Sticky bolt lift not due to pressure

[js2013]

At http://www.6mmar.com/6XC_II.php I read that sticky bolt lift (in this instance) was due to using Norma brass in a tight chamber.

Due to a tighter chamber I would expect pressure to go up a little but not a huge amount, and the sticky bolt after firing would be caused mainly by the lack of clearance in the chamber and possibly brass on the soft side. Would you agree?

 

[SheepDog]

Your logic has a flaw. A small chamber won't make sticky extraction. If the case chambers without effort, and the pressures are within the guns tolerance, the case should extract easily. The brass case will not expand more than the chamber allows and it will spring back to a size smaller than the chamber unless there is enough pressure to expand the chamber beyond the brass's ability to rebound. The only thing that causes that condition is more pressure than your gun will tolerate.
Dirty, "ballooned" or rough chambers can cause sticky extraction but you can see these effects on the brass. Tapered chambers are rarely "ballooned".
There are occasions when a brass cartridge has been over annealed where it can lose the ability to spring back but it would be a case of bad brass or improper annealing by the reloader.

 

[js2013]

A small chamber won't make sticky extraction. If the case chambers without effort, and the pressures are within the guns tolerance, the case should extract easily. The brass case will not expand more than the chamber allows and it will spring back to a size smaller than the chamber unless there is enough pressure to expand the chamber beyond the brass's ability to rebound

Yeah that's what I used to think also. But the person who wrote the article seems to know his stuff, add that with some folks saying Norma brass can be soft, and I think the article makes a valid point. We'll see if anyone else chimes in.

 

[SheepDog]

The physical metallurgy of brass hasn't changed and cartridge brass still can't expand more than the steel chamber it is fired in. I think the guy wants to sell his reamers or services is more likely the reason behind the "problem".
If you follow the money you can usually get the answers.

 

[BoydAllen]

Back in the day, a friend had a rifle that had a Remington 6BR chamber. He wanted to change to Lapua brass, and at first he had his smith polish out the back of the chamber so that it would accept the Lapua brass's slightly larger head diameter. (Of course he had to do a lot of trimming because of the difference in neck length.) The fit on loaded rounds was close at the back, but there was no problem chambering them. The result of this was that he would get a sticky bolt with no other pressure signs, using mid book loads. After that his smith bought a reamer that was designed for Lapua brass, including the longer neck, that had more clearance at the back of the chamber. This allowed him to load to significantly faster velocities without getting a sticky bolt, and when he did, there were other pressure signs as well.
When a round fires, at peak pressure, both the case and the surrounding chamber expand. The chamber snaps back all the way, but the brass does not quite get there, which is why we get tightness at the base of the case after several firings unless a FL or body die is used. (assuming stout loads) With too little clearance, this can happen on the first firing.

6PPC shooters have learned this when they mistakenly thought that less clearance is always better, and ordered chamber reamers with too little clearance at the back of the chamber, getting into bolt click problems that they had not had with the same loads in slightly larger chambers.

Jump forward a few years from my friend's 6BR experience to a project that a friend got me involved in. A meticulous reloader, he wanted a German Weatherby rebarreled with a short throat, tight neck chamber in .300 WM. We spec'd a reamer that allowed 180 gr. hunting bullets, to touch the rifling when loaded to magazine length. Without load data, we were forced to drop way down and work up to find out where we were with pressure. We did that, loading at the range, neck sizing to see how fast things tightened up and where. We stopped the test after the belt expanded the second time (The first time was on the initial firing with a bottom book load and no pressure signs). There was an ejector mark on the head of the case, and the primer showed pressure as well. We had gotten to a charge weight that was well above the top book load for a regular Weatherby chamber (that would have had considerable free bore).

Having learned from my friend's 6BR I used stock Weatherby body diameters at the belt, above it, and at the shoulder. After that last firing (we had used a single case for all of them) after letting the brass return to ambient temperature, I chambered the fired case, and it was not tight. It had only been neck sized. Draw you own conclusions.

