Action Strength

Donald,

Chrome Moly action

3 lug action....hint hint

I have a S/S 2 lug action of the same brand and it wont handle the pressures I can get out of my Panda...I always thought the reason was because of the smaller surface area of the lugs that would be causing the problems but it shouldn't on a 3 lug.

Steve
 
It´s not a 3lug.

I have a 2lug SV action, that handles 31grs or so without any noticable stiff bolt lift. But, I know of a shooter who have a exact copy of mine, who have problems.

The strange thing is that this doesn´t seem to be that unusual problem...
 
P.Ericson,

The reference to 3 lug was a hint to the brand, sorry for the confusion...I accidently shot my Panda powder load in my Bat one day and had to trash my cases and the load was only 30.5gns....probably not the same brand of powder you are using but the Panda has been using the same cases for 12 months or more.

Steve
 
Steve Nash said:
Donald,

Chrome Moly action

3 lug action....hint hint

I have a S/S 2 lug action of the same brand and it wont handle the pressures I can get out of my Panda...I always thought the reason was because of the smaller surface area of the lugs that would be causing the problems but it shouldn't on a 3 lug.

Steve
Click to expand...
Steve I'm certain Jackie wrote in an earlier thread that this is a CM 2-lug. You are right on the make. However, the 3-lug actions do by design have less mechanical advantage.

IMO, in this part of the rifle accuracy quest we are in a very fine balance between what we need, for accuracy, and what we want. The 3-lug is one of those items. In this case we want a fast throw, but we want a short throw. We want to use excessively high pressure loads, but we don't want to disturb the bags...and so on.
 
Jerry

Gene Bukys has a 3-lug Bat that he shoots "upper load window" loads in with no problems at all. It's the one that he won the World Championships with. ............jackie
 
Some findings

Early research has found two items of concern so far. The surface area of the locking lugs on a Panda have 42.5% more surface area than "said" action. This increase in surface area is also in the way of taller lugs (.145" vs .090") which will not shear the bolt lube away nearly as bad as a shorter lug. Less lug area also contributes to micro-galling of the lug surfaces due to greater load per square inch of lug surface area. The shorter lugs also build surface area more slowly than a taller lug when the bolt is rotated.

Another finding (if I'm not mistaken) was a thread relief in front of the locking lugs. Since the lugs on said action only measured .9" across, this relief diameter of aprox. 1.065" would mean that the receiver ring could have had .07" greater thickness per side for less front receiver ring deflection.

I do not have one of these actions in hand, so I make it clear that I could be wrong about some of these dimensions and findings. I have only had phone conversations with owners of these actions.

My final concern would be that I rarely proof read what I type. In my earlier post I spelled modulus (modules) please excuse my typing. I won't proof read this posting either.

Michael
 
mturner said:
........... would mean that the receiver ring could have had .07" greater thickness per side for less front receiver ring deflection.



Michael
Click to expand...

Michael,

At the risk of deflecting this (good :) ) thread I've got a question.

Just a knee-jerk opinion will suffice.

When one considers the "bolt thrust" unloading effect on the threads, and the necessary clearances, just how effective is the receiver ring at receiving/containing/resisting expansion? And do you think that tightness of the barrel has a marked effect on this? I am NOT referring to thread fit but to tightness imparted by the barrel wrench. Regarding thread fit or clearance my reaction is that .001 or .005 or .010 is all same-same re containment.... it's screw-on torque that I'm talking about.

I will say this, it is my opinion that TIGHT, like 125ftlb or more, torque on a barrel should preload the threads for better transfer of expansion loading to the rec ring.....

thoughts?

al
 
Al

You are correct in your thinking. Threads are supposed to be preloaded, just like a spring. High performance engines are assembled by tightening the rod bolts using a stretch guage. This is far more accurate than a torque wrench since it actually measures bolt stretch.

The shoulder that seates against the front of the receiver ring also squares up the barrel for proper point of aim. If the thrust on the barrel becomes greater than the preload stretch of the barrel threads in the receiver ring, not only can it cause hard bolt lift, but it can also cause point of aim change if the shoulder of the barrel and the receiver ring gap under pressure. This is why a BR barrel not tightened enough can cause poor groups.

