The "click" ????
- Thread starter tiny68
- Start date
So Jim.
A sandpaper finish will let the brass, grab the chamber walls, on expansion. Less force on the bolt.
This would create less stretch of the brass.
I was looking at a polished chamber would ease brass extraction. But, that would increase stretch/expansion. Okay I get it.
Now about a die. I polished a couple of dies. The dies had picked up some brass dust. And was scratching the brass. 9mm and .40 S&W. Yea I know. We only talk about 6ppc here.
Anyway after polishing. The die stopped the dust collection. And the brass extracts from the die easier.
I like to shoot bowling pins, also.
A sandpaper finish will let the brass, grab the chamber walls, on expansion. Less force on the bolt.
This would create less stretch of the brass.
I was looking at a polished chamber would ease brass extraction. But, that would increase stretch/expansion. Okay I get it.
Now about a die. I polished a couple of dies. The dies had picked up some brass dust. And was scratching the brass. 9mm and .40 S&W. Yea I know. We only talk about 6ppc here.
Anyway after polishing. The die stopped the dust collection. And the brass extracts from the die easier.
I like to shoot bowling pins, also.
I'm not Jim, maybe he will answer you. Jim's a lot smarter than me.
BUT...... I can't quite agree with your scenario.
Here's how I see it:
OPINION ALERT!!!!
First of all, IMO the "click" we're referring to here has little to do with "bolt thrust." "The Click" refers to a condition where the bolt lifts EASILY and only "clicks" at the top of the stroke, when the primary extraction ramp is encountered.
Now as to other extraction bugbears, the various conditions which cause difficulty of primary extraction, I see several disparate conditions.
-The Firing Cycle is as follows:
The firing pin drives the case forward with 20-30lb of force, it is stopped by either the shoulder of the chamber or possibly the extractor hook. It is NOT stopped by a deep-seated bullet.
The case stays there (IMO).....this is KEY, or at least key to my argument
.--- MY contention is that the body of the case stays there REGARDLESS of whether the chamber is polished or not, provided said chamber is dry.
---Others contend that a polished chamber allows the brass to slide back some.
Now, we're dealing with several separate phenomena regarding the various difficulties of primary extraction........ The "click" as described in the OP being only one of them.
#1--IMO the FIRST one, the one referred to in the OP is click caused by a too small chamber. This click is the result of the head of the case expanding radially (getting fatter) until it hangs up in the chamber. ALSO IMO, this casehead expansion is primarily the result of gas being metered into the primer cup which hydraulically expands the casehead, this is why cases with small flashhole/small primer will "take more pressure." Compare achievable velocity/pressure of the Lapua .243Win case VS the new 6.5X47L case to see this in action. IMO the answer here is to make your chamber larger at the butt. Also IMO polishing or not has no effect on this. In identifying this click it's important to note the absence of drag on the bolt during the upstroke.
#2--Second is radial expansion of the chamber. A large case like the .300WSM case coupled with a small tenon will allow a chamber to expand radially, to swell like a balloon momentarily, and then to collapse back after the firing event which traps the case. Case springback is often described as being "around .001" which is essentially true. Your chamber neck diameter is normally right at .001 larger than your fired brass neck diameter. But does the BODY also exhibit .001 springback? All I know is that in some cases it's possible to make a situation where chamber stretch exceeds springback of the brass. I don't know whether or not polishing a chamber could have an effect on this. (It "should", IF polishing actually makes the chamber "more slippery.") This extraction problem MAY or may NOT be accompanied by drag on the upstroke.
