headspace on mb Bat

[double g]

Best way to measure headspace on mb Bat while chambering, barrel shoulder is not exposed? DG

 

[butchlambert]

Need more info. Is it a glue in?

 

[double g]

not glue in

 

[Eddie Harren]

OK. I'll bite. Why is the barrel shoulder not exposed?

 

[Erik Cortina]

Are you trying to measure headspace on action or barrel?

I'm with Eddie, why is the shoulder not exposed?

 

[effendude]

I believe the MB has a longer body/tenon and the threads are inside the action about an inch. The last inch of the action doesn't have threads. That said, thinking as I am typing which usually gets me into trouble, the barrel still must have a shoulder to torque against the built in recoil lug. Should really be no different than a standard action in regards to setting headspace.

Scott

 

[double g]

Effendude is correct

 

[dbramley]

I found this thread because I have the same question. The MB action has a .935, if I remember correctly, "sleeve" forward of the shoulder where the shoulder of the barrel tennon contacts the action. A lot of people use a feeler gauge on the space between the shoulder and action, with headspace gauge in place, to approximate the depth required to chamber. Once this space becomes 10 thou or less most people cut to feel of bolt closure. The sleeve forward to this shoulder is there to provide more bedding surface and support for long heavy barrels. Due to the sleeve this space typically used for measuring is not accessible. My plan is the thread the barrel and indicate it (high side pointing up). Once that is done and while action is screwed onto barrel I am going to put a "collar" around the barrel and tighten it up when it is against the sleeve. This should give you a place to measure from, at least to get you close.

I would be interested to hear if anyone has any other suggestions.

Dan

 

[Erik Cortina]

Headspace is the distance from the shoulder to the bolt face.
Subtract (end of sleeve to shoulder distance) from (end of sleeve to bolt face distance) and that is your headspace.

Just re-read original question.
After you have headspace, subtract .001" for thread crush and that is your measurement from back of headspace gauge barrel shoulder. Use depth gauge for this.

It's quite simple guys.

 

[dbramley]

.935 from shoulder to front of sleeve

 

[Eddie Harren]

Same situation as on the Stolle "Teddy" and "Polar" actions. Measuring and Math, what a concept.

 

[Scott Harris]

If it's just headspace measurement, then that is simple math as mentioned above. But some of you may also be using feeler gauges between the shoulder and action face to determine how much further to push the chamber reamer. Obviously that technique will not work with this action because of the shroud. Here is one alternative technique (assuming you've already fitted the action to the barrel):

1. Use a Lambert reamer stop and set it initially well short of final depth (.050" to .100"). Cut until the reamer stop is hit.
2. Thread the action on and index it at 12 O'Clock on the lathe. Put a GO gauge in and attempt to close the bolt. Now, back the action off the barrel until the bolt closes. Measure exactly how many full & fractional revolutions the action was backed out when the bolt closes. Translate action revolutions into thousandths. For example, if you had to back the action off one and a half revolutions(1.5) on a 16TPI thread, then you are 1.5x1/16 =.094 short of final chambering depth. Now you know how much further you have to go with your reamer.
3. Using the example above, I would advance the reamer stop .080, and then repeat step 2.
4. Once I get below .010" or so, I only advance the reamer stop .004 or less(some number smaller than or equal to the distance between the GO and NO-GO gauge). This way you will never push the reamer past the NO-GO

Hope that helps someone.

Regards,
Scott

PS. You can use this technique without a reamer stop, but it's a lot easier with one.

 

[Erik Cortina]

Scotharr, the issue with that method is that you can not chamber two barrels to identical headspace.

All you need to do is use the headspace gauge and a depth micrometer.

Let's say headspace is .981"
Deduct .001" for thread crush.
Target distance from back of to gauge to barrel shoulder. .980"

Ream a partial chamber, clean out and insert to gauge. Measure from back of go gauge to the barrel shoulder. If the measurement is 1.010" then you have .030" to go for headspace. Ream another .020" and check again. Distance from back of headspace gauge to shoulder should now be .990", which means now you have .010" to go. Do this until the distance from back of to gauge to barrel shoulder is .980".

Not only is this easier, it also allows to chamber multiple barrels to the exact same headspace.

After you ream to target number, check by putting action on barrel, tighten it, and insert to gauge. Bolt will drop on to gauge. Insert no go, and bolt will not close on it.

Measuring and math is my preferred way as it offers much better repeatability than feel.

 

[Scott Harris]

I use shim-stock to precisely set the final headspace with the GO-Gauge

 

[dbramley]

Thank you scotharr, the "constructive" advice is appreciated by myself and I am sure the OP.

 

[Dusty Stevens]

1.074"
a measurement that pops up quite often on bat actions when dealing with headspace.