Brass vs Aluminium corrosion? PMI Magnum Pump help!

[Stan]

Hi all,

My cousin just gave me a bag with some of his old gear from the 80's including a PMI 68 Magnum pump just like the top gun in this thread
here. Trouble is, it's been sitting i the bag since the mid-80's and it's locked solid.

Problem is, i think that the aluminium bolt has corroded inside the brass body.

The knob in the Red circle moves back and forwards a few millimetres but the main part of the bolt in the Blue Diamond won't budge... Any ideas on hw to free it up? In particular, is there any product i could pour down the barrel that would dissolve any corrosion between the aluminium bolt and brass barrel to help loosen it up before smacking it with a hammer?

Many thanks in advance.

Stan

 

[Gee Tee]

It could also be the ball detents in bolt (green star) that have siezed. Try standing it in a bucket with some derv/parrafin mix for a few days - make sure you pour some down the barrel. I've also used plusgas and 3 in 1 penetrant - work better than WD40 but needs to soak in well.

http://www.rolfesdiy.co.uk/productDetail.asp?PID=26575&categoryID=2537

http://www.freewayuk.co.uk/product/2118/802-10-plusgas-aerosol-400ml

 

[Canon Fodder]

Probably the balls in the star like Gee Tee says, it's just a hole through the bolt with a spring in the middle to "lock" the bolt forward and prevent blow back, when you eventually get the bolt out watch them for flying away (personal experience). If soaking it in something doesn't work try tapping them with a hammer on each side, the only thing that could really rust in there is the spring between the balls or possibly the balls themselves.

Don't worry to much if you end up lossing the balls, it'll work without them, you'll just have to keep your hand on the pump handle when you fire. A lot of people take them out on purpose since it makes the pump stroke much smoother.

 

[Stan]

Thanks both. I've tried soaking in hot sopay water originally incase it was just the usual paint residue and dirt clogging it up. That didn't work.
Tried soaking in various oils inc WD40, etc over night and that didn't work.
The ball bearings are free and moving so that's not the issue.

I'm getting more and more convinced that the surface of the aluminium bolt has corroded making it effectively swell inside the brass tube.

Smacking a wooden dowel down the barrel with a hammer has zero effect!

Starting to think it might become a door stop... but i really want to get it back up and running before Christmas to show my cousin.

 

[Gee Tee]

You could try heating it in an oven for a while or gently heating breech with a blow lamp

I'm sure if you left it to soak in pentrating fluid long enough it'll let go

 

[Canon Fodder]

try posting in the "ask the experts" section on mcarterbrown.com - someone will know how to get it out on there, actually in that hole under were the blue diamond is you can see the pin that drags the hammer back, that pin runs in a slot between the two tubes of the body, if the bolt is partially turned so that pin is out of line the bolt won't go back (to completely remove the bolt you'll have to twist the bolt so you can see the end of that pin then unscrew it or push it in depending on what type it is). It's fairly easy to twist the bolt a bit when you're taking the pump arm out so it could be that.

 

[onasilverbike]

Stand it up in a jam jar full of diesel and leave it for a week, then apply the hammer if it doesn't come apart.

HTH Stan.

 

[Stan]

try posting in the "ask the experts" section on mcarterbrown.com - someone will know how to get it out on there, actually in that hole under were the blue diamond is you can see the pin that drags the hammer back, that pin runs in a slot between the two tubes of the body, if the bolt is partially turned so that pin is out of line the bolt won't go back (to completely remove the bolt you'll have to twist the bolt so you can see the end of that pin then unscrew it or push it in depending on what type it is). It's fairly easy to twist the bolt a bit when you're taking the pump arm out so it could be that.

Thanks fella. It's already under discussion on mcarter brown.

The pin is not stopping it from moving. It's lined up with the slot and is right at the front of it (muzzle end) and i'm hammering the bolt towards the rear of the gun... ie - it shouldn't be having any affect.

Keep the suggestions coming.

 

[Stan]

Stand it up in a jam jar full of diesel and leave it for a week, then apply the hammer if it doesn't come apart.

HTH Stan.

Have you seen the price of diesel lately!?!?

I'll give it a go when i have time.

Thanks fella,

Stan

 

[Gee Tee]

I normaly try shouting obsenities and kicking tools around the garage as a last resort

Doesn't often shift anything but it makes me feel a lot better