blowback, and spring spec? Thoughts?

redlightrich · December 11, 2017, 10:03 AM

Hello all, as I tune my 22lr auto pistols, I wonder about the effect of lowering hammer and recoil spring spec.

On a locked breach, the unlocking occurs when the pressure reduces to a pre-determined amount. Any change in recoil or MS weight may effect the opening time.

Switching gears, on a blowback, when using a lower power MS and or recoil spring, can that serve to slow or speed the slide/bolt? Can it allow the slide to begin it's rearward travel BEFORE the round built its full power?

My "experiment" uses 2 very similar pistols, A CZ PCR (75d Compact) and a CZ 75B, both have their own dedicated Kadet kit installed. A Kadet kit, converts a centerfire pistol to 22lr caliber. It is a full system.
I can't swap these kits, as the rail is a bit wider on the PCR, which takes the Kadet kit without any fitting. The PCR kit will not install on the 75b. The 75b will work on the PCR, although the barrel assembly is noticeably loose. being that kit was fit to the 75b frame.

The PCR using a 17# MS and a "cut" recoil spring ( 1.5 coils cut off) struggles to cycle SV ammo.
The 75b with factory 20# MS, and factory length recoil spring cycles SV ammo reliably.
I realize this isn't a perfect comparo, but similar treatments were done to both, including slide rail polish and slide stop fit.
The same mags are used for testing.

I am considering returning the PCR to factory condition just to retest.

I am not seeking help to tune my PCR further. I am seeking knowledge on the effects of installing lower or higher power springs on a blowback design.

I would think the engineers, who design these kits attempt to find the best compromise, but being I am not an engineer, that is just a guess.

Merry Christmas

Rich

**4V50 Gary** · December 11, 2017, 10:16 AM

Blowback relies on the mass of the bolt for locking the action. The spring provides the power to return the bolt to closure. Weakening the spring will slow the bolt's return. Strengthening the spring can slow the unlocking and if too strong, can return the bolt faster than the magazine spring can push up the next cartridge. This was the problem with attempting to convert a selective fire version of the M1 Garand to take the BAR magazine.

Remember that engineers take this into consideration in designing their firearms. They also take into consideration the power of the cartridge - something the military has power over but something that the engineers can't really take into account for the sportsman. The sportsman generally uses SAAMI spec which the engineer can account for, to handloads which can be anywhere on the map.

As for "aftermarket kits", they are designed to do one thing: make money. Sometimes they an fill a niche market where the user will fine tune the firearm and ammunition. Other times they only suck ducats from the buyer who believes (s)he is getting a more reliable firearm. I'm against playing with springs.

Mobuck · December 12, 2017, 07:25 AM

IMHO Reducing spring tension will likely result in battering of parts.
You should be able to see if the bolt is opening while there's significant pressure in the barrel by looking at your empty cases. If they're swollen in front of the rim, the bolt is opening too quickly.
I've seen some modified pistols set up to function with sub-sonic or low noise ammo but with the disclaimer to "not use HV ammo"(or even standard velocity for that matter).

redlightrich · December 13, 2017, 08:04 AM

Thank you both. That answers a lot. Weakening the spring may take things in the wrong intended direction. As soon as the weather climbs above 10 degrees or so, I will restore the recoil spring to factory spec, and retest. I will do my best to keep the MS at 17# being it all but eliminated my trigger creep.

As a side note, both Kadets function perfectly with HV ammo. My quest is perfection with CCI SV ammo. I have 1 running perfect, one to go.

I will say, the CZ kit is better made, and functions better than most 22lr kits, but is not perfect. It is a compromise to fit many different CZ models.

Interestingly, the Ruger MkIII 22lr pistol, which cost less than the Kadet kit, functions with almost boring reliability, almost regardless of what it is fed. It is also plenty accurate, so I believe it was well engineered.

There are people, like myself, who will tune and tweak their Kadet, and get great results, reliability and accuracy, in a very comfortable package.

I am a tinkerer, in a continual search for knowledge and understanding.

Thank you again, your input places me on the right track!!

