200 vs 180 .45 load

A minor dilemma has appeared.  I normally use 200 G SWC (Brazos) above 3.6 grains of Bullseye.  Both my guns are tuned for this load.  I today tried some 180 G SWC (again Brazos) with the same 3.6 of BE.  Shoot well but it is obvious I need a bit more ooomph to allow slides to function as I like.  Just a few more facts.  Gun 1. is a 1911 with 12 pound recoil spring.  Gun 2. is a Smith 745 with "light" recoil spring.  

Is this to be expected?  I'm going to make some up with 3.8 and 4.0 of BE.  Won't be able to shoot them for a couple of days.

Any thoughts or suggestions?  Thanks in advance.  bob

Yep  f=mxa.
Lighter bullet (same style) needs more a to get the same f to make the gun work.

Steve is on the right track, but it’s momentum which is mass times velocity.

For 3.8 BE my velocity was 700.... so.. 200x700 has to equal 180 x V?

Doing the math, V? Comes out to be around 780.  That would need at least 4.2 BE.  So try that..  I’d bracket it for 4.0 to 4.5.

And in my 745 with the light spring 3.8 was problematic but 4.0 to 4.2 functioned ok with 200s.

Yes, you will need more powder for a lighter bullet to operate the same slide and spring weight. 

Sometimes a tighter crimp will increase pressure without increasing powder charge.

I'm using Brazos 180 flat base with 4.7 titegroup and a slide mounted 9000sc, 13 pound recoil spring. Still less felt recoil than the Brazos 200 swc with 4.3 titegroup.

For what’s its worth I shoot 200 SWC and 185 JHP for matches
200 SWC 3.8 of N310 
185 JHP 4.5 of N310

For what it's worth I use a 10 pound spring and it works for 184 or 200 grain loads with 3.8 of bullseye. However use a buffer on your spring guide and not the black kind.

The 180 doesn't seat as far into the case as the 200, either. So you will have a larger volume inside the case with the same amount of powder and get lower pressure. Just increase the powder charge .1 or .2 with the 180s.

I am running 4.0 grains Bullseye with a 200 LSWC, in cold weather, 4.1 grs. My buds shooting 185 grain bullets are all running a tenth of a grain more Bullseye than I am.

I'm running 3.8 BE with 200 gr Brazos and 12# spring with a Primary Arms slide mounted optic.  I could probably drop the spring rate a bit but it's working fine and is accurate.  I tried 4.0 BE and it kicked the brass way out.

Federal Gold Medal Match is a 185 FMC SWC.  It goes about 775 fps.  I try to match that.
It takes 4.5 bullseye or 4.7 WST.

David