Author Topic: CZ P-10C Striker Spring and HBI Trigger Rates *Warning* Very Nerdy Stuff  (Read 603 times)

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Offline earlan357

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*Copied from my blog* http://minivandoorgunner.blogspot.com/2017/09/cz-p-10c-striker-spring-and-hbi-trigger.html

One of my pet peeves is how gun companies rate springs.  Springs are typically rated in force/distance.  Gun companies typically label springs with just pounds.  A Governent 1911's recoil spring weight is the pounds exerted at 1.625" of compression.  Commander? 1.125"  Officers ACP? 0.700".  So when I look at a Glock 5.5# striker spring, what is that actually measuring? 5.5 pounds per inch?  5.5 pounds when cocked in the gun?  A 5.5 pound predicted trigger pull weight?

Who cares right?  Springs are cheap.  Just buy a few and measure the trigger pulls.  But trigger pull doesn't tell the whole story about how a trigger feels.  Take-up and reset are also effected by different spring rates and lengths, as is the energy delivered to the primer.  I'm also a huge nerd and like to geek out on little details.  So if you're eyes are glazing over, scroll down to the results below.

I figured that the only way to predict the effects the striker springs in my P-10C, would be to find their spring rate (pounds/inch) and calculate the spring pressure when the striker is in various positions in the slide.  I picked up a simple spring rater from Brownells and setup a super scientific spring lab.


The Spring "Lab"


Adjusting for 1" of Compression


I used a camera tripod to hang the scale and assembled each spring into the rater.  I pulled the red spring tube down to the table, measured the distance, then adjusted the legs.  I repeated this until the tube consistently hovered 1" above the table surface.  Then I could take a weight reading.  Pulling down on the red tube would compress the spring until it hit the table.  This gave me a rough spring rate in lbs/inch.








Then I measured the length of each springs at rest, and the length of the spring when installed on the striker.  I got 1.371".  Then I had to figure out the distance the striker compresses the spring when it catches on the trigger bar, essentially the half-cocked position.  I removed the striker spring, then measured the distance from the strikers rear face to the exit of the slide at full forward and half-cock.  Subtracting one from the other gave me an approximate distance of 0.316".  With the trigger held to the rear, I could measure the fully cocked striker at 0.437"  Unfortunately, I didn't have enough hands to get photos of measuring the striker positions.

Striker Spring Length Installed


With these measurements I could calculate spring pressure at the forward, half-cock, and break positions.  Here's the raw spreadsheet:



Here it is broken down to % reduction in spring pressure at three striker positions.
FWD is when the striker is fully forward in the slide and free of the trigger.  This is the last bit of "shove" the spring can give the striker before its momentum carries it into the primer.
Half is when the striker is caught on the trigger (trigger forward) at the start of pre-travel.
Break is when the striker is at maximum compression as it's released from the trigger.



Below are the trigger weights for each spring with HBI Theta Trigger, measured from the hook at the bottom of the trigger.



While it's obvious my measurements aren't 100% accurate, the spring weight data does correlate with the observed trigger pull weight.  However, the returns seem to diminish as decreasing striker weight does not scale linearly with weight at the trigger.  The HBI 3.5# reduces striker load at the break by 9% and results in a 9% lighter trigger.  The Wolff 5.0# reduces striker load by 32.6% at the break, but only 19.9% at the trigger. Interestingly enough, the lighter 5# spring has more spring pressure at the full forward position. 

Obviously there are a ton of other variables that effect trigger pull weight.  I'm not about to try to calculate the friction generated by each spring due to the slightly different diameters and number of coils.  No two springs are alike, and neither are guns.  But in my sample size of one, I'm going with the Wolff 5# Glock spring.

Offline Cyanide

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Re: CZ P-10C Striker Spring and HBI Trigger Rates *Warning* Very Nerdy Stuff
« Reply #1 on: September 14, 2017, 02:30:50 AM »
Great write up Earl! Quick question for you (and other P-10 C gurus), any clue as to which spring I would need to raise my trigger pull from 5 1/4# up to 6 1/2-7#?

Offline earlan357

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Re: CZ P-10C Striker Spring and HBI Trigger Rates *Warning* Very Nerdy Stuff
« Reply #2 on: September 14, 2017, 09:07:24 AM »
Great write up Earl! Quick question for you (and other P-10 C gurus), any clue as to which spring I would need to raise my trigger pull from 5 1/4# up to 6 1/2-7#?

Not sure.  Wolff makes a 6# Glock spring but according to my measurements it wouldn't be much stronger than the CZ factory spring.  The other way to increase trigger weight is to decrease the weight if the trigger springs, the 2 that pull the trigger to the rear.  Haven't played with those though nor found a compatible replacement.

Another effect the striker spring has is that it works against the recoil spring when it catches on the trigger bar.  A heavy enough striker spring would prevent the slide from closing.

You could also cheat the reading by pulling closer to the top of the trigger. 

Offline Indy_Tim

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Re: CZ P-10C Striker Spring and HBI Trigger Rates *Warning* Very Nerdy Stuff
« Reply #3 on: September 14, 2017, 05:59:36 PM »
Great write up!

Offline Bossgobbler

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Re: CZ P-10C Striker Spring and HBI Trigger Rates *Warning* Very Nerdy Stuff
« Reply #4 on: September 14, 2017, 07:11:59 PM »
Here is a copy of what Schmeky posted on springs.

Here is a simplified home method for accurately measuring the actual springs "rate":

A spring is designed with a specific strength, which is dependent on the material, the diameter of the wire and the pitch of the coils. The spring constant (k) (also known as Hooke's Law) is a measure of the strength of a compression spring and can be easily measured.

