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Lightest Mainspring Weight for 45acp?


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My next build is going to have two uppers, one in 45acp and the other in 9mm. I usually use a 15# MS in my 1911s. What's the lightest any of you have gone with 45acp? I really don't want to change MS every time I swap uppers. I'm hoping 15# will cut it, maybe with an extended firing pin. But I think 17# is a safer bet. I have never had ignition problems with 15#.
thanks!

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I haven't gone below 17# with 9mm guns on Rem/CCI primers.  At one time I ran the same in some 45 guns setup for "minor" ammo.  Haven't had issues with ignition on either.

 

My opinion is that I'd want more than that to control/slow slide motion for 45 ACP.  (I personally run 23#.)  You may have some benefit running a flat bottom firing pin stop on the 45 and then round on the 9mm top.

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19lbs in everything

Except 10mm 23lbs

Keeps hammer speed up and positive ignition.

If I was build a two slide gun in 9 and 45 I'd probably go 19 to 21 if shooting factory ammo in the 45 I'd be at 21

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I run a variety of 17, 18 and 19 lb. mainsprings in my 1911s including two 45s, and 2011.  I currently running 19s in both Open guns (1911 and 2011), a 17 in one 45 and an 18 in the other 45.  When it is time to change them I'll probably go with all 19s. It makes little difference in trigger weigh, but it does feel different.  Going from 17 to 19 raises trigger weight from 2 lb. 2 ox. to 2 lb. 7 oz.  There is no reason in the world to use a 15 lb. spring.  I can get 100% reliable and safe 1.5 lb. trigger pulls with both 17 an 19 lb.  So why a 15?  If you want your slide to move back faster, alter your firing pin stop.

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As zzt states, you'll get better trigger feel with a heavier spring.  And with proper hammer and sear work, you can easily get below 2 lb pull weight with a 19 lb spring (or heavier) and it will be 100% reliable with any brand primer. 

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Exactly. It hardly if at all affects the trigger pull and is more reliable in terms of smashing primers, and it slows the slide speed down a hair, so nothing but disadvantages to go lower

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I had 15#'s in 2 1911's.  One was a 45 acp/400 CorBon and the other a 45 acp w/barsto barrel.

Had a few light strikes on one 45 when the barrel hood finally developed a bit of play, must have had well over 50,000 rounds.  Put a 17# in and it all worked again.

 

The issue is at that low weight everything must be closer to minimum spec's.  A good tight barrel hood to slide fit, primers seated a bit below flush and to ice the cake use Federal Primers.  Federals are the easiest to light off.  If you can't use Federals try it and see, worst case scenario replace it with a 17#, if still having issues go 19#.

 

The other thing to consider is the lighter the mainspring the less resistance to slide momentum.  Depending on how it feels to you, it may require you to increase your Recoil Spring or have less of a bevel on the Firing Pin Stop.  All of which will change the timing, duration and feel of the slide functioning.  And that translates into where your sights are after a shot.  Which is a key to obtaining fast, accurate splits.

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