AR Failure To Feed Problem

[Lasers]

Did I accidentally log in to ARFcom?

LOL I was thinking we were going that direction for a minute...but it seems to have self corrected a bit

 

[titsonritz]

ive had to make gas ports bigger in certain circumstances.

Did you discover the need to increase size before or after the build and test fire?

A pin gage check will tell you up front. People use drill bits but that only gets them in the rough ballpark and considering pin gages measure in one thousandths of an inch increments it's a pretty big ballpark.

 

[rjmt]

So a barrel with a massive gas port is offest by a BCG with a leaking gas key putting brass at 4 o'clock, according to that chart that would a "perfect ejection" pattern and everything is hunkey-dory, but the reality is it is only a matter of time before short stroking and FTF will occur.

Knowing the gas port size is where it all starts, I'll confirm the size with a pin gage every barrel on every build I do, that will tell me if there are going to be problems before they occur and removes a lot of guess work.

I don't disagree with knowing the gas port size - several manufacturers of AR released rifle with improper port size, causing FTF
how many people know their gas port size?
all my barrels are custom and the manufacture included gas port size with barrel information
but do most AR owners know? how many know what it's supposed to be?
how many on this forum took apart their upper to pin gage there gas port?
my comment is the chart is a good reference to start
and if your starting to get FTF, chances are you ejection pattern will change
if your gas port was improperly sized, you have a serious problem
but how often have you seen this?
I read of it with a specific barrel maker years ago, but not recently

 

[CLee0507]

I would bet most commercial AR's have considerably larger gas ports than they should. Manufacturer's do this on purpose to increase reliability with cheaper ammo because "Johnny Civilian" doesn't always use NATO pressure 5.56. This creates problems. The buffer weight is not a fix for this.

 

[titsonritz]

how many people know their gas port size?


all my barrels are custom and the manufacture included gas port size with barrel information
but do most AR owners know? how many know what it's supposed to be?
how many on this forum took apart their upper to pin gage there gas port?

if your gas port was improperly sized, you have a serious problem
but how often have you seen this?


View attachment 736955

how many people know their gas port size?
Too few I'm sure. IMO if you build your upper you should know your port size.

all my barrels are custom and the manufacture included gas port size with barrel information but do most AR owners know?
Same answer. (I would still measure it to personally confirm).


how many know what it's supposed to be?
I think using what Colt and the Military is a good point of reference and that information is out there.

how many on this forum took apart their upper to pin gage there gas port?
Was speaking mostly about builds but for myself if I remove the LPGB or FSB I measure the port. I have a few I haven't taken apart so have not measure them.

my comment is the chart is a good reference to start and if your starting to get FTF, chances are you ejection pattern will change.
I'll get changes in ejection patterns by changing ammo. All I care about is...Does it cycle reliably? Does is lock back on the last round? Does it go into full battery? If it does that I don't care where the brass lands.

if your gas port was improperly sized, you have a serious problem but how often have you seen this?
Typical what I'll see is over-sized but both do happen.

Regarding that port size chart, I see it before and think it is all over the place. A Colt M4 gov profile and SOCOM (14.5"), 6920 gov profile are all carbine length gas and all measure 0.062-0.063", I would consider 0.078 way large and 0.086 to be massively oversized for a 14.5-16" barrel, I think all those max port sizes are really. That is part of the problem of not knowing what you are getting.

 

[titsonritz]

I would bet most commercial AR's have considerably larger gas ports than they should. Manufacturer's do this on purpose to increase reliability with cheaper ammo because "Johnny Civilian" doesn't always use NATO pressure 5.56. This creates problems. The buffer weight is not a fix for this.

You are 100% correct.

Here's the "fix"...
Black River Tactical Store - Shop BRT

 

[v0lcom13sn0w]

Did you discover the need to increase size before or after the build and test fire?

A pin gage check will tell you up front. People use drill bits but that only gets them in the rough ballpark and considering pin gages measure in one thousandths of an inch increments it's a pretty big ballpark.

in one case, the rifle was already built. would not cycle. short stroke every time. the gas port was smaller than the closest drillbit to the size it should have been. considerably smaller.

i dont have any pin gauges.

 

[titsonritz]

in one case, the rifle was already built. would not cycle. short stroke every time. the gas port was smaller than the closest drillbit to the size it should have been. considerably smaller.

i dont have any pin gauges.

