Weird Rem 700 Chambering Measurements Question

[INTJ]

This is my third Rem 700 chamber job. (I am not a fan, I am a BAT Man .) It's the fourth if you count the Christensen (another action with that silly protruding bolt nose).

Said bolt nose is the weird issue. I trued the action (Manson hand tools) taking a minimal amount off the receiver face, lug recesses, and bolt face. I marked them with Dykem and cut off just enough to clean up the unevenness. I then lightly lapped the lugs. Primary extraction is fine.

Here is how it measured AFTER I trued it. I measured several times and got the same readings each time.

Receiver face to lugs: .705
Receiver face to bolt nose: .552
Recoil Lug Thickness: .191

This makes a tenon of .886 (.705+.191-.010)
This makes a bolt recess of .153 (.705-.552)

So I cut the tenon to .886 and threaded it
I then cut the bolt recess to .153

When I checked the bolt nose and front of the lugs for clearance with plastigauge, I had more than .010 of clearance. I had to cut back the shoulder another .004" to arrive at .010" of clearance on the nose and lugs. (It will be .008 when torqued in the barrel vise.)

So what did I do wrong? I had everything cut to the measurements. Why does my tenon have to be .004" too long to get the desired bolt clearance?

 

[Carl S]

Was the dimension from the receiver face to each bolt lug the same. .012" clearance when torqued wouldn't hurt anything.

 

[boltfluter]

If you missed any of your numbers a .001 or .002 adding or stacking tolerances would easily account for this. Assuming all measurements are correct to begin with. Just a thought.
Paul

 

[LVLAaron]

I err on the side of caution. When I do the recess, I get it close, and then start screwing the action on and testing bolt close. When it closes barely, I take an 8 thou pass and call it done.

 

[INTJ]

Was the dimension from the receiver face to each bolt lug the same. .012" clearance when torqued wouldn't hurt anything.

Yea. They were within .0005" to .001".

 

[INTJ]

If you missed any of your numbers a .001 or .002 adding or stacking tolerances would easily account for this. Assuming all measurements are correct to begin with. Just a thought.
Paul

I guess that makes the most sense. That's why I like the Plastigauge to double check. I guess after I do a few more the math will work out better.

 

[INTJ]

I err on the side of caution. When I do the recess, I get it close, and then start screwing the action on and testing bolt close. When it closes barely, I take an 8 thou pass and call it done.

I do that exactly that way on flat faced and cone bolts. I think you are like me and still fairly new at all this compared to many here, and I still hand fit and measure every clearance I can. We really should be able to machine to the numbers though.......

 

[kendog]

SOMETIMES you can get interference from the little fillet formed at the front of the locking lug(s) and bolt nose that can drive you nuts. Bit me a few times in the past. Make sure you cut a significant chamfer or round the area with a three cornered tool at the outer periphery of the bolt counter bore. Copy OEM Rem barrels at this feature.

 

[AlNyhus]

Or make your life much easier and eliminate the counter bore in the barrel.... -Al

 

[Dusty Stevens]

Was the bolt pushed back during the measuring phase?

 

[WSnyder]

Is the sharp edge of the recoil lug hitting the root of the barrel shoulder? Trips people up all the time. Either chamfer the barrel shoulder ID side of the lug or undercut the root of the barrel shoulder like Remington did.

 

[Machinist John]

I check bolt clearance this way. First, hand tight, pull the bolt back and forth and read the indicator.

Then when torqued, same as above, pull the bolt back and forth.

Then I check with the headspace gauge in the chamber, then with a virgin empty cartridge brass in the chamber.

From years of automotive machining experience, I do not trust plastigauge.

 

[INTJ]

Was the bolt pushed back during the measuring phase?

Yes. Bolt stripped, action vertical in a soft jawed vise

 

[INTJ]

I check bolt clearance this way. First, hand tight, pull the bolt back and forth and read the indicator.

Then when torqued, same as above, pull the bolt back and forth.

Then I check with the headspace gauge in the chamber, then with a virgin empty cartridge brass in the chamber.

From years of automotive machining experience, I do not trust plastigauge.

The dial indicator says I have .005" of clearance. If I add back the .004" I took off the shoulder it would be .009", which is within .001" of my original measurements and within tolerance.

So is the dial indicator checking bolt movement actually telling me the clearance? I guess it would be the minimum of the bolt nose or the lugs, whichever hits first.

 

[INTJ]

Figured it out. As long as the bolt handle isn't touching the receiver when it is pushed forward, the dial indicator method works. Still don't know if it's the bolt nose or lugs touching, but it does give the minimum clearance which is what I want.

 

[INTJ]

Recut to my numbers.




When torqued it should be about .008.

Learned something again. TRUST what I measure with my precision tools and don't use plastigauge--except maybe on coned bolts.

 

[LVLAaron]

You've got thousands of dollars in precision gear... Don't rely on a 10 cent piece of plastic

 

[INTJ]

Oh yeah, the tip by @kendog and @WSnyder on breaking the edge of the recess before measuring is spot on. I always do that before polishing the chamber, but that sharp edge was worth .002".

 

[WSnyder]

Since this is a discussion about fitting Remington's this might be of some use. When truing up Remington's (and something to check while detailing any Rem style action) is to take the sharp corner off the top left lug abutment (when looking in from the front (Rt hand action)). This is where those annoying linear scratches at the front of brass near the shoulder can come from during ejection. I use an assortment of Gesswein diemaker stones to clean up and detail the various parts of an action. I always check and hit this spot especially after truing the lug abutments.

As Dave Tooley says "Don't make the phone ring!".

This one has not been cleaned up yet. Those ramps will get cleaned up a touch too.

 

[boltfluter]

Recut to my numbers.

View attachment 1363211
View attachment 1363210

When torqued it should be about .008.

Learned something again. TRUST what I measure with my precision tools and don't use plastigauge--except maybe on coned bolts.

Nice job INTJ, you are well on your way! Nice catch by Robert. We have some of the most talented people I have ever seen on this forum. Always something to learn. Carry on men!

Paul