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Old March 3, 2010, 10:44 AM   #1
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Join Date: February 10, 2010
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Kimber Ultra Carry II Recoil Spring.

I’ve read here and there that one should consider using a heavier recoil spring if the intention is to shoot +P ammunition. The spec sheet for my Kimber UC II states that my stock recoil spring is rated at 18 lbs. To avoid a wall of text I’ll enumerate my questions below.

1) Is 18 lbs sufficient for very occasional use of .45 +P ammunition, or should I go ahead and step up to a heavier spring?

2) The recoil spring assembly incorporates two separate springs, but I have only seen outer springs for sale. Am I correct in my assumption that the outer spring is the only one that needs replacing, or have I simply missed something?

3) If I do change to a heavier spring, be it just the outer or both inner and outer, would there be any necessity to revert to a lighter spring when firing standard pressure rounds?

Thank you in advance for suffering my ignorance. Handguns are a new beast to me and I clearly have much to learn.
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Old March 4, 2010, 12:45 AM   #2
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I know people have different views, just will say have been shooting for many years, loading over 25, and do minor gun work. I carry the Kimber CDP 4”, it has the Officer Size grips makes a good carry gun.

I tend to load even practice stuff on the warm side and run a spring with more then stock weight. I use shock buffs for practice not carry with +p that is if the gun functions properly. I have a 1911 9mm Springfield with a 9lb spring, put in 12, and it runs fine.

I have not owned a gun with the dual springs but my answer would be, if you shoot stiff ammo, add some weight. That is that as long as it feeds fine.

My 2 cents
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Old March 4, 2010, 08:39 AM   #3
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Thank you for your input, Keys. I suppose there will be some trial and error on my part, figuring out how the weapon functions with a new spring and various loads.
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Old March 6, 2010, 09:09 PM   #4
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Someone will correct me if I'm wrong, but I believe a Gov't Model uses a 16-18 lb spring.
A Commander size maybe 20 or so, and the 3"ers use (IIRC) a 24 lb spring.

Check with Wolff springs as they sell springs for everything.
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Old March 6, 2010, 11:02 PM   #5
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The ejected cases should land ~ 5 feet from the shooter.
There may be some competition shooters that want lighter springs than that, but 5 feet balances reliability with reducing felt recoil and reducing wear on the pistol.

What I wrote in 2003
1) For a semi-automatic case fired 5 feet form the floor, the time to
reach the floor is
t= square root ((2)distance / acceleration )= root (5'/32'/sec/sec)= .54 seconds

2) In a Colt .45 the ejector contacts the case when the slide is back
1.3". The farthest the slide can travel is 1.8" where it hits a stop. If

the spring is perfectly sized for the gun and the round, then the slide
will just run out of energy at the stop. Assume Vslide = 0 at 1.8".

3) Energy Slide at 1.3 inches = (force) (distance)= (16lb
spring)(1.8-1.3=.5")=.66 foot pounds of kinetic energy left in slide
when it hits the case

4) Energy is also = 1/2 mass velocity squared = .5 (mass of slide=
weight of slide/ grav accel=12 oz/32 ft/sec/sec)(V squared)

5) Combining equations 3) and 4): Vslide at 1.3" = square
root(E/(.5mass)) = root(.66 ft lb/((.5)(.023 lb sec sec /ft)) = 7.6

6)Center of gravity [this should be moment of inertia, but that would be
work] is .25" from extractor claw and ejector hits the case at .35" from the extractor claw.
Velocity of case = (.25"/.35") velocity of slide at 1.3" = (.25/.35)7.6
feet/sec = 5.4 feet per sec = 3.6 miles per hour

7) Combining 1) and 6): Distance case travels=
(Velocity)(time)=(5.4ft/sec)(.54 sec)=2.9 feet horizontally from the

And Wolff FAQ wants your empties to land from 3 to 6 feet. They must
want the slide to barely hit the stop.
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Old March 7, 2010, 07:07 AM   #6
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Most full sized 1911's are designed to use a 16# spring. However, whenever I order springs, I always order both the 16# and 18.5# springs and try the heavier spring in my gun first. In most cases I find the gun to cycle snappier and feel better. There are those that would say I am accelerating the wear on the pistol. One of my Kimbers has well over 60,000 rounds fired with the heavier spring and the gun looks like new. And...if something did break, I would replace/repair it. I'm very happy with the performance.
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Old March 9, 2010, 10:05 AM   #7
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Thank you all for bringing great advice to my ears (metaphorically, of course). As suggested I have searched out a Wolf spring set that will, hopefully, do the trick.

As a new member to the forum I must say I am delighted to find such a receptive and knowledgeable community.
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