Six pointed Star marking on Sten mag.

[Brit plumber]

You can only get 19 in my mags too. If you put a full length spring in you don't even get 19 in.

---------- Post added at 08:56 AM ---------- Previous post was at 08:53 AM ----------

And although I've not tested my theory, the reduced legs of the platform stop it bottoming out before the 19th round. So the shortened spring and platform sit further up/lower down the magazine when 19/20 rounds are loaded.

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[Peter Laidler]

Well, you learn something new every day! Thanks chaps. Maybe one day I ought to write a book about the Sten. As a matter of interest (as I don't have a Sten mag and certainly not an Indian reduced capacity mag) how many can you get into an Indian mag with a normal spring and platform?

[browningautorifle]

I ought to write a book about the Sten.

"If" you do I should send mine for an autograph...

[Peter Laidler]

While I don't disagree about the change in platform design and spring length in the Indian 'shorty' mags, I've spent an hour wracking my brain as to the mechanics of why, sat in car while wifey was shopping for, well, anything if the past is anythng to go by..... The two wires (rubbing strips or RS's) simply narrow the width of the mag internally and give a more friction-free surface. It's this narrowing of the width that gives the mag its single stack feed. But even that isn't quite true factually or mathematically. That's because when the rounds contact the r/s's they still form left/right/left/right columns but just not to the same degree. As for the reduced friction, then this is a matter of fact because one little known point in mag feed systems is that as the rounds roll up the sidewall of the mag they will attempt to rotate of course. BUT, they try to rotate the next rounds in the OPPOSITE direction.AGAINST the direction they are directed to by the mag sidewall. It's horrendous in there! That's why of course, any sensible mag has ribs. Not just for corrugated strength but to reduce friction too. Hold on........, I'll come to the platform next....... The REALLY clever mag designers incorporate ribs that as well as doing that, also hold absolute control over the circular mag spring by forming a box like section in which it runs. No distortion, rollers = very little friction............ Just as the maestro George Patchett did with the Sterling.

As for shortening the length of the platform front and rear 'legs'...... Without one here, just going from memory and the design course mech notes, then in reality, you can only shorten the front and rear legs to equate with the compressed length of the platform spring which sits with them. If they have shortened them, then this can be the only reason why. Less sidewall friction = less workable load for the spring to overcome = less poundage spring needed. Mmmmmmmmmmm If it ain't broke then don't fix it.

At work we had a sectioned Sterling mag against a sectioned Sten mag for comparison. Maybe I should have had a sectioned Indian shorty mag sectioned too as a sort of halfway house between two opposites. Sorry to go off at a tangent. Just getting over my Grand National loss from yesterday!

[Vincent]

.... As a matter of interest (as I don't have a Sten mag and certainly not an Indian reduced capacity mag) how many can you get into an Indian mag with a normal spring and platform?

You can just get 19 rounds in. But I don't think it wold be crunchy proof. If the magazine will fit in the housing with the breech block forward, cocking the gun will probably drive the rounds/platform against the floorplate and force it off. I will check it later and let you know.

[Flying10uk]

The modified Indian platform is blued and the standard one is plain phosphate finish. As can be seen the legs have been shortened slightly on this Indian modified example as well as having the top of the platform flattened off. The spring has been shortened by approximately 1 1/2".

Is the marking from the Indian Workshop that did the conversion?

[Vincent]

Is the marking from the Indian Workshop that did the conversion?

That’s correct. ICR = Indian Central Railway. There’s a page or two on them in Peter’s Sten book.

[Vincent]

While I don't disagree about the change in platform design and spring length in the Indian 'shorty' mags, I've spent an hour wracking my brain as to the mechanics of why, sat in car while wifey was shopping for, well, anything if the past is anythng to go by..... The two wires (rubbing strips or RS's) simply narrow the width of the mag internally and give a more friction-free surface. It's this narrowing of the width that gives the mag its single stack feed. But even that isn't quite true factually or mathematically. That's because when the rounds contact the r/s's they still form left/right/left/right columns but just not to the same degree. As for the reduced friction, then this is a matter of fact because one little known point in mag feed systems is that as the rounds roll up the sidewall of the mag they will attempt to rotate of course. BUT, they try to rotate the next rounds in the OPPOSITE direction.AGAINST the direction they are directed to by the mag sidewall. It's horrendous in there! That's why of course, any sensible mag has ribs. Not just for corrugated strength but to reduce friction too. Hold on........, I'll come to the platform next....... The REALLY clever mag designers incorporate ribs that as well as doing that, also hold absolute control over the circular mag spring by forming a box like section in which it runs. No distortion, rollers = very little friction............ Just as the maestro George Patchett did with the Sterling.

As for shortening the length of the platform front and rear 'legs'...... Without one here, just going from memory and the design course mech notes, then in reality, you can only shorten the front and rear legs to equate with the compressed length of the platform spring which sits with them. If they have shortened them, then this can be the only reason why. Less sidewall friction = less workable load for the spring to overcome = less poundage spring needed. Mmmmmmmmmmm If it ain't broke then don't fix it.

At work we had a sectioned Sterling mag against a sectioned Sten mag for comparison. Maybe I should have had a sectioned Indian shorty mag sectioned too as a sort of halfway house between two opposites. Sorry to go off at a tangent. Just getting over my Grand National loss from yesterday!

Very interesting post, Peter. It had never occurred to me the rounds would try to rotate in opposite directions.

[Flying10uk]

It had never occurred to me the rounds would try to rotate in opposite directions.

Presumably that's why the Sterling mag has 2 rollers incorporated into it's platform?

The base plate of the Sterling mag which I happened to have on my bench visually looks very similar to that of the Sten, I happened to noticed over the weekend. I didn't check them to see if they are the same or if they are interchangeable but does anyone know if they actually are?

[Peter Laidler]

Not interchangeable. The two rollers in the Sterling mag were actually very slightly tapered to take into account the slight taper of the case and curvature of the magazine. This was another bit of sheer genius to come from George. He calculated mathematically the radius needed to ensure that the - anyway, it's all to do with the ackerman principle of angular travel and wotsit!

Thinking out aloud, you'd think that after 1959 when India was producing thousands of Sterling magazines a day, that instead of modifying Sten mags, they'd just incorporate into the design a feature to make them useable in Stens. George Patchett had thought of that too in the design. He made sure that tight fisted nations couldn't just buy Sterling mags to make their Stens more reliable. Nope....., they had to buy Sterling guns in order to use Sterling magazines!