#3--Third is longitudinal stretch. This effect is the one most commonly associated with "bolt thrust." In the case of a front locking lug bolt action rifle longitudinal stretch of the action is primarily limited by locking lug abutment support and tightness of the barrel threaded joint. This support is a subject in itself! But support aside, it is certain that a lubricated chamber WILL increase boltface loading or "bolt thrust." I qualify this by saying that in a "zero headspace condition" boltface load must nearly approximate the load generated by a greased case EXCEPT FOR the inertial ramming effect generated by the moving case. Conversely, in a dry chamber it's entirely possible to shoot loads which produce a nearly zero load on the boltface. ZERO longitudinal stretch, ZERO bolt thrust. In chambers which exhibit some headspace "normal" loads, those which approximate factory or Mil-spec loads, will commonly show a "popped up primer" indicating that the case stayed forward and only the primer came back to the bolt face.
Parker Ackley DID FIRE a 30-30Win Ackley Improved in a lever action rifle, Win94 with the locking abutment removed. He simply cammed it shut and fired it to show that bolt thrust was nearly zero. In this case Mr Ackley counted on the headspace and the effect of the case gripping the chamber walls to counter rearward thrust. Also important is that the load be such (40,000-45,000psi???) that the brass case itself is strong enough to contain the pressure without yielding.
In my experiments I used the .243AI chamber, .243 Lapua brass, and a chamber with .006 headspace. I used the popped up primer as my gauge. IN THIS CASE chamber finish had no measurable effect. In my case I could routinely fire a factory .243 round in either the rough or polished chamber and the case would STAY forward, the primer would pop above the surface of the case head.
Bolt thrust, zero.
Now, when pressures build to the point that the brass case is yielding, bolt thrust again becomes a factor, BUT NOT BECAUSE OF SLIPPAGE. In my experience it's the result of the case STRETCHING back to the bolt face. The old "incipient casehead separation" situation. Do it enough times and you'll bust the casehead off.
So, the term "less stretch of the brass" from the quoted post need to be quantified. "Stretch" of the brass can mean two things.....in a near zero headspace condition "stretch" might just mean the effect of the brass vessel expanding along with the chamber and bouncing back, whereas true "stretch" would indicate that the brass yielded and stretched back to the boltface with NO longitudinal springback. OR, that even with zero headspace the load was indeed so hot that it stretched the entire chamber longitudinally, brass and all, so far that the brass could not spring back far enough to "let go."
True longitudinal stretching of the brass case will nearly always include drag on the upstroke.
Some cases like the unmodified 22-250 case will show an added effect I call the "Morse Taper Effect." In this situation the chamber expands both radially and longitudinally and upon collapse the case is found to be wedged into the chamber like a Morse tapered chuck shank. "Improving" the 22-250 case by giving it more parallel sidewalls will eliminate the "Morse Taper Effect." In this case you will get drag on the upstroke and a very solidly jammed case, the old "hammer the bolt handle open" problem.
It is my opinion that with a properly sized barrel shank, a properly tightened barrel, a properly supported action and NEAR ZERO HEADSPACE one can run well beyond the yield point of the brass case, 20-30,000psi beyond it, and still expect clean extraction. It is also my opinion that the finish of the chamber does not affect this.
It is further my opinion that when firing rifles WITH HEADSPACE, like factory rifles or poorly fitted custom jobs, at pressures which exceed the yield point of the brass case, the body of the case stays forward while the head of the case stretches back to the boltface. Regardless of chamber finish.
UNLESS the chamber is lubricated, in which case all bets are OFF because the case will slide. IMO lubricating cases is a silly way to fix a problem which shouldn't exist.
As always....... I'm completely open to correction
I'd love to understand this better.opinionsby
al
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PTucker
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Alinwa
I agree with everything you have said except for one thing ---
The firing pin drives the case forward with much more than 20-30 lbs of force
The firing pin spring alone produces about 20 lbs of force. when we accelerate that pin with about 20 lbs of force over about .25 inches of travel we end up with quite a bit more force due to the hammer effect of the pin striking the primer.
If you apply 20 lbs of force using the end of a firing pin, you can’t even indent the primer, you have to hit it with a hammer.
Paul T.
