So what happens to the Bolt

[Riesel]

This came up on another thread and so as to not hijack the thread I'll start this one because, well, I have often wondered. You just finished chambering a Remington 700 and have the headspace set somewhere around 3 thousand between go and no go. Bolt nose clearance is set at five thousand and the lugs are showing full contact. You install trigger and when closing the bolt the rear portion of the bolt lifts due to the trigger but the bolt closes without any issues. OK, upon releasing the sear, does the bolt go back to it's formal centerline, full lug contact postion thus making the jacked up bolt issue a non-issue? Seems to me everything goes back to the centerline, everything straight with the bore of the barrel. Without getting real technical, am I missing something?
Thanks
Riesel

 

[Ggmac]

This came up on another thread and so as to not hijack the thread I'll start this one because, well, I have often wondered. You just finished chambering a Remington 700 and have the headspace set somewhere around 3 thousand between go and no go. Bolt nose clearance is set at five thousand and the lugs are showing full contact. You install trigger and when closing the bolt the rear portion of the bolt lifts due to the trigger but the bolt closes without any issues. OK, upon releasing the sear, does the bolt go back to it's formal centerline, full lug contact postion thus making the jacked up bolt issue a non-issue? Seems to me everything goes back to the centerline, everything straight with the bore of the barrel. Without getting real technical, am I missing something?
Thanks
Riesel

Howdy , I'm getting back slowly to the forum . A very good explanation of the angled cocking piece is by Bill Calfee , in precision shooting magazine and his own book . The article is " just relax " I think .
What I was referring to in the other post was that some times the bolt nose recess is cut tight , not taking into account the Kant of the bolt . The larger the difference between the bolt and raceway , the larger the tilt . Which if the bolt nose recess was tight , the bottom front MAY hit or the top rear ( of recess ) will try to push the bolt straight , and away from the top of the receiver . ONE of the reason Borden bumps was used .
Pm me if you want to read the Calfee stuff but it may take time to locate it .

Forgot to add , his theory is that the vibration that happens when the bolt slaps down into position , sets up measurable nodes (?) that are much faster than the bullet . So all this happens before the bullet exits . The only shooters capable of seeing a increase are the ones far above my shooting skills .
But any improvement helps , right ?

 

[ab_bentley]

This came up on another thread and so as to not hijack the thread I'll start this one because, well, I have often wondered. You just finished chambering a Remington 700 and have the headspace set somewhere around 3 thousand between go and no go. Bolt nose clearance is set at five thousand and the lugs are showing full contact. You install trigger and when closing the bolt the rear portion of the bolt lifts due to the trigger but the bolt closes without any issues. OK, upon releasing the sear, does the bolt go back to it's formal centerline, full lug contact postion thus making the jacked up bolt issue a non-issue? Seems to me everything goes back to the centerline, everything straight with the bore of the barrel. Without getting real technical, am I missing something?
Thanks
Riesel

To combat this issue, I started TIG'ing two small welds on really sloppy bolts, to act as Borden Bumps.

Alex pointed out that he checks for even clearance on the rear bridge after truing, ensuring minimum disturbance on firing.

Adam

 

[Ggmac]

Spring loaded rear scope base screws ! Just kidding .

 

[tobnpr]

Firing pin shoves the case tight into the chamber, until the shoulder (or whatever part of the case that sets headspace) makes contact and stops forward movement.

Forward movement stops, primer ignites and backs out slightly, pressure increases and case grips the chamber walls.

Casehead stretches back to boltface, primer reseats and lugs absorb the force of bolt thrust.

Since all this happens after the sear is no longer lifting the rear of the bolt, I've never understood why it matters. Presumably, the lugs and internal abutments are lapped/machined for perpendicularity when there is no misalignment caused by the sear- so what am I missing here?

 

[Ggmac]

Firing pin shoves the case tight into the chamber, until the shoulder (or whatever part of the case that sets headspace) makes contact and stops forward movement.

Forward movement stops, primer ignites and backs out slightly, pressure increases and case grips the chamber walls.

Casehead stretches back to boltface, primer reseats and lugs absorb the force of bolt thrust.

Since all this happens after the sear is no longer lifting the rear of the bolt, I've never understood why it matters. Presumably, the lugs and internal abutments are lapped/machined for perpendicularity when there is no misalignment caused by the sear- so what am I missing here?

