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For anyone who has lost part #73, detent spring.


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#1 kilo_g

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Posted 10 January 2014 - 01:11 AM

Hi guys,

I recently had the pleasure of discovering that the previous owner of my LM4 had lost the detent spring before the PTR even reached my hands. After noticing the bolt catch wasn't working right, I took everything apart and did the popular filing down of the edges where the catch meets - only to realize it was the detent spring.

Disclaimer: $1.75 is a small price to pay to buy the replacement from the pro shop, but they are currently out of stock. If you can get the KWA spring, by all means, you should probably do it. It will save you from using this experimental fix and it's potential future drawbacks.

I looked around for solutions and in one post, someone suggested to use a Bic lighter spring as a temporary replacement. What I ended up doing was taking the spring from the Bic lighter and trimming it down to fit the hole of the bolt catch group where the detent plug (?) and spring go. After firing 10 mags through the PTR, I can confirm that this works.

However, there are a couple quirks and this fix requires some fine tuning. Be sure to have the bolt catch in its rest position when you decide where you cut the spring - you want it have just enough decompression to nudge the plug out a little bit when the bolt catch is actuated. In my case, I cut from the center of the Bic spring and kept the factory "curled" end (this end goes against the plug, the cut end is the part that meets the lower receiver).

Anyway, I hope this helps anyone who has lost this spring (part #73) as I could not find any definitive confirmations that this works.

#2 SR105

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Posted 10 January 2014 - 09:54 AM

Thanks for the info! I should also point out that this is for the older LM4 owners out there. The current LM4 bolt stop has been designed to function just like the real thing, so there is no detent anymore.

#3 SnowboardeR1298

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Posted 28 January 2014 - 02:49 PM

View PostSR105, on 10 January 2014 - 09:54 AM, said:

Thanks for the info! I should also point out that this is for the older LM4 owners out there. The current LM4 bolt stop has been designed to function just like the real thing, so there is no detent anymore.

What exactly do you mean by the new LM4 bolt stop? I bought the LM4 last May and it has the same detent function. Are you referring to the bolt catch update? (part #16)

Edited by SnowboardeR1298, 28 January 2014 - 03:21 PM.


#4 SR105

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Posted 29 January 2014 - 08:41 AM

View PostSnowboardeR1298, on 28 January 2014 - 02:49 PM, said:

What exactly do you mean by the new LM4 bolt stop? I bought the LM4 last May and it has the same detent function. Are you referring to the bolt catch update? (part #16)
Yes I am referring to the updated bolt stop. The updated one no longer requires the old detent.




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