AMT Backup 45 Tuning

[smokemup]

Hey all. Here's a project guide for all you AMT owners and enthusiasts. I know we're surprised that some of these had reliability issues, but the fixin' is easy enough for us back porch smiths.

I wrote up some notes on the firing pin, should one want to modify it. It's not necessarily the sole cause of light strikes, but it's a start. Then there's a squared hammer face, tolerances, and the springs thing. Oh, and sometimes some crappy ammo.

So let's all jump in here and tune on these wonderful little cast stainless suckers!!

AMT Backup 45 Firing Pin.pdf

 

[Carne Frio]

Thanks for the great post. I have a Backup 45
and two 10mm Longslide Javalinas.

 

[Skans]

I had an AMT 45 Backup. After I did a little fluff and buff on it, it was a solid, reliable little 45. Occasionally, it would not fire on the first pull of the trigger. I figured out that this was because the cartridge wasn't seated 100% in the chamber. This happened as the chamber got dirty from shooting it. The cure was:

1. polished the feed ramp and very lightly polished the chamber.
2. replaced recoil spring with aftermarket wolf spring
3. clean chamber with gun scrubber or something similar after 50 rounds and run a bore snake through it.

 

[smokemup]

Here's a pic after polishing the AMT Backup .45 feed ramp...

 

[smokemup]

Correcting poor slide to frame fit on mine...

This image shows the rearward overlap of the slide. Although it's hard to see well, when the slide and frame are in proper alignment, the hammer appears be be fully seated on the firing pin surface, which is the greatest benefit of proper alignment.

I had already done a writeup on how to align the slide to the frame, so instead of rewriting it, I'll link the PDF file here. This was done on a Canik55 C-100 9mm with internal rails, but the process is the same.

Slide Alignment Link

 

[smokemup]

Want to also add to the alignment process writeup that the guide rod on the AMT Backup 45 is an active component to the takedown assembly pin. If you remove material from the barrel lug you'll need to do one of two options. Tig or braze material on the end of the guide rod (takedown pin stop) or remove material from the guide rods retaining shoulder. See the PDF link for details.

Guide Rod Mod Illustration

 

[smokemup]

Couple of pics...

Guide rod after cutting shoulder:

Completed slide to frame fit:

 

[smokemup]

Trigger Bar Spring

If you hear a slight 'click' when pulling the trigger, or sometimes a magazine gets caught on something when inserting it...

It's the Spring!

You want that spring to have just enough tension on it when the grip is attached so that the spring is not floppy loose (in and out). The click is coming from the spring popping out of the interior cutout. A stuck magazine is from the same issue. The spring may block the travel of the magazine.

But it's a simple fix!

Bend the rear leg slightly out. When the grip is attached it will keep the spring from traveling into the magazine well.

Pic 1. The point of bend. You can move the bend point up a touch more, but not down any further (I almost messed up). As anything else try little step at a time. Too much bend and the tension of the spring on the grip will give you a crappy feeling trigger. The goal is to remove some of the floppiness. Start with half as much bend as shown.

Pic 2. The spring installed.

Pic 3. The grip cutout for the spring.

Pic 4. The spring does not protrude into the mag well, nor does it pop off the grip cutout and cause that 'click' sound.

 

[Skans]

I've always said that the AMT 45 Backup is a good little "kit" gun. It comes with all the parts, even assembled, but you have to consider it only 95% finished. It has everything you need (in most instances) to make a rock solid reliable DAO 45acp.

 

[smokemup]

Hammer Alignment

Let's analyze this test result. Here's the setup... Graphite covered hammer face, and paper. Pretty complicated, huh?

How much this is impacting a solid hit on the firing pin is unknown to me.

 

[smokemup]

Aligning the hammer the best I could. Also got inspired to do a little polishing!


Blue layout fluid (Dykem)

Medicine. No, really!

Lot's of this action starting with 320 on up to 2000 grit

Ohhh, ahhhh....

Just reflecting on all this...

All to get this result. I'm thinking this is not too shabby, with pretty decent impact all around the firing pin. Still has more impact force at the top, which means the hammer angle is forward just a touch, but at least now it's striking the entire face.

 

[peggysue]

I got my AMT Back Up in 1994 when they came out. Small heavy pistol that has been a great little pistol. It is very reliable with ball ammo. I polished the writing off the slide. Polished the trigger smooth and round which lessens the pull feel. I polished the feed ramp. Took off some coils off the hammer spring. Just enough to reduce the heavy pull yet leave it still reliable.( I bought an extra spring back them from AMT so i still have the original.) The hammer is part of the function of the pistol. It slows the slide. Also fitted a grip sleeve on it.
Regretfully there are better small 45's that came out since and are better. So it sits.

Enjoy

I have an AMT Longslide, OMC 380 I got in 1976 and a Auto Mag 22Mag I got in 1986. They all work. The little OMC a pre curser to AMT had to go back to the factory for reliability issues. AMT was one of the first companies to make pistols of stainless steel. Grease the slides prevent gauling.
I am old.