BRNO Problem

daithi

I have a CZ BRNO .22lr
I'll do my best with the gun lingo, and appologise where i have not used the correct names for the parts....
Im not part of a gun club, i just do a bit of target and varmint shooting on the farm at home.

The problem i have noticed(noticed is a mild word i suppose) is that every hundred rounds or so a casing explodes, this is not really caused any problems, the bullet still fires, and the vent holes in the chamber do their thing and pressure and gas is vented through them.
I had initially put it down to a flawed caseing (i always use hyper sonic remingtons) the only time this has been a real problem was when my hand was near the vent holes and i got a nice temp black tatoo for myself (bit sore too).

I inspected the gun fully each time i use it and each time this happens, the gun is always kept clean. On a recent inspection i noticed that at the point where the left pins that grab the caseing on the bolt meet up with the left vent hole, there appears to be a notch on the chamber/barrel, on inspection of the previous shells that popped, i could see by the alignment of the pin mark on the rim that they all popped at same point corresponding to this notch.

What im wondering is if this is a flaw or part of the design? looks like a flaw to me.
If it is a flaw, what can i do about it, do i have to scrap my gun, should i bring it back too my dealer (bought it second hand from a dealer 2 years ago for 200 euro i think), do i send it to a gunsmith.
If it helps i can try get a good pic of it.

I have taken extremely good care of this gun since i bought it, i even restored the stock completely as it had a few scratches etc on it .

Oppinions?

jaycee

every hundred rounds or so a casing explodes

Hmm.. not good.

i always use hyper sonic remingtons

I have a Brno ..and it hates these . I found they produced the worst groups
of any ammo ..really inconsistant with a lot of flyers.

Perhaps they aren't seating correctly because of either wear in the gun or maybe occasional "out of spec" bullets .

how about other types of ammo..?
Any probs ..or is it just with this brand..?

daithi

I used some eley's b4, did not notce any difference(or take note if any rounds popped), the bullets fit nice and tight into the chamber, no problems there.
What ammo would you recommend yourself?

to clarify, its the rim that splits in the casing, not completely just a small hole

Barry Aldwell

daithi wrote:

I inspected the gun fully each time i use it and each time this happens, the gun is always kept clean. On a recent inspection i noticed that at the point where the left pins that grab the caseing on the bolt meet up with the left vent hole, there appears to be a notch on the chamber/barrel, on inspection of the previous shells that popped, i could see by the alignment of the pin mark on the rim that they all popped at same point corresponding to this notch.

Sounds like the extraction of brass has worn away part of the bore.

daithi

sounds like potential candidate alright, ill see if the extraction pins match the notch in any way

daithi

Here are the pics...
PS no match between any markings on the pins and the notch in photo

jaycee

I used some eley's b4, did not notce any difference(or take note if any rounds popped), the bullets fit nice and tight into the chamber, no problems there.
What ammo would you recommend yourself?

For general shooting .. I find the RWS very good ..but hard to get,
The federal bullets seem ok . You can buy them in Valuepacks of about 325 to a box.

For target the Lapua superclub (Subsonic) work pretty well and Lapua standard club are pretty good too.

I have found them the best balance between cost and results.

Any chance of posting a pic of the bolt face and extractors ?, I'd also examine the bolt to see if there is any movement at all when its closed.
It may just be a combiination of the fact that there may be lighter brass in the remingtons and some slight wear in the rifle .... and once every so often
you get a slightly "Hotter" load or thinner brass and ..Pop .

Best of luck with it..

civdef

Get the rifle to a gunsmith straight away, don't shoot it in the meantime. Rimfires are relatively low pressure rounds, and the cases shouldn't be rupturing. It's very hard to tell from pics on a computer, but it does look like there is a bit of a gap there at the near end of the extractor slot in the breech. This would result in part of the case being unsupported, which could lead to the results described.

Bottom line, the gun isn't working properly, isn't safe, and needs to be looked at.

Citizen_Erased

Not to say you shouldnt take that to a gunsmiths immediately but that is a grove that allow the extractor to pull the case out of the chamber. More than likely the hook or whatever that grabs the case is malfunctioning. It also looks like bad design because that notch appear larger than that on my gun increasing the chances of an explosion in the event of the previously mention malfunction.

civdef

Yes, there is supposed to be a slot there for the extractor to fit into, but going from the picture, it may be a bit enlarged where it meets the chamber, which could result in the case failing due to insufficient support.

There is nothing wrong with the CZ452 design, it's one of the stronger rimfire actions out there. I can think of other designs that might give a more dramatic experience if a case ruptured in this manner.

I've seen hundreds of these rifles, this is the first time I've heard of a problem of this type. Something has gone wrong with this rifle (less likely to be the ammo, I reckon) and it needs attention before it's used again.

macnas

Is that an extractor mark to the right of the rupture on the bullet??

daithi

I will include some more photos.
Thanks for the info, looks like i will have to get it to a gun smith to be safe. Who is good in the southeast?
That mark to the right is expansion at the base of the round between the rim and the rest of the caseing, it extends around most ot the round, on the opposites side of the round there is a similar expansion mark in the brass, but i have never had a problem this side

There is no movement in the bolt when it is locked in place, rock solid actually

I will add that the bore is quite tight on this rifle, it does generate a lot of pressure, i know this from when i was getting the scope sighted in the shop, the gismo they use to fit down the bore for sighting it would barely get in there. More pressure can be viewed as good and bad i suppose.

The photos were done in a rush, i never tried macro photography b4 so the focus is not great.

In the photos with a long line of caseings beside them, the caseing at the enf is flawless as it is a subsonic round.

Citizen_Erased

Maybe there is to much headspace ie the bolt is too far from the face of the chamber. This can allow the case to slide back and hence explode?