Saubier.com  



Go Back   Saubier.com > Saubier.com Forums > Small Caliber Discussion Board

Reply
 
Thread Tools Display Modes
  #1  
Old 01-18-2018, 08:50 PM
montdoug montdoug is offline
Supporting Member
 
Join Date: Sep 2006
Location: Bozeman Montana
Posts: 6,164
Default Bolt locking lug contact or lack there of.

This situation came up on my new CZ 527 Varmint .222 but it's an issue certainly not exclusive to CZ's. I use to be long on Remington's and dealt with it on them as well.
On the CZ and I'm a well known fan, but in honesty they are a bit coarse around the edges in machining etc. I became a fan back before the dollar tanked and a Remington 700 was $800.00ish and a CZ 527 was $500.00ish. I was gonna use em as a wildcat platform anyway so more and more CZ's showed up at my house. The wood was sometimes stellar and in spite of the slightly rough edges they shot like crazy.
Forward to my latest 527. I decided to test the bolt lug engagement as usual, when I did the lug on the left wasn't bearing at all, the right side about 70%.
I had the rifle bedded into the new Bell and Carlson stock and while there I had the barrel shortened and an 11% crown put on it as well as having the lugs lapped to 100% on both sides making contact. I'm gonna take the exact same loads that on the first firings were running slightly above half inch to slightly under an inch and retest em. Only variable I can't duplicate in the timely fashion I'm wishing I could is temp. A load at 70 degrees and the same one at 10 degrees just ain't gonna shoot the same so looks like I'm waiting a couple three months .

I got to wondering how many others check this measurement on all new factory rifles besides bored old Montanans in winter ?
__________________
"Shoot safe!!"
montdoug
Reply With Quote
  #2  
Old 01-19-2018, 02:00 AM
Kerry Kerry is offline
Senior Member
 
Join Date: Feb 2007
Location: oklahoma panhandle
Posts: 203
Default

I got to wondering how many others check this measurement on all new factory rifles besides bored old Montanans in winter ?[/quote]

Doug
being you have extra time on your hands would you be so kind as to explain how you do this to a somewhat younger Oklahomans:

thanks
Kerry
Reply With Quote
  #3  
Old 01-19-2018, 04:40 AM
georgeld georgeld is offline
Senior Member
 
Join Date: Sep 2006
Location: Pueblo, CO
Posts: 5,832
Send a message via MSN to georgeld
Default

Doug:
Did you get my pm last night????????
__________________
George

"Gun Control is NOT about guns,
it's about CONTROL!!"
Reply With Quote
  #4  
Old 01-19-2018, 12:44 PM
Alan in GA Alan in GA is offline
Supporting Member
 
Join Date: Sep 2006
Posts: 1,581
Default Bolt lug contact...

I would be concerned if one of the two lugs had zero contact. If both have at least some contact I don't have concern about it. I do clean and lubricate the back of the bolt lugs and the abutments in the action during high round count gopher shoots!
Also, the bolt in my 7,000 round count 17 Ack Hunt slides easily back and forth as the rifle is pointed up or down, unlike when it was new. (CZ 527).

Last edited by Alan in GA; 01-19-2018 at 12:52 PM.
Reply With Quote
  #5  
Old 01-19-2018, 04:09 PM
TinMan TinMan is offline
Senior Member
 
Join Date: Sep 2006
Posts: 2,800
Default

I'm with Alan in GA. I check new or new to me rifles for lug contact. Never found one totally non-contacting on one lug. I have lapped some for better contact for a couple of rifles when I felt like it might help. I do clean and lube lugs regularly and have the handy Sinclair lug cleaning tool for traditional two lug bolts.

Regarding the machining on CZs, both my 527s are okay, but when my 452 in 22WMR was new, it had a very 'sticky' bolt action, and very tight to slide. Upon inspection, there were sharp burrs on the ID of the action/receiver. A few minutes attention to de-burr the sharp edge of the ID with a very fine hard stone and it slicked up the action just fine. I have also used a stone to lightly de-burr the sharp edges of CZ magazines lips that have sharp edges and scratch cases.