 

[SheepDog]

I think you cleared it up very nicely; "...after letting the brass return to ambient temperature, I chambered the fired case, and it was not tight. It had only been neck sized."

 

[dkhunt14]

You are correct Boyd. The guys that tightened up their reamers to try and keep the pockets tight all ran into this. Brass grows more on the first firing or two then slows down in growth after that. If you don't let enough clearance built in you will fight bolt click and hard extraction. Matt

 

[dkhunt14]

I think you cleared it up very nicely; "...after letting the brass return to ambient temperature, I chambered the fired case, and it was not tight. It had only been neck sized."

What Boyd is saying is the Stock Weatherby dimensions were bigger and that is what he based the new reamer on. There was room for the case to grow. Just ask anybody that tightened up their reamer dimensions. They will tell you. The same problem exists if you try to shoot Lapua brass in a 6BR Rem chamber. It will get tight after a firing or two. Matt

 

[SheepDog]

What Boyd is saying is the Stock Weatherby dimensions were bigger and that is what he based the new reamer on. There was room for the case to grow. Just ask anybody that tightened up their reamer dimensions. They will tell you. The same problem exists if you try to shoot Lapua brass in a 6BR Rem chamber. It will get tight after a firing or two. Matt

What you're saying is that you have brass that can expand beyond the chamber size. That it fits well before firing and is larger than the chamber after firing. That tells me that the pressures are high and allowing a steel chamber to expand more than the brass case can spring back from. Either the brass is too soft or the pressures are too high.

 

[dkhunt14]

What you're saying is that you have brass that can expand beyond the chamber size. That it fits well before firing and is larger than the chamber after firing. That tells me that the pressures are high and allowing a steel chamber to expand more than the brass case can spring back from. Either the brass is too soft or the pressures are too high.

I am saying if you tighten up the reamer and shoot it once or twice it will get tight. Match shooters have ran into this. I know shooters that have polished out the back of the chambers to help solve this.

As a good example one gunsmith ordered a reamer. It was a 300 WSM. The .200 line was .554. Everybody had trouble ejecting brass and couldn't shoot max loads. I ordered another reamer exactly the same throat and went .555 on the 200 line. I had him run the reamer in the same 2 guns that I had problems with and now the problem is gone. Everybody with the new reamer had no trouble and everybody with the old reamer had trouble. A mere .001 on the back end created the trouble. Matt

 

[BoydAllen]

This happens with loads that do not exhibit any signs of excess pressure. Most will never experience the problem because most do not spec out reamers, and most standard reamers, even those for target applications are not close enough to the dimension of unfired brass to cause the problem to occur. That I why I gave specific, real world examples that I have direct personal knowledge of, including all of the relevant details. This sort of information does not grow on trees. I grow weary of conjecture that thinks that it trumps carefully observed experience.

 

[SheepDog]

OK, explain to me how the brass can expand to a point where it causes hard extraction if the pressure is not high enough to deform the camber more than the brass can recover from.
The chamber is what controls the amount that the case expands - it doesn't expand a given amount regardless of chamber size, it just expands to the confines of the chamber and then contracts when the pressure is reduced.

You are blaming the chamber for a pressure effect.

 

[dkhunt14]

OK, explain to me how the brass can expand to a point where it causes hard extraction if the pressure is not high enough to deform the camber more than the brass can recover from.
The chamber is what controls the amount that the case expands - it doesn't expand a given amount regardless of chamber size, it just expands to the confines of the chamber and then contracts when the pressure is reduced.

You are blaming the chamber for a pressure effect.