*Things You'll Need
*Washers
*Ruler or scale
*Calculator
*Electronic balance

1) Place the spring vertically on a flat surface. If the spring does not lay flat, apply a small amount of adhesive to the end of the spring to keep it from falling over.

2) Measure the height of the spring with a ruler or scale.

3) Stack washers on the top end of the spring until the spring has compressed about halfway.

4) Measure the height of the compressed spring. Do not include the stacked washers in the measurement. Subtract the compressed height of the spring from the original height of the spring to get the spring displacement (x).

5) Place the stack of washers on the electronic balance and read its weight (F).

Calculate the spring constant (k) using the formula k = F / x. If the uncompressed spring has a height of 1 inch, the compressed spring has a height of 0.5 inches and a total of 0.25 lb of washers were placed on the spring to compress it, then k = (0.25) / 0.5 = 0.5 lb/in.

Offline Deetroit

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Re: CZ P-10C Striker Spring and HBI Trigger Rates *Warning* Very Nerdy Stuff
« Reply #5 on: September 15, 2017, 11:34:12 AM »
Great write up Earl! Quick question for you (and other P-10 C gurus), any clue as to which spring I would need to raise my trigger pull from 5 1/4# up to 6 1/2-7#?

I too would like to bump up the trigger pull weight to 5ish pounds.
 

Offline earlan357

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Re: CZ P-10C Striker Spring and HBI Trigger Rates *Warning* Very Nerdy Stuff
« Reply #6 on: September 15, 2017, 12:44:55 PM »
Great write up Earl! Quick question for you (and other P-10 C gurus), any clue as to which spring I would need to raise my trigger pull from 5 1/4# up to 6 1/2-7#?

I too would like to bump up the trigger pull weight to 5ish pounds.

Where are you measuring from?  My readings were from the bottom of the trigger resting against the hook.  It's easier to get a consistent reading but unrealistically low.  From the middle, where my finger actually sits, it's more than a pound heavier.

Offline Cyanide

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Re: CZ P-10C Striker Spring and HBI Trigger Rates *Warning* Very Nerdy Stuff
« Reply #7 on: September 15, 2017, 12:51:14 PM »
Mine was measured from the middle of the trigger.

Offline .45 acp nut

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Re: CZ P-10C Striker Spring and HBI Trigger Rates *Warning* Very Nerdy Stuff
« Reply #8 on: September 17, 2017, 03:31:38 AM »
Yes, that was VERY nerdy!.................................. And informative!
Sempr Fi!

Offline schmeky

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Re: CZ P-10C Striker Spring and HBI Trigger Rates *Warning* Very Nerdy Stuff
« Reply #9 on: September 17, 2017, 12:14:34 PM »
earlan357,

Awesome post on the springs.  I agree completely, seems everyone uses a different methodology for measuring springs, so the average shooter can't readily decipher what a spring actually does or even what to expect.

I really admire the time and detail you invested.  This should help CZ owners get a better handle on what to expect from your sample of springs. 

Offline earlan357

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Re: CZ P-10C Striker Spring and HBI Trigger Rates *Warning* Very Nerdy Stuff
« Reply #10 on: September 18, 2017, 10:58:41 PM »
***Update***

I figured I should also calculate the amount of energy the spring can deliver to the striker.  I calculated the potential energy in Joules of each spring at the fully cocked position, just before the striker goes forward.  The results were surprising.

**Chart originally posted had bad data**  Correct numbers below.

Due to the amount of preload, the lightest springs don't necessarily impart less energy.  With its longer starting length, the 3# HBI trigger imparts 28% more force on the striker than the 3.5# even though it reduced trigger pull by 6% more.  Again, my measurements aren't perfect and I did not take into account the inertia of each spring or friction.  Still, the Wolff 5% and 5.5# Glock springs seem to offer the best balance of weight reduction and striker energy.
« Last Edit: September 19, 2017, 09:17:15 AM by earlan357 »

Offline dwhitehorne

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Re: CZ P-10C Striker Spring and HBI Trigger Rates *Warning* Very Nerdy Stuff
« Reply #11 on: September 19, 2017, 04:28:04 AM »
That's interesting.  I picked the 3.5 HBI spring solely over the 3 because of my concern over possible light strikes. I will have to try it out.  David

Offline Indy_Tim

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Re: CZ P-10C Striker Spring and HBI Trigger Rates *Warning* Very Nerdy Stuff
« Reply #12 on: September 19, 2017, 07:45:31 AM »
I did the same thing.  I'll have to give the 3.0 a try too.

Offline earlan357

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Re: CZ P-10C Striker Spring and HBI Trigger Rates *Warning* Very Nerdy Stuff
« Reply #13 on: September 19, 2017, 09:15:59 AM »
Oops.  I transposed some numbers from my spreadsheet when I was creating the image.  That's what I get for doing math after 10PM.  Here's the correct chart.


Offline Thebillsman

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Re: CZ P-10C Striker Spring and HBI Trigger Rates *Warning* Very Nerdy Stuff
« Reply #14 on: September 20, 2017, 11:03:37 AM »
Oops.  I transposed some numbers from my spreadsheet when I was creating the image.  That's what I get for doing math after 10PM.  Here's the correct chart.



Would you mind interpreting the Energy j and % ratings? I am only considering the HBi 3.5 and Stock, so in theory does HB's 3.5 strike the primer with 7% more force? Will it effect the velocity of the round?
P-01 Omega with LOK G10s
P-09 mounted with an APL
P-10C FDE