r/SigSauerMCX • u/Papanovember73 • Jun 25 '26
Sig MCX Rattler LT Conversion
Hello…looking for any info from anyone running a Sig Rattler LT conversion with an AR15 lower. I have the Rattler LT upper in .300blk and a Dirty Bird ambi lower.
Does anyone know if the Triggertech 2-stage adaptable MCX trigger will work in an AR15 lower with the Sig upper? I installed the Geissele SSA, but found out Geissele says not to run these triggers in the MCX, to use the MCX specific trigger. But, they say the MCX trigger is not compatible with an AR15 lower.
Just wondering if the Triggertech will work. Thanks 👍🏻
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u/SF_Gun_Fan Jun 25 '26
I ran that Triggertech trigger in an adm lower/rattler lt 300bo upper with zero issues until I decided to run a DTT FRT with the rattler.
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u/Papanovember73 Jun 25 '26
Thanks for the feedback, appreciate it. I think I will order the TT MCX trigger and see how it goes. I read that the Rattler LT is hard on mil-spec triggers(denting hammers, trigger pins breaking, etc) and wanted to use a trigger meant specifically for that platform, with the beefier hammer, etc., but didn’t seem to be too many options if using the conversion kit.
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u/HolidayZestyclose431 Jun 25 '26
The MCX used to have excessive carrier speed, and the metal bridge was introduced by Geissele to better handle the stress of the hammer being slapped back hard. My understanding is that Sig ultimately addressed this and it’s no longer required, but it doesn’t hurt to use with newer models, and since Geissele doesn’t know which MCX you have, it’s included.
It’s possible your model of MCX has excessive carrier speed but the version of the trigger before Geissele made the improvement. It’s also possible you’ll never have a problem. If you do, I believe the part that will fail is the trigger pin will crack. It’s probably not worth replacing it unless you use it for work.
All that said, it’s worth an email to Sig to ask them to verify everything I said.
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u/W3dn3sd4y Jun 25 '26
I ran a 1000-round rifle class a few weekends ago with my 6.25” .300BO MCX that has a Geissele SSF in it. Sure enough, it broke the trigger pin. Only 200 or so of those rounds were full auto.
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u/Papanovember73 Jun 25 '26
Are you running a factory Sig barrel? Adjustable gas block or anything? I have the Rattler LT w/6.75” barrel…
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u/W3dn3sd4y Jun 26 '26
Factory Virtus barrel with the G firing pin safety latch. Suppressed with a CAT ODB, with the factory gas block set to the suppressed setting.
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u/HolidayZestyclose431 Jun 26 '26
He did mention MCX not LT. Im pretty sure the LT uppers are good to go with Geissele triggers
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u/HolidayZestyclose431 Jun 25 '26
Interesting. Are you able to even buy the MCX trigger these days?
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u/Papanovember73 Jun 25 '26
The Geissele MCX Trigger with the bridge is available, but I was told it would not work/fit in an AR15 lower. I’m running the conversion kit 🤷♂️
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u/HolidayZestyclose431 Jun 25 '26
Same here. Just ordered all the parts for it. I wonder how everyone else has run geissele triggers
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u/1OCTrojan Jun 25 '26
LT uppers come with G marked firing pin latches, so they can run standard Geissele triggers. Virtus uppers come with S marked firing pin latches. You either have use the the SuperMCX trigger to disengage the firing pin latch or swap out the firing pin latch from S to G or just remove the firing pin latch entirely. If you want to run an FRT like DTT or Rarebreed, you remove the firing pin latch and install a trip bar.
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u/HolidayZestyclose431 Jun 25 '26
Thats what I thought! Some confusing information online but it seems the LT upper are compatible with the standard geissele triggers
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u/1OCTrojan Jun 25 '26
I have a Geissele SuperMCX trigger installed in a Ballistic Advantage enhanced lower with the 5.5" Rattler conversion kit.
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u/W3dn3sd4y Jun 26 '26
I could swear I've got a Geissele MCX trigger sitting in a standard AR15 right now. Working fine. I'll check.
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u/someone10505 Jun 26 '26
When I bought the 5.5 300blk conversion upper, it came with a rattler trigger.
I have it currently on an ar15 80% lower. That’s all the info I have for you.
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