Last edited by TinMan; 01-19-2018 at 04:12 PM.
Reply With Quote
  #6  
Old 01-19-2018, 04:13 PM
Bayou City Boy Bayou City Boy is offline
Supporting Member
 
Join Date: Sep 2006
Location: Tomball/Klein, Texas
Posts: 3,989
Default

Quote:
Originally Posted by montdoug View Post
I got to wondering how many others check this measurement on all new factory rifles besides bored old Montanans in winter ?
Quote:
Originally Posted by Kerry View Post
Doug
being you have extra time on your hands would you be so kind as to explain how you do this to a somewhat younger Oklahomans:

thanks
Kerry
First off - I too would be concerned in this day and age, especially with today's technology, if I had a new factory rifle with only one lug contact. That is not a home style, "I'll lap the lugs with some grit while watching Oprah this afternoon" type of operation to get things right. I have a machinist friend who describes something like that very well with his, "It was whopper-jawed from the git go" terminology. To get both lugs contacting in that scenario with a home lapping job might cause serious head space issues with the rifle.

To answer the "how you do this" question, machinist blue Dykem (not sure on spelling) applied to the back of the bolt lugs is a good way to check for contact. Begin by making sure that the lug race ways in the action are clean. In addition, anything such as external extractors like found on CZ rifles need to be removed so as to not interfere with the results. Try the same closing the bolt operation several times so that you can see repeatable results on the dye material wiped off each time. In a pinch, Magic Marker can be used, but for it to work the action and the locking lugs need to be completely clean and totally oil free and dry. Even a bit of oil in the lug race way will cloud the answer by wiping off the marker.

I have a couple of very good gunsmiths that I trust their opinions on things, and both have told me that on a factory rifle, if you have 50%-60% contact on both lugs, do nothing other than shoot the rifle as normal. Normal use will improve things, and after maybe a 100 rounds fired, accuracy will improve as much as its going to based on locking lug contact alone. Both said that the 50%-60% contact described above on a new rifle is enough to keep things in their proper locations for good accuracy if everything else is lined up properly to begin with.

Having lugs lapped for ~100% contact is a fairly normal thing to have done when getting a barrel installed on a rifle. In this scenario, a good smith will use a spring loaded device that is threaded into the action to provide resistance on an already squared-up bolt face surface while closing and opening the bolt so that total lapping can occur. After all is square, a new barrel chambered and threaded with the proper head space is installed. If a factory barrel is left intact while lugs are lapped if only one is contacting, any good smith worth paying money to would check to insure that head space was not compromised. If it is, the only answer is to unscrew that barrel and re-chamber and refit it to the action insuring good head space measurements.

Keep in mind that locking lug contact is only one of several factors that can affect a rifle's accuracy potential. Having good locking lug contact alone does not insure an accurate rifle if other things like the bolt face being square with the action threads and the action face, a totally good chambering/thread cutting job on the barrel, and other related issues, are not present.

-BCB
__________________


I miss mean Tweets, competence, and $1.79 per gallon gasoline.

Yo no creo en santos que orinan.

Women and cats will do as they please. Men and dogs should relax and just get used to the idea.

Going keyboard postal over something that you read on the internet is like seeing a pile of dog crap on the sidewalk and choosing to step in it rather than stepping around it.

If You're Afraid To Offend, You Can't Be Honest - Thomas Paine

Last edited by Bayou City Boy; 01-19-2018 at 06:23 PM. Reason: terminology..........
Reply With Quote
  #7  
Old 01-20-2018, 02:13 AM
GrocMax GrocMax is offline
Senior Member
 
Join Date: Oct 2012
Location: McKinney TX
Posts: 488
Default

If you did an FEA on a standard 2 lug repeater receiver the lower (right) lug will bend back more under pressure than the top. No metal behind it, taken away for feed ramps.

Now an OEM with a lot of test equipment and a full engineering staff might already know this and preload the bottom lug? Food for thought.
Reply With Quote
  #8  
Old 01-20-2018, 11:50 AM
rickiesrevenge rickiesrevenge is offline
Senior Member
 
Join Date: Feb 2009
Posts: 1,706
Default

Doesn't matter if there is slop in the bolt body. Greg Tannel explains this well in his video. Basically the trigger pushes up on the back end of the bolt lifting the top lug off the abutment. When the trigger is pulled the back end of the bolt falls and then both lugs can make contact while the round is fired.

