300bo conversion

[Slowride]

First off, thx for the help and I am no gunsmith. I’ve pieced a couple together, but have no real experience tuning an AR.

I decided to convert an Aero 556 to 300, so I bought an upper and attached it. Haven’t shot it yet, but it will FTF simply Chambering supers every third or fourth round. The end result of what I’d like to do is to be able to run subs.

So the general question is, what sorts of Parts should I exchange out before I even shoot it to eliminate the basic issues first? Thx, SR

 

[cmshoot]

If I’m understanding that you haven’t fired it yet, then you’re saying it’s a feed issue. Shoot it and see what happens.

Load several magazines with 1 round each. Load and fire. Look for vigorous ejection, and the bolt locking back every time. If it doesn’t lock back, or the brass is kind of rolling out of the gun,

 

[cmshoot]

Does the issue occur with more than one magazine, or with different types of ammo? Switch ‘em up.

Most importantly, don’t worry about it until you shoot it and see what happens. I’ve seen folks induce a malfunction when chambering rounds by hand.

 

[Slowride]

Failure To Feed, or Failure To Fire?

Apologies, failure to feed, haven’t fired it yet. Just got the upper and slapped it in. Rounds are Sig 125gr. Trying not to waste ammo figuring out obvious changes. Alum mags only at this point, trying to eliminate the pmag issue

 

[cmshoot]

Mags could be the issue. Get some .300Blk specific mags.

 

[Slowride]

Apologies, failure to feed, haven’t fired it yet. Just got the upper and slapped it in. Rounds are Sig 125gr. Trying not to waste ammo figuring out obvious changes. Alum mags only at this point, trying to eliminate the pmag issue

Mags could be the issue. Get some .300Blk specific mags.

If I’m ultimately moving to subs, should I just go ahead and change particular items? Gas block, buffer, etc.?

 

[harrycalahan]

Mags could be the issue. Get some .300Blk specific mags.

Ive always wondered about this. What is the difference between 556 and 300 specific mags? Ive always used 556 pmags/gi mags with no issues.

 

[cmshoot]

If I’m ultimately moving to subs, should I just go ahead and change particular items? Gas block, buffer, etc.?

Don’t spend money until you try the parts you already have.

 

[cmshoot]

Ive always wondered about this. What is the difference between 556 and 300 specific mags? Ive always used 556 pmags/gi mags with no issues.

Not all .300Blk’s need special mags. The only one I ever owned ran fine with standard 5.56 PMags. Some guns run better with special mags.

 

[GodBlessTheUSA]

When you do shoot it, if you have any problems, like FTF(feed), FTE(eject), or the bolt won't lock back, or you stove pipe, etc, try setting your phone camera on slow motion and get a video of you shooting. This can help dramatically by pinpointing exactly what is happening. I've tuned ARs that were cycling too fast, or not cycling enough, and I even found one upper's ejection port to be too small. Slo mo is the way to go.