AR-15 In 7.62x39R, Problems...

Did you ever send this back to Colt for Warranty work before you did all these modifications???

That should've been the first step you took when you first had the issues.

Now with all the changes/mods you did, it is very hard to figure out what is really causing your issue. What you should do when any problem with the AR arises, is to single out an issue one at a time (not make a whole bunch of changes).

An AR15 not cycling properly is usually a gas issue whether is a gas leak, mis-aligned gas tube/block, BCG issue, etc. Of course it could caused by other things, but you really should've sent this back to Colt for warranty/defect issues.

Sorry to hear about your issues and good luck sorting it out.
 
Customer purchased the bolt/barrel at a gun show and got an upper receiver, dragged it in here and said when I get time,
Put this stuff together.

Then about a month later, he dragged a stripped lower receiver in here that accepted AK mags, dumped it off for me to assemble.

I FINALLY got the lower to work, more or less,
The upper has never ran on any lower.

Colt told me 'It's yours, Good Luck' when I called them.

The new bolt came in today, I haven't had a chance to try it out yet, maybe Monday...
 
Got to the range just before dark, and this rifle did something it's never done before,

Fired twice in a row.

Even got it to feed (not reliably yet) off AK-47 mags...

Got a 10 shot string before I got froze out and couldn't see the target/backstop clearly,
So maybe this thing is going to run.

I'm NEVER doing an 'AR-47' again...

It appears the feed lips on the AK mags are a little too long, makes the bullet angle up too much trying to reach the chamber.

I rounded over the sharp edges on the AK mag to simulate some wear (new mag, sharp, rough edges) and that made it feed somewhat more reliably,
Along with a little speed lube, and I got a 10 shot string out of it.

I do some work on the feed ramps to see if that helps,
I would rather not cut the AK mags if I don't have to,
I would rather the rifle ran stock AK mags if possible.

Anyone ever seen one of these goofy things? AR-47 lowers?
This one has a two digit serial number,
I would NEVER buy the 'First' of anything.
The first release is always a 'Beta' test inflicted on the public...
 
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Jeep, glad to hear you got it going. I was rubbing a bald spot on my noggin trying to come up sith some sort of mental picture to pin your woes on. I've seen one of those lowers, but thankfully I had either too little money or too much sense to go that direction.
 
Glad to know you got it running with the new bolt.
Did you replace the entire BCG?
Have you had time to look at the old one for failures?
I'd really like to know.
 
Checked the head spacing, a little sloppy but acceptable.
Didn't change anything but the bolt.

Went out today, with a lot of thin viscosity, slick lube, and some work on the feed ramps.
Yes, I know, REALLY good way to screw things up...
Just reduced the 'Pop up' angle a little and slicked things up and those bullet noses are getting up where they need to be.

Reducing the angle of the ramp kept the round from nosing up as much,
It was nosing up so much the bolt was loosing the bottom of the round and getting into the side of it with the new bolt.

The AR bolt doesn't contact as much of the back of the round as the AK bolt does, so when the nose tips up, the mag feed lips pivot the round pretty far forward, so the round rotates around its center,
The back slips out from under the bolt lugs and hits the side of the case.

Polishing the chamber side (Forward) end of the feed lips,
Simulating mag wear, taking a little off, polishing the 'Saw Teeth' finish on that AK mag helped a ton!

When its not cutting into the goop they coat the cases with,
It slows down the bolt speed considerably!

Polish up the feed ramps, add some thin lube to the cases while in the mag,
And remove a little from the chamber nut feed ramp so the rounds don't quite rotate as much,
And it starts to feed on both AR & AK mag lowers.

I only have 10 round Mags for AR lowers,
They will run all 10 rounds fairly reliably.

I have several brand new soviet era 30 round mags,
Every single one is sharp as saw teeth on the mag lips,
Experimenting on a $10 mag is OK, but cutting a 75 round drum worth $75 to $100 is out for now...

Again, I can run about 10 rounds through a drum, but I will get stoppages.

Back to the cheap AK mags while I'm working it out!

