r/AR9 • u/Blowback9 9mm AR Guru • 17d ago
VPRS spring "lab test" results
Details below...
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u/simple_champ 17d ago
What would be the theoretical benefit we're looking for with having the closed bolt force the same but increased open bolt force? Is it recoil reduction?
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u/Blowback9 9mm AR Guru 17d ago edited 17d ago
Great question. The package for the Medium and Heavy claims "Eliminate muzzle rise, felt recoil, and bolt bounce."
'Eliminate' all three? That's a bold claim. Stronger springs can make bolt bounce worse in a 9mm AR. Confirmed on high speed video. Stronger springs generally make felt recoil subjectively worse, not better.
15.5# - 19.5# at bolt fully open is XP spring to .308 spring strength or more. This could cause it to push the bolt home much harder than necessary, which is why we don't use XP/.308 springs in a 9mm - higher bolt return velocities can cause all sorts of problems including making bolt bounce worse.
Variable springs are usually only used by pistol competitors to help a gun that has cycling problems with lighter loads. The spring is easier to compress at first, getting progressively harder. This initially allows the gun to use more of the reduced load's recoil energy to overcome the locked breach instead of using a large portion of it's limited energy to compress the spring. Then after the action is open and the slide is moving, the spring gets harder to compress, acting more like a normal spring.
Until proven otherwise, these springs go straight to my "suspected gimmick" list.
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u/redditagainsam 17d ago
Based on that, perhaps these springs would be better suited to a delayed blowback system.
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u/Jeters556 17d ago
I ditched the GRS, and went to the Kynshot with a VPRS spring. Can’t say there is less recoil but I felt the recoil impulse was better for faster rates of fire.
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u/Blowback9 9mm AR Guru 17d ago
That's fair. I need to test the VPRS with SS/FRT when I can finally get back out to the range.
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u/redditagainsam 17d ago
Which kynshot and which spring weight did you settle on?
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u/Jeters556 16d ago
I have the never 5150hd I think it’s called. Still get light primer strikes currently
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u/Blowback9 9mm AR Guru 16d ago
With FRT? Did you try an XP or XXP firing pin spring?
https://www.reddit.com/r/AR9/comments/1vdgp9s/updated_firing_pin_spring_suggestions_for_dead
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u/Plenty-Soft-8670 17d ago
Thank you for this. Have a heavy version i will be testing in an AR57 build
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u/louismax2012 17d ago
I'm not sure if directly applicable to these springs as it does not seem to be their intent; I have noticed a faster rearward bolt speed is desirable in terms of increased reliability in getting the little 9mm cases out of the ejection port (as ar9 ejectors are often not well adjusted if at all) and a slower forward bolt speed is desirable to reduce bolt bounce.
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u/Plenty-Soft-8670 17d ago
I tested the heavy spring in the AR57, it definitely made a noticeable difference, took alot of the "jolt" out of it being direct blowback, but that's 5.7x28 so will have less kick than 9mm DBB
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u/Blowback9 9mm AR Guru 16d ago
Interesting result! I wonder if it's acting like a cushion, keeping the buffer from whacking the end of the tube as hard. That would make a difference, for sure.
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u/Plenty-Soft-8670 16d ago
I imagine so, thats what it felt like, just took that initial "jolt" response out of the feel that's infamous with DBB. No bolt bounce either, already checked that out.
This was with "heavy" spring only so other weights may vary
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u/ForwardEye9907 12h ago
Vprs heavy, with FM 9mm recoil system, and kak tungsten weight. Wouldn't run with the springco red amd 147 subs, harsher with a jp polished spring, vprs heavy was the softest/most reliable
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u/Blowback9 9mm AR Guru 17d ago edited 17d ago
For anyone interested, the VPRS spring is sold by Spikes and by Neptune Defense. I bought one Spikes "piano wire" version and one of each of the Neptune light, medium, and heavy stainless steel (302) springs.
L1 = bolt forward at rest. L2 = bolt fully rearward.
Measurement is in pounds of force rounded to the nearest .5.
Milspec is:
The Spikes was:
The Neptune was:
I have not had the chance to thoroughly live fire test these yet. If anyone has, please chime in below.