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Design/Manufacture issue with AGM M4


Stealthbomber

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Bought one of these yesterday, took it to bits today and found that AGM have screwed up the way they've manufactured the bolt catch.

 

It's a pretty easy fix but if you want a working bolt catch and you're not happy about using power tools, stay away from the AGM M4.

 

I'm just taking some pictures and I'll edit this post when I'm done.

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Ok, here we go...

 

The problem isn't with the catch itself. It's with the hammer block.

 

DSC_2060.jpg

As this pic shows, there's a pin poking out of the hammer block right beside the top of the bolt catch.

This hole goes right the way through the hammer block so there's nothing to stop the spring pin from falling right out.

 

DSC_2057.jpg

This pic shows where the hole is drilled and also the pin next to it.

 

DSC_2061.jpg

With the hammer block dismantled completely (the allen screw is loctited so make sure your allen keys are good quality) the green dot shows where the hole for the pin SHOULD have been drilled.

Note that, on the other half of the hammer block, you can see a (poorly cast) pin that the spring is probably supposed to seat on.

 

DSC_2064.jpg

Final pic shows how spring pin is SUPPOSED to be positioned inside hammer block in order to press on lower end of bolt catch.

 

 

 

AGM, you fail big time.

Everybody else, remember where you heard it first. ;)

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Ummm, no. That is how the stock WA is drilled as well, and those work.

It might work some of the time because it's the spring in the MAG that pushes the bolt catch upward.

 

Ths spring is supposed to hold the bolt catch unlocked.

The length of the spring pin is SHORTER than the open-ended hole it's sat inside so it physically cannot do ANYTHING in its current location.

Actually, that's not true.

It can drop out when the bolt catch is engaged and get lost inside the gun.

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Sorry, I am not a techy. Does that mean it works as long as you don't loose the spring or it never works?

 

Edit: Okay you just explained it.

 

I had two AGMs and on both the bolt stop worked. Well, I didn't shoot much, so maybe prolonged use may cause trouble, I dunno.

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Sorry, I am not a techy. Does that mean it works as long as you don't loose the spring or it never works?

Basically, it means you'll have a rattly bolt catch that can engage randomly, particularly if you're holding the gun at an angle and you'll probably cause premature wear to the bolt catch and bolt carrier because the catch isn't being held unlocked as it should be.

 

In it's current location the spring pin doesn't do ANYTHING.

The only thing it can do is come loose and get mangled up in the other workings of the gun.

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Basically, it means you'll have a rattly bolt catch that can engage randomly, particularly if you're holding the gun at an angle and you'll probably cause premature wear to the bolt catch and bolt carrier because the catch isn't being held unlocked as it should be.

 

In it's current location the spring pin doesn't do ANYTHING.

The only thing it can do is come loose and get mangled up in the other workings of the gun.

Yah, I think I know what you mean. There's always some friction between bolt catch and bolt carrier, right?

Think, I was just lucky it worked for me. Is there an easy fix for this, maybe just replacing parts?

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The length of the spring pin is SHORTER than the open-ended hole it's sat inside so it physically cannot do ANYTHING in its current location.

Actually, that's not true.

It can drop out when the bolt catch is engaged and get lost inside the gun.

 

I find myself quite far from my AGM and camera so I cannot dispute anything you say with pictorial evidence, but it would seem to me that a longer spring is all that's needed. From memory I can say that the spring pin in question has a narrow diameter head to poke through the hole and engage the bolt stop. If that smaller portion is too short to engage properly than that may be the issue - but it certainly doesn't require an entire redesign or machining of the hammer block as you described it.

 

In either case Stealth, I've got to say this topic comes of as rather sensationalist. There's no question clone manufacturing is bound to have issues, but labeling the AGM as some half-assed assortment of pot metal doesn't do much to help the situation. Unless you are trying to scare people away, reading your post it would appear you are.

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I find myself quite far from my AGM and camera so I cannot dispute anything you say with pictorial evidence, but it would seem to me that a longer spring is all that's needed. From memory I can say that the spring pin in question has a narrow diameter head to poke through the hole and engage the bolt stop. If that smaller portion is too short to engage properly than that may be the issue - but it certainly doesn't require an entire redesign or machining of the hammer block as you described it.

