failure to cycle? - Valmet petra .308, pls help

Discussion forum for all things Valmet!

Moderator: AGG

Post Reply
User avatar
bulm5
Posts: 11
Joined: Sun May 29, 2016 1:27 am
Location: Mauritius

failure to cycle? - Valmet petra .308, pls help

Post by bulm5 » Thu Mar 28, 2019 12:29 pm

Hi all,

Relying on your expertise!
I have a semi auto Valmet Petra .308, I am using it for boar hunting. lately I have experienced some annoying failure to cycle a new round now and then, the empty case is not ejected and stays in the rifle after firing.
Last time it happened I had a boar in my sights 50 feet away as a last opportunity before dark, and when I pressed the trigger...nothing happened apart of the click of the hammer on an empty case! By the time I noisily cycled a new round in the chamber the boar was long gone. What could be the reason for this? It is an intermittent issue but annoying enough that I cannot help checking if the empty case properly ejected and a new round fed after each shot, this is a noisy process...Could it be the ammo? the cleaning? Too much or not enough oil in the mechanism, I clean the rifle & gas tube after each hunt with Ballistol and remove excess of oil after cleaning.
I don't recall having had this problem for the first years I used the Valmet, since day one I only used the affordable south African brand of ammo Proamm available in my country and was quite happy with it, but now I wonder if I should not upgrade to better ammo, I have a box of Sako rounds and will try them on my next hunt, but if you have some idea about what could be the problem pls let me know...to increase gas pressure and strengthen the cycling, I was thinking about perhaps using a sound moderator?

thanks a lot,

Fred

GoodGuy
Posts: 907
Joined: Sat Oct 04, 2003 4:31 am
Location: Virginia

Re: failure to cycle? - Valmet petra .308, pls help

Post by GoodGuy » Sat Mar 30, 2019 5:34 am

Hi Fred...

It sound like you're doing what you need to do to diagnose your rifle's issue. It seems your rifle is "short stroking" after firing resulting in insufficient bolt movement to fully eject the fired cartridge. You've done well to clean and inspect your rifle's gas system (cylinder and piston). I would suggest, too, that you use a good bore light to inspect your rifle's chamber. Sometimes a "rough" chamber might hold onto a fired case long enough to deter proper ejection. If the chamber is rough, scrub it well and, if necessary, polish it to eliminate the roughness.

Your plan for trying different ammunition is also a very good idea. It's possible the ammunition you're using has burn rate or pressure characteristics that make it problematic for any semi-automatic action rifle. Also, it's possible that the metal used in the case itself expands to hold onto the chamber but fails to contract in time to properly "release" its hold from the chamber wall. This can be particularly problematic if the chamber is a little rough (see above).

Lastly... inspect the extractor in the bolt head closely. Make sure it has some tension on it and that it "grabs" and holds onto the cartridge case (i.e., make sure the cases don't slip off from the extractor too easily).

Good luck!
Dallas

User avatar
bulm5
Posts: 11
Joined: Sun May 29, 2016 1:27 am
Location: Mauritius

Re: failure to cycle? - Valmet petra .308, pls help

Post by bulm5 » Sun Mar 31, 2019 8:38 am

Thank you very much, I checked the extractor and chamber, tomorrow I will go hunting after work and check what is happening when I fire the .308 sako cartridges, if they do not stick to the chamber and extract well I will start using these instead of the PMP for the hunt, and use the cheaper ammo for plinking...

regards,

Fred

User avatar
bulm5
Posts: 11
Joined: Sun May 29, 2016 1:27 am
Location: Mauritius

Re: failure to cycle? - Valmet petra .308, pls help

Post by bulm5 » Mon Apr 01, 2019 1:53 pm

well, I think I nailed the cycling issue to choice of ammo, I used sako .308 rounds instead of PMP on my evening hunt today, and experienced no issue with cycling! even bagged an easter pig :-)
Attachments
20190401_175411a.jpg

Post Reply