On my single actions I used for hunting I shimmed the mainspring so it had more tension. My old .45 Ruger Blackhawk will light off Large Rifle primers just fine. Not only does the harder smack light the primers better, I did not get unburned powder when using my favorite powder - 2400 - like a lot of people complain about.
Here is an explanation why .......

(The following is a note from Mic McPherson on primer strikes.)

In the day, when ballistics labs used manually fired universal receivers, every ballistician eventually got bored and, instead of gently pulling the lanyard until the hoop slipped off the spur on the rotating hammer (very similar to a Colt SAA hammer design, when it rotated far enough, the spur would not hold the lanyard loop and the hammer fell), they yanked the lanyard. Every time, when they did that, they noticed two things:

They recorded higher velocity
They recorded lower extreme spread and standard deviation in any long string of shots

Note that the Universal receiver has a light hammer with a 90-grain firing pin and a hammer spring similar to a typical Ruger SA, give or take. It just does not have much striker energy. The Striker tip is, however, smaller than a typical gun -- about 0.625", as opposed to about 0.70" for a typical modern gun, so it always set off the primer, despite marginal striker energy.

Note also the testing that our late friend Terry did with revolvers where he tested progressively lighter striker springs and found progressively lower muzzle velocity.

These two are related.

When you yank the lanyard on a Universal receiver, it rotates the hammer fast enough so that as the lanyard comes free, the energy of rotation in the hammer causes it to continue to rotate against the spring and therefore compress the spring significantly more than when the hammer is rotated slowly until the lanyard slips off. And, the design allows the hammer to rotate much farther than the slip-off point.

So, we have proof that more striker energy results in more velocity and more ballistic uniformity. This is because of how primers work. Compression of the pellet compresses gas contained in microscopic pockets found throughout the pellet. Compressing a gas adiabatically heats it. If compressed fast enough, that heat cannot conduct and radiate into the surrounding material fast enough to keep the temperature of the gas below the ignition temperature of the surrounding material -- identical to how a diesel engine works. So, if you compress the pellet more violently, you get more ignition centers within the compressed portion of the pellet.

More ignition centers means that the pellet burns faster and that means that it burns in place more completely (less unburned material blown more-or-less uselessly through the flash hole). That means more hot gas is generated to do a better job of penetrating into the charge and directly igniting more of the granules.

Terry Murbach showed years ago that it is the hard whack that works the best. Primers that are hit harder light the powder better. He used a S&W revolver that had a leaf mainspring. He ran some loads through the chronograph with the spring set at full strength. Then he began lightening the spring tension. The lower the tension, the lower the velocities. After a certain point of lowering the spring tension you start getting misfires.

I swapped out a number of Blackhawk mainsprings with Old Army ones to decrease lock time but I never chronographed them before or after.

I found New Model Rugers that I tried would not reliably fire a Large Rifle Primer. Sometimes it took 3 tries or more to get them to go. The transfer bar system soaks up some of the hammer energy apparently. Or it could have been light hammer springs.

On sixguns that I used for Cowboy Action I lightened the hammer spring and I never worried about it. But for carry and hunting I want to reliably light off the primers.

Colt and Ruger Single Actions?" "Before I know better." So many folks seem obsessed with lightning mainsprings and they do give a nice smooth light action but only suited for Fast Draw blanks. John Linebaugh and Hamilton would never let a gun out of their shop with a light mainspring. Just this past week I had to change the mainspring on a brand-new sixgun. In this case it was an 1858 Remington .36 which was giving me misfires and hang fires. Percussion caps need an even heavier blow than primers for reliable ignition. The Remington is set up nicely with a strain screw as Smith & Wesson double action sixguns, however it was in all the way so I tried to shim it by flattening out an empty 22 case. The idea worked fine except when tightening the screw which put a little more bend in the hammer spring it would slip out from under the hammer. The new spring solved everything.

Very interesting! I don’t believe ever ready anything about that before. I guess I always assumed a primer lit the same no matter how it was whacked! Do you mind if I share this info to a local page, Jim?

--
https://facebook.com/M2bKydex/