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Gap between gas piston and drive block

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#1 Barely



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Posted 29 August 2016 - 05:30 PM

Can someone tell me whether it is normal to have a small gap between the gas piston and the drive block?
Upon a recent disassembly of my MKA, I noticed that the gas piston was NOT seated fully in the gas block by about 0.157" according to my caliper.  I suspect that the gas piston not being fully seated may be allowing some gas to bleed off.
On my MKA, understand that I've never been successful with any version of a low-brass round that I've tried.  I do have the low power recoil spring and flat washer installed to supposedly help with cycling low brass shell as well as I've increased the size of the gas ports and attempted to "tune" the mags.
The drive block shown in the picture is from Tooth and Nail.  Be aware that I fully seated the gas piston in the gas block for this picture.  Therefore, the .157 gap being shown is between drive block and the gas piston head.  What caught my attention was that upon disassembly, the gap was between the gas piston lip and the gas block not being seated fully.  Seems like a gap here would allow some off the gas to be bleed off that is needed for cycling the action.
Thanks in advance...

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#2 unforgiven


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Posted 29 August 2016 - 05:37 PM

too much gap


about .025 to .045 is correct

#3 Blackstuff



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Posted 13 September 2016 - 06:28 AM

That much gap will also quickly crack your gas block as it will get 'hammered' by the piston, rather than pushed. If you've got a side charging handle forend I'd recommend you get the V2 gas block from T&N as its just basically a hefty block of steel. I don't know what material the originals were made of (presumably some kind of aluminium alloy) but I went through one every 6-8 months

Edited by Blackstuff, 13 September 2016 - 06:28 AM.

#4 tshong



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Posted 19 November 2016 - 01:13 AM

Hey guys,


Stumbled on this thread and wanted to ask. Is there suppose to be a little wiggle at that gas block? I made a video here:


#5 Blackstuff



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Posted 22 November 2016 - 03:34 AM

Whether its SUPPOSED to be there I couldn't say, it is there however in all of the BR99's/MKA1919's I've handled. I've also personally been through two guide rods, two bolt carriers and 5 gas blocks and they've all had a degree of wiggle in them.

#6 Grima


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Posted 24 November 2016 - 02:33 PM

After reading this thread, I had to check my BR99

Zero gap, You hear the bolt lock when the piston is pushed fully home by the drive block.

Zero braking parts. Lost count of how many 1000's of cartridges its done.

Maybe I got one that was made wrong but works right.

Can make a Utube vid to prove it, all original parts, no tinkering or mods.

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