Trigger weight on hardball gun too light!

About 18 months ago I picked up a used Springfield Custom Hardball .45.   Have yet to shoot it in an EIC match so far just weekly bullseye matches.   It has a very crisp light trigger on it.  I picked up a trigger pull scale a little while back and finally measured the trigger.  Sometimes it comes in right 4 lbs but most of the time  it measures at 3.5 lbs.   What can I do to make it EIC legal?

bend the appropriate finger of the spring to put more pressure on the trigger/sear.

I wouldn't adjust my trigger weight based on the results of a pull gauge.  Some pull type scales are not that easy to get a good reading with as your varying results attest too. 

I'd use either a NRA approved weight set (not cheap) or one designed like it even a home made one using a known weight is fine - if you reload you have plenty of lead around to use for weights.

Then you can think about adjusting the sear spring.

- Dave

With the gun cocked unloaded of course, put pressure on trigger, does it have resistance and spring back nice or does it have a very little resistance and feels weak? if its weak, slightly bend the middle spring leaf slightly down, this will stiffen up the free play on the trigger and add a little to the trigger weight. If the trigger feels good but still is less than 4lb slightly bend the far left spring finger down, this will add weight, you might have to do this a few times to get it just right, if your measuring with a manual or electronic, try using a dead weight this will give you a true reading, search trigger weight on here and several members have posted how to home make one.

If it's of interest, you might have a look at a page on building a very inexpensive weight on my site:

A Do-It-Yourself Trigger Weight

I weighed the trigger today with a coat hanger and ziplock bag full of 158 gr plated bullets.  Total weight was 4 lbs 0.1 oz.  the gun failed 5 tries.  Started removing bullets until it could pass.   Ended up with a weight of 3lbs 11.9 oz.  I measured the weight on my postage scale.

The adjustment you need to make will be very small.  Follow David R's instructions above.