I have not tried the JP captured spring in my LMT but I see that DSG carries the spring as well as buffer tubes. I suppose you could just order a tube with it and keep your LMT parts aside for another build/sale? If I had not recently purchased one of Slash's heavy buffer combos I'd being going this route myself.
From the article:
What I didn’t know is that the buffer has to be modified to fit LMTs. Their Stock looks like a carbine stock, but it’s a bit longer.
So the Captured buffer came with a nylon semi translucent plastic plug to use for A2 length buffer tubes. So I guess you would use that for the modification to fit the buffer to the LMT length tube. In the interest of always overdoing something, I decided to make it out of solid teflon. I wound up making two because the measurements are not easy to get with a caliper while the assembly is in the tube. So I thought I would document what I have done. Initially I got .700″ for the length and made it like that. It wound up fitting like a d*%k in a shirt sleeve. So back to the drawing board. It was easy to measure the error after having the first plug and the second one went as well as I could have hoped.
It dropped in easily without binding, slid back out without having to go fishing for it and still engaged the buffer retainer with about .010″ of press on the pin. I opted to not drill out the center of the plug, but it may be a good idea in case you ever had to go fishing for one that was too tight in the tube. (Several people online and JP said you should/could remove the retainer pin and spring, but I know how difficult it would be to disassemble the stock on the LMT.) So I preferred to keep the pin and hopefully still use it. So if you were wondering the same thing (assuming long term that I want to go back to the traditional buffer, I haven’t done any permanent alterations to anything).
I have one in my MEGA .308. I used a standard milspec receiver extension with the JP captured spring but still had to fill in a little space to get the spring to contact the bolt carrier when assembled. JP said to drop a quarter down the receiver extension to fill in the extra space if needed. This worked well for me and fixed the accuracy issues I was having. I only had about .08" of play between the bolt carrier and JP captured buffer and it was doubling my group sizes.
For the SR-25 / LMT MWS, I would cut the included spacer to fit those extra long extensions.