed Dennis mention his 60` crowning tool I bought them right away, that was 4 years ago. Since I already had a bunch of reamers and pilots, the tool cost was low.
About the 90` degree crown versus a 60` crown chamfer, I think it is obvious that flat based bullets and boat tail bullets may have different sensitivities to the crown shape.
About the 90` degree crown versus a 60` crown chamfer, I think it is obvious that flat based bullets and boat tail bullets may have different sensitivities to the crown shape.
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highseas
Guest
Probobly a real dumb ass question, but whats obvious and why? and which prefers which?
Note that I used the word may. My point was that if we are considering a scientifc approach to a test because we suspect there could be a better method, then doubling or tripleing [by using rebated boat tails] the differential would incresase the propability of finding a combination that is superior. I meant no rhetoric nor inclination but since it is the internet that is almost impossible to convey. I would love to do the test myself but do not have the proper rifles to do so.
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nhkuehl
Guest
You may have something there about FB vs. BT and crown. I had a new factory rifle that keyholed with FB bullets, but not BT... I never found out why, because the barrel was replaced under warranty. I just recrowned a barrel that was keyholing (FB, wasn't shooting BT) and set the muzzle back 1/2". The stub I cut off would allow a .219" pin gage to slip fit through and the remaining barrel would only allow a .218" pin gage to slip in. There was no visible damage to the crown. It would be interesting to see test results on the relationship to crown angle and bullet design. - nhk
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highseas
Guest
I thought maybe you had something you found by either accident or through trial. I was getting really interested as I have a factory REM 308 PSS that doesnt seem to want to group with a bullet I have had good success with. You might have the basis for an interesting test.
Joe Ponto
New member
The piloted/bushing chamfer tool sounds like a great idea however it isn't a perfect solution either. There are clearances in that can cause some grief. Once you have piloted reamer now you need the pilots or bushings. I will post a few pictures of a customers rifle that is currently in my shop. I haven't looked into the bore but the crowni s priceless and might well have been cut by hand and a piloted tool.
Further, whenever you stick something in a barrel, you run the risk of scoring the rifling. Contaminants/chips can cause some serious irritation of the nicely lapped rifling.
Proper lathe setup, and sharp tools do not have this potential. Bore scopes are wonderful tools to examine the quality of the work...before it leaves the shop.
Further, whenever you stick something in a barrel, you run the risk of scoring the rifling. Contaminants/chips can cause some serious irritation of the nicely lapped rifling.
Proper lathe setup, and sharp tools do not have this potential. Bore scopes are wonderful tools to examine the quality of the work...before it leaves the shop.
dennisinaz
New member
The crown isn't what was causing those bullets to keyhole. Even if the crown is horrible, a stable bullet will right itself and make a straight hole- just not exactly in the same place every time. A bullet keyholes because it is not stable- for whatever reason, voids in the core, insufficient RPMs to hold it etc.
As for boat tail vs flat base, it has been my understanding and experience, to some degree, that flat base bullets are more forgiving of a bad crown that a boat tail. Not sure why but it just seems that way. When I have had accidents out hunting and boogered up a crown, I have found that the flat based bullets have shot measurably better than the boat tails. My sample is small so take it for what it's worth.
I like to load boat tail bullets because they are EASIER to sit in the neck- I use them because most of the stuff I shoot is for long range, where a BT actually makes a difference. I cut my crowns with a sharp HSS tool. I cannot run my 4-jaw fast enough to make carbide work. My 4-jaw is rated at 400 rpm and I need at least 1000 to make carbide work properly. If the tool is sharp, the crown needs no deburring or lapping or whatever. The human eye, especially looking through a loupe, can detect very small differences in cuts. When I make the bevel cut, I start at maybe only .005. If this circle doesn't look perfect, them my setup is jacked and I start over. I know if I go deeper, it will be as uniform as I can make it.
The piloted tool sounds handy, but I question how well it really cuts at those low rpms??
JerrySharrett
Senile Member
That "what ever" reason CAN be. in the example of the FB bullet, gas exiting unevenly around an irregular crown edge which upsets the spin axis.
Yes, the bullet may right itself eventually but it is more influenced by the wind while it is "off axis" and not "asleep"!!
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Ken Worth
Guest
You will get a much better finish with HSSCo properly ground than you will with carbide regardless the spindle speed.
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nhkuehl
Guest
Keyholing
A friend and I purchased the same model rifles and and shot them side-by-side with the same load. Twist (1:9) and velocity (3100 fps) gave an Sg of 1.61+. One rifle keyholed the other didn't. Like I said the barrel was replaced so I don't know what caused the keyholing. - nhk
A friend and I purchased the same model rifles and and shot them side-by-side with the same load. Twist (1:9) and velocity (3100 fps) gave an Sg of 1.61+. One rifle keyholed the other didn't. Like I said the barrel was replaced so I don't know what caused the keyholing. - nhk
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nhkuehl
Guest
Twist
Yes, twist was verified 1:9. You can see by the targets it wasn't a stability problem or the bullets would have dispersed further. I've purposely loaded rounds below Sg 1.0 and fired them to see what would happen and didn't get keyholing, but the groups opened up and the bullet holes were oblong. You can also see a comet tail around at least one of the bullet holes on the target I posted indicating molten lead (friction). I've drilled holes in various locations in jackets to see if I could get the comet tail or unbalance a bullet enough to keyhole and couldn't, just larger groups. The profiles of the bullets look like a flat spin rather than tumbling. - nhk
Yes, twist was verified 1:9. You can see by the targets it wasn't a stability problem or the bullets would have dispersed further. I've purposely loaded rounds below Sg 1.0 and fired them to see what would happen and didn't get keyholing, but the groups opened up and the bullet holes were oblong. You can also see a comet tail around at least one of the bullet holes on the target I posted indicating molten lead (friction). I've drilled holes in various locations in jackets to see if I could get the comet tail or unbalance a bullet enough to keyhole and couldn't, just larger groups. The profiles of the bullets look like a flat spin rather than tumbling. - nhk
I read this old thread.
I cut off an inch.
I made the 90 degree cut with high speed steel, not carbide.
I cut the chamfer at 60 degrees with a tiny boring bar.
I got it to not grab threads off a Q-tip.
Now I am worried that my 60 degree angle was from the wrong line.
I had the compound set up for like 60 degree threads.
The Lothar Walther factory cuts are on the left. My cuts are on the right.
I cut off an inch.
I made the 90 degree cut with high speed steel, not carbide.
I cut the chamfer at 60 degrees with a tiny boring bar.
I got it to not grab threads off a Q-tip.
Now I am worried that my 60 degree angle was from the wrong line.
I had the compound set up for like 60 degree threads.
The Lothar Walther factory cuts are on the left. My cuts are on the right.
Attachments
AMMASHOOTA
Gary Gruber
The latest process is to simply cut a flat crown moving from the inside out then using a brass crowing ball of my own making and to lap it to the bottom of the grooves. Ball is about a 100 thous. over groove size, and the barrel is dialed in through the head stock prior to all work taking place. Being a cast bullet competitor the lube leaves a very prevelant lube star on the face of the muzzle showing the end results.
JLouis
JLouis