 

In either case Stealth, I've got to say this topic comes of as rather sensationalist. There's no question clone manufacturing is bound to have issues, but labeling the AGM as some half-assed assortment of pot metal doesn't do much to help the situation. Unless you are trying to scare people away, reading your post it would appear you are.

True! The AGM costs just 25% of the original WA and only 16% of the comparable G&P and even less compared to the almighty Inokatsu. What do people expect? It can't get any cheaper, unless you want it for free. :D

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Or even just a piece of wire glued in place to seal off one side of the hole?

 

The pin is supposed to be loaded in followed by the spring, when the hammer/firing block is dropped in the lower receiver that end is sealed and the spring pushes the small pin through the hole to lock the bolt stop. Assuming proper tolerances of each part are accounted for, you don't have to mod anything.

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ino assemlby seems to have it in same place as the AGM (and WA)

 

ino3imajpgJPEGImage33082395pixels.jpg

 

ino1edcrop.jpg

 

though it looks to have the spring on the outside i.e. pin goes into the block small end first (I'd assuming to rest against a shoulder? ie opposite end of the whole is smaller than its bore) with the spring simply placed in afterwards so that its trapped by indide wall of the receiver when the block is slid into place

 

that could be inncorrectly drawn but would seem a bit odd for them to have drawn it incorrectly in both of their assembly drawings

 

possibly AGM have just assembled it incorrectly i.e. put two and two together and assumed that the spring should slide over narrow end of the pin and then the lot should go in spring first?

 

edit think Kalmar beat me to it

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The pin is supposed to be loaded in followed by the spring, when the hammer/firing block is dropped in the lower receiver that end is sealed and the spring pushes the small pin through the hole to lock the bolt stop. Assuming proper tolerances of each part are accounted for, you don't have to mod anything.

A longer spring would allow the spring pin to protrude through that hole but there's nothing, on my gun at least, to stop it falling all the way out.

 

I can see how it might work in that location but the fact is that, as it comes from the factory, it DOES NOT WORK for its intended purpose.

 

FWIW, the spring pin is exactly the right length for service in the revised position.

It's also slightly puzzling why AGM cast the hammer block as a copy of the G&P one and then drilled the hole in the same place as a WA gun.

If they drilled the hole where it looks as though it belongs all the components would function correctly.

 

*EDIT*

FWIW, I know this sounds a bit "sensationalist" but I figured it was worth it to make people aware that they WILL have issues with the AGM M4 bolt catch as it leaves the factory.

 

*EDIT2*

While fiddling around with this, it's become apparent that the bolt catch can sometimes just stick in place and not lift as it should.

If your bolt catch isn't working some/all of the time, try this for yourself.

Hinge the upper receiver forwar then, with the mag out, press on the bolt catch to ensure it IS free to move up and down.

Now poke your finger up into the mag-well and try and lift the bolt catch lever.

 

If you can't lift the bolt catch lever easily, all the time, then the catch is sticking.

This happens because the catch tries to twist slightly as you push up on the lever.

On my gun the slot in the AGM body is cast a bit rough and there's casting residue around the edge of the hole.

File this away to make the hole very slightly wider and the bolt works perfectly.

 

To be clear, I'm not suggesting this is part of the original design fault. I'm just saying that if your bolt catch sticks this might cure it.

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Can we sort this out before someone ruins a perfectly functioning gun ?

If advice hasbeen given in error it needs rectifing, does the AGM come with a manual to check ?

I was going to buy one end of the month and would like to know if this is sound or bad advice ?

 

Edit to answer above edits : so it's good to go then with minimal fuss :)

 

Super.

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DSC_2057.jpg

 

by looks of above the spring is on narrow end of the pin and the whole lot is getting inserted in that hole

 

spring should be seating in the end of that hole after the pin is fitted, and with pin inserted narrow end first.

