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300 blackout cycling issue


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#1 OFFLINE   jpmxrider489

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Posted Jun. 09 2018 - 07:50 PM

I just built a 300 blackout upper. I am having cycling issue. I believe the issue is undergasing.  The case doesn't even make it all the way out of the chamber to extract. I have built multiple rifles and not had this issue before. I have tried a lighter buffer, lighter buffer spring and basically mixing parts to see if i had something faulty.  I have dont want to have to buy a adjustable gas block. My barrel is also dimpled. Not sure if anyone has any other ideas? This also is a 9 inch barrel. I can be a possibility that my gas block shifts but I dont know what to do. 




#2 ONLINE   MontanaLon

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Posted Jun. 09 2018 - 08:36 PM

Any signs of gas leakage at the block? Bolt key screws tight and staked? Gas block properly aligned? Gas rings on the bolt? 

 

Was this with 1 type of ammo or every ammo you tried? All supersonic, subsonic or both?

 

If you are undergassed an adjustable gas block won't help until you get it more gas. You have to be overgassed or at minimum adequately gassed for it to even help to have an adjustable gas block.




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#3 OFFLINE   jpmxrider489

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Posted Jun. 10 2018 - 11:02 AM

I tried American eagle and Remington ammo both super sonic. I tried multiple bcg but yes everything is tight. I dont see any signs of leaking around the gas block but I didn't shoot a bunch because it fail every shot. I am fairly close to drilling the gas port on the barrel but before that I might just get a new gas block and tube.


#4 OFFLINE   Retcop

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Posted Jun. 10 2018 - 11:18 AM

I recently read an article about that caliber, 

It takes a relatively large amount of gas when running unsuppressed.

 

The conclusion was to enlarge the gas port, and if you ever want to run suppressed,

you're gonna need an adjustable block. I know you said you did not want to, but if you ever plan on running suppressed....

 

The 300 was designed for a very specific purpose, and is prone to these problems in the AR platform when not suppressed. 

That was what this article was saying in its attempt to help folks with hiccuping 300's, anyway. 

 

Does a carbine length gas system even work with a 7.5' barrel, or are you using pistol length ? 




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#5 OFFLINE   Longhair

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Posted Jun. 10 2018 - 11:32 AM

Does a carbine length gas system even work with a 7.5' barrel, or are you using pistol length ? 

He said that he has a 9" barrel. A carbine length gas system is about 7", so it won't work reliably with a short barrel. A pistol length system is required.

My hunch is that the port is slightly undersized for an unsuppressed application.




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#6 OFFLINE   Retcop

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Posted Jun. 10 2018 - 11:51 AM

He said that he has a 9" barrel. A carbine length gas system is about 7", so it won't work reliably with a short barrel. A pistol length system is required.

My hunch is that the port is slightly undersized for an unsuppressed application.

Thanks, don't know where I cam up with 7.5. 

 

Sometimes we ask a lot of the AR gas systems. It is amazing what the design can do

beyond what it was designed for. 

 

Mr Sullivan and Surefire have come out with a new BCG and buffer for those designs that push the envelope of reliability and

wear and tear on the bolt. 




#7 OFFLINE   jpmxrider489

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Posted Jun. 18 2018 - 11:40 AM

I just tried putting the light recoil spring in again with installing a new set screws in my gas block. The old screws I thought caused it to walk. However this didnt change anything. I as going to get a new tube and try that as well. But I read about many people having a working gun with my setup but also read issues as well. Guy at my local gun shop said if the barrel is to tight or loose, it could cause this? The torque spec on barrels is a wide range.  Is my only option making the gas port larger? I dont think a lighter BCG would change anything. I tried the light spring and taking out a weight in the buffer but no change. Thoughts?  




#8 OFFLINE   Longhair

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Posted Jun. 18 2018 - 12:04 PM

When you replaced the gas block set screws, did you inspect the port for obstruction? Did you look to see that the port is centered in the carbon around it? Have you checked the tube & block to know that they're clear?

If you did all of that and it's still not working properly, then it's time to carefully open up the port. Do it one drill size at a time (it's easier to open it a little more than to close it back up after you open it too much).


Edited by Longhair, Jun. 18 2018 - 12:05 PM.



#9 OFFLINE   jpmxrider489

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Posted Jun. 18 2018 - 01:54 PM

I did all the above. The gas tube is a tad kinked. It got kinked when tightening the barrel a hair. But could that cause this? Any thoughts on barrel tightness affecting extraction? What size bit is the stock hole. I know i could easily figure that out.  I try and open the hole this weekend.




#10 OFFLINE   bamashooter

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Posted Jun. 18 2018 - 05:19 PM

Ballistic Advantage shows their Performance barrel to be ported at 0.0995". Who's barrel do you have? That'd be a #39 when using a drill bit index.

 

KUPFQyR.jpg


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#11 OFFLINE   jpmxrider489

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Posted Jun. 19 2018 - 06:57 PM

I got the barrel from classic firearms.  Here is a link.

