Aluminum Bronze Sten Breech Block

[Vincent]

OK, what don't I know? What is the benifit of a higher rate of fire with a suppressor?
Of course I guess I should talk since I have a suppressed MAC 10, 9mm, but then I don't know of any way to slow the MAC down or I might.
Sarge

To add to a little what Peter said. The gun takes standard supersonic ammunition, but the bullet never reaches subsonic speed. To achieve this the barrel has several vent holes where the expanding gas is bled off into two chambers. By bleeding the gas off this way the pressure is kept down to the point where the bullet stays below the speed of sound. It’s this lower pressure that requires the lighter breech block, because there’s not enough energy remaining to push the mass (weight) of a standard breech block back onto the sear.

Peter wrote the book on the Sten. It’s the best resource I have for my Sten recreations. I reference it and his book on the Sterling VERY often. They are so packed with information that’s impossible to remember it all, and I’ve read them cover-to-cover several times. I highly recommend them. They are not just technical references. They are entertaining too. I often laugh out loud as search for something.

So, if you use it with standard ammo in a standard gun, you get a higher rate of fire. These are all meant to operate with the parts as issued. I once made up a set of drive springs for an M3 greasegun using the butt springs from a Bren. When I touched off, it sounded like an Ingram...ran about 1000 RPM instead of 300. Neat.

Yes, you do get a higher ROF and you do need a stronger return spring, or a buffer. The higher energy has to be absorbed somehow or the breech block is going to hammer the endcap.

[Peter Laidler]

It's always worth remembering that there are sooooooooooooooo many variables in the world of 9mm that we, in our infinite wisdom, TELL the designers that our GS requirement for the product, in this case a silenced SMG, is XYZ and the finished product must operate 100% of the time, silently with UK standard 9mm Mk2z ammunition. At the start of the project any non standard ammunition was not even a point open to discussion.

I seem to remember somewhere in the back of my brain that the commercial Mk5 Sterling had a hard buffer ring seated into the back of the return spring cap. There wasn't one in our L43's but we needed one when we fired off a load of captured Iraqi 9mm made by Gevelot

[Brian Dick]

I had a bunch of that French ammo in .45 ACP many years ago. A 1911A1 pistol wouldn't even set off the primers. A suppressed MAC 10 set them off though. The backyard of my old house in Florida was filled with the projectiles! I had just phosphated the gun for a client and he obviously bought the whole case of ammo after a little quiet "test".

[Vincent]

I seem to remember somewhere in the back of my brain that the commercial Mk5 Sterling had a hard buffer ring seated into the back of the return spring cap. There wasn't one in our L43's but we needed one when we fired off a load of captured Iraqi 9mm made by Gevelot

Attachment 66246

My Mk5 buffer.

It has to be pretty hot ammo for breech block to hit the buffer.

[Peter Laidler]

It's a very fine balance Vince between not engaging the sear and getting a distinctly unwelcome burst of automatic fire and passing the sear to get that single aimed killer shot. Just a bit more poke from some makes of commercial ammo and you'll hit the buffer. That's why our L34 was mathematically calculated to operate faultlessly, every time, on RG Mk2z ammo.

I couldn't help but wonder why the rear of the commercial breech block wasn't machined flat to give it more surface area to beat against the buffer. You can imagine how David Howroyd, Bert List and I cringed to see private L34/Mk5 owners using their guns for bursts of gunfire - or indeed a whole magazine on full automatic - on various video's. Remember too that the barrel vents can carbon up over a short period of time and become almost blocked. They've got to be cleaned out

[browningautorifle]

Seems some can't understand those were meant for a single shot unless emergency use. That's why the Delisle was priceless, one couldn't get carried away. If it got bad, let the Bren go loud from 200 behind you.

[Vincent]

It's a very fine balance Vince between not engaging the sear and getting a distinctly unwelcome burst of automatic fire and passing the sear to get that single aimed killer shot. Just a bit more poke from some makes of commercial ammo and you'll hit the buffer. That's why our L34 was mathematically calculated to operate faultlessly, every time, on RG Mk2z ammo.

That’s a very good point, Peter. The L34 was made to work with the standard Mk2z ammo. I have been looking for some ROF Radway Green Mk2z for a while. The closest commercial equivalent I’ve found is 124gr RUAG. The gun runs flawlessly on it.

I have some Pakistani Mk2z... but there’s no way I am ever going to put that crap in my Mk5.

There is one brand of commercial ammo that’s right on the edge of the unwelcome burst you mentioned. What would normally be a double tap sometimes becomes a triple or quadruple tap.

I am lucky to have several types of commercial ammo available and several different springs and options for adding weight to the recoiling mass. I will eventually have a combination for 158/147gr and one for 115gr in addition to the 124gr set up I have now.

I couldn't help but wonder why the rear of the commercial breech block wasn't machined flat to give it more surface area to beat against the buffer.

Maybe the radius at the back of the breech block has to be there to keep the breech block from damaging the spring?

You can imagine how David Howroyd, Bert List and I cringed to see private L34/Mk5 owners using their guns for bursts of gunfire - or indeed a whole magazine on full automatic - on various video's. Remember too that the barrel vents can carbon up over a short period of time and become almost blocked. They've got to be cleaned out

An overnight soak in Slip 2000 carbon killer works wonders. The carbon wipes off with a rag and a brass wire brush does the trick on the barrel vents.

Seems some can't understand those were meant for a single shot unless emergency use. That's why the Delisle was priceless, one couldn't get carried away. If it got bad, let the Bren go loud from 200 behind you.

Personally, I was taught to double tap the target with the Sterling. The De Lisle is a .45 and a single shot was probably good.

[browningautorifle]

I was taught to double tap the target with the Sterling

I can see that too. We were taught double tap too, but had no suppressed stuff. Sub Machine Gun C1... but the vids are monkeys going through whole mags, as stated. The Delisle was for a single round at a few yards rather than sending a man in close.

[Vincent]

From the outside it might look like an original Mk5, but most here in the US have fairly modern suppressors. They are not limited like the ones from 70 years ago. They can take thousands of rounds of full-auto fire between cleanings and they are not difficult to clean. They don’t get carbon lock like the older ones. You can also chemically treat the internal components and the carbon just washes away in solvent. It’s no more difficult to clean than any other gun.

Another big advantage is the reduction in weight. These new suppressors are very light compared the original. The guns with them are much less nose heavy, making target acquisition faster.

The original was fantastic in its day. It has just been improved on, that’s all.

[browningautorifle]

That's right, now J or K baffles and the like.