HEAD SPACE

[Webster]

I thought I would pass this on. A product that used to be called plastic gauge can be purchased at Auto Zone for about $6.50. It's intended use is to determine bearing clearance in engines. In the pack you get two plastic gauges, one covers 0.001" to 0.003", the other covers 0.002" to 0.006". The gauge is a precise diameter thread of plastic. Each thread in the kit is about 12" long. You only need about a 1/4" piece to use it. The plastic is put between two surfaces then torqued down. If the clearance is less than the diameter of the thread, the thread gets flattened. You compare te width of the crushed thread to the pictures on the paper envelope.

I put a piece of 0.001 - .003 thread on a case head and closed the bolt. Looks like my bolt face is about 1 thou off of being perpendiculur to the bore center line. A stack up of bolt face, bolt lugs and receiver lugs. Will give it one more thou shoulder bump. Looks like the primer could be seated about 1 more thou.?

 

[Bart B.]

Most new case heads are quite square to their long axis.

After their first firing, they flatten to the bolt face.

If the bolt face is square to the chamber axis, all is good.

 

[Webster]

Most new case heads are quite square to their long axis.

After their first firing, they flatten to the bolt face.

If the bolt face is square to the chamber axis, all is good.

Looking at my picture of the thread across the primer. Do you think the priming tool pushed the top of the primer cup concave about 1 thou?

 

[Bart B.]

Looking at my picture of the thread across the primer. Do you think the priming tool pushed the top of the primer cup concave about 1 thou?

No.

The thread appears to have been pushed into the hole in the bolt face and not into the primer. And the primer is below flush with the case head.

Put a straight edge across the case head to see how flat the primer cup is.

You'll also see how much below flush to the case head the primer is. Or use a depth micrometer.

 

[Toolbreaker]

I put a piece of 0.001 - .003 thread on a case head and closed the bolt. Looks like my bolt face is about 1 thou off of being perpendicular to the bore center line. A stack up of bolt face, bolt lugs and receiver lugs.

Was the .001" difference favoring the 12:00 position in the action? You might try measuring it again with the trigger & firing pin removed. It's possible that the the cocking load is pushing your bolt upward in the back, throwing the measurement off somewhat.

 

[dstoenner]

Was the .001" difference favoring the 12:00 position in the action? You might try measuring it again with the trigger & firing pin removed. It's possible that the the cocking load is pushing your bolt upward in the back, throwing the measurement off somewhat.

That is what Bill Calfee complained about for the 40x rimfire action. He actually rebuilt a trigger sear and bolt piece to have a 90 interface and it improved accuracy

David

 

[500Stroker]

I thought I would pass this on. A product that used to be called plastic gauge can be purchased at Auto Zone for about $6.50. It's intended use is to determine bearing clearance in engines. In the pack you get two plastic gauges, one covers 0.001" to 0.003", the other covers 0.002" to 0.006". The gauge is a precise diameter thread of plastic. Each thread in the kit is about 12" long. You only need about a 1/4" piece to use it. The plastic is put between two surfaces then torqued down. If the clearance is less than the diameter of the thread, the thread gets flattened. You compare te width of the crushed thread to the pictures on the paper envelope.

I put a piece of 0.001 - .003 thread on a case head and closed the bolt. Looks like my bolt face is about 1 thou off of being perpendiculur to the bore center line. A stack up of bolt face, bolt lugs and receiver lugs. Will give it one more thou shoulder bump. Looks like the primer could be seated about 1 more thou.?


View attachment 1037220

Sometimes it's the simply things that work the best. Keep up the good work

 

[rockable]

Works great for checking headspace on a rimfire, too.

 

[divingin]

Was the .001" difference favoring the 12:00 position in the action? You might try measuring it again with the trigger & firing pin removed. It's possible that the the cocking load is pushing your bolt upward in the back, throwing the measurement off somewhat.

Ejector and extractor might be causing the difference as well, assuming they're in there.