Asking cause I got a Colt Sporter Lightweight which needs a new buffer.  I had  a no name 2.9 oz or so buffer in it and the rubber tip battered itself into pieces.

I tried a Colt H buffer and a H2 buffer and a new Colt carbine spring and it appears to be shortstroking, can't get 10 rounds off before it jams

Gas rings are good did the gas ring test and the key carrier bolts are tight and still staked.  Rifle ran good until I started mucking around replacing the buffer and spring

Got a standard weight carbine buffer on order from Brownells and will try that next

The Sporter's BC is the half moon type and has less mass than other Colt bolt carriers like this (picture from the 'net)

No, it doesn't.

It "might" benefit from a heavier one just to bring the reciprocating mass up to the design spec since you have a lighter carrier.  However, it was designed to work with factory 3 ounce buffer and factory spring weight.  

I have had buffer tips beat themselves up, and this can be caused if the previous owner way overlubed it often, and left it standing up, letting the oil run down to the buffer tip over decades.  I had an old (black tip) buffer tip soften because of this.  

If it starts short stroking on a H buffer, I seriously doubt it is overgassed with a standard carbine buffer.


What ammo did you have problems with?

A heavier buffer will probably reduce the hammering that destroyed the cushion on your current buffer.

You can buy a replacement cushion if you want to replace the damaged one.

How many rounds do you think wore out the original?

high quality reloads from same batch that worked well in the Sporter before replacing the buffer in the Sporter Lightweight.  Same reloads worked flawless mag after mag in my Steyr AUG and work OK in my other AR15's

about 20K or so.  The original buffer was a no name buffer.  With the missing tip it weighs 2.8 oz

So feel somewhat confident a new standard buffer would work, just curious if lighter bolt carriers require lighter buffers since the Sporter isn't working with a H or H2 buffer

Thank you

Lighter BCG should use an adjustable gas block. Any buffer weight you use after that doesn't matter if you tune it. But I prefer a light carrier w/ a light buffer and agb

Just use a standard carbine buffer. That is all these had to begin with.

There are just too many factors in a reload.  Just because they work in other guns, the port pressure caused by different burn rates is just too variable.  This might the be barrel with a gas port size that is just barely overgassed enough to run spec ammo.  Unless you are just stuck on that load, I'd absolutely get some high quality M193 before I considered anything short stroking.  I'd bet dollars to donuts that thing will run fine on XM193 with an H buffer and a factory spec regular power carbine spring.

I think the only purpose of a light BCG is with an adjustable gas block. Get the lightest BCG, and the lightest buffer, then use the least amount of gas. That's the only way I'd do it anyways.

I had one of Colt's half moon carriers, and it hardly qualified as being lightweight. If I'm not mistaken, it was in the realm of 10.5oz. They were designed to be compatible with Colt's sear blocks way back in the day, and seemed to beat buffer faces to death.

Anyway, I would restart with a carbine buffer, and enhanced or extra power spring. Even with the slight reduction in mass, Colt never made any changes to the buffer, or action spring in carbines that were equipped with these oddball carriers.

I'm curious to see if the carbine buffer fixes this.  Please post results

Most of my builds have full auto carriers and H2 or H3 buffers, they run fine.

Even my undergassed 14.5" middy can run a FA carrier & 9mm (5 oz) buffer reliably.

Just put a .300blk pistol together and it wasn't even trying to cycle with a semi auto carrier and a std. buffer. I'd swiped a bcg from another rifle and had to buy another so I bought an AIM lightweight bcg (about 9 oz). But before that, I'd taken two weights out of a std. buffer and replaced them with a spacer from a rifle buffer, they weigh almost nothing so it only had one steel weight. Was gonna try that to see if it would cycle. If I didn't need another bcg I would have used that.

If nothing else, would be a simple way to see if it runs OK.

Also, the FA carrier I started with in my .300blk was a PSA premium, even in other rifles it ran but seemed to have some 'drag', may have been out of spec. The .300blk 8" pistol upper it was in was also PSA.
Next time I'll skip a PSA carrier and stick with AIM, this is my 3rd and they've all been better than what I paid for them.

I have an adjustable gas block and have an H2 buffer with a standard BCG. It's adjusted about halfway closed and runs/cycles great with ejection at 3-3:30.

