The Firing Line Forums

Go Back   The Firing Line Forums > The Skunkworks > The Smithy

Reply
 
Thread Tools Search this Thread
Old January 8, 2020, 02:19 AM   #1
MM60
Junior Member
 
Join Date: January 8, 2020
Posts: 1
Trying to Fix an Under-Regulated Revolver Barrel

Hi Everyone! I've been reading the forum for several years and finally decided to join. For my first post, I'm hoping to find an answer to a rather technical question...

I purchased a S&W Model 60 (J-Frame) revolver and the barrel is under-regulated. When acquiring the sight picture, the front sight is slightly but clearly canted to the right. I test-fired the revolver on a full-sized IPSC silhouette target at 25 yards with my own 158gr .357 Magnum loads and all shots grouped in the top left shoulder area of the target (the target's right shoulder) when aiming for center of mass.

The last time I sent a revolver to Smith & Wesson for service work, it was gone for about three months to have a different length barrel installed, and I had to immediately send it back to them when the work was done for being improperly regulated. Two weeks later it was returned to me better than before but still a hair off. That being said, I would prefer to fix my Model 60 myself if possible.

So here is my question... If the barrel is under-regulated approximately 2° (meaning it needs to be tightened 2° into the frame) and I had the proper vice block for the barrel and a frame wrench with the proper J-Frame inserts (I can fabricate these myself) so that I won't bend the frame, can I simply tighten the barrel myself? Or would I still need to remove the barrel and turn the shoulder down using a lathe?

According to this document from Brownells...: https://www.brownells.com/userdocs/l...ck_Fixture.pdf

...S&W J-Frame barrels are threaded 36 TPI and move .028" per full turn of the barrel. I'm calculating that .028"/360°=0.00007"per degree of rotation. So if I need to tighten the barrel by 2°, then that should tighten the barrel's shoulder against the frame by only 0.00014" – 14 ten-thousandths of an inch. That seems infinitesimally small to me, but I'm not sure whether or not such a measurement can be set on a good lathe (I am not a machinist) or would even need to be. Without access to a lathe or the skill to use one, would attempting to simply tighten the barrel myself by 2° – with the proper hand tools – likely crack my frame or over-stress my barrel? Or would this be a safe and reasonable thing to do? Thanks!

Edit: This is not a pinned-barrel model.

Last edited by MM60; January 8, 2020 at 02:21 AM. Reason: adding information
MM60 is offline  
Old January 8, 2020, 11:18 AM   #2
FrankenMauser
Senior Member
 
Join Date: August 25, 2008
Location: In the valley above the plain
Posts: 13,402
Only someone with the revolver in their hands can answer that question.
There are many factors to consider, including condition and how tight the barrel is already.

It could be that the barrel will easily turn and over-shoot the mark. Or, it could be that the 'infinitesimally small 0.00014"' will be just enough to cause problems.
__________________
Don't even try it. It's even worse than the internet would lead you to believe.
FrankenMauser is online now  
Old January 11, 2020, 11:51 PM   #3
44 AMP
Staff
 
Join Date: March 11, 2006
Location: Upper US
Posts: 28,677
One question, before any others, is the direction you need to turn the barrel to get the sight "straight" loosening or tightening it??

Generally when a fixed sight gun isn't on target people look for other ammo to see if its on target with a different load, or they look at filing the sights to get on target with their chosen load.

You're absolutely sure the gun being off isn't your reloads or just you having a bad day??? I'd try other ammo and other shooters before doing any shop work.
__________________
All else being equal (and it almost never is) bigger bullets tend to work better.
44 AMP is offline  
Old January 12, 2020, 02:02 PM   #4
T. O'Heir
Senior Member
 
Join Date: February 13, 2002
Location: Canada
Posts: 12,453
You should define what you think "under-regulated" means.
You can't even see 28 thou, never mind 14 ten-thousandths of an inch. I'd seriously question ".028" per full turn of the barrel." too.
Has anybody else shot the thing?
How did you determine the barrel isn't right? Your "all shots grouped" really doesn't prove or disprove anything.
__________________
Spelling and grammar count!
T. O'Heir is offline  
Old January 13, 2020, 02:04 AM   #5
4V50 Gary
Staff
 
Join Date: November 2, 1998
Location: Colorado
Posts: 21,824
Generally it is an easy fix with a wrench w/inserts and barrel block and drill rod to support the bbl.
__________________
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!
4V50 Gary is offline  
Old January 13, 2020, 06:19 PM   #6
Unclenick
Staff
 
Join Date: March 4, 2005
Location: Ohio
Posts: 21,022
Mr. O'Heir seems to have missed that you are not seeing the crush itself, but rather the rotation, and 2° is plenty easy to see. Have you confirmed that 2° at the radius of the front sight tip from the bore centerline moves the tip far enough to compensate for the error in POI?

You are talking only 0.154 thousandths of additional crush. That is not enough additional stretch to matter to functionality. Also, if you get a copy of Jerry Kuhnhausen's, The S&W Revolvers, A Shop Manual, on Page 84 he shows the slightly negatively angled shoulder at the root end of the barrel tang and comments that some amount of crush room remained available on all S&W barrels that he's removed. This means you can turn it in further. He also shows the equipment for barrel removal and installation.

You may want to first remove the barrel and apply a very thin layer of anti-seize or automotive assembly lube. Even a little motor oil will make it easier to turn past the original location. Anti-seize makes it easier to get the barrel off again in the future if you need to.

Since these guns have a removable front sight insert, and since these are known to bend if the gun is dropped on its sight, an alternative would be to intentionally bend it. Replacements are available.
__________________
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Benefactor Member and Golden Eagle
Unclenick is offline  
Old January 14, 2020, 11:11 AM   #7
Jim Watson
Senior Member
 
Join Date: October 25, 2001
Location: Alabama
Posts: 18,486
I did the calculations and presented FLG with a diagram of how much my Italian single action's barrel was going to have to be "tweaked" to correct windage. It is a routine operation on those guns and I don't see why it would not work on a newfangled double action.
Jim Watson is offline  
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 12:59 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2021 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Page generated in 0.06553 seconds with 8 queries