Brass expands more on the first couple of firings. Then it slows down and the die can manage it. Sometimes if you get a custom tighter die it will take care of it. But if clearances are real tight, a die won't take it back to new brass size. It all happens because there is not enough room for the brass to grow and rebound. The factory chambers are bigger then the dies. The dies manage to bring the brass back. Even if you neck size the brass grows bigger with each firing. Measure your brass and you will see this. It does slow down after the first couple of firings. Matt

 

[BoydAllen]

Your visualization is faulty. With ordinary clearances and pressures within safe operating limits both the chamber and brass expand at peak pressure, but the brass does not snap back all the way to its un-fired dimension. It ends up larger than it was before firing, and every time that it is fired without being body or FL sized it ends up just a bit larger, until it reaches the point where it is tight in the chamber. On that firing it and the chamber stretch as usual but because of the close starting clearance, the brass does not snap back to a dimension that is less than that of the chamber. If you start out with just enough clearance so that the loaded round can chamber, but not a bit more, you can reduce the number of shots that it takes for this to happen to one or two. It is not surprising that you have not run into this. Most chambers are not close enough to the size of unfired brass to have this problem. I would say that such chambers are rare. That is the reason that I gave the examples that I did, so that readers might learn about something that they might not have seen, and so that they can avoid making a specific mistake when designing a custom reamer.

 

[dkhunt14]

Sheepdog, maybe you can call Dave Kiff or JGS and ask them want happens if you tighten up a reamer on the back end. I am sure they know and will tell you. Matt

 

[swd]

OK, explain to me how the brass can expand to a point where it causes hard extraction if the pressure is not high enough to deform the camber more than the brass can recover from.
The chamber is what controls the amount that the case expands - it doesn't expand a given amount regardless of chamber size, it just expands to the confines of the chamber and then contracts when the pressure is reduced.

You are blaming the chamber for a pressure effect.

Because brass is softer and will stay in more expanded state than the steel barrel. Trust what everyone is telling you. It has been a know phenomenon for quite a while. An extra .001/.0015 in the right place, the .200" line, will go from a sticky clicky bolt to one that extracts perfectly.

 

[butchlambert]

Norma brass is soft? Chuckle chuckle, Mentioned above I think, a tight chamber and fat dies do not go hand in hand. I don't have that problem because I spec a die reamer .003 at the web and .002 at the shoulder tighter than my chamber reamer.
You can't size a small piece of brass with a fat die.

 

[Judd]

These guys have obviously never owned a 6brx ...if I don't full length size that brass after 2 firings I'm dealing with bolt click...if I full length size I rarely will have a piece of brass that causes bolt click. It's the size of the brass in front of the case head.

Listen to dkhunt, Butch and Boyd...they know exactly what they speak of.

 

[Albany Mountain]

I had noticeable hard lift on a 308 Win. I asked a decent gunsmith (Randy Gregory) who does his own barrel making and he advised to go to a small base die. His reasoning was that every chamber needs some clearance for expansion and shrinkage before extraction and I was probably shooting a tight chamber. The small base die solved the problem for this barrel.

Small chambers, can they be caused by worn reamers???

 

[mikecr]

I found the opposite as many, but with qualifiers.
I built a 6.5wssm Imp with a chamber of my own that I fitted to new brass. That is, no more than 1thou total clearance, at any dimension, over new brass. I then ran pressure testing to find MyMax load(which is a point of needing FL sizing, I don't FL size). I was able to run pressures way beyond SAAMI max before hitting the beginning of body sizing requirement. I had hit MyMax at ~3290fps.
My accuracy node, which is within the 26cal mid node, is 3025fps with 139Laps. By QL this is 65Kpsi(right at SAAMI max).
With this & 35+ reloads later, I still have no need to size the bodies at all (and never have).

I know others had tried the 6.5wssm without success, but a difference I notice is that they did not run a magnum diameter action/tenon. So they did not have enough barrel steel around the chamber. Some did not run with a coned breech, which extends threading to better support breech expansion. Nearly all used high clearances at the web area..

If your clearances and pressure cause the brass to yield, it will, and it will not spring back with prior recovery.
Mitigate yielding all together, and the brass will spring back recover, full amount, --> forever.
Where it appears this doesn't work, there is something here they missed in their design.

Notions here in the shooting mob remind me of past shade tree/hot rod mechanics, swearing that where things break you need even more clearances.. Eventually I (and pretty much everyone else) learned (from Smokey Yunick) that this was never true, there was never credible basis in it, and in fact the truth was just opposite.
Now modern engines, including the highest performance among them, run tighter clearances than ever.