Full auto rifles - is it all about the sear?

[the count]

I keep hearing that an improperly polished sear can turn a semi auto into a full auto. Is that really all thats needed? I just saw a youtube video on de-milled full auto Uzi kits that are made legal and besides the sear a bunch of other parts need to be changed too......?

So whats the scoop?

(all purely theoretical, no intention to make a full auto anything!)

 

[John828]

A pretty sensitive topic

 

[Arizona_Mike]

Most guns are designed with firing pin weights and springs such that they won't run away if the sear fails and the hammer or striker merely follows the bolt or slide at bolt or slide velocity.

I had some disconnector issues on a 9mm AR15 and it never once fired. On the other hand, in the 1990s I had an SKS that would slam-fire (in battery) intermittently when using soft Remington primers (only when freshly cleaned and lubed) just from the momentum of the free-floating firing pin. The gun was not defective at all just very smoothly milled. The solution was just to switch to Winchester or Federal primers.

A badly working sear would be uncontrollable, intermittent, and unsafe and probably not give you much full auto. You may be confusing the disconnector with the sear, but even removing the disconnector will not make most guns run full auto (unless it is open bolt) and there are very few "grandfathered" open bolt semis out there.

You can only legally rebuild a demilled MG as a semi auto closed bolt gun. It's been a long time since the BATF deemed all open bolt semis to be machine guns because they are so easy to convert.

 

[Willie Sutton]

The answer is "No".

That's the actual answer, and it's a really simple one.

The explaination can be long winded, but the answer is still no.


If you use a demilitarized full auto parts set to build up a semi-auto firearm for your own education, you will only end up using about 70% of the parts, and if it fired originally from an open bolt you'll be re-enginnering things and using even less of the original parts set in order to have it as a closed bolt mechanism. For building a semi-auto Uzi, you would end up using about, oh... maybe the handguard and the plastic pistol grip and a few pins. Nothing else would really be retained.



Willie

.

 

[Sam1911]

Over-polishing certain firing group parts could cause a gun to double or triple uncontrollably a few times, sort of like how taking a hammer to your car's throttle linkage might make it stick wide open sometimes (hey, it goes FAST! ), and other times not work at all, or be uncontrollable, and/or really, really dangerous to try to use.

True controllable full-auto operation is achieved in several ways depending on which gun you're thinking of, but over-polished and screwed up sear and hammer hooks, or busted disconnectors are not one of them.

 

[Cee Zee]

I've had semi-autos double for a variety of reasons. I've never had one go full auto but I've seen rifles that I thought were right on the verge of doing just that. For example I saw an SKS in a LGS that had the firing pin channel so glommed up the firing pin was stuck forward. In an SKS that can mean full auto before you know it.

There are different reasons a gun might go full auto. I've had guns cook off rounds too. It pays to be careful. I've also seen complete idiots convert their rifles to full auto and that was on rifles that weren't ever supposed to be capable of going full auto. I guess he showed them. He showed me too. He pulled up in my yard and said, "Watch this." His dad had ran him off of his property because he didn't want to go to prison. I guess he figured I didn't mind. What a putz.

 

[zoom6zoom]

From a design standpoint, the easiest thing to design is a full auto only, open bolt gun. Of course, it's been illegal to build your own since '68. It's also one of the reasons why it's easy for a damaged firearm to go out of control on you. I get really nervous when I see folks thinking they can improve the performance of their firearms with a file or a Dremel after watching a video or two...

 

[Aaron Baker]

Of course, it's been illegal to build your own since '68.

'86, actually. '68 was the date that foreign machine guns could no longer be imported, while '86 was the cut-off for domestic full autos. Hence the (relative) plethora of Mac variations available for (relatively) cheap.

Aaron

 

[bflee]

I have a Savage made Revelation 22lr that could easily get me sent to prison! I lost the front trigger guard screw several years ago without realizing it. I loaded up with 15 rounds in the tube, cocked it, and pulled the trigger. It shot eight rounds at full auto and only stopped because a case got hung. I flipped it out and it shot the other seven. I figured out after loading it three or four times that it would do the same 8 run and jam consistently. I then noticed my front trigger guard screw was missing. I replaced it and it went back to being my old trusty 22 semi auto. It is alot easier and cheaper to shoot that way!

 

[Arizona_Mike]

Probably some kind of bump fire going on.

 

[Anmut]

No. Polish your sear too much and you'll get at best double feed and at worst an out of battery detonation.

 

[mboylan]

That's not how full auto works. A kitchen table job like that without a properly designed auto sear addition will get you one of 3 results in order of most likely.

1) The gun doubles or triples until it jams

2) The gun runs away and keeps firing when your finger is off the trigger

3) The gun fires out of battery and blows up in your face

 

[jmorris]

Some designs are harder to make semiauto than full. Others can be made dangerously fullauto with a "trigger job".