I use my AR-15 lower for both my 223 varmint upper and my Tactical Solutions 22LR conversion unit upper.

Recently it has been mostly in the 22LR configuration. When I just cleaned it I noticed that the front of the buffer tube shows signs that the stop pin in the bottom of the cavity is beating up the outside edge of the buffer face. The vertical face of the buffer tube has chatter marks on its edge all the way around. Is this at all normal?

Was it the 223 that did this damage of the 22LR conversion unit? It seems very unlikely it could be the 22LR conversion unit as it uses its own recoil system and the one in the stock only backups the conversion unit in recoil. The gun regularly gets 22LR Std Vel ammo which it likes. I don’t remember using Hi Vel but it is possible (??). Could it be that the conversion unit actually pushing the buffer tube to the rear and the buffer easily over powers the closing of the conversion unit and slams into the stop pin?

I had not noticed this damage in the past but I really was not looking for it. I have no idea whether the 223 or 22LR caused it.

Anyone got any ideas?

LDBennett

PS: I can email a picture.

That type of damage is usually a result of the buffer retainer pin being machined to far back in the receiver. Your bcg should depress the buffer when you close your rifle and push the buffer off the pin. Open your rifle and close it slowly and watch to see if the bcg is pushing the buffer off the pin.

Or a short BCG.  A friend bought one and ended up with a chewed up buffer.

Would it better to use a rigid spacer in the stock to replace the buffer and recoil spring since the recoil spring is in the Conversion unit and does not use the buffer and its spring?

Please explain again how the position of the buffer  retaining pin can cause this? and what is the "bcg"? I am not understanding the mechanism that creates the damage????

How can a short buffer cause this problem when there is a spring behind it???

Is this a 223 problem or a 22LR Conversion Unit problem or a lower problem????

I am a little confused.

LDBennett

I found the problem! It is the Conversion Unit doing the damage.

When the gun is fired the bolt moves to the rear against the Unit’s recoil spring. The spring, as it collapses, drags on the guide rod and the guide rod is kicked back against the edge of the buffer and marks it (the buffer is aluminum and easy to mark). So I see the mechanism (the guide rod lines up perfectly with the damage to the buffer), and when I move the bolt back I can feel and see the rod dragged to the rear by the Units recoil spring collapsing. It definitely is the Conversion Unit doing the damage.

I emailed TacSol about the problem. They must have seen it before! We'll see if they even respond. I'll add a plastic buffer to the face of the buffer so the rod can do no further damage or try to figure out how to keep the guid rod from moving to the rear at all.

Thank you all for inputs.

LDBennett

I'll offer a different take.  Are your bolt carrier AND your 22 kit perfectly smooth at the back?  I'll bet it isn't.  A small bur on the rear of the carrier/adapter (it could be anywhere) can cause plenty of visible damage to the buffer, and it can look like it's the retainer that's at fault.  Make sure the carrier and adapter are smooth before deciding that there's a manufacturing defect in your lower.  One incredibly useful troubleshooting rule is "make sure the problem isn't caused by a cheaper part before you think about replacing a more expensive part."

Edited to fix "logic" in what I typed...

I am positive it is the Conversion Unit recoil spring guide rod. There are marks on the end of the rod, it is able to move to the rear to touch the edge of the lower's buffer in recoil, and the marks on the buffer match the end of the Conversion Unit recoil spring guide. It is most definitely the Tactical Solutions Conversion Unit.

Any TacSol Unit with this design would do the same in any gun it was installed in. I can not believe TacSol did not find this problem. Now, my Unit is several years old and the latest version may have a modification to keep this from happening. A simple set screw to hold the guide rod in place would do the trick. I am awaiting their response but I am not holding my breath while waiting and actually expect them not to answer my email about the problem.

