recoil spring

I doubt you will ever break a recoil spring, it will just loose it's tension slowly. How often should you replace it. I don't think Smith has come out with an official answer I have a contact there I can ask and report back.



I will also give you my recommendation: I think every 5,000 is reasonable especially if using full power loads. Would definitely not go over 10k without a swap I think you'd be looking for trouble.



$15 for Speed shooter guide rod (one time purchase)

$8.95 IMSI spring (every 5k)

sounds like cheap insurance.



Dan

Here is my questions and the responses(bold) I got from a S&W engineer:



1. People have asked what kind of interval you all suggest changing the recoil spring assembly. (our suggestion is 5000 rds. when we shot endurance guns we shot some springs over 10000 before replacing, as long as the gun reliably closes in full battery the spring is doing its job.)

2. What are the recoil spring rates you guys are using in the 9, 40, 357 (currently we use the same spring for all three 9/40 and 357, in the future we will be using a heavier spring in the 40 and 357 as far as spring rates they are something like this;



current 9/40 spring "marked blue"

10lb

k=3.7 lb/in



future spring for 40/357 and possibly 45 spring "marked green"

13lb

k=2.9 lb/in)

They do know what the spring rate is. It is 10#. The fact that they are considering changing it, I don't think indicates that there is anything wrong with the 10#.



You need to understand that in the M&P design you do not need a heavy recoil spring to keep the barrel in battery during ignition. The only thing the heavier spring would is slow the slide's velocity down a bit. Do they need to slow its velocity more? NO, slowing the slide more would reduce the slides impact on the frame but the current combination has already demonstrated exceptional durability . So, I don't think changing the spring weight is really going increase it's durability much, maybe they think they can get take it just a bit farther.



This is just my guess: :roll:

I think the current spring set up was intended to run both 9 and 40 and would be easier to make just a single assembly. But now with the 45 coming out they are going to have a Blue (10#) and a Green(13#). So if it will run on the same spring as the 45 and you have to produce a new assembly anyway why not give it a try. I fit gets a little more durability, bonus.



I could be wrong all together and this is just evolution in action, they found it just works better with the 13# 8)



As far as factory replacements just give them a call ask for part #279740000 $6.36



As far as lighter springs IMSI makes an 11# spring which if the 13# IMSI feels like stock I may deduce that the 11# may feel lighter. But again I may be in left field (been there before and the grass was nice )



Dan