A much weaker AR15 carbine buffer (action) spring

[zukiphile]

I need an AR carbine action spring that would be perhaps a third the weight of a normal spring. I don't know any source for a profoundly less powerful spring, but would be happy to hear any ideas on where to look.

My plan is to file one side of a spring and see how that reduces strength. Is there a better way to reduce the power of a spring?

[Sharkbite]

Use a JP Enterprises “silent captured spring” and replace the spring with whatever weight you need.

https://www.google.com/url?sa=t&sour...umDceblj0iUSZE

[zukiphile]

I believe the JPE unit requires a hollow bolt carrier. Also, $.

I would like a spring that will function with a carbine buffer body and will yield to four or five pounds of weight when in the compressed length.

[44 AMP]

I will assume you are aware of the damage that can be caused firing the rifle with too light a spring.

Talk to the people at Wolff Springs. They might have some insight, and possibly something that will do what you want, safely.

Filing, cutting coils, stretching, or any other physical changes to the spring are a trial and error thing, very possibly not consistent, or durable.

What's the gain if you weaken a spring, and on shot #3 or #33 it breaks? Bolt slams back hard, possibly breaking the buffer tube, or perhaps, even the lower receiver...

Talk to the people who make springs, then, go from there.

Just curious, WHY do you need such a light spring??

[zukiphile]

This is for a rimfire application, and I'm trying to use existing materials where possible. I'd like to retain the carbine buffer. For some off beat, i.e. non-22lr rimfire systems, the ability to add weight would be useful.

I perused Wolff. One of the great things about 1911s is the wide range of spring weights available, but then I'd need to do something different for the buffer body.

I didn't see weight ratings for shotgun magazine springs, and they are likely a bit too small in diameter. From what I recall of loading a shotgun once, the rate was essentially linear over an impressively long distance.

For preliminary testing of parts, I could clip coils off a regular carbine spring but I'm confident that I'd end up with a steeply progressive rate.

[krunchnik]

Is this for use in a AR15 22 LR upper or conversion unit??

[zukiphile]

Yes. It's a modification of a CMMG unit.

[Double K]

There was a good bit of discussion on this subject on rimfire central, you might look there.
Here's a 22lr I put together, bought a RR lower and put all high end parts in to it, CMMG upper. It's very accurate as sporters go.

[zukiphile]

For preliminary testing of parts, I could clip coils off a regular carbine spring but I'm confident that I'd end up with a steeply progressive rate.

I took almost half the length, 16 coils off the length of as AR action spring; it's barely longer than the receiver extension uncompressed, but it does close the bolt.

The travel of a rimfire bolt is less than a couple of inches, so I have a more linear resistance from the spring over that distance than I anticipated. Despite having gotten this to work, I still think that starting with a weaker spring of the same outside diameter as an AR action spring would be better.

[krunchnik]

The main spring is of no consequence on the conversion CMMG bolt-it only holds pressure on the unit.
The spring that does all the work is the one on the bolt itself.So modifying the mainspring does nothing but ruin a good spring.

[Double K]

If I remember correctly a standard strength spring is required for the CMMG upper because it acts like a buffer when shooting high velocity ammunition, it prevents damage to the back of the CMMG bolt.

[zukiphile]

Originally Posted by krunchnik

The main spring is of no consequence on the conversion CMMG bolt-it only holds pressure on the unit.
The spring that does all the work is the one on the bolt itself. So modifying the mainspring does nothing but ruin a good spring.

For this application, the AR action spring is the action spring for the CMMG bolt. The work done in a stock CMMG BCG by the very thin spring in the spring shroud is performed by a spring in the receiver extension.

That's why I need it to be much weaker.

[zukiphile]

Would any of you know the internal diameter of the spring used in 12 gauge shotgun tube magazines?

I'm wondering whether one would fit around the slim portion of an AR carbine buffer.

[45flaco]

Originally Posted by zukiphile

Would any of you know the internal diameter of the spring used in 12 gauge shotgun tube magazines?

I'm wondering whether one would fit around the slim portion of an AR carbine buffer.

@zukiphile
The shotgun mag tube pring is likely around 0.80" outside diameter, as it fits in a tube slightly larger than the rim of a 12 gauge shell.
A buffer likely won't fit inside it without lathe work.
But, they'd be about the right spring weight

[zukiphile]

Thanks for the note.

There is a lot less unused space between the buffer body, buffer spring and interior of the receiver extension than I had imagined. I was able to get it to function with a cut down rifle buffer spring, but that wasn't a good solution because it had too little force at extended length and too much when compressed.

Until I can find a different spring, I'll use a 1911 action spring, a big nail and a buffer made from a couple pieces of polymer. 1911 springs come in a full array of weights and are designed for approximately the same range of travel as a 22lr.