300 blackout bolt not locking back

[Northtogladwin]

I'm running a 300 blackout 9 inch upper from aero precision, it has a q cherry bomb with a trash panda on it, the lower is from a 5.56 pistol so I have a kak industries buffer in it (the lightest of the 3 pack) like 1.7 oz and that helped it lock back more often, better than standard buffer was, I'm going to get a reduced strength buffer spring, I'll only shoot subs,

The gas block looks square, anything else I should look at, the gas ports open as much as shell go

 

[hafejd30]

Other than the spring you may need a lighter bolt carrier. My 8” aero runs flawless with standard everything and 200 gr S&B subs. TBAC ultra 9

I use a full auto carrier in mine

 

[Northtogladwin]

Other than the spring you may need a lighter bolt carrier. My 8” aero runs flawless with standard everything and 200 gr S&B subs. TBAC ultra 9

I use a full auto carrier in mine

The bcg I have is a standard cheap boy, I'll try my dd one to see, thanks!

 

[alamo5000]

I'm running a 300 blackout 9 inch upper from aero precision, it has a q cherry bomb with a trash panda on it, the lower is from a 5.56 pistol so I have a kak industries buffer in it (the lightest of the 3 pack) like 1.7 oz and that helped it lock back more often, better than standard buffer was, I'm going to get a reduced strength buffer spring, I'll only shoot subs,

The gas block looks square, anything else I should look at, the gas ports open as much as shell go

What ammo are you using? If it's home grown what powder/bullet combo is it?

 

[Northtogladwin]

What ammo are you using? If it's home grown what powder/bullet combo is it?

208 grain hornady amax

 

[alamo5000]

208 grain hornady amax

With what powder?

Or is it factory ammo?

 

[Northtogladwin]

With what powder?

Or is it factory ammo?

Factory, my bad

 

[alamo5000]

It's next to impossible to diagnose the problem without looking at the gun in person and seeing what it's doing.

How is the ejection looking?

If you have a few supers load one round at a time of various grain weight ammo and see if it locks open. Basically try to find the line where it starts to have trouble.

A more complete examination of the rifle is in order I think. Not enough info to really diagnose things.

 

[Northtogladwin]

Thanks for the input I'll look it over again and try a sprint for now!

 

[hafejd30]

Just FYI I chased an issue with my SBR where I opened the gas port to the point the rifle would sling brass to the next county before the bolt would lock open

Turned out to be a faulty mag the the follower was getting hung up on.

300 BO with a standard spring, buffer, M16 carrier and 9” barrel should work

 

[Northtogladwin]

Just FYI I chased an issue with my SBR where I opened the gas port to the point the rifle would sling brass to the next county before the bolt would lock open

Turned out to be a faulty mag the the follower was getting hung up on.

300 BO with a standard spring, buffer, M16 carrier and 9” barrel should work

I'll try every mag I have a designate 3

 

[Sniperstud]

Mine was behaving similarly, and it was consistent with all magazines. I finally pulled the gas block and measured the gas port with pin gauges and a caliper. The port measured .0625”, which would be correct for 16” carbine gas, 5.56. However, it should be in the .093”-.100” range for 300BO subsonics in that barrel length range. My barrel is a 10.3”. I opened the port to .095” and it runs like a Swiss watch with standard buffer and spring, and M16 carrier.

 

[Northtogladwin]

Mine was behaving similarly, and it was consistent with all magazines. I finally pulled the gas block and measured the gas port with pin gauges and a caliper. The port measured .0625”, which would be correct for 16” carbine gas, 5.56. However, it should be in the .093”-.100” range for 300BO subsonics in that barrel length range. My barrel is a 10.3”. I opened the port to .095” and it runs like a Swiss watch with standard buffer and spring, and M16 carrier.

From the factory it says it's a 0.1060 gas port size, I'll be at my range this weekend so I'll be able to test everything out!

 

[Snuby642]

I would look into spring being too stiff.

Does a factory 5.56 pistol lower come with an extra power spring?

 

[Northtogladwin]

I would look into spring being too stiff.

Does a factory 5.56 pistol lower come with an extra power spring?

In getting a reduced power spring

 

[Snuby642]

I saw that in post one, just agreeing best course of action.
I grease up my springs.

I got lucky and my 10.5 AAC 300blk upper runs everything with a standard lower. I have not even put an agb on it. (Should)

It is however a filty pig and will spew stuff on your face, glasses, the eoteck. Lol

I have to stop and clean up depending on wind.

I have not tweeked on it because it runs anything suppressed or not.
So I just chew the gsr.

Not sure how they did that .

 

[st1650]

Get the JP SCS with the adjustable weights and spring kit. It's literally the best 300BLK addition you can get. Don't fuck with your gas port size. Also maybe consider a Faxon 300blk lightweight BCG.