[Seth]

I have 2 mainspring housings for my STI, one with a light spring and one with a substantially heavier one. Unfortunately, I do not know what the weights are, but the difference is notable. Both will strike the primer with enough butt to light it off.

My question pertains to gun timing. The heavy one makes racking the slide from battery a chore, which as I can imagine effects the timing of the gun during its cycle. The light one feels, well, lighter. Anytime I hand someone the gun with the heavy one, the immediate response when racking the slide is 'WHOA that's tight'.

On a theoretical level, is there any reason not to run the lighter spring if the primer is lighting? What effect does the lighter mainspring have on trigger reliability? Is the lighter one more likely to follow or vice versa? The reason I want the light one is that it makes the trigger pull (already a tad heavy at 3.75#) a little more pleasant.

Thanks.
Seth (your 2011 student in training)

[Chris Keen]

Good question Seth. One that I too am curious about now that you bring it up.

[Seth]

It seems that there's so much mystery surrounding gun setup. If I call my smith, he'll tell me just to leave it all alone, but I don't learn anything that way and it doesn't help me tune the gun to my own liking.

I need info.

[HSMITH]

The way to choose is using hit factor as long as reliability is good with both.

I am a little tight on time this morning, I will see if I can get back later and put my thoughts on why down.

[Seth]

Hit factor?

[Aircooled6racer]

Hello: I am not a gunsmith but I would use the lighter mainspring if you don't have any other issues. The heavier spring will increase the lockup time as you would expect it to. The heavier mainspring will also give you that increased slide racking tension as well. It also gives a slight more muzzle flip. You can also look at your firing pin stop to see if it has a large or small radius. That makes a big differnce to slide racking feel and timing. If the light mainspring you are using makes the gun go bang everytime I would leave it in there. With the little knowledge that I have I hope this helps some. Thanks, Eric

[JeffCSR]

Increased dwell is needed sometimes.

For example, if you had a 10mm you'd want a squared 1/16" Radius firing pin stop Plus a heavy(23#) mainspring. This will help tone down the rearward slide battering in this type of situation.

I ran a 5" 10mm with that combo; 20# Recoil spring 23# mainspring and squared F.P. stop and it ran fine.

I've played with this too in my 45s when using a 10# or 12# recoil spring with medium to light loads.

I've heard it helps also in 1911 design mini-guns where the shorter actions need that extra dwell to help slide / recoil /feed problems but personally I've never owned or shot anything but 5 inchers.

This post has been edited by JeffCSR: 21 December 2008 - 09:02 AM

[Chris Keen]

What I think H is talking about is try 'em both on a stage you setup at the practice range, and then check your times against each other. Maybe even run a Bill Drill or some other form of a standard test on the timing of the gun so you can compare the 2 diferent spring weights, and the timing changes they bring.

[HSMITH]

CHRIS KEEN, on Dec 21 2008, 10:12 AM, said:

What I think H is talking about is try 'em both on a stage you setup at the practice range, and then check your times against each other. Maybe even run a Bill Drill or some other form of a standard test on the timing of the gun so you can compare the 2 diferent spring weights, and the timing changes they bring.

EXACTLY right. Points over time is the way to do it in as many different scenarios as you can. You can set the gun up to feel really stable when test firing and think it is just awesome to find your match scores go to hell in a handbag.

It is my opinion that a 1911 has distinct two recoil impulses, the first is on firing and the first part of slide travel, the second is when the slide hits the frame and stops rearward motion. If you look you can see it in the front sight and feel them in your hands.

The heavier mainspring will slow the first part of slide travel and take some energy from the slide. This will make the first recoil impulse harder and lift the front sight higher as well as lessen the second impulse. Overall recoil for many seems reduced. The lighter mainspring does exactly the opposite and many feel the gun is more 'harsh' to shoot. The firing pin stop radius also plays a big role here, it determines the amount of leverage the slide has on the hammer and mainspring. Buy a couple uncut and play with them as well, just don't run a square bottom or nearly square bottom, it tends to egg out the hammer pin hole in the frame over time and can wreck the frame.

Provided the gun is built correctly you should not see a change in groups or point of impact, the bullet should be long gone from the bore before the slide and barrel start to unlock regardless of combo used. If you do see a change I'd suggest getting your gun to a good 1911 plumber for a check up.

With neutral hammer and sear geometry the mainspring should have at most a couple ounces of affect on the pull weight, with positive geometry it will be much more pronounced. Positive geometry isn't a bad thing as long as the pull weight is reasonable. With negative geometry it won't last anyway so it doesn't really matter but you will see very little or no change in pull weight, this is a bad thing.

Remember, the springing of the gun and firing pin stop is a system.

[Seth]

Thanks Howard. The FPS is clearly a hand cut, smaller than STI radius.

Does the reduced mainspring pressure have any effect on trigger reliability? In my little head, I see less pressure on the strut = less chance of follow with enough sear spring pressure.

Is that reasonable?

[HSMITH]

Try one with a long radius.....

It shouldn't affect trigger reliability, what you are thinking is common but the real deal for hammer and sear reliability is the geometry of the two and depth of contact. If that isn't right it won't work, and hammer follow 'fixed' by more sear spring pressure and/or less mainspring is just a band-aid that might cover the problem up for a while but won't do anything to heal it.

[Seth]

Thank you. I appreciate your time. I always learn something.

S.