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Old January 19, 2012, 01:25 AM   #1
RsqVet
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Making the AMT backup 45 run

Forgive me if this is long, really looking for advise of more experienced gun tinkerers than I.

Ok so I finally bit on a Backup 45, a gun that has long fascinated me. I found one that appears unfired / as new and then found a shop that still had new magazines on the shelf and got 5 for 8 bucks a pop.

This is the pre firing pin safety model, prior to various takeover / buyout and so forth. Actually a pretty low serial number so my thought is hopefully better quality control than what AMT is know for. Thus far it's accurate, and I like the size etc.

So far the only issue with the gun is feeding. What it appears to me is happening is that the AMT magazine follower design is frankly flawed in that it has almost no support or stability at the front end of the magazine therefore with a mag loaded with 5 or even 4 rounds it tends to tilt down allowing just enough of a change in the nose angle of the round that it nose plows into the feed ramp rather than feeding. This seems worst with the top 2 rounds in the mag and some mags basically would not easily chamber a round from a full mag and would not feed reliably from a 5 +1 configuration sometimes having issues with round 4 as well. This seemed to be all of the feeding problems with this gun.

The stock AMT follower is of the simple USGI flat steel design with a bent leg that rides in the back of the mag column and a small step for the slide stop that stabilizes it at the front of the mag. Yes I have tired new mag springs despite seemingly "new mags. Even cut down 1911 springs for more "power" to no good effect.

Sitting around at my bench I started looking at an Ed Brown 7 round mag, this is one of the metal form ones he sells, not the newer 8 round mag with a removable base. This mag has a follower that is 2 pieces with significant front support for the follower riding in the mag tube and a fixed / slanted base for the rounds to ride on. So I put this in one of the AMT mags and other than requiring the removal of a few coils of the mag spring it seemed to work in that it keeps the rounds from nose diving and the top rounds now feed with absolute reliability.

This has however come at the expense of 2 other issues --- even with coils removed this follower makes the mag darn tight to seat in the gun when the mag is loaded to 5 rounds. In addition the last round has low spring strength pushing it up so occasionally the last round mis-feeds.

I know that many have discussed the feed lips on the AMT mags, I have examined the lips on all of my magazines and the lips all appear identical and within spec for a 1911 mag which it is based on as I have plenty to compare to. I

So my question is where to go from here. Overall I feel like I am making progress in I have identified some issues and fixed them and the issues that are there are happening less frequently than when I started. Options I am considering are:

1. Add a few coils to the mag spring with the new follower and simply call it a 4 round mag and be happy, a 5 shot 45 acp of this size is still a good carry gun to me and flatter than a J frame which appeals to me. Looking at that mag size it strikes me that 5 might be… well over-optimistic.

2. Go on a spring buying spree and see if I can find one that can be cut to a size that will work in the configuration with what I believe is the better follower…. Maybe try power mag 10 round springs or sig P245 mag springs… basically I need something that has a very high spring rate so I can have relatively few coils under the follower and still have ample power for the last round.

Any other thoughts from anyone would be much appreciated, I will work on posting pictures to better illustrate the progress of this gun project.
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Old January 19, 2012, 10:15 AM   #2
khegglie
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I wonder if you should try another stock mag or two first before you do more mods.
My AMT didnt have any mag issues at all.
I should a kept it.
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Old January 19, 2012, 01:26 PM   #3
Clifford L. Hughes
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RsqVet:

When I was selling guns during the 1970 and the 1980 the AMT's gave me problems with returning them for repair. Most of the time it was for failure to feed. I tried th stear my customers to someting else; however, there were no other small .45 auto loaders available. Do yourself a favor and use the Back Up for a fishing weight. Is your life worth carring a unreliable pistol?

Semper Fi.
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Old January 23, 2012, 11:47 AM   #4
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Any one else with input --- I have tried 5 factory mags and all are about the same reliability wise, I am looking towards heading down the road of making it a reliable 4 + 1 gun with the new follower and heavy mag spring.

Clifford --- I know, I know. I have plenty of other guns I could carry, seecamp 380, a number of 1911's and a few J frame smiths to name a few. None are compact 45's like the AMT is, and like I said a flat gun that is 5 shots has some advantage to me over say a J frame. I don't know too much out there in the market that is 45 ACP and the size of the backup. Considering it for carry would be a bit off in the future if I can get it running, until then it's a bit of a fun exercise for me since I like working on guns. Like so many things it appears to me the AMT is not fundamentally flawed, rather it's about 10% off in some areas but being a very small 45 that 10% leads to more problems than say a 5 inch 1911 where 10% in many areas might still give you a gun that feeds ball ammo just fine.

Anyway this turns out I have had some fun and learned a bit that I may apply if I ever decide to mess with an officer's size 1911, but a 200 dollar AMT is a lot cheaper than an officer's sized 1911 if as many say, sub 4 inch barrel 45 acp guns just don't work.
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Old January 23, 2012, 01:16 PM   #5
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I had an AMT 45 Backup and here's what I can tell you:

1. I really liked this gun and it can be made very reliable contrary to all those who will try to tell you they are junk.