I thought about getting a lighter BCG to take advantage of the AGB, but before spending that kind of money I tried lighter buffers (I have the KAK adjustable buffer kit). While a lighter buffer like 2oz or even 1oz let me turn the gas down and still get last round bolt hold open, it would fail to feed correctly when trying multiple rounds in the magazine. It still seemed to need the greater mass to reliably strip and feed the next round from the mag. I needed at least an H buffer before getting reliable feeding

low mass buffer systems should use an adjustable gas block and a good buffer spring. You could get bolt bounce.

I have a JP low mass carrier, 2oz buffer, Syrac adj gas block and Tubbs constant force flat wire spring in 3 gun. I don't recommend this for everyday shooting.

Use a milspec-ish BCG and H or H2 form most applications.

I did this when I used a LAW Tactical folder unit in a build by going with a LW bolt carrier and a T2 buffer.  That combo still allowed me to move towards, along with some other component changes, neutralizing the extra weight from the LAW unit.

 I will, hoping it comes in by Friday and I can try it out this weekend.

My 6920 came with a H buffer and the H2 buffer I bought for the Sporter works great in the 6920 as well.  The H and H2 buffer doesn't work in the Sporter LW.  The Sporter  came from the factory with a fixed stock and thus the longer buffer.  Thinking now the Sporter is gassed right, not over gassed, not under gassed, just needs the standard weight buffer which I had but bit the dust

So basically use a stronger spring when using lightweight BCG and buffer to help with stripping the next round?

I have both a Tubb flatwire standard and lightweight spring. I had the lightweight spring installed. I'll try it with the other one.

The following are the different spring rates that were told to me by Tubb....

Standard milspec is 7.2lb in battery, 16.5lb compressed
Tubb standard is 11lb in battery and 15lb compressed
Tubb lightweight is 7.5lb in battery and 14.2lb compressed

well....

Finally went to the range today to try the gun with these buffers from Brownells.  Standard weight, one is from Brownells and the other from Rock River, both are excellent quality

Attached File


First I did the single round in a magazine, shoot it, to see if the bolt catch worked, locking the bolt carrier back.  It did.  Tried another magazine, it did as well.  This looked promising!

Then I went to test a full 20 round magazine. I truly expected this to resolve the issue but it didn't.  I could only get about 6-7 rounds off before getting a jam like this

Attached File


Now I'm bummed.  Gun turned from an ultra reliable firearm to a Jam-O-Matic.

A little backstory.  I bought Colt LE6920 when the ban first expired.  Even though it didn't have the sear block like the Colt Sporter Lightweight did, it did come with a cut out bolt carrier.
A year or so ago the 6920 was misbehaving and I thought it was the extractor or something.  Thought it would be a good idea to get a new BCG, so I bought the Colt AR15/M16 group, slapped it in the 6920 and it worked fine ever since.  Had the side affect of giving me a spare cut out bolt carrier for the Sporter Lightweight as well, as the 6920 doesn't require the cut out carrier even though it came from the factory that way

Then I read up on troubleshooting and that cut out bolt carrier, the one on the bottom, had worn gas rings:


Attached File


 I did the test where you extend the bolt, stand the BCG on a table and see if the bolt pushed in.  It did.  So I replaced the gas rings on the bolt for that bolt carrier

I did the same test for the bolt carrier from the Sporter Lightweight, as you can see it passed:

Attached File


Ends up looks are deceiving and I was deceived.  Even though it passed the test, a light touch would make the bolt push in.  On the LE6920 carrier, more effort was needed.

On a whim I swapped the Sporter's BCG with the LE6920's BCG that had the new rings and test fired the Sporter

No jams! 

This was with one of the new standard weight buffers.

I put the Colt H2 buffer in the Sporter and test fired again.  No jams! 

Decided to do one more test, 3 x 30 rd mags and 1 x 20 rd mags.

Bam bam bam bam ...bam bam....bam! 



No jams, no failures.  Running like a champ, this was with my high quality reloads as well.

So in conclusion, the standing the bolt carrier on a table test gave me a false positive.  Going to put new rings in the Sporter's original bolt and test it next range trip.

Gloated all the way back from the range.