Correct recoil spring weight?

Hi,

I purchased this fine gun locally from someone who is getting out of the sport.  Today was my first range trip testing ammo from sand bags.

I was having some failures to eject and the slide was not locking consistently after the last round.  

For now, I'll be running 4.5 grains of N310 with Zero 185 JHP.  What weight recoil spring should I order for this set up?  The spec sheet said the gun was sold with a 12 lb recoil spring but I'm not sure that's what was in the gun when I got it.  

Here's some additional info.  Thanks,

Dave

Make sure you have oiled the barrel hood, muzzle at bushing, slide rails, and FLGR if you have one before shooting.

You may just need to drop a pound or two off your recoil spring.  Around 10-lb is common with an optic, depending on the gun and load.

Perfect, thanks for the info.  It was well oiled.  I have a 10 lb spring on hand and will try it next weekend.   
Thanks, 
Dave

What was the temperature? Sometimes you have to go up by .1 or .2 grains in the cold. 

I run an 11lb spring in my wad gun. I use the absolute lightest oil available (in my case FP10 or Marvel Machine Gun oil). Occasionally I have a kickback failure in the cold at 4.3gr of Bullseye. In the summer no problems at 4.1 for the short line. 

I would think that 4.5 would work fine with a 12 or an 11lb spring. Though my hammer spring is an 18 and yours is a 20. 

If you are buying springs, by the Woolfe kit that includes 10-15. That will give you choices if the 10 is causing battering.

Thank you for the info.  I'm in Hawaii so it's warm.  I am also using FP10 oil.  

Somewhere I read on this forum that N310 seems to be less powerful than before.  I would agree with that.  I had some loaded with 4.2 grains / 185 Nosler (same as test target) and they were not accurate and malfunctions increased.  I stopped after 3 rounds due to constant malfunctions.  

Thanks,
Dave