5 years ago
for the collegiate pistol team I help coach. These are Pardini PGP-
75's, which are bolt action:
To set the "headspace" (gap between the bolt face & chamber), they use a
hardened eccentric bushing at the base of the bolt handle. It rides in
the slot in the action, and rotating the bushing adjusts the headspace.
If the headspace is too large, you get unreliable ignition, and/or
The bushing position is set at the factory, and clamped with the bolt
handle, which screws down on top of the bushing. Both the bolt handle
threads and the bushing are treated with some sort of 30 year old
Italian threadlocker (maybe even epoxy). I've experimented with a
variety of solvents, and acetone & lacquer thinner won't touch it.
Methylene chloride (paint stripper) softens it up, and allows cleaning
off the exposed threads & loose bushings.
On some pistols, the bushing slips & just needs to be repositioned. On
others, the bushing cracks & has to be replaced. Spare parts are very
scarce, and we only have a few extra bushings.
I have one pistol where the bushing is OK, but must have slipped during
installation. It works OK, but the headspace is well past the nominal
upper limit. I got the bolt handle off with a strap wrench, and
expected that the bushing had slipped, but it is firmly stuck.
I've had it soaking in paint stripper for a month now, but I suspect the
gap between the bushing & the bolt stud is too small to allow enough
solvent in to undo the bushing in less than geologic time.
The other approach for dealing with most threadlocker is heat (~ 300F?).
I can make a specialized soldering iron tip that I can slip or clamp
over the bushing to free it. The iron I currently have is temperature
controlled, but at 700F. I could also go & buy a cheap resistive iron
and use it with a variac to control the temperature down at a better
Thank you for anyone who has stuck with me so far. Here's the question:
I would really like to salvage the bushing. What's the best way to get
it off without wrecking the heat treat? It's quite thin (< 0.5mm), and
I will be applying heat on the outside to get through to the inside.
The best options I've come up with are:
1) Use my 700 degree iron, with a tip mounted with a small brass block
with a hole that is a slip fit over the bushing. If I cock the tip at a
slight angle to get good thermal contact, I should be able to pull the
bushing off as soon as the threadlocker lets go, and then the bushing
should fall free from the heat source.
2) By a cheap iron, and make the tip clamp securely onto the bushing.
Then use a variac/dimmer to sneak up on the temperature. I have a set
of Tempilac sticks that I can use to tell when it has reached certain
temperatures. I also have an infrared thermometer, but I don't think it
goes hot enough for this. With this approach, I am unlikely to get the
bushing much hotter than required to melt the threadlocker, but it will
be at that temperature for much longer.
3) Contact Italy and try to get more replacement bushings. That could
take months, and is not a sure thing. One reason I want to salvage this
one is the spares we obtained earlier may have been the dregs. Some of
them are not very eccentric, and many are not a very good fit on the
4) I can certainly continue to leave the bolt soaking in paint stripper.
I have other projects to keep myself busy, and if I can repair all the
other pistols, the pressure will be off. It doesn't seem to affect the
metal, and if I keep it sealed up, I can try to wait it out.
5) Quench after getting it free. Given how hard they are, quenching
presumably wouldn't make it much harder. However, it could become more
brittle, and likely to crack.
6) Make new bushings. I have no idea how involved this would get. I
did a rough hardness test on a cracked one using hardness files, and it
was ~ RC60 (which may be why it cracked...). I don't have any
experience or equipment to do sophisticated heat treating. I'm assuming
that heat treating will probably distort them a bit, and/or mess up the
surface finish enough that a light grind would be in order. I can
certainly rig up a Dremel as a tool post grinder for that. The big
advantage with this is that I can make a bunch. I know of at least one
other college team that has even more dead ones than we do.
Other ideas & comments?