From: aeporro@ariel.lerc.nasa.gov (Bob Porro)
Newsgroups: rec.guns
Subject: Re: Recrowning...........
Date: 15 Apr 92 14:04:13 GMT
Organization: NASA Lewis Research Center

In article <53222@mimsy.umd.edu>, megatek!hollen@uunet.UU.NET (Dion Hollenbeck) writes...
##>>>> On 13 Apr 92 17:33:49 GMT, FRAMPTON@skitzo.dseg.ti.com said:
# 
#FRAMPTON>     Has anyone ever recrowned a barrel on thier own?
#FRAMPTON>     Can it be done without worry?
# 
#FRAMPTON>     When at my folks this weekend, I picked up my old
#FRAMPTON>     "very first" .22.   Its an Ithaca single shot. I
#FRAMPTON>     looked at the end of the barrel and noticed there
#FRAMPTON>     wasn't a crown anymore.
# 
#Yes, it is I, humble gunsmith's apprentice.  Just did this last week
#in fact on my benchrest gun (22PPC).  Shot a .224" 5 shot group at 100
#yards while fireforming brass, so I must have done something right.
# 
#Some points about re-crowning.  You need a good lathe which is capable
#of being adjusted to minimum runout of the barrel when in the chuck.
#The exact amount of runout depends on what accuracy you want.  I am
#not satisfied until I get the runout under .001", but you see what
#type of accuracy I am going for.  Be reasonable.  If your lathe is not
#capable of getting under .003" runout, whatever accuracy you may be
#satisfied with, you might as well forget doing it yourself.
# 
#After centering the barrel in the chuck, you need to get a SHARP!!!!!!
#tool.  This is CRITICAL.  If you push the metal instead of cutting it
#cleanly, you will leave burrs inside of the bore and these will cause
#problems when the bullet exits.  One way to tell if you left burrs is
#to spin the barrel slowly and put a Q-tip lightly touching the
#rifling.  If any cotton sticks to the barrel, you have burrs.  
# 
#Regardless of what shape your crown is, the angle at which the face of
#the crown meets the bore should be 14 degrees.  This is the
#theoretical best approximation of the angle of the gases exiting
#behind the bullet and will disturb the gas flow as little as possible.
#Again, this all depends on what accuracy you want.  Cut it straight
#across and it will still probably shoot well, but not optimally.
# 
#If you get burrs in the bore, you can make a jig which is a ball
#bearing soldered into the end of a tube.  This can be chucked into the
#tailstock and coated with lapping compound and run up against the
#crown to lap out the burrs.  The problem with this is that you will
#then change the optimal angle of 14 degrees ever so slightly.
# 
#All in all, since you are doing a .22 rifle, if your lathe is fairly
#accurate and you lap out the burrs, it should be good enough.
# 
#One of the first things a benchrest gunsmith will do when a reliably
#accurate rifle "stops shooting" will be to recrown it.  This is one of
#the simplest remedies and most often what is the cause of sudden loss
#of accuracy.
# 

How do you chuck the barrel into the lathe if it is still attaced to a
receiver?  Is there another approach where a lathe isn't used for cases when it
is not practical to remove the barrel from the receiver, i.e., is there a
specialized crowning tool that self-centers itself in the bore of the barrel? 

******************************************************************************
| Bob Porro                    || (The opinions expressed here are not       |
| aeporro@venus.lerc.nasa.gov  ||  necessarily those of the management ?\*!) |
|                              ||                                            |
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