OK - so.... I'm still lost. You guys know WAY more about this than I. All I can do is meagerly follow along with logic and smile and nod for the rest. However, Peter did succinctly set out where we are. To recap:
1. Steel case rounds blow out (mostly but not always on the first round from the mag) We still don't know why
2. Brass cased rounds don't seem to blow out or even bulge. But DO get stuck in the chamber (most of the time)
We have a number of possible causes
1. Premature ejection
2. Firing out of battery
3. Head Spacing too tight
I have no experience in this - only logic. Does the fact that the blowouts are only with the steel and the case sticking is only with the brass help us to logically work this out? I don't know.
If it is the same problem being reflected in both types of rounds - you have to explain how they are connected.
If it is two or more problems - you have to be able to attribute them as they don't happen simultaneously (i.e. the Steel never sticks and the Brass never blows)
I am going to take the rifle back to the range this weekend with both steel and brass ammo to gather more data point for us.
I will lightly oil some of the brass and see what happens.
I will see if the brass sticking condition persists and if it follows any pattern.
If anyone wants me to try something with it at the range in order to gain data or eliminate a concern, please let me know. I will likely be going on Sun.
I would just ask you to oil the brass cases to see whether this helps the extraction and ejection. If it does, then from that you and we will KNOW that it is the brass cases obturating (or sticking) too tightly in the chamber.
I would just ask you to oil the brass cases to see whether this helps the extraction and ejection. If it does, then from that you and we will KNOW that it is the brass cases obturating (or sticking) too tightly in the chamber.
Exactly what are you trying to achieve? The thread started out to try to find out why you couldn't shoot 54r steel cased light ball in your semi Bren. You were concerned about the cost of brass cased ammo. The Yugo heavy ball, from what I can tell, is still about 50% for large quantities at best more than the steel cased 54r. Is the Yugo ammo corrosive?
You rightly noted that many other semi Bren users are shooting 54r steel cased light ball in their Brens without the problems you are experiencing. There is something wrong with the way your Bren is functioning.
You are now trying 54r brass cased heavy ball and the cases are sticking. Just as Peter suggested some oil may solve this particular problem. The Bren, its predecessors, the ZB guns, or caliber variations were never designed to require oiled cases to allow proper function. Any military firearm that did is just an obscure footnote to history.
IMO you may get your Bren to function marginally with the brass cased heavy ball but you haven't solved the problem with your gun nor have you solved your initial question in this thread.
I would ask you to over lubricate everything the gun, including the return spring and inside the buffer tube. Soak the back end of the carrier and the bolt. Use a light weight gun oil.
If you have some Slip 2000 gun lube, use it. You can use it in the gas system, piston and cylinder. If you don’t have Slip, leave the gas system dry.
The only reason I suggest oiling the cases Joe is to eliminate a couple of problems that have arisen. The first is that the brass cases sticking in the chamber indicate to me bad (or marginal) P-Ext and/or a badly reamered chamber where the softer but more pliable case will expand into the reamering marks and cause the sticking.
I feel that if the contributors were to sit around a table, we'd have thgis solkved in an hour, But a semi auto new-made Bren is all very new to me and I am truly grateful for the time and instruction everyone has passed on.
I've also learned something else too........... As a rule I look at weapon orientated problems and things as an Armourer with an eye to my Mechanical Engineer qualifications/way of thinking. With this, I've learned to do the opposite. Look at it as a Mechanical Engineer but with an Armourers hat on!
if the head space is too tight the bolt cant go up enough to let the carrier go all the way forward.
the bolt needs to be all the way up and the carrier needs to freely move under the bolt with no drag. there should be no change in drag on the carrier when its tested with or with out the bolt.
if you have bolt to carrier interference caused by insufficient head space or other issues such as the recess in the receiver not finished to the proper depth or the bolt and carrier not matched to the receiver. with a properly chambered round the bolt should not be exerting any downward pressure onto the carrier.
strip the gun turn the receiver upside down and insert just the carrier. it should move freely under its own weight when you tilt the receiver up and down 30 degrees.
now do the same test with the carrier and the bolt. its should lock and unlock just by tilting. the carrier should travel forward until the piston post stops it.
now with a stripped bolt and a dummy round do the test again. with your finger hold the carrier to the rear. insert the dummy into the chamber. tilt the receiver down at 30 degrees and release the carrier. parts should go forward and achieve lock up. unlock should be achieved by tilting up 30 degrees (a slight bump might be needed)
put 2 layers of masking tape on the dummy round and repeat
if you pass all these steps the gun is good. if one of these steps fails then you have a problem
The only reason I suggest oiling the cases Joe is to eliminate a couple of problems that have arisen. The first is that the brass cases sticking in the chamber indicate to me bad (or marginal) P-Ext and/or a badly reamered chamber where the softer but more pliable case will expand into the reamering marks and cause the sticking.
Peter makes a very good point.
It's not difficult to make a casting of the chamber with a low temp casting alloy like Cerrosafe. Then you measure the casting and see exactly what you have.
You don't need a fancy ladle like the one in the video. A big steel soup one works fine.
if the head space is too tight the bolt cant go up enough to let the carrier go all the way forward.
the bolt needs to be all the way up and the carrier needs to freely move under the bolt with no drag. there should be no change in drag on the carrier when its tested with or with out the bolt.
if you have bolt to carrier interference caused by insufficient head space or other issues such as the recess in the receiver not finished to the proper depth or the bolt and carrier not matched to the receiver. with a properly chambered round the bolt should not be exerting any downward pressure onto the carrier.
strip the gun turn the receiver upside down and insert just the carrier. it should move freely under its own weight when you tilt the receiver up and down 30 degrees.
now do the same test with the carrier and the bolt. its should lock and unlock just by tilting. the carrier should travel forward until the piston post stops it.
now with a stripped bolt and a dummy round do the test again. with your finger hold the carrier to the rear. insert the dummy into the chamber. tilt the receiver down at 30 degrees and release the carrier. parts should go forward and achieve lock up. unlock should be achieved by tilting up 30 degrees (a slight bump might be needed)
put 2 layers of masking tape on the dummy round and repeat
if you pass all these steps the gun is good. if one of these steps fails then you have a problem
His carrier only has one rail. Is the test going to work the same?
PM
Originally Posted by 