Aaron
Reply With Quote
  #9  
Old 01-20-2018, 02:26 PM
Bill K Bill K is offline
Senior Member
 
Join Date: Aug 2012
Location: N.E. Kommie Kalifornia
Posts: 6,304
Default Bolt locking lug contact or lack there of.

Quote:
Originally Posted by rickiesrevenge View Post
Doesn't matter if there is slop in the bolt body. Greg Tannel explains this well in his video. Basically the trigger pushes up on the back end of the bolt lifting the top lug off the abutment. When the trigger is pulled the back end of the bolt falls and then both lugs can make contact while the round is fired.

Aaron
And I would say Tannel has a whole bunch more experience on it, than many of us shade tree smiths.. Bill K
Reply With Quote
  #10  
Old 01-20-2018, 03:18 PM
Bayou City Boy Bayou City Boy is offline
Supporting Member
 
Join Date: Sep 2006
Location: Tomball/Klein, Texas
Posts: 3,989
Default

Quote:
Originally Posted by rickiesrevenge View Post
Doesn't matter if there is slop in the bolt body. Greg Tannel explains this well in his video. Basically the trigger pushes up on the back end of the bolt lifting the top lug off the abutment. When the trigger is pulled the back end of the bolt falls and then both lugs can make contact while the round is fired.

Aaron
Quote:
Originally Posted by Bill K View Post
And I would say Tannel has a whole bunch more experience on it, than many of us shade tree smiths.. Bill K
What Rickie is describing is exactly what Greg is doing with his bolt bushing concept. He is simply trying to minimize/reduce the rear bolt lift and resulting possible bolt lug movement by keeping the front of the bolt in place while the striker is falling and traveling forward just prior to the primer strike. He is presuming good initial bolt lug raceway contact with both bolt lugs prior to and at the exact moment of the rifle firing.

As for FEA testing which is actually Finite Element Analysis that involves compute modeling and testing of various engineering designs - presumably analyzing stress in the example of a rifle action. One thing that any staff of OEM engineers would tell you is that transferring stress from one point to another is not a good way to control metallurgical stress on the design element itself which is designed to have two bolt lugs sharing the pressure to some comparable degree at the moment the rifle fires.

Hence if only one lug is contacting at the time of firing, transferring some of the chamber pressure/bolt thrust pressure/stress from one lug to another in a time frame that makes the blink of an eye seem like decades is not a good design parameter. The second lug is now being dealt not only the bolt thrust pressure that it was designed to contain, but the transfer of energy is being done with an element of rearward movement that is comparable to hitting an object with a hammer to further test its strength at the same time.

That is not something that any rifle builder engineering staff wants to see nor do they design a rifle action so that it will experience those two different forces almost simultaneously on a regular basis.

A shooter will want both bolt lugs contacting the action race way at the impulse time of the rifle firing - both for an accuracy inducing point of view which minimizes movement in the front of the bolt, but more importantly from a safety point of view.

It sounds like Doug's gunsmith took care of the bolt lug issues when he had the rifle, so Doug may or may not experience better accuracy from the rifle. From a purely engineering point of view, his action is now a better design for containing pressure in the manner that the OEM engineers designed the action to do it.

Was it dangerous prior to having the lugs seated by the smith? No. But over time with considerably use/firing, the transfer of energy at the moment the rifle fired from one lug to both would have caused set back on both lugs (for different reasons) that would not help in any manner.

-BCB
__________________


I miss mean Tweets, competence, and $1.79 per gallon gasoline.

Yo no creo en santos que orinan.

Women and cats will do as they please. Men and dogs should relax and just get used to the idea.

Going keyboard postal over something that you read on the internet is like seeing a pile of dog crap on the sidewalk and choosing to step in it rather than stepping around it.

If You're Afraid To Offend, You Can't Be Honest - Thomas Paine
Reply With Quote
Reply

Thread Tools
Display Modes

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. The time now is 08:47 AM.


Powered by vBulletin® Version 3.8.1
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.