And the back of the Conversion Unit and the front of the gun's buffer are perfectly flat with no burrs. The TacSol is a step above the CMMG Conversion Unit (I installed one for a friend and got a close look at the two designs and compared them. The machining of the TacSol Unit is much superior as is the design. I was NOT impressed with the CMMG Unit but it actually works fine. The TacSol Unit has this little problem but definitely is superior in use and accuracy.

LDBennett

You posted your "a ha!" while I was typing my post.  Glad to hear you figured it out.

Talked with TacSol today and they have never heard of anything like this. They asked for pictures so I emailed them the rear of their Unit and the damage to the buffer. So we'll have to see what they say. I suspect it will take some time for them to ponder this if it has not happened before, according to them.  I have studied the heck out of the parts and while what I suppose happens, it is still not totally clear. I see damage farther into the buffer than what the recoil spring guide rod could do unless the gun is springing partially open during firing. It is all very confusing.

I'm waiting on the buffer which I may stick on the end of the unit, over the recoil spring guide rod end. I'll test to see if that stops the problem. I also thought about making a sheet metal shield to stick on the end of the unit to stop the motion of the units recoil spring guide rod during firing. We'll see when the buffer arrives. Brownells is notoriously slow on shipping and send by the slowest form possible. There really is no hurry. It just that I am anxious to solve this problem.

LDBennett

I'm late to the party. I had the same damage from a cmmg conversion so I started to use a plastic spacer from I think tacsol.

Additional inspection seems to indicate that the Conversion Unit may not be the culprit. The damage along the edge of the buffer seems to go beyond where the Conversion Units recoil spring guide rod could reach. (??). All very confusing.

My next guess is that the recoil spring when in use with the 223 upper is surging during recoil and the tiny pin that retains the buffer in the lower is hammering on the buffer's edge as the surging buffer driven by the recoil spring goes through its motion. As any AR shooter knows you can hear the spring twang after the gun has recoiled so it must be moving back and forth. The damage coincides with that pin but the pin shows no sign of hammering anything. I have a better recoil spring for the lower's buffer coming this week as well as the Brownells buffer pads. I'll have to install both and see what the results are with the 223 upper and then with the TacSol 22 Conversion Unit upper.

This problem's mechanism and solution are veyr evasive at this point regardless of hours of pondering the parts and pieces and damage??????? I'm usually better at solving gun mysteries!

LDBennett

Because the pin is steel and the buffer is aluminum.  If the conversion kit is shorter than a standard bolt in your upper, then the buffer is contacting the pin under recoil and bounce.
Get a Taccom pressure plug or something similar.

Make sure your bolt carrier group is pushing your buffer off the buffer retaining pin when you close the upper on the lower. If it doesn't push the buffer off the retaining pin then every time your gun cycles the buffer is hitting the pin instead of moving with the bcg.

OK...Forget my earlier assumptions!  Here is what I did and how the range testing turned out:

I replaced the stock recoil buffer spring with one from Damage Industries of a different spring wire that minimizes the surging of the spring during firing (the twang you hear when you fire an AR. I put an Acrylic plastic buffer about 0.070 inches thick on the face of the gun's buffer (from Brownells supposedly for this gun).

I took both my 223 upper and the 22LR TacSol upper to the range. I first shot 100 rounds of 22LR, a mixture of both Std Vel and Hi Vel and inspected the new  Acrylic plastic buffer for any damage. There was none.

I next shot 40 rounds or 223 full load ammo made from Hornady 75gr HPBT Match bullets. Again I inspected the new  Acrylic plastic buffer for any damage. There was none.

While I was not able to isolate what caused the initial damage to the buffer face, the problem is gone. I can't ask for anything more. Guessing at what fixed it proves nothing so I won't. In the past I offered up several scenarios as did others so if you want just pick one.

The problem is gone and I am happy.

LDBennett

My 9mm broke a standard weight ar15 buffer in half last Friday, had some awesome looking concave quarters at the rear of the tube as well lol

Why were you running a standard weight buffer?
That thing had to be violent...