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Happy Camper
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7,794 Posts
Discussion Starter #1
How can one measure the spring tension on a magazine? Specifically, I need to know how to do this on a drum magazine?

I am trying to calculate the pressure the drum spring produces and need an in-the-ballpark measurement is all, nothing precise.

tia,
- Jerry
 

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Master Endmill Breaker
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1,367 Posts
Couldn't you just press down on the follower with some type of scale? Maybe place a block on a scale and press the magazine down onto it. The scale should read whatever poundage of pressure is necessary to move the follower. Just a thought... It's going to change depending on how many rounds are in the mag when it's full and when it's empty. At least you could get an idea of where you're at.
 

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Master Endmill Breaker
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1,367 Posts
Load that beast up and see how much tension there is when the spring is wound! I'm shooting in the dark here.

As cheap as the Suomi drums are, just chop one up. You know that it's spring is strong enought to feed 71 rounds. Just wear one of those anti-shark chainmail suits when you cut that baby free! You said you didn't want to, but it's right there. It's designed to feed 71 rounds of 9mm. Come on, just cut one up.

If you use the Suomi spring to turn your center rod and auger, you should be golden. For your follower, you could use a couple sections of steel tube that were slotted and coupled with a square of sheet metal, ala Romanian drum follower. If you slotted them, they would be able to shift to follow the pitch of the auger, and still line up straight when they got close to the feed lips.

I'll draw up a quick pic of what I'm talking about later tonight.
 

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Happy Camper
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7,794 Posts
Discussion Starter #5
Yes please do, I'd love to see the follower. I've never seen a Romanian drum follower before, so if you have a pic, please let me know so I can understand what you mean.

Here's an idea about the spring tension - I could put a torque wrench on the winder mechanism to gauge the tension. I would load it, then wind the spring (7 turns IIRC), measure, then disengage the spring, wind 4 turns, measure, etc. to get an average tension. This would give me at least a ballpark measurement. I'll meausre the Suomi drum the same way.

I've got 2 Suomi drums on order, *AND* I think I've found a supplier that has off-the-shelf springs that will meet our needs. If so then resources are no longer an issue.

The springs I've found go up to 10 lbs tension in the size I'm looking for, so if it is something like 20 lbs. then it may not feed correctly.

- Jerry
 
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