Although I have going a thread on my ongoing issues with a poorly cycling Aero Precision upper & lower 308 I decided to make this topic a thread of its own, since the issue is arguably stand alone and may help others.


Long story short:

I mistakenly ordered two Lantac 308 bolt carriers. Forgot I ordered one in the past and guess what shows up today? These are supposedly top of the line.

When testing both with the Aero Precision upper I find my existing one slides easily in the upper and even has some "slop".

The second? Gotta force it in even before the bolt makes contact with the barrel!

WTF?? Any thoughts? How can 2 supposedly identical Bolt Carriers fit so differently in the SAME upper? Either the upper is way, way out of spec or one of the carriers is. Any ideas?


Link to Lantac: https://www.lantac-usa.com/AR15-M16-M4-Rifle-Accessories/762NIB.html

They're obviously not identical.

Did Lantac and Aero Precision coordinate efforts when they designed their critical components?

If not, I would never buy a BCG to go in another receiver set it wasn't designed for under the same roof, by the same engineers and drafters.

I'm not sure if I completely agree, but with the 308 it is a completely different beast then the AR15.  LanTac makes great parts and I have run their eBCG in the AR15 platform for years.  Run their muzzle breaks as well and they are great.

Their BCG for the 308 platform is a fairly new product for them and I have a build that I am going to be using one on I just haven't gotten around to finishing.

Send me a PM and I will give you contact info for a great contact at LanTac that might be able to help you out.

Both BCGs are from Lantac. Aero said not a problem and Criterion liked them as well. Even to my untrained eyes there are differences despite identical packages and model numbers. One came from Lantac directly.  The other, Midway.
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Done, thanks.

Look at the pics I just posted. They are NOT the same. Subtle differences even to me, a layman.

Tolerance stacking.

I have no idea what this is. All I see are two part assemblies from the same manufacturer labeled and numbered identically.

One carrier slides freely in the receiver. The other does not. Not how the extractor is different. I wonder if one is earlier/later production than the other and why any changes were made.

Problem solved: One of the BCGs has a poorly fitting firing pin retaining pin. Will only go in far enough with a punch and light hammer. Finger pressure alone would not force it in far enough. Called Lantac, they were most polite and appreciative.

I stopped by their booth at SHOT, and am aware of their products, which I like.

In the pics, there appears to be some variation in the thickness of the bottom carrier rails.

It happens.  I've seen AR15 carriers in the after-market all over the place, some that had a rough start fitting in uppers, labeled a "National Match" carrier.

They worked out the bugs and sized them accordingly.