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When the carrier is traveling rearward into the buffer tube does the buffer bumper make contact with the end of the buffer tube during the cycle of operation?
Yes. Why?
According to SOTAR this gap 68723 should be a minimum of 2 quarters which is .133-.135
Having measured several I’m seeing a variation of .080 to .155
The .133-.135 minimum is to prevent the carrier key from impacting the lower receiver in the event the buffer bumper compresses.
Out of the guns I’ve measured that are less than .133 there’s no indication of carrier impact.
I’m wondering if there is a TDP spec for this gap?
Are you seeing any unusual wear on the BCG that is affecting reliability? Are you having malfunctions?
Evil Black Rifle
08-20-22, 07:48
Chad from SOTAR knows his AR stuff, if he recommends a specific gap, you should probably follow his advice. IDK of a TDP specific gap, but I think Chad also says if the gap is on the low end, or there is contact, you can use one quarter as a spacer in the bottom of the receiver extension tube.
Are you seeing any unusual wear on the BCG that is affecting reliability? Are you having malfunctions?
Being a part time Armorer I get to measure stuff to collect data.
There doesn’t seem to be a baseline for this.
According to SOTAR this gap 68723 should be a minimum of 2 quarters which is .133-.135
Having measured several I’m seeing a variation of .080 to .155
The .133-.135 minimum is to prevent the carrier key from impacting the lower receiver in the event the buffer bumper compresses.
Out of the guns I’ve measured that are less than .133 there’s no indication of carrier impact.
I’m wondering if there is a TDP spec for this gap?
There is no specified gap, other than adding up the various lengths.
If you buy quality parts, you will wind up with the correct gap.
Buy quality and think about it no more.
Oh, btw, his numbers are too conservative, the length of the carrier, the length of the key and the depth of the hole plus the fact that one turn of the tube in ,063", mean the range is going to be greater that what he gives.
To answer the question directly:
Yes the bumper contacts the end of the tube.
It is the thing that stops rearward motion in the normal cycle of operation.
The bumper does compress slightly and then rebounds, adding to forward carrier velocity.
When the carrier is traveling rearward into the buffer tube does the buffer bumper make contact with the end of the buffer tube during the cycle of operation?
To answer the question directly:
Yes the bumper contacts the end of the tube.
It is the thing that stops rearward motion in the normal cycle of operation.
The bumper does compress slightly and then rebounds, adding to forward carrier velocity.
Thank you Clint!
There is no specified gap, other than adding up the various lengths.
If you buy quality parts, you will wind up with the correct gap.
Buy quality and think about it no more.
Oh, btw, his numbers are too conservative, the length of the carrier, the length of the key and the depth of the hole plus the fact that one turn of the tube in ,063", mean the range is going to be greater that what he gives.
He didn't give a range. Only a minimum.
When I add up all the tolerances, I get something closer to 1/8 inch (0.125") as a minimum . . . and over 1/4 inch (0.250") for a maximum.
From actual measurements taken with pin gauges I've recorded a range from 0.110 to 0.167
These are only samples from Colt, BCM, and SOLGW
The SOLGW with the VLTOR A5 buffer system are the ones that measure in the lower range and I have yet to hear or see any negative affects.
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