 

(Video on youtube showing the block being stripped on a stock WA confirms thats the intended assembly order is pin first then spring, and the Ino diagrams show the pin inserted narrow end first)

 

Soooo, is there a shoulder within the hole drilled on that block that prevents the pin slipping straight thru when inserted on its own? ie hole narrower at end of the block so that only narrow part of pin can slide thru

 

If not, is there a shoulder on the WA version of that part? ie does it use a shoulder to stop it falling straight thru or does it just rely on length of the pin (a shoulder on the hole is only reason I can think of to have a shoulder on the pin, give the one on the pin doesnt look like its used to seat the spring?)

 

ie have AGM drilled the hole straight thru both blocks at a single diameter while WA have it stepped, or have WA themselves got a straight single diameter hole straight thru too, and rely on something else to prevent the pin going too far thru the block?

 

Judging by the image its long enough that the other inside side of the receiver would prevent it travelling far enough to completely drop thru and clear, but it still looks like its got sufficient tavel for its spring toforce it under the rear of the bolt catch if theres no shoulder to limit its travel?

 

 

 

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Can we sort this out before someone ruins a perfectly functioning gun ?

If advice hasbeen given in error it needs rectifing, does the AGM come with a manual to check ?

I was going to buy one end of the month and would like to know if this is sound or bad advice ?

The AGM manual is a copy of the WA one and it shows all the parts "laid out on a table" so it doesn't show which bit is supposed to go where.

 

IF the spring was longer and IF the hole in the end was a smaller diameter and IF you turned the pin around then it should work as it came from the factory.

 

On my gun the hole drilled through the hammer block allows the spring pin to escape so nothing else is important. If the pin can slide out completely there's nothing to keep it in place as the gun is shot.

 

TBH, It's not the end of the world in either case.

 

I'd suggest, as a minimum, when you purchase the gun a new owner open up the receiver and check if this spring pin IS working to lock the bolt-catch down.

If it's not, remove the mag catch (which allows you to remove the hammer block) and then slide the hammer block up and out.

You should be able to see this spring on the left, just behind the bolt catch.

Give it a poke with a jewellers screwdriver and see if it comes out of the right-hand side.

If it DOES then you really need to do what I've suggested.

If the pin CANNOT ascape through the hole in the right-hand side then you have the option of fitting a longer spring OR doing what I've suggested.

 

To be honest, I don't doubt that the bolt catch CAN operate without this doohickey working.

I'm more concerned that I've seen lots of pictures of mangled bolt catches and bolt carriers over the last couple of months and I can't help wondering how much of this damage is caused because the bolt catch can "jump" slightly during every shot and will rinterfere with the bolt carrier.

 

Basically, the bolt catch NEEDS to be sprung in some way to stop it fouling the bolt carrier.

The spring AGM fit doesn't do this.

 

*EDIT*

Snorkelman: That's exactly what I'm saying. There's a 2.5mm hole drilled straight through the hammer block. There's nothing to hold the pin in at the right hand side.

 

Beyond that, just out of curiousity I have tried flipping the pin around and, even then, the length of the spring and pin is such that it fits all the way into the hole with nowt poking out.

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Soooo, is there a shoulder within the hole drilled on that block that prevents the pin slipping straight thru when inserted on its own? ie hole narrower at end of the block so that only narrow part of pin can slide thru

 

Yes there is, on the WA and as far as I can tell on the AGM as well. I believe you are a special case - maybe they screwed up, maybe it broke off - I don't know. All I do know is that I haven't had this issue and it hasn't been reported by anyone else.

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block2.jpg

 

stealth - so by sounds of it your block is like thrird cross section above - straight thru hole not shouldered as per the first one

 

when you say length of spring and pin isnt long enough do you mean while spring is still over narrow end of pin (4th one down) or even when placed behind fat end of the pin - 2nd and 5th ones down

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lol, ya have the spring and pin the wrong way around, as the others have said.

 

I have compared both the WA and AGM, both have a sort fo collar inside the hole where it gets narrower, the thinner end of the pin should go in first followed by the spring and it shouldn't be able to fall through, if it can then you have a faulty part.

 

seems like an isolated case too, i've seen quite a few of them by now and haven't seen this problem.

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