A factory gun, nice.

There are some inexpensive sets available but hit me up next time if you want/need to measure a port.

 

[Soren]

I had a couple free minutes today and took the hand guard off. One of the set screws on the gas block has started to work it's way loose. So, the gas block was a little loose and in the inside looks like this...


I have a new gas block and gas tube on order. Hopefully, it'll be here in a couple days. Yes, I'll make sure I use some loctite.

 

[v0lcom13sn0w]

the hole looks flame cut

 

[Soren]

the hole looks flame cut

It's definitely not round anymore. Probably got that way from wobbling while firing.

 

[titsonritz]

I had a couple free minutes today and took the hand guard off. One of the set screws on the gas block has started to work it's way loose. So, the gas block was a little loose and in the inside looks like this...
View attachment 737437

I have a new gas block and gas tube on order. Hopefully, it'll be here in a couple days. Yes, I'll make sure I use some loctite.

Is that gas block aluminum? Is your barrel dimpled?

 

[rjmt]

good find
what manufacture gas block was this?
and I take it this was a carbine length gas system?

 

[Soren]

good find
what manufacture gas block was this?
and I take it this was a carbine length gas system?

No, mid length. I have no idea who the gas block manufacturer was. I built this rifle five or six years ago.

 

[rjmt]

I hope this was your only issue, keep us informed

 

[Mecanik]

Mid length gas port with a loose/misaligned gas block.Looks like a little leakage around the gas tube also. Hmmmmmm I think you found your problem. I'm so glad for you.
There was one build in my past that gave me similar problems as yours. It was an SPR 18 inch barrel with a rifle length gas port. So of course the dwell time was a bit shorter than normal just like yours. It ejected the case's but wouldn't always lock back so I knew it was close but not quite there. Because it always ejected I just kept shooting it and after a while it finally started to lock back. A friend of mine told me it was designed and intended to be used for 77 grain NATO ammo which I had never heard of at that time but was told it's factory loaded for the military quite hot. I was shooting standard 55 grain reloads of my own concoction so my pressures were a bit low. That's about the time I started to read about dwell times and buffer weights and how all that affects extraction and ejection. That Eugene Stoner was a smart dude.

 

[titsonritz]

Mid length gas port with a loose/misaligned gas block.Looks like a little leakage around the gas tube also. Hmmmmmm I think you found your problem. I'm so glad for you.
There was one build in my past that gave me similar problems as yours. It was an SPR 18 inch barrel with a rifle length gas port. So of course the dwell time was a bit shorter than normal just like yours. It ejected the case's but wouldn't always lock back so I knew it was close but not quite there. Because it always ejected I just kept shooting it and after a while it finally started to lock back. A friend of mine told me it was designed and intended to be used for 77 grain NATO ammo which I had never heard of at that time but was told it's factory loaded for the military quite hot. I was shooting standard 55 grain reloads of my own concoction so my pressures were a bit low. That's about the time I started to read about dwell times and buffer weights and how all that affects extraction and ejection. That Eugene Stoner was a smart dude.

Reviewing Black Hills' MK 262 Mod 1 Ammo
IMI makes a good version too.
500 Rounds IMI Razor Core 5.56 77 Grain OTM in 20 round boxes - MK262 Mod 1

 

[eldbillbo]

I have seen more problems posted on boards due to those kinds of blocks than anything else since they hit the market. I have never trusted them and would never use them on a rifle that mattered. Fine for lightweight girl guns. Anytime I use them I dimple the barrel and tighten and Loctite the crap out of them.

 

[Mecanik]

Reviewing Black Hills' MK 262 Mod 1 Ammo
IMI makes a good version too.
500 Rounds IMI Razor Core 5.56 77 Grain OTM in 20 round boxes - MK262 Mod 1

Yep, that was the ammo I was talking about and the exact barrel I had. It was marked SPR Mk 12 I didn't really understand the significance of all of it at the time and should have kept the barrel but sadly sold it and moved on to other things. I ordered the barrel from Midway on sale for some ridiculously low price and thought nothing of it. It was a stainless barrel with 1-8 twist.

 

[Medic!]

You know I like factory guns.



But just because I can't put a gun together right.
Doesn't mean others can't.



A lot of things are that way.