I agree with everything you have said except for one thing ---
The firing pin drives the case forward with much more than 20-30 lbs of force
The firing pin spring alone produces about 20 lbs of force. when we accelerate that pin with about 20 lbs of force over about .25 inches of travel we end up with quite a bit more force due to the hammer effect of the pin striking the primer.
If you apply 20 lbs of force using the end of a firing pin, you can’t even indent the primer, you have to hit it with a hammer.
Paul T.
Well, First off....I don't really know crap about the technical aspects but this is instance. A friend of mine had a Rem 788 (which in my opinion, amplifies the bolt thrust) that he had custom barrels in 7-08. The gun shot very well and extracted easily with the load he was using. One day, he shows up at my range and he has to tap the bolt handle up with a rubber mallet. I said "hold on" of course and looked the case over for signs of excessive pressure. He said that it was the exact same load he was shooting, loaded at the same time. We talk for a while and during the conversation, he gets around to saying he was looking at the chamber and thought it was a little rough so he used some polish and polished the chamber up some. Well, I told him that may be a problem form what I heard and explained why. Well, he said he didn't think so. A couple of months later, he said he was shooting and still had the same problem and one of lugs on the 788 had come off and he sent the action back to remington to get it fixed, which they did. He then decide to rough the chambe like I said and bingo, problem went away.
Just a real story, don't know it worth.
Hovis
Just a real story, don't know it worth.
Hovis
ALINWA:
Except! I will agree with most BUT if we polish a chamber, do we not have more surface area?
I built a Colt in 22 Cotterman Super Jet of which the reamer did an excelent job of finish however I had case setback with that chamber and had to use 80 grit to stop the setback and tying up of the cylinder so the peaks and valleys must provide more "bite" than a polished chamber of more surface area.
I have a Kiff Reamer of Gamboa design for the 308 Palma that is small at the base and I would get the click until I use a SB die to reduce the cases, the reamer was designed for the Winchester cases and the Lapua would click bad until I small based the die.
Clarence
Except! I will agree with most BUT if we polish a chamber, do we not have more surface area?
I built a Colt in 22 Cotterman Super Jet of which the reamer did an excelent job of finish however I had case setback with that chamber and had to use 80 grit to stop the setback and tying up of the cylinder so the peaks and valleys must provide more "bite" than a polished chamber of more surface area.
I have a Kiff Reamer of Gamboa design for the 308 Palma that is small at the base and I would get the click until I use a SB die to reduce the cases, the reamer was designed for the Winchester cases and the Lapua would click bad until I small based the die.
Clarence
I'm not Jim, maybe he will answer you. Jim's a lot smarter than me.
BUT...... I can't quite agree with your scenario.
Alinwa. Thanks.
My point was. We were mixing apples and oranges.
Dies and chambers.
Factory and Custom.
Duane was asking about polishing dies.
BUT! The information is very helpful. From you and Jim. And everyone.
BC is a great tool.
Thank you Hovis.
IME the real problem with the 788 is something I've heard called "bolt compression." I first heard of it in about '95 when I asked Allen Hall to true up a 788 for me. He talked me out of it for that reason. The problm stems from the rear locking lugs.
Regarding the polished chamber, sounds like you're one of several who have experienced cases sliding in a polished chamber.
I'm very curious to hear more.
al
Clarence,
it would seem to me that the opposite is true. A polished chamber has the least surface area.
Now the question becomes one of the true high pressure slippage coefficient. Does the increased pressure/area make up the difference?
more stories please
al
Paul,
I'm a math idiot so I'm never sure how to express firing pin force. I used to tell people to "stand the loaded round on the table and drop a 26lb ROCK on the nose of the bullet!" to show that it takes a lot of steenking neck tension to hold back a case. (From the force generated by the firing pin) But I've since dropped this analogy.
That said, I agree. I've done some firing pin and primer testing and it does take a real smack to dent the cup. A large enough smack that in many older case designs it was enough to reset the shoulder of the case!
al