Keep that torque to a minimum of 100 ft. lbs in my opinion, and use a good lube to keep the friction from preventing proper thread preloads.

Michael
 
I khow that P.Ericson is using VV N133, he has shot different LOT# of this powder. I have tried his gun and the bolt lift is very smooth and soft even with these high loads.
 
mturner said:
You are correct in your thinking. Threads are supposed to be preloaded, just like a spring. High performance engines are assembled by tightening the rod bolts using a stretch guage. This is far more accurate than a torque wrench since it actually measures bolt stretch.

The shoulder that seates against the front of the receiver ring also squares up the barrel for proper point of aim. If the thrust on the barrel becomes greater than the preload stretch of the barrel threads in the receiver ring, not only can it cause hard bolt lift, but it can also cause point of aim change if the shoulder of the barrel and the receiver ring gap under pressure. This is why a BR barrel not tightened enough can cause poor groups.

Keep that torque to a minimum of 100 ft. lbs in my opinion, and use a good lube to keep the friction from preventing proper thread preloads.

Michael
Click to expand...

Michael,

while I agree with all this, I must have been unclear. This isn't the thrust of my question.

When a barrel is properly seated, let's say with 100-125ftlb torque and properly lubricated threads...... Does it follow that this setup will show less radial expansion or deflection?

In simple terms, will the chamber expand less? Is there a difference between tight and loose barrels re expansion of the chamber? (Given similar tenon diameter.)

al
 
Jerry, I agree, but... The 3 lug does offer something that no 2 lug does and that is safety buy virtue of it's full diameter bolt body. This seems to effectively seal off the chamber area from the shooter. Safety is paramount, IMO. So is performance and there are a number of shooters that seem to be doing quite well with the 3 lugs.. Lots of fish to fry------
 
When Gene Beggs was doing his indexing experiments with an undersized tenon and an intermediate threaded bushing that was adjustable, to allow barrel index changes, he ran into bolt tightness issues at lower load pressures than were normal with the same action and a tenon that was of standard diameter. Since I believe that Gene would tighten both in a similar fashion, this would lead one to the conclusion that as far as radial expansion of the chamber goes, the tenon itself is the determining factor.
 
Al

Yes, there will be less overall expansion from the bolt face to the end of the chamber if the threads are properly preloaded. I hope I have answered your question better this time.

At the same time, I'm positive that thread preloading is not an issue with Jackie's action. I remember over a year ago that Jackie resolved a problem with another guys BR rifle that was not grouping to satisfaction. Jackie found the barrel was not properly torqued.

Michael
 
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mturner said:
You are correct in your thinking. Threads are supposed to be preloaded, just like a spring. High performance engines are assembled by tightening the rod bolts using a stretch guage. This is far more accurate than a torque wrench since it actually measures bolt stretch.

Michael
Click to expand...

Michael,
Just 1 small correction. A few of the prostock teams are using torque angle on there steel rods vs a stretch gage;)

This is just a hunch on my part. I'm not a custom rifle builder. I wouldn't be surprized that Jackies problem isn't alignment with the bolt fit in the receiver.
 
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Doug

I talked to Cecil Tucker, and he said he fixed the very same problem I am having with the exact action.

The one they had experienced a tight bolt lift, plus it tended to spit shots. What they did was, using a progressive courser lapping compound, (from the finest to about 300 grit), and literally lapped the entire bolt in the raceway so that they achieved some clearance. As you know, these actions are noted for close bolt body to action fit. He said it cured the problem.

He summised that maybe the bolt was simply too tight, and upon firing, the who thing just sort of binds up.

Well, I came in early this morning, and did the same thing. I spent the better part of two hours working on it, and I now have about .001 more bolt to action clearance than before.

I either ruined this thing, or cured it. I hope to get to the range tommorrow and see........jackie
 
Walt Berger and Dennis Thornberry

Both these guys have the chrome moly 2 lug Bat action. Don't know if they load upper window loads. You might ask them if they are having your situation with action operation.

Stephen Perry
Angeles BR
 
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