Unsupported case, again.

[dnellans]

With all the discussion decided to check a Lapua 223 to see how it measures up vs this Surgeon I did.

 

[dnellans]

It doesnt give a spec for exposed case. I just cut the cone angle to spec but set it up as tight as I could and it was about .175 exposed case. Probably would be fine, but I was uncomfortable, so I changed the cone angle until I got to .160". It still fed fine. I think you could get into trouble on those if you put a big chamfer at the back end. I dont chamfer the back end of chambers, just hold a little 400 emery on them to knock the sharp edge off. Never had a feeding issue.

Can you post a pic of the barrel and bolt Alex? I’m not sure I’m visualizing what is happening on that Cadex - I’ve never seen one.

 

[Alex Wheeler]

Its gone, they use a flat boltface with coned breach

 

[VA_XTC_Shooter]

I see this type stuff quite often with new age gunsmiths. Most cater to the prs crowd and i guess the reasoning behind it is trying to fix feeding issues. I think they used a wood counterbore on that one. This is a danger on prefits as well- the counterbore vs. headspace is luck if its right. As you can see it doesnt take much to be in dangerous territory

How to you recommend verifying a pre-fit has enough case support?

 

[Doug Beach]

How to you recommend verifying a pre-fit has enough case support?

Stick your go-gauge in there, and see how much sticks out.

 

[Dusty Stevens]

^^^

 

[Ksracer]

How to you recommend verifying a pre-fit has enough case support?

Stick a piece of new or resized brass in the chamber. It should be supported nearly all the way to the extractor groove. If you can see anything more than a tiny sliver of the case wall, I would have somebody knowledgeable look at it.
Also, just because they make a lot of prefits doesn't mean they are knowledgeable on it or will be candid with you. The one I posted a picture of came from a well-known company that used to be well respected on this forum.

 

[VA_XTC_Shooter]

OK, so no different than any other barrel, verify the Go Gauge isn't sticking out too far (between 0.125" and 0.130"). I just wasn't sure if there was some prefit-specific trick.

 

[dnellans]

You need to know what your

OK, so no different than any other barrel, verify the Go Gauge isn't sticking out too far (between 0.125" and 0.130"). I just wasn't sure if there was some prefit-specific trick.

Only difference between a prefit and a "regular" barrel is that they're making the barrel to a spec rather than being able to test fit it. Despite all the improvements in action tolerances and claims that everything is within a thou of measurement X,Y,Z (and don't get me wrong, its amazing actions can hit what they do), there is no substitute for having an action in hand for getting things dead nuts.

The issue of how much chamfor is being put on chamber isn't really a pre-fit issue, someone above just noted that they think its a large chamfor on some pre-fit manufacturers.

 

[jzerfoss]

I decided to revive this because the 223 i just had done seems like it has too much unsupported case body but the case head to the base of the recess measures .162" plus or minus a thousand or 2 because I'm using calipers.

 

[boltfluter]

Counter bore looks mighty deep to me! What is the measurement from front of lugs to end of bolt nose?

Paul

 

[DaveTooley]

Might be a few thou deep but nothing to worry about. When I chambered on a manual machine here's how I determined all my numbers.
Measure headspace Let's say .887"
tenon length .887-.010"= .877"
measure bolt nose depth usually around .150" or a bit less on a Remington
turn and cut the chamber
to cut the counterbore touch with a boring bar and go to the bolt nose depth of .150"
that automatically gives me .010" end clearance.
You're at .160" +/- a bit.
Cases I've sectioned are pretty solid/thick out to .190"

 

[jzerfoss]

Here are some measurements. It's headspaced fine. The action face to the front of the lugs is .965". The barrel tenon length is .958". The bolt nose depth in the barrel is .151". The tip of the bolt nose to the front lug/bolt face is .135". I talked to the Smith and he said he'd never seen a deviant bolt nose that wasn't .151" and that he would fix it but it should be safe. With the recess being. 015" too deep that ends up exposing .015" more case than needed. What do you guys think?

Here is a picture of the last barrel cut perfect.

 

[dnellans]

I normally shoot for .005 bolt nose clearance but I know others who shoot for .010 in a hunting gun just to handle a little more potential grime. You’re at .016

Look at my picture and measurement on a 223 lapua earlier in the thread. Its .18x before you’re even out of the case head, let alone thick web sides.

Your shooting with .019 of case head still in the chamber. Unless there is a really big chamfer on the chamber mouth (which it doesn’t look like) I wouldn’t sweat it.

 

[boltfluter]

Personally I would fix it, but that is just me. I run about. 005 clearance as well. Just my .02. If you are happy that's all that matters.

Paul

 

[jzerfoss]

Personally I would fix it, but that is just me. I run about. 005 clearance as well. Just my .02. If you are happy that's all that matters.

Paul

I'm more worried about safety than anything. I tend to run things on the spicy side.

 

[boltfluter]

I'm more worried about safety than anything. I tend to run things on the spicy side.

Then I would definitely get it fixed. No question.
Paul

 

[dnellans]

I agree with Paul - if you’re uncomfortable, then having it fixed is a small inconvenience versus having a gun you never will want to shoot.

 

[Ggmac]

Fix

 

[jzerfoss]

Thanks for the opinions gents.