Merry Christmas

Rich

December 11, 2017, 10:03 AM	#1
redlightrich Senior Member Join Date: January 24, 2016 Posts: 323	blowback, and spring spec? Thoughts? Hello all, as I tune my 22lr auto pistols, I wonder about the effect of lowering hammer and recoil spring spec. On a locked breach, the unlocking occurs when the pressure reduces to a pre-determined amount. Any change in recoil or MS weight may effect the opening time. Switching gears, on a blowback, when using a lower power MS and or recoil spring, can that serve to slow or speed the slide/bolt? Can it allow the slide to begin it's rearward travel BEFORE the round built its full power? My "experiment" uses 2 very similar pistols, A CZ PCR (75d Compact) and a CZ 75B, both have their own dedicated Kadet kit installed. A Kadet kit, converts a centerfire pistol to 22lr caliber. It is a full system. I can't swap these kits, as the rail is a bit wider on the PCR, which takes the Kadet kit without any fitting. The PCR kit will not install on the 75b. The 75b will work on the PCR, although the barrel assembly is noticeably loose. being that kit was fit to the 75b frame. The PCR using a 17# MS and a "cut" recoil spring ( 1.5 coils cut off) struggles to cycle SV ammo. The 75b with factory 20# MS, and factory length recoil spring cycles SV ammo reliably. I realize this isn't a perfect comparo, but similar treatments were done to both, including slide rail polish and slide stop fit. The same mags are used for testing. I am considering returning the PCR to factory condition just to retest. I am not seeking help to tune my PCR further. I am seeking knowledge on the effects of installing lower or higher power springs on a blowback design. I would think the engineers, who design these kits attempt to find the best compromise, but being I am not an engineer, that is just a guess. Merry Christmas Rich

December 11, 2017, 10:16 AM	#2
4V50 Gary Staff Join Date: November 2, 1998 Location: Colorado Posts: 21,840	Blowback relies on the mass of the bolt for locking the action. The spring provides the power to return the bolt to closure. Weakening the spring will slow the bolt's return. Strengthening the spring can slow the unlocking and if too strong, can return the bolt faster than the magazine spring can push up the next cartridge. This was the problem with attempting to convert a selective fire version of the M1 Garand to take the BAR magazine. Remember that engineers take this into consideration in designing their firearms. They also take into consideration the power of the cartridge - something the military has power over but something that the engineers can't really take into account for the sportsman. The sportsman generally uses SAAMI spec which the engineer can account for, to handloads which can be anywhere on the map. As for "aftermarket kits", they are designed to do one thing: make money. Sometimes they an fill a niche market where the user will fine tune the firearm and ammunition. Other times they only suck ducats from the buyer who believes (s)he is getting a more reliable firearm. I'm against playing with springs. __________________ Vigilantibus et non dormientibus jura subveniunt. *Molon Labe!*

December 12, 2017, 07:25 AM	#3
Mobuck Junior member Join Date: February 2, 2010 Posts: 6,846	IMHO Reducing spring tension will likely result in battering of parts. You should be able to see if the bolt is opening while there's significant pressure in the barrel by looking at your empty cases. If they're swollen in front of the rim, the bolt is opening too quickly. I've seen some modified pistols set up to function with sub-sonic or low noise ammo but with the disclaimer to "not use HV ammo"(or even standard velocity for that matter).

December 13, 2017, 08:04 AM	#4
redlightrich Senior Member Join Date: January 24, 2016 Posts: 323	Thank you both. That answers a lot. Weakening the spring may take things in the wrong intended direction. As soon as the weather climbs above 10 degrees or so, I will restore the recoil spring to factory spec, and retest. I will do my best to keep the MS at 17# being it all but eliminated my trigger creep. As a side note, both Kadets function perfectly with HV ammo. My quest is perfection with CCI SV ammo. I have 1 running perfect, one to go. I will say, the CZ kit is better made, and functions better than most 22lr kits, but is not perfect. It is a compromise to fit many different CZ models. Interestingly, the Ruger MkIII 22lr pistol, which cost less than the Kadet kit, functions with almost boring reliability, almost regardless of what it is fed. It is also plenty accurate, so I believe it was well engineered. There are people, like myself, who will tune and tweak their Kadet, and get great results, reliability and accuracy, in a very comfortable package. I am a tinkerer, in a continual search for knowledge and understanding. Thank you again, your input places me on the right track!! Merry Christmas Rich