The meaning of "crush"

[ridgeway]

I hear "crush" referred to alot in reference to chambering. The 3 thou crush to one guy may mean something else to another. Just trying to figure out the true meaning.

So the 3 thou crush is crushing brass HS .003?

So for example I want to chamber a 6 AI for .003 crush. A BAT zero heaspace is 1.074 on go gauge. Now for that .003 crush...my HS on go should be 1.071?

 

[swd]

So the 3 thou crush is crushing brass HS .003?

So for example I want to chamber a 6 AI for .003 crush. A BAT zero heaspace is 1.074 on go gauge. Now for that .003 crush...my HS on go should be 1.071?

Yep you've got it. This is generally used in reference to form Ackley type cases but also a few others.
On The first fire form the case is only being "crushed" right at the neck shoulder junction because of the difference between the shallow shoulder angle and the steeper chamber angle. This pushes the case head hard against the bolt face so it can blow the shoulder forward without stretching the case web.

 

[Alex Wheeler]

I chamber to 1.078 on a BR go gauge for the 6bra on a Bat. .004" crush is standard practice for Ackleys.

 

[Shawnba67]

I thought i had once heard "crush" in reference to the reduction of headspace after final torque. Say you chamber until the no go guage almost closes on a hand tight barrel,then when you torque it it "crushs" .002 or so to be near perfect headspace. I never really understood the term used this way but Ive read it a couple of times

 

[ridgeway]

Thanks for the info...

 

[geraldgee]

I thought i had once heard "crush" in reference to the reduction of headspace after final torque. Say you chamber until the no go guage almost closes on a hand tight barrel,then when you torque it it "crushs" .002 or so to be near perfect headspace. I never really understood the term used this way but Ive read it a couple of times

Am I correct in thinking that to pick up .002” as described above, one would have to turn the barrel An additional 20+ degrees past full thread engagement ?

At what point in the tightening process would the threads begin to distort? While I may not have my terms right, I thought the shoulder on the barrel determined chamber headspace - that the action would come to a dead stop on the shoulder of the barrel. Would additional torque create a bind between the barrel and the action?

Just trying to understand - thank you

 

[tclaunch]

I hear "crush" referred to alot in reference to chambering. The 3 thou crush to one guy may mean something else to another. Just trying to figure out the true meaning.

So the 3 thou crush is crushing brass HS .003?

So for example I want to chamber a 6 AI for .003 crush. A BAT zero heaspace is 1.074 on go gauge. Now for that .003 crush...my HS on go should be 1.071?

rigeway, shortening the distance is going the wrong way. I use 1/2 thousands "crush" and chamber to 1.0745" I just want a light feel of the case in the chamber, not a lug galling hard push.

Edit to say .003" is not "wrong" we all have different ways to get the same thing done.

 

[ridgeway]

I go by numbers and a depth micrometer with custom actions. All my BAT Chambers, I goto 1.077 on my go gauge. If you want to crush brass, wouldn't the chamber need to be shorter?

 

[JRS]

Wouldn't the correct go-gauge be easier?

 

[tclaunch]

I go by numbers and a depth micrometer with custom actions. All my BAT Chambers, I goto 1.077 on my go gauge. If you want to crush brass, wouldn't the chamber need to be shorter?

Lower numbers on the depth Mic, is longer chamber. Crush is adding to the 1.074"

 

[ridgeway]

Sorry for the confusion. I am referring to the HS length. I use a collar and depth mic to determine the length on go gauge. So the smaller the number on my depth mic does make a shorter chamber.

Bottom line I guess regardless how one gets there...the brass should be tight against the chamber shoulder for the "crush"

 

[alinwa]

I hear "crush" referred to alot in reference to chambering. The 3 thou crush to one guy may mean something else to another. Just trying to figure out the true meaning.

So the 3 thou crush is crushing brass HS .003?

So for example I want to chamber a 6 AI for .003 crush. A BAT zero heaspace is 1.074 on go gauge. Now for that .003 crush...my HS on go should be 1.071?

ridgeway (wordman?)..... if hanging around forums (or anywhere 3 or 4 men gather together) teaches anything it's that "true meaning" is a slippery fish!! Folks go to their respective graves fighting over "true meaning" and rarely hear each other.

here's how I treat this situation.

First of all it helps to know WHY the 'crush' ........ and the answer is "to make good, consistent, tractable cases" which, coupled with fit is the true secret to consistent accuracy. (Many aren't aware that this is WHY) If you don't care about case life and aren't going for .250 accuracy then just chamber willy-nilly and make the chambers good enough to fire the case the first time and live blissfully, happily enjoying life's rainbows.

So then HOW??? is this accomplished? What does 'crush' accomplish? It keeps the case from moving forward under the impact of the firing pin. This IS the absolute solution to the case-making conundrum.

"Seating long" and greasing cases are cheesehole ways of trying to "fix" and over-long chamber situation. They produce usable, even winning cases but they will NEVER agg with good cases. Nor will they withstand the scrutiny of inspection for runout.

So, to answer your question, I use crush figures from .002 to .014 to accomplish my goal of HOLDING THE CASE BACK under 35lb of pressure.

Pick up a cinder block or a small anvil.....or, if you're standing in the kitchen making cawffee reach over and unplug the microwave..... and pick it up and balance it on your palm like a waiter carrying a Large Pizza or a platter of plates.

Bounce it around a liddle..... feel that weight on your palm.



This WEIGHT, this RESISTANCE is what you're going for.


Now go chamber your rifles such that you have to seriously PALM the bolt closed, almost bruising your palm, and you will get results that will bring a smile ...... birdies will sing and unicorns will dance and you will have to concentrate on the task at hand to remember to GREASE YOUR BOLT LUGS!!!

enjoi

al

 

[alinwa]

ooops..... I typed over you.

Looks like you already get it.

 

[eddief]

If you are doing this for customers, then get the correct gauge for your AI from the reamer maker. That gauge will hold up in court if ever needed, a lot better than your Mic will.

If your not doing this to pay your bills, then have at it any number of ways.

 

[Northridge]

Even though we use the term "crush fit" it may reference the extreme. more of a lightly compressed case hold than a crushing fit..

Shawn Williams