View Full Version : Finding the high spots when fitting a slide

May 17, 2011, 01:19 PM
I got a .40 caliber conversion kit for my EAA 9mm Witness match pistol. The kit includes a barrel, slide, a spring w/rod, and one mag.

The Witness is based on the CZ 75 design with full length rails on the inside of the frame and grooves on the outside of the slide.

The slide is tight so it needs to be fitted to the frame. I may try to do this myself. Some folks have said that it's fairly straightforward as long as you take it slowly and resist the temptation to use power tools.

I don't want to mess with the frame at all in order to maintain the way it fits to the original 9mm slide.

What's the best "medium" for finding the areas that need filing? I've heard of using magic markers or sharpies, nail polish and chalk.

The markers are pretty hard to see on blued steel. The nail polish is easy to see but I think it would go on too thick. I'm going to pick up some chalk tonight.

Is there something better out there? What's the "standard" tool for this (if there is one)?

May 18, 2011, 11:12 AM
Black magic maker has worked well with me for many years. However, "dykem layout blue" or other brands are available from brownell's. Typically when fitting a slide to a frame, 600 grit lapping compound is thinly applied to the frame rails & slide grooves. The slide is then moved to & fro on the slide to closely mate the two surfaces, but that brings up potential problems with the original slide to frame fit. Most likely the fit will be loose !!!!!

May 18, 2011, 12:28 PM
I have not worked on a Witness,but I suggest:
It goes on snug.That means you are just providing some running clearance.You probably do not have more than .001 or .002 to take off,and likely less.
Very often,the corner conditions are where the problem is.Whhere the corner cut is made on the inside,the corner is defined by the tool radius.Some radius is necessary for cutter strength.The cutters wear,and the inside corners become less perfect.
The outside corners are easy,they are a sharp edge created by two flat cuts.Then the outside corner must be broken by a chamfer or hand operation.
It is very possible all that is necessary is a little judicious dressing of outside corners.
Then consider,what is left is a height and width.I would caliper the frame and slide withs on the bearing surfaces.If you find a measurable clearance,say .002 or more,you know that no stoning /lapping need be done on the width.Conversely,if you measure line to line fit,you can carefully flat file or stone just any hi spots off.Dont remove the low spots in whatever tool finish you have.
I do not recommend touching anything until you identify exactly where you have interference.
I think the magic marker works good.Try good light and magnification,a loupe or Opti-visors.
You have very little steel to remove,remember,it goes together.My hunch,its the corners.

May 18, 2011, 07:54 PM
Thanks for the replies!

The magic marker is getting easier to see, especially after the bluing is rubbed off...

I'm taking it slowly but so far nothing seems to have changed except some of the finish is rubbed off inside the slide groove. I suspect the files I have are made of softer stuff than the slide.

I'll make sure to look more closely at those corners. The bottom surface of the groove has some marks that look like the toolhead that cut the groove may have done a little chattering right where things seem to be rubbing the most.

May 19, 2011, 01:05 AM
OK,I'll tell you often when I fit two parts together,I look where the marker is worn off.Those are the only spots making contact.You dont need to cut any surface that still has ink.Leave the low spots alone.Actually,while unsightly,the low spots in a choppy tool finish give a place where grit can escape from the running surface,think sand cut.They also retain some lube.
I do not know if they are still available,but I used to get a file called a kant file.It was a double ended file,each end about 2 in of teeth,very tapered,I'd guess 10 deg a side.On one end,the edges were safe,no teeth,and the other end the edges cut,but the flats were safe.That would be a good tool.
You also might consider looking online at MSC for polishing stones of the proper size to fit,go with a hard rectangular stone about 600 grit.
Clean thoroughly to remove grit befor trying the fit.

May 19, 2011, 12:34 PM
I made good progress last night. I think I'm about 3/4 of the way there. I'm hitting the range after work to test some loads for the plastic pistols tonight so I'll probably get back to the fitting over the weekend.

I know what you mean about thoroughly cleaning before trying the fit. At this point, there is a noticeable difference in fit between having the marker on the slide or not.

May 20, 2011, 11:20 PM
before I did anything, I would go shoot the heck out of it to break it in good. be a shame if you loosened the tolerances too much. If it doesn't break in the way you want it to, I might put some lapping compound on the appropriate areas and go shoot it some more to let it polish itself in.

May 20, 2011, 11:27 PM
This might be worth a look, particularly the part about abrasives:


May 21, 2011, 01:45 AM
Publius & Sarge,

Thanks for the replies!

The slide was too tight to function so shooting it out of the box was not an option. I'm pretty close to where it needs to be at this point. Right now, it'll go into battery if the slide is all the way back and I depress the slide release. Anything less than all the way back and it stops just shy of going fully into battery, creating a very dangerous situation. My late father, who was a range officer and weapons instructor (101st Airborne) would spin in his grave if I ever did something like that.

The other issue is that this is caliber number 2 for this gun. I have absolutely no intention of retiring the original 9mm slide and barrel which shoots better than any of my other pistols. That means I have to avoid anything that would remove metal from the frame, so no lapping compound. Well, maybe a tiny bit right at the end but I'm not there yet... and I'd need to detail strip & clean the frame (again) to make sure none of that 600 grit got into the works while lapping before any live fire testing.

