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7/11/2025 12:22:40 AM EDT
I stuck an FRT in my MPX and it works OK, but I'd like to slow down the rate of fire from what I'm guessing is currently in the 1000 RPM range to something more like 700.  With an AR9 I'd just add weight to the bolt and/or use a heavier buffer, but that doesn't appear to be an option with the MPX.  Is there anything I can do to slow it down a bit, or am I out of luck?
7/11/2025 6:48:22 AM EDT
[#1]
ILWT makes heavier recoil springs.
7/11/2025 7:03:18 AM EDT
[#2]
Quote History
Quoted:
ILWT makes heavier recoil springs.
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This
7/11/2025 9:34:29 AM EDT
[#3]
Geissele has a recoil spring kit too.  Not sure if it is theirs or just one they sell.
7/11/2025 10:05:19 AM EDT
[#4]
Thanks guys.
7/12/2025 11:01:53 AM EDT
[#5]
Geez some days I’m preoccupied I guess. I’m using the In Lead We Trust adjustable gas plug. I bought the spring kit from Geissele basically at the same time, but didn’t need the springs with the gas plug.

But I’m not running my MPX with a FRT either. Now MCX that is another story.
7/23/2025 5:08:21 PM EDT
[#6]
Which FRT works in the MPX?
7/23/2025 5:11:46 PM EDT
[#7]
Quote History
Quoted:
Which FRT works in the MPX?
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Delta Team Tactical / Rare Breed.  You also need to put a sear trip in the MPX upper.
8/1/2025 12:00:18 PM EDT
[#8]
Where do you get the sear trip?
8/1/2025 12:08:11 PM EDT
[#9]
Quote History
Quoted:
Where do you get the sear trip?
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https://frankensteinarmory.com/products/frankenstein-tsb-lite

Parker Mountain Machine makes them too, but I believe they are currently out of stock.
8/1/2025 1:37:22 PM EDT
[#10]
Thank you!
10/21/2025 2:35:36 PM EDT
[#11]
Are heavier springs enough?  I have a Copperhead-K I need to slow down, and I see ILWT offers both 120% and 140% springs.  Supposedly the Geiselle spring sets are still available if you call in, too.
10/22/2025 6:15:26 PM EDT
[#12]
OST
10/23/2025 1:20:57 PM EDT
[#13]
Quote History
Quoted:
OST
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Gesundheit?
11/2/2025 6:47:24 PM EDT
[#14]
FWIW I finally got around to trying the ILWT springs and all they did was induce malfunctions every 3-4 rounds.  Back to the factory springs and everything works OK again.
11/3/2025 5:22:54 PM EDT
[#15]
I put a ILWT reduced size gas plug (their smallest) and their higher rate springs in my Copperhead-K, it runs slower and well but has occasional failure to LRBO.  I’m going to try the original springs and see what happens.
4/29/2026 10:37:25 AM EDT
[#16]
Quote History
Quoted:
I put a ILWT reduced size gas plug (their smallest) and their higher rate springs in my Copperhead-K, it runs slower and well but has occasional failure to LRBO.  I’m going to try the original springs and see what happens.
View Quote


Did you get the MPX ROF to slow down successfully?  I heard the heavier recoil springs will slow it down better than the gas plugs, but that is the opposite in Blowback systems.  It is also the opposite in the MCX Rattler.  I have 18% reduced springs in the Rattler, and it slowed from 900 rpms down to 650 rpms.
4/29/2026 1:12:27 PM EDT
[#17]
Question-

It’s been said that FRTs are super hard on the internals of the MPX, the bolt in particular.

How many rounds do you have through yours and do you see any issues?
4/29/2026 4:47:03 PM EDT
[#18]
Quoted:


Did you get the MPX ROF to slow down successfully?  I heard the heavier recoil springs will slow it down better than the gas plugs, but that is the opposite in Blowback systems.  It is also the opposite in the MCX Rattler.  I have 18% reduced springs in the Rattler, and it slowed from 900 rpms down to 650 rpms.
View Quote


The reduced gas plug did slow it down a little and made suppressed shooting easier.

Quoted:
Question-

It’s been said that FRTs are super hard on the internals of the MPX, the bolt in particular.

How many rounds do you have through yours and do you see any issues?
View Quote


This is the reason I finally pulled the FRT out of my MPX - concern about part breakage.
5/9/2026 1:50:51 PM EDT
[#19]
Thoughts on using a Wolff AR-15, AR-10 Hammer Spring Extra Power or BRA Enhanced Power Hammer Spring to reduce the ROF in MPX?

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