View Full Version : 300 Blackout upper help!

February 3, 2013, 10:52 AM
I just recently finished my 300 blackout upper for my AR-15. I took it to the range the other day to sight in the scope. I was shooting 110 gr supersonic ammo. The rifle fired however it did not cycle the next round into the chamber. The rifle ejects the spent round and everything it just seems as if the bolt doesn't come back far enough to pick up the next round. I am running a 16" barrel with a carbine length gas system. A gentleman at the gun store suggested clipping the buffer spring, changing the buffer, and possible boring out the gas port in the barrel. I switched out the buffer but am a little wary about cutting my buffer spring or drilling out the gas port. I dont want to do anything that may inhibit the .556 upper that I have for the same AR. Any ideas on if clipping the buffer spring would affect the .556 upper and it will help the .300 blkout?

February 3, 2013, 05:52 PM
anyone...beuller beuller...

February 3, 2013, 06:13 PM
The buffer spring is a relatively cheap part to replace if everything goes badly for you, and clipping a loop or so off of it isn't going to destroy your rifle. I've heard of people doing this more than once. I would most definitely try modifying a $15 buffer spring before I opened up the gas port on a much more expensive barrel.

February 4, 2013, 02:29 PM
1. Try different ammo.
2. Make sure nothing's binding in the gun.
3. Make sure the gas key isn't loose.
4. Make sure the gas ports in the barrel and gas block are aligned.
5. Post more detail about the gun; parts, who assembled, etc.

With all respect toTripHlx, clipping the buffer spring, while a relatively safe/inexpensive thing to do, will cause other issues. Cutting a spring INCREASES its rate. While you'll have less pre-load, by the end of the carrier's stroke, the spring will be exerting more force than the unaltered spring. So it probably won't fix your problem. (The higher rate also puts more stress on the spring, increasing the likelihood that it will break.)

February 4, 2013, 11:26 PM
I would do these steps

1st. Check to make sure the gas port/tube is installed correctly. If that doesnt solve the problem go to next....

2nd. Make sure you have the lightest buffer installed. If that doesnt solve the problem go to next....

3rd. Drill out the gas port... For this Google "300 AAC Blackout gas port size"

February 6, 2013, 09:04 AM
Thanks for the response. I have tried using 110gr supersonic ammo and 220gr subsonic ammo. I purchased a heavier buffer spring and that hasnt worked either. I'll be checking the gas port tonight and making sure it is lined up properly. I assembled the gun myself and this isnt my first build. I'm positive the gas port is fitted correctly but it never hurts to double check. I'm really trying to find cheaper ways to modify the gun without having to modify an expensive barrel like someone stated above.

I'll keep everyone updated. If there are any other suggestions please feel free to post.

February 6, 2013, 12:35 PM
Another thing to check is to make sure the gas port is actually the proper size. I've heard of times where a gas port isn't sized right before so worth checking

February 6, 2013, 01:31 PM
What is your gas port size now?

Clipping the buffer spring will change how your 5.56 upper runs.

Read my article on AR-15 gas system function to pick out your symptoms.