 

https://www.classicf...ackout1in7twist




#12 OFFLINE   bamashooter

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Posted Jun. 19 2018 - 07:30 PM

I got the barrel from classic firearms.  Here is a link.

 

https://www.classicf...ackout1in7twist

The link is for a 10.5" barrel. Carbine - length w/ a .125" gas port.

 

I find no 9" .300 blackout barrel on their site. Wouldn't that have a pistol-length gas system? How about removing the handguard and posting a pic?




#13 OFFLINE   jpmxrider489

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Posted Jun. 20 2018 - 10:00 AM

I cant figure out how to upload pics on here. But that link is the barrel i did buy. 




#14 OFFLINE   bamashooter

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Posted Jun. 20 2018 - 10:48 AM

I cant figure out how to upload pics on here. But that link is the barrel i did buy. 

Ok. 10.5" barrel.

 

If you have a pc / laptop, this is a good way.

 

1. Join a free photo hosting site. This is a very good one. https://imgur.com/

 

Being logged into imgur, do the following:

 

Upload you photos from your computer to imgur.

 

Photos will appear as large thumbnails.

 

Left click on one of your photos and it will "open" to a larger size.

 

On the right side of that large photo will be a column of options available.

 

One of those options will be titled  BBCode (message boards & forums)

 

Associated with that "title" will be a "copy" button.

 

Left click the copy button.

 

In a text box within the forum, right click, select "paste" and you'll be good.

 

For future reference regarding Imgur, after being logged in, you'll see your member name in the right hand upper corner

 

Hovering over your name launches a few options. The first option is "images". Select that and all your images will appear as thumbnails if they aren't already visible.

 

When you have those thumbnails visible, there's a green colored "add images button to the right. If you click on that, it will open your folders and you can then go find a new photo in your computer, select it, choose the "open" button (or just double click the image) and it will upload it to Imgur.

 

If you need help, holler.




#15 OFFLINE   jpmxrider489

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Posted Jun. 20 2018 - 06:06 PM

Thank you for help on uploading. Ill try and get them up. But that link is the exact one I have.  This was the description of it. 

 

Premium Grade Parkerized AR-15 Heavy Barrel, 10.5",1 in 7 twist 
Gas port drilled for carbine length gas setup and threaded for comp.
Barrel Extension in the rear with M4 feed ramps... drilled with a 0.125" gas port opening at carbine length. It has a .750 gas block diameter,  ready to install into the receiver.




#16 OFFLINE   jpmxrider489

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Posted Jun. 20 2018 - 06:07 PM

This does have a carbine length gas system. 




#17 OFFLINE   bamashooter

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Posted Jun. 20 2018 - 06:38 PM

This does have a carbine length gas system. 

I believe you. But if I recall you or someone listed the barrel as 9". The ad is a carbine-length gassed 10.5" barrel. You should be able to measure the handguard and determine barrel length or measure "through" the handguard (so to speak). If it's 10.5" were you expecting / wanting a 9"?

 

The gas block is simple enough to remove / install. Have you introduced air or blown through the barrel (with everything sealed except gas tube end) to determine good flow? Either the gas port in the barrel or gb could be too small, an obstruction could be somewhere along the flow from barrel to and within th gas key, etc.

 

You mentioned the possibility of the gb slipping, if you remove / install or not I'd make a couple of index / registration marks on the gb and barrel where they touch each other. That will tell you if any movement occurs.

 

I see you used multiple bcgs with same result. Gotta be something upstream such as the tube or ports since every other "visual" seems to be a go.




#18 OFFLINE   bamashooter

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Posted Jun. 20 2018 - 07:14 PM

I'll quit bugging you after this.

 

If using Windows XP, 7, 10, this is an excellent, quick, and easy image resizing tool. Typically, when I take a pic or at times download one, it's likely larger than needed, especially when posting in forums, emails, etc.

 

As you see in the link, after the tool is installed, you can right click on an image and now the resize tool will be included in your drop down menu.

 

Here's what I do 9 out of 10 times.

 

Right click image and select [Resize Pictures] This launches the resizer tool.

 

Select the button along side [small]

Select the button along side [Resize the original pictures]

Click [ok] and you're done.

The pic will be saved in the same folder as the original.

 

Suggestion: The first time using the tool, do not select [Resize the original pictures],  This will keep your original and add the smaller one with the word (small) added to the file name of the newly resized image. You'll now have two images of the same object, etc.

 

Here's the link to the download / install: https://www.digitalr...image-resizing/




#19 OFFLINE   jpmxrider489

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Posted Jun. 21 2018 - 10:42 AM

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#20 OFFLINE   jpmxrider489

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Posted Jun. 21 2018 - 10:52 AM

I did spray soapy water and blow in and did not see any bubbles or leaks. I am hoping you guys tell me my gas port is to small based on the pics above. I did want the 10.5 barrel because it was on sale when I ordered it. The other thing I could try is dimple the second set screw on the barrel. 







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