Somewhere between 10 & 15 rounds in those 30 round AK mags, and it fails to feed.
I suspect too much mag spring pressure on the bolt bottom.

Anyway, when I get time, I'll side by side compare the bolts to see what the differences are.
 
Since you're using AK magazines

If the magazine spring is exerting too much pressure via the cartridges against the bottom of the bolt carrier, that could be causing the drag.
 
The old bolt has much shorter lower lugs.
Might have been allowing the rounds to slip out from under them MUCH sooner,

The gas ring boss on the bolts are different.
The gas ring boss on the NON-cycling bolt was way under size compared to the new bolt.

More support for the gas rings?

That's pretty much all I can find for a difference between bolts.

-----

It seems to be cycling just find when you use the charging handle, but it wouldn't pick a round up to save your life in live fire.
AGGRAVATING!

Now, reducing 'Pop Up' angle on the feed ramps a little helped some,
Combined with taking just a little off the mag lips,
And polishing the saw teeth off those lousy quality mags seemed to be the other half of the situation.

Since these are never used mags, the springs are STOUT,
I have cut the mag spring down a little in one to reduce pressure, and I'm going to see how that runs.

All this has to break in also,
This thing hasn't got but about 100 rounds run through it,
Most of the anti-corrosion coatings are still in place and slowing things down,
Nothing is operation lapped into place yet.

I'm hoping to run AK mags in it WITHOUT modification,
But some use wear wouldn't hurt anything.

The spring in that AK mag is at least 3 times as long as the mag body, and it's REALLY difficult to push the follower down, even with both hands with just 10 rounds in the mag...
I think I need to get one that has been used some,
The spring has weakened and the lips polished and see if an older, used mag works better.

When I use an AR lower, and AR mags, it feeds OK,
Not great, a little slow and gritty,
But they are unused also, and only hold 10 rounds...

This has been a REAL pain!
My record is unbroken, 35 years and never failed to get an AR cycling,
But this IS NOT my finest hour or my best work...

Just to top it all off,
The guy that owns this piece of mismatched parts says he doesn't want it anymore, for me to sell it for the bill...

Great. I'm NOT a dealer, selling isn't my deal...
Something else I have to do to make a nickel of any kind on this deal.
 
The actual time I have in it, about $1,700 to $1,900, I'm not exactly sure anymore.

If he hadn't started with every mismatched part he could find, it would have been MUCH easier!
(And a crap load cheaper!)

I'd take $700 to get out of it,
But you have to know, it's AS IS...

It's cycling, but not reliably as I'd like,
And I've had to cut the AK mag spring to reduce pressure to get it to shoot more than 10 rounds in the mag.

Smoothing down feed lips, GENTLY reducing the sharp edges got the basic AK mag feeding,
Reducing the spring pressure got the mag to feed more than 10 rounds...

GOING REAL SLOW,
I'd like to get it firing AK mags as intended,
Even if you have to hunt used mags that are otherwise unmodified...

I haven't started on the drum yet,
Trying to figure out how to get a common AK mag to work first.

AK mags, $10,... Drums $100+...
So I'm doing my 'Cutting' on a $10 mag first.

This thing wasn't about to spoil my AR record, it runs, just not as reliably as every other AR I've ever done...
Record intact!

On the other hand, this isn't an AR, it's some hybrid that isn't exactly either AK or AR...
"FRANKEN AR" would be a better description...
(mostly referred to in unprintable 4 letter words around here now!)
 
Well, I'm 90% there...
If I use a worn mag, the thing will run a 30 round mag with little issues.

If I take a new mag, I need to work lips, weaken spring.

If I use a drum, I can run about half the drum,
But spring pressure gets too great when I crank up the drum spring for the last 30 or so rounds,
So you stop about half way through, wind on the spring some more, and get the last 30-35 rounds mostly without issues...

I don't care about looks,
But with a drum, this thing gets looks like you wouldn't believe!

I think if I need this kind of mag capacity,
I'll stick with a regular AR and a Delta Drum.

It shoots surprisingly accurate for a 7.62x39mm,
I still refuse to shoot steel jacket ammo, no matter how cheap!
Maybe it will stay accurate...
 
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