Something strange, can anyone explain?

Charles, if the current Benchmark published data is off it wouldn't explain why light loads show pressure signs, and slightly heavier, i.e., 0.5 and 1.0 gr charges show no pressure signs at all. It's not really a problem now that I see what happens, but I'm glad I was chronographing those loads or I might have stopped at my starting load.

I'm beginning to believe that Hovis may have hit on something with the lower pressures not expanding the cases enough to grip the chamber before they've been jammed back into the bolt face although they've only been jammed back 2 thou. The cases I was using have previously been fired 3 times, but sized in a small base die a couple of times in an attempt to get the previous chamber to "work". That would do more work hardening of the cases than sizing in a normal FL die I'm sure.

I had a Panda in 6 PPC that gave stiff bolt lift at anything much over 28.5 gr of N133 with Fowler 65 gr bullets. That charge produced 3350 fps as I remember, and if I'd tried maybe 29.5 gr I might have gotten up to 3450 fps. Doesn't make any difference now though since it's gone to a new home.
 
Straight wall cases are supposed to stick to side of chamber better on firing, so the
improved wildcatters say. Someone on here with a lighter load and brass combo that has sticky
bolt lift needs to anneal whole top half of a case and try same combo and see of
the sticky lift is lessened. I'd be glad to if I had those calibers and guns..this is something
that is very important for us wildcatters and reloaders to know.Ed
 
The cases I had the problem with were only fired 3 times, so shouldn't have needed annealing.

I may have to load those same loads over and see if the same problem repeats. I'll get that done and report back. Not the exact same cases, but others that have been fired the same number of times from the same lot number of cases.
 
Maybe the cases were a little hard. Maybe cases not annealed down
far enough past the shoulder. Some cases I made wildcats from
had that problem. Maybe cases we are talking about being small and
built strong, a little hardness is stopping the chamber wall grip.
Big cases the hoop stress is much greater to make brass move out.

If annealing case stops problem, IE the case apparently slamming too hard into the bolt;
Then somehow maybe get guys that have noticed the extra spikes on their traces to test same
loads and calibers.They so far can't find a reason.Ed
 
Uh, well guys this is sort of embarrassing, but since I opened my big yapper up here's what I discovered at the range yesterday. I started off shooting a load that had worked well with no signs of excessive pressures, but went from CCI 450's to CCI 400's with 35.0 gr of Accurate 2520 and 55 gr Ballistic Tips. The first four or five rounds gave stiff bolt lift, and I noticed that the first case felt like it had a very light coat of oil on it. Uh, let's try a warm load with a chamber that's not dry shall we. After those first few rounds were fired the chamber had "dried" enough that bolt lift was restored to a normal level and things proceeded well.

So it appears that the problem was one I created myself by not drying the chamber after cleaning the bore. After cleaning the bore with a powder change I ran a bore mop into the chamber to dry it, and no more problems with extraction or bolt lift.

Live and learn, I've been shooting for something like 50 years, and KNOW that a lubed chamber is not a good idea except for fire-forming maybe, but will now be careful to make sure the chamber is dry before I shoot.

Thanks for all the replies.
 
I have always polished my own chambers, because I guess I like nice finishes. I also FL size everything I shoot with
Imperial sizing die wax, which always leaves a somewhat slippery case following paper towels. I get bolt click with
one thing, that is to many clicks on my Jones. The plan that a chamber surface needs to have tooth, meaning slightly
rough is seriously flawed. With a correctly fitted bushing shiny barrels can be installed and removed
with less slipage than a rough barrel.
 
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