Read Bill Calfees explain . Much better at it than I . It does make a difference .
Bolts are square when neutral , meaning no sear pushing the top lug off .
Just because the firing pin hits and the bullet starts to move , vibrations have already started . If everybody is striving for ultimate accuracy , all unnecessary movement needs to be eliminated .
Like I said earlier , we mortals will never know the difference . Just one more thing to keep you awake at night ! Read his book !
Or have articulated bolt heads , or 90 deg Sears , or ?

 

[BoydAllen]

A lot of this stuff has been verified by actual test. People often confuse themselves when they try to do the whole thing in their minds, totally based on assumptions. A friend had a 700 that tended to spit shots. (Hart barrel, good barreling job and bedding) When he sleeved the bolt the problem went away. His bolt had more than average clearance, but I think that the example is valid. There is a lot of evidence that vibration that is generated in and by the bolt has a major influence on accuracy.

 

[Alex Wheeler]

All actions un seat the top lug (rem trigger). Some more than others. Very early on max pressure happens. At that point both lugs are seated. The down side to tight bolt fit is all the dimensions become critical and the tight fit means things have to be perfect for both lugs to seat stress free.

 

[alinwa]

To combat this issue, I started TIG'ing two small welds on really sloppy bolts, to act as Borden Bumps.

Try drilling/threading a couple 10-32 studs thru the rear receiver ring, polished tips inside with lock-nuts outside. Then you can tune with it.

I'm not joking.

 

[hoz53]

Try drilling/threading a couple 10-32 studs thru the rear receiver ring, polished tips inside with lock-nuts outside. Then you can tune with it.

I'm not joking.

funny i was thinking that right before you posted it.

 

[Cloudrepair]

Try drilling/threading a couple 10-32 studs thru the rear receiver ring, polished tips inside with lock-nuts outside. Then you can tune with it.

I'm not joking.

I was thinking about that with brass tiped screws looks like others where also

 

[Cloudrepair]

I was thinking about that with brass tiped screws looks like others where also

I wonder how that would compare to sleaving?

 

[boltfluter]

Question for you experts. Would it be feasible or practical to sleeve the back of the bolt and run a tighter than normal clearance on the bolt nose diameter to mitigate some of the vibration. Looking forward to the answers. Finally an interesting discussion.

Paul

 

[Ggmac]

All actions un seat the top lug (rem trigger). Some more than others. Very early on max pressure happens. At that point both lugs are seated. The down side to tight bolt fit is all the dimensions become critical and the tight fit means things have to be perfect for both lugs to seat stress free.

NOT ALL ACTIONS !!!!
Actions with articulated bolt heads , actions with the sear on the side , actions with 90 degree Sears , all of thes actions don't unload the top lug .

 

[Ggmac]

Question for you experts. Would it be feasible or practical to sleeve the back of the bolt and run a tighter than normal clearance on the bolt nose diameter to mitigate some of the vibration. Looking forward to the answers. Finally an interesting discussion.

Paul

Borden bolt bumps ! That was his answer . Canjar , even Mr. Walker had at one time designed a 90 sear for the Remington .
The amount of play is the critical factor . The greater the play , the bigger chance of POSSIBLE problems .
Yes a tight fit at lock up , either with a sleeve or bumps will help . But remember , unless your shooting in the teens you probably won't see a better group .
NO on the bolt nose .

 

[Dusty Stevens]

Question for you experts. Would it be feasible or practical to sleeve the back of the bolt and run a tighter than normal clearance on the bolt nose diameter to mitigate some of the vibration. Looking forward to the answers. Finally an interesting discussion.

Paul

Im not an expert but i do know if the bolt nose hits the barrel you wont be happy with the target. Weird vibrations.

 

[hoz53]

Question for you experts. Would it be feasible or practical to sleeve the back of the bolt and run a tighter than normal clearance on the bolt nose diameter to mitigate some of the vibration. Looking forward to the answers. Finally an interesting discussion.

Paul

Boyd A posted about this not long ago and about a gunsmith he knows who has done this i believe. pm him

 

[sdean]

Spring loaded rear scope base screws ! Just kidding .

I pour an epoxy top bushing through those holes. Not kidding!!

 

[boltfluter]

Im not an expert but i do know if the bolt nose hits the barrel you wont be happy with the target. Weird vibrations.

I was asking about tightening up on the diameter of the bolt in the counter bore, not on the bolt nose touching the back of the barrel.

Thanks, Paul

 

[Ggmac]

I pour an epoxy top bushing through those holes. Not kidding!!

It'll work but a 4-40 screw tapped into the bolt along the left raceway area and filed down to cam ( not as tightly as crammed would imply ) the bolt down . As you know it doesn't take much . I just don't like the bolt getting snug , with dirt grease etc . With the cammed method all functions remain normal