The otherdecision is whether or not to do anything about re-bluing the slide. The finish is now gone from any bits that I filed, polished or otherwise worked over. Only the front inch or so of the slide rails would ever show, so for now, I plan to do nothing. I have no idea what it would cost to refinish the entire slide professionally, but if my normal maintenance procedures prevent it from rusting, it'll be a low priority.

May 21, 2011, 02:55 AM
I was a gunsmith for five years. Why only five ? Long story for another time, but here's my ten cents worth. Guru1911 is right about starting off with fine abrasive paste on slide and frame being the standard approach. But not for you because you want to work on the slide only.

Start by deburring both. You'd be surprised what difference that can make. Of course good quality guns have fewer machining burrs than lesser quality guns, but you get them on all guns. In my part of the world, South Africa, there are a lot of people without much money, so the inexpensive Norinco pistols sold well before legislation became prohibitive.

We'd get two identical pistols, one would function perfectly, the other would regularly malfunction. The difference in all cases was burrs, and the problem pistols were all fine after deburring. In a few, the deburring was so extensive that I chose to reblue the gun.

Anyhow, my point is that you should look at that first, because it is the easisest and most obvious thing, and you might find that a few burrs are causing most of the stiffness.

If not, move to the next stage. You need a set of needle files, preferably rifflers, because rifflers are curved for reaching into narrow grooves and recesses. But use them sparingly with a light touch. The other useful tool is a small piece of steel thin enough to reach into the groove. A small piece of wet or dry wrapped around that will do a good polishing job. Better yet, aluminium, less risk of digging into the slide if it slips.

How to see the high spots ? The bright spots on the gun's own blue will tell you at the first run through. After that, "reblue" the bright spots with cold liquid gun blue. I used Birchwood Casey, does a better job than engineers marking blue.

If the slide and frame are very precisely made, the stiction could be full length. I suspect, however, that a few high spots is what you have. If you take it easy and carefully, I reckon you'll have no trouble fixing it. And what you'll learn doing it will encourage you to do more of your own smithing. I found that some gunsmithing is very precise and exacting, but 90% of it is fairly straightforward stuff, in which care and caution are the main ingredients.

Wet or dry paper is the key tool for polishing before blueing. And for the sort of work you want to do. Its the dark grey stuff, silicon carbide. Start with 180 or 220 grit, then 320 and 400. 320 is fine enough for a soft sheen finish, 600 is almost mirror finish but not quite, 1000 grit is high polish, and 1500 is a mirror finish. You shouldn't need finer than 400 for what you are doing.

Sometimes a small piece of hardwood works better than steel or aluminium.

A quality name is no guarantee of smooth machining. All the 1911s I worked on were very rough inside, in my opinion. As were some other quality makes, rifles as well as handguns. I did a lot of deburring, in fact it became something of a routine procedure when working on a gun for unrelated reasons.

May 21, 2011, 03:17 AM
I was so focussed on the slide rails, I didn't notice your comments about re-blueing. Doesn't sound like it needs it, but here's some brief advice. Blueing is technically easy and can be done by anyone. But it is a fairly precise business in terms of temperature control, and the timing of the various operations (degreasing, rinsing,etc).

Hot blueing doesn't take on top of existing blue. But that can work to your advantage. I have reblued guns that didn't really need it, like revolvers with nothing worse than holster wear on the muzzle and cylinder, because their owners wanted it done. As no polishing was needed, I just degreased and reblued them. The existing blue remained as it was, and the new blue blued the worn bits. The downside can be that sometimes you don't get an exact match, but usually that's not important.

But be warned that, if you want to completely reblue the whole gun, you'll have to disassemble it completely. Then you'll have to strip the blue in pool acid. Often the acid and degreasing will leave a highly polished gun matt. In most cases you have to repolish it. Polishing a gun for blueing is not difficult, but is a slow and painstaking business. My experience was that I could get a very nice result, but not quite the same standard as Smith & Wesson for example. To try to describe it more accurately, my reblued guns were decently smooth all over, and a nice solid black, what I'd call a good finish for a working gun, but if I were to reblue a Python, the result would not be as good as the factory finish.

You need to understand that before you start. Where polishing and blueing skills really shine is in refurbishing rusted or damaged guns. I once refinished a Browning HP. Indistinguishable from a factory pistol, despite a good bit of reshaping where the serial numbers had been roughly filed off.

That sort of reconditioning is ideally suited to the home workshop. Nor do you need expensive equipment for handguns. I half wrote a book about it but abandoned it when I figured there was no market. Maybe I should finish it.

May 23, 2011, 01:28 PM
I got the slide fitting pretty well now. I did do a little de-burring on the frame but otherwise left it untouched.

The new .40 slide now operates with just a touch more resistance than the old 9mm one which has maybe 3,500 rounds through it. I can also feel and hear a slight "ka-chunk" as the barrel locks up to the slide which I can't detect at all with the old 9mm setup. We'll see if it's still there after a couple hundred rounds.

I did notice while doing this that the 9mm and .40 slide are exactly the same. Both barrels fit in either slide. If I ever add another caliber to this gun I may just buy the barrel next time.

May 23, 2011, 03:13 PM
I would always finish fit them with a little white rubbing compound and then Brasso on the rails of 1911s, after i got the slides and frame to match.