Aero M5 lower moriarti 20" upper short stroking

[Mike61096]

Hey guys I'm new to the forum and I'm hopefully posting this thread in the right spot. I've been doing some research and trying to figure out why my new build (aero m5 complete lower  w/moriarti arms 20" 308 upper) is short stroking. Additionally I have no last round bolt hold open. I took my hand guard off and inspected the gas tube alignment and positioning of the gas block. All seemed right. I then u screwed my gas block to inspect the port on the barrel. I measured the port size and found it to be around 0.078 inches. A chart I found online said that for a 20" barrel with 0.75" diameter should have at least a 0.093" port on the barrel. Could too small of a hole in the barrel be causing my short stroke issue? Any and all help is appreciated. 

[Armed Eye Doc]

4 hours ago, Mike61096 said:

Hey guys I'm new to the forum and I'm hopefully posting this thread in the right spot. I've been doing some research and trying to figure out why my new build (aero m5 complete lower  w/moriarti arms 20" 308 upper) is short stroking. Additionally I have no last round bolt hold open. I took my hand guard off and inspected the gas tube alignment and positioning of the gas block. All seemed right. I then u screwed my gas block to inspect the port on the barrel. I measured the port size and found it to be around 0.078 inches. A chart I found online said that for a 20" barrel with 0.75" diameter should have at least a 0.093" port on the barrel. Could too small of a hole in the barrel be causing my short stroke issue? Any and all help is appreciated. 

A gas port that is too small will definitely cause it to act exactly like your rifle does.  Before you start drilling it (which may be what it needs), there are other questions about the rifle to be answered.  

1. How many rounds do you have through your rifle?  What ammo are you using?

2. What length gas system?  Carbine, mid length or rifle?

3. What length is your receiver extension (buffer tube)?  Rifle or carbine?  What is the internal depth of it?

4. What buffer length are you using and how much does it weigh?

There may be more but that's a good start.

 

[Mike61096]

7 hours ago, Armed Eye Doc said:

A gas port that is too small will definitely cause it to act exactly like your rifle does.  Before you start drilling it (which may be what it needs), there are other questions about the rifle to be answered.  

1. How many rounds do you have through your rifle?  What ammo are you using?

2. What length gas system?  Carbine, mid length or rifle?

3. What length is your receiver extension (buffer tube)?  Rifle or carbine?  What is the internal depth of it?

4. What buffer length are you using and how much does it weigh?

There may be more but that's a good start.

 

I have about 30 rounds through it so far. I was using zinc point 149GR NATO M80 BRASS. Upper has a rifle length gas system. I have a carbine receiver extension and internal depth is 7 inches. Buffer length is 2.5 inches, weight is 3.8oz.

[Armed Eye Doc]

9 hours ago, Mike61096 said:

I have about 30 rounds through it so far. I was using zinc point 149GR NATO M80 BRASS. Upper has a rifle length gas system. I have a carbine receiver extension and internal depth is 7 inches. Buffer length is 2.5 inches, weight is 3.8oz.

You have not had nearly enough rounds through it to say how well it will perform.  You should be sure that your rifle is very well lubed each time before a shooting session.  It takes lots of lube until the parts work together well.

The receiver extension is good.  Your buffer is the right length but should be about 5.4oz.  It is not heavy enough to control the normal function of the rifle.  That said, yours is not functioning normally at the moment.  Manufacturers will frequently put a smaller gas port to compensate for the lighter buffer.  Sometimes it will function and sometimes it doesn't.

I forgot to ask what length buffer spring and how many coils does it have?  The spring is another source of recoil malfunction.

I also should ask if your rifle will hold open on an empty mag when you hand cycle the last round?

@98Z5V can answer the gas port sizing question.  He is a savant when it comes to holes. 

[98Z5V]

Gas port size for that specific config of 20" rifle-gas barrel will need to be 0.093"~0.096".   That recoil system will give you problems, too.  Just keep the receiver extension, buy a Sprinco Orange recoil spring, and a KAK 2.5" heavy buffer - that KAK buffer weighs 5.3oz, and will do the job.  Check your gas tube protrusion into the upper receiver.  It should come midway into the cam pin cutout in the upper receiver.  If it's short, replace it with a legit-real Armalite AR-10 rifle-length gas tube.

^^^  Those things right there will get your gun running to eat any factory ammo that you throw at it. 

Gas tube should look like the pic in this link below.

 

Edited November 16, 2021 by 98Z5V

[Mike61096]

41 minutes ago, 98Z5V said:

Gas port size for that specific config of 20" rifle-gas barrel will need to be 0.093"~0.096".   That recoil system will give you problems, too.  Just keep the receiver extension, buy a Sprinco Orange recoil spring, and a KAK 2.5" heavy buffer - that KAK buffer weighs 5.3oz, and will do the job.  Check your gas tube protrusion into the upper receiver.  It should come midway into the cam pin cutout in the upper receiver.  If it's short, replace it with a legit-real Armalite AR-10 rifle-length gas tube.

^^^  Those things right there will get your gun running to eat any factory ammo that you throw at it. 

Gas tube should look like the pic in this link below.

 

Thanks for that information. I went ahead and ordered the heavy buffer and orange buffer spring. I'll drill out the barrel tomorrow and then update the thread the next opportunity I have to try out the rifle at the range. 

[98Z5V]

1 hour ago, Armed Eye Doc said:

He is a savant when it comes to holes. 

You jackass...