I purchased an H3 buffer from Brownells with the intention of removing two of the tungsten bits to make a carbine buffer I already owned into an H2 and then the Brownells one would be an H1.

I was able to get the Brownells buffer apart, but I had to use pliers to rip off the plastic (rubber?) end cap.  It was very difficult but I was able to get it off without any noticeable damage.

Now trying to put it back together is impossible.  I still have about an 1/8" left to go and have tried everything including hitting it with a large hammer while it is on concrete.  I just can't get it go that last 1/8" and thus cannot put the roll pin back in.  Part of me wants to say screw the roll pin, this thing is never coming apart again.  But alas I figured I would ask arfcom for suggestions.

I did try heating the buffer up to get it to expand a little, but I was only using a hair dryer and it was definitely not enough heat to effect much.  I would throw it in the oven or something but am concerned about the plastic part melting of if the plastic part expands with heat more so than the metal part and that would be counterproductive.

How tall are all of the buffer weights and spacers, removed from the buffer, compared to the depth inside the buffer?

The buffers and spacers were all the same size.  I didn’t use a caliper to confirm, but they darn looked the same size.  And judging by how hard it was to remove the end cap, this is about right for it to be this difficult to reinsert.

The problem to me seems to be that since the bumper part of the buffer is slightly bouncy, as per its intended use, the blows from my hammer are being dissipated rather than pushing the cap down any further.  Again, it was extremely difficult for me to remove the cap.  I really see the only possible fix for me to heat the ,teal tube part and maybe that will get me enough clearance to hammer the cap down the rest of the way.

Then I need to hope that the roll pin hole is exactly aligned...

Maybe if I use a soldering iron to heat the tube?

Freeze the cap
heat the tube

Remove the bumper and file/ sand around the perimeter until it is able to be forced in.

About to try this one.  If that doesn't work then I will sand down the cap a little.

Got a vise?  May work better than a hammer.

You put an extra spacer in it.

Measure the internal depth of the buffer and the section of the bumper to make sure they are equal, if not a tad more depth in the buffer.

And, when you try to force the bumper in it compresses and some of that transmits to the part inside the buffer.  Try the idea suggested of the dishwashing soap for lube and then use some pliers to try to twist the bumper down into the buffer.  Don't push as much as twist and it should go.

If you do damage the bumper you can get replacements from KAK.  I modified a buffer a couple years back and bought bumpers from them to use/have for spares in case I did it again on another build (used an AR15 buffer spring and modified rifle buffer for an A1 stock on a DPMS GII carbine.)

Lil bit of lube (hand sanitizer works if you don't want anything persistent inside it) and a bench vise will get it sorted a LOT quicker than thwacking it with anything.

Thanks for all of the replies.

I tried the freeze/heat method and it allowed the bumper to be hammered super slightly lower but still not enough.   The pin hole, while not low enough, was also not lined up on one side.  Kind of strange that one side was pretty well lined up and the other side was not.

I did take it back apart again and there were no extra parts.

I foolishly decided to try pounding the roll pin in, thinking it may pull the bumper the rest of the way.  Unfortunately once I got the pin half way in it was not lined up on the other side and is now impossible to get out.  Pulling with pliers was laughable and the pin was misaligned so there was no way to push it out from the other side.

I made the decision to drive the pin in the rest of the way and then file down the 1/8” of pin sticking out.  So the end result is a bumper that is impossible to pull out of the tube held together by its own friction, and now is pinned on one side, so I am pretty confident his thing will never come apart.  The buffer is maybe 1/16 inch longer overall.

If I were to do it again, I would not have attempted to put the pin in, but once I did that it was basically too late to do anything else.

1/16" longer can mess with your bolt clearance of the bolt catch and may not allow normal LRBHO.

This... don't let that fucker beat you...