2. Buy a new Wolf spring for the slide - a weak recoil spring is the biggest problem folks have with this gun.

3. Do not use aftermarket magazines. I tried two out at a gunshow, and neither would even fit in the gun properly - they were complete junk! Make sure your factory magazine hasn't been abused - they are pretty rugged.

4. I polished the feed ramp using a combination of about 6 different grit sandpapers (600 - 1500) and some buffing compound - no dremel, all by hand.

5. I also lightly polished the frame rails, some trigger parts - all by hand.

6. Keep it clean! When the chamber gets dirty the cartridges don't seat 100% all the way - this means you might have to pull the trigger more than once.

Once I completed my work on this gun, and as long as I kept it clean, it was completely reliable with both hollow point and ball .45. Really, if you just replace the spring and polish the feed ramp and use good magazines, you should be just fine. I would have to clean it after about 100 rounds, give or take.
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Old January 23, 2012, 02:09 PM   #6
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There is a guy that goes by the handle of "LOS" that is on this forum and others, and he seems to have a pretty good knack for trouble shooting, and overall suggestions for .45 ACP AMT Backup.
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Old January 23, 2012, 06:15 PM   #7
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Quote:
All the a recoil spring does is bring the gun back into battery.
The AMT 45 tends to a have weak recoil spring. I've had problems with two used stock springs that weren't any good - the new Wolf replacement did the trick. This means that it is either not shoving the cartridge all the way into the chamber, or the slide is not completely forward, or both. The way I know this is because a) if you pull the trigger repeatedly, it will eventually knock the slide/cartridge forward and fire; and b) when it fails to fire if you manually push the slide forward it will then fire. This is mainly caused by a weak recoil spring. Secondarily, it is caused by a rough or dirty chamber.
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Old January 24, 2012, 08:14 AM   #8
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Failure due to weak recoil springs is actually a known issue with these larger caliber "pocket" type guns. The stroke is much shorter than a standard pistol and there is less slide momentum. Look at the Rohrbaugh R9 - they recommend that you replace the recoil spring after only a few hundred rounds to keep it reliable. The newer pocket 9mm's, like the Diamondback use double recoil springs that are quite stiff.

Wolf makes a good spring for the AMT .45 Backup. It's about a $10 fix.
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Old January 24, 2012, 08:20 AM   #9
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Quote:
The specs on 1911 clones leave a great deal to be desired I have found. Try a Chip McCormick or Wilson high end mag to see if it cures the problems. Good luck!
The pistol in question is not a 1911 clone!
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Old January 24, 2012, 11:23 AM   #10
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Fixed Mine

Back in the early-mid 90's I owned an AMT 45 Backup. I found ALL my problems with it were cured by placing about 600 feet of Atlantic sea water above it.
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Old January 24, 2012, 11:33 PM   #11
los
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Quote:
Originally Posted by Rangegod
... Back in the early-mid 90's I owned an AMT 45 Backup. I found ALL my problems with it were cured by placing about 600 feet of Atlantic sea water above it.
Thats just all kinds of wrong..!


.





Last edited by los; January 24, 2012 at 11:41 PM.
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Old January 24, 2012, 11:36 PM   #12
los
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And a short video clip....:

http://s2.photobucket.com/albums/y6/...t=MVI_0003.mp4
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Old January 26, 2012, 05:48 PM   #13
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New to this forum and joined because of this thread. I have also just bought a AMT 45 backup. It is new but has been sitting in someones safe for a while as it does not have the High Standard markings. I have a 380 SA 380 backup and have for many years. It has always went bang when the trigger is pulled. I haven't had to chance to get mine out for extended shooting. I did fire 4 rounds(2 fmj and 2 hp) in the back yard to see if it worked. I put the hollow points in the middle to see if it would jam. The reason I bought it was I wanted something with more firepower than the 380 and since I don't own any 9mm and didn't want another caliber the 45 was the logical choice. I also want to carry it in my pocket with no holster and a round chambered like I do the 380 now. So the heavy trigger pull is just fine as I don't want to shoot my leg off with a light trigger. Keep us informed on what you do and how it shoots. I didn't think the recoil was bad at all. It seemed the same as my full size Kimber 45. Sorry for being so long I just had a lot to say.
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Old January 27, 2012, 08:48 AM   #14
Skans
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454me, the AMT 45 Backup has what it takes to be a good solid reliable .45acp. Don't let others convince you otherwise. Some need a new spring and a little polishing, but if it works (by that I mean a significant number of rounds without problem) then leave it alone and enjoy it.
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Old February 19, 2012, 12:47 PM   #15
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I just got one of these a few days ago, used. It's an older one, made in Irwindale, CA. (SN = DA46XX) I had "hoped" this would be one of the reliable ones. Unfortunately, after a fairly thorough cleaning and lube, I am having the feed problems. I am shooting Winchester "white box" ball ammo. The feed problem jams at the base of the feed ramp (magazine feeding too horizontal) or jams into the top of the barrel (magazine feeding too vertical). My thoughts are to polish the feed ramp and address the magazine issue. However, I am not sure what to do with the magazine? I think it could use a good cleaning. How do I "thoroughly" clean a magazine without a removable base plate? What other suggestions would anyone have? Does anyone have any good links to fixing the problems with this gun?
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Old February 19, 2012, 01:30 PM   #16
arentol
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Seems like a really bad time to buy one of these with this little item coming available soon:

http://www.gunsamerica.com/blog/springfield-armory-xds/

Either you will find you want the XDs instead and end up selling the AMT, or people replacing their AMT's with XDs's will depress the market for AMT's and prices will drop considerably so if you had just waited a bit you could have saved a fair amount of money.
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Old February 19, 2012, 02:15 PM   #17
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That Springfield looks real nice! I also have been debating on the Kahr PM45 and the PM9 prior to purchasing the AMT. I still may trade for the PM9 if I can't get this feed problem fixed. Oh well, got my Sig P238 back my pocket and I guess that's where it will stay until I fix the AMT or find another "deal"?
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Old February 19, 2012, 03:07 PM   #18
454me
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Axel on this type of magazine you depress the follower in the top of the magazine and put a paper clip through one of the holes in the mag to keep the spring down. Then the follower will come out through the top. I haven't tried this yet with one of them but it should work. They had to get it together somehow.
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Old February 19, 2012, 04:47 PM   #19
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During the 10+ years I've had an AMT 380, it has never fired a box of ammo with failing. It's good for the first round but can't be depended on beyond that.
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Old February 19, 2012, 04:56 PM   #20
Axel Foley
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454ME, Thanks! That makes since. How do you like your BU?
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Old February 19, 2012, 05:02 PM   #21
Axel Foley
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tnhawk, that's unfortunate. I hope with enough tinkering I can get this thing to a point I can rely on it. Funny though, I have thought this might just be a single shot gun as far as reliability.
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Old February 19, 2012, 05:10 PM   #22
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Mine carried for off duty and always worked even for head shots at 15 feet or so. However that DA trigger with YARDS of pull and no clean break finally got me to a colt and SW DA. Pocket carry was always some what iffy because of its weight. IWB was the only real way to carry it for me.
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Old February 19, 2012, 06:03 PM   #23
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Ahoy RsqVet,

After researching and hearing all the bad news about the AMT 45 BACK UP, I took a chance on a like-new condition one, on sale for $250.

Before shooting a single cartridge I disassembled (taking pics along the way to refresh my memory for re-assembly) the pistol completely. I found the internals in machined rough condition. Polished and buffed every single part...everything...very carefully. The hammer assembly is the worst, a real swine, but must be disassembled and thoroughly fluffed and buffed. This was time consuming, but when finished, the action becomes as smooth as a hot knife passing thru soft butter, with a silky, consistent, firm trigger pull. Very slick.

The owner must, in effect, re-manufacture the pistol, then keep it clean and well lubed. 100% flawless function.

Amazing how accurate these little AMT 45 BACK UPs are, 3/4" groups doable at CCW distances, and how well they handle the recoil of the 45 ACP cartridge. Mostly use for ankle carry, on occasion pocket or IWB (requires wide strong belt).

Only problem are the grip screws, they must be tightened after every range session, as they come loose. Lost one.

Good luck.
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Old February 19, 2012, 09:21 PM   #24
454me
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Axel I have the 380 backup and thinks its a great gun. Many years and rounds through it. If it ever malfunctioned I can.'t remember it. I just bought the 45 backup a few weeks ago. I haven't taken it to the range yet but i did load 4 rounds in it and it fired them with out any problems.
That's about all I want to fire in the subdivision I live in. I do expect some jams until I get it broken in. I have pictures in my link showing the 380 and 45 side by side. They always tell you to practice the tap rack bang drill for the 1911's. I have practiced it but the only 1911 I have is a Kimber custom classic. It has never jammed on me so I have to put snap caps in it to get a failure. Remember to hold the gun tight. Sometimes the failures are from limp wristing the gun. I looked at all the small guns out there and some sound like they are the same size but are so wide it feels like a brick in your hand. I want to pocket carry it and like the hard trigger pull so I don't shoot myself in the leg. I do hear people talking about the trigger being so heavy you cant hit the target at 25 or 30 feet. Around here that's not self defense anymore its hunting.
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Old March 3, 2012, 12:11 PM   #25
marinoperna
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Backup

Los,.

Ever find the video for fine tuning the 45 we talked about a while back?

Just got another but it too has a wobbly slide so my shots have never been as good as what you posted. Any ideas on how to tighten it up?

Don't think I've ever asked - What do find for the best accuracy, trigger pulling wise?

Regards
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