Bolt Rings

[Specialized Armament]

Is the McFarland one piece bolt ring an improvement over the three ring system?

From Brownell's:

Stops Gas Leaks & Eliminates Sluggish Bolt Performance

Single spiral of spring steel loops around the bolt three times and leaves no path for gas leakage. Replaces conventional three-piece “piston ring”-style sets that can accidentally line up, causing a major leak from the gas expansion chamber in the carrier.

I thought the ring gap alignment myth had been debunked for years. That being said, what other problem has the part solved?

[rebelEMPIRE]

If and when the rings line up, the amount of gas pressure blow-by is not enough for concern. In your car engine, it's a big deal because you lose a lot of power if that happens, but in your BCG, you only need enough pressure to ensure proper cycling of your bolt and carrier. It's been proven by others that your Bolt can run on just one ring; the others are there as merely back up.

-rebelEMPIRE

[TehLlama]

I can see a definite application on a competition rig, or when running a part-time suppressed weapon on a hard schedule (with minimal gas port and heavy buffers), but the stock ones should be adequate unless you're tinkering with trying to use as little gas as possible.

[Muddyboots]

Take a look at Mike Panonne's book on the M4. He comments on the gap issue and alignment. If it is NO issue with the three ring set up, I can't see any need for a one piece ring that may not conform to the carrier as well as three smaller rings.

Muddyboots

[tpelle]

I'm thinking that the gaps in the rings pretty much close up when the bolt is in the carrier anyway.

[Quib]

Take a look at Mike Panonne's book on the M4. He comments on the gap issue and alignment. If it is NO issue with the three ring set up, I can't see any need for a one piece ring that may not conform to the carrier as well as three smaller rings.

Muddyboots

True, and a good point.

I think I’ve mentioned this here before:

- 3 rings provide redundancy.
- Loose one ring, you still have two.
- Loose two rings you still have one.
- With a one-piece ring, loose it, and you have none.

[5pins]

I'm thinking that the gaps in the rings pretty much close up when the bolt is in the carrier anyway.

That’s what I have always though. Just how big is the gap when the bolt is? I would think it’s pretty small.

[TehLlama]

I'm a bit amazed they didn't make the one-peice ones shorter to allow a single stock gas ring to be used for redundancy.

[Quib]

I'm a bit amazed they didn't make the one-peice ones shorter to allow a single stock gas ring to be used for redundancy.

I should probably keep this idea, and market it for myself. The next thing you'll see are these style rings on the market:

- Instead of a solid one-piece ring coiled similar to a spring, design three separate rings that instead of a gap, have a slight overlap.

These rings would eliminate the gap, still flex and give for variances in the bolt carrier while in operation, and allow for the removal of individual rings in the event that a ring failed.



http://farm5.static.flickr.com/4028/4652997981_2621d751e9_b.jpg

[Army Chief]

Instead of a solid one-piece ring coiled similar to a spring, design three separate rings that instead of a gap, have a slight overlap.

Conceptually, this is a very sound idea, but I'm wondering about the potential for these sharp, angled edges to catch and foul themselves on the edges of neighboring/adjoining rings with even the slightest misalignment under normal rotation.

AC

[Quib]

Conceptually, this is a very sound idea, but I'm wondering about the potential for these sharp, angled edges to catch and foul themselves on the edges of neighboring/adjoining rings with even the slightest misalignment under normal rotation.

AC

I thought about that too.

The design though in one form, has already been in use for years. If you've ever disassembled and rebuilt a landing gear strut or a pneumatic or hydraulic actuator, you've probably had to replace Teflon back-up rings which are of the same design.

If designed correctly, with the correct angle at the meeting point, I think there's a possibility it might work. The drawing posted above was simply to get the basics of my idea across. The rings could be installed and designed in such a way, that rings passing each other do not snag one another at the overlap.

[5pins]

What is the inside diameter of the carrier where the gas rings ride?

[Quib]

What is the inside diameter of the carrier where the gas rings ride?

I measure .5375"

[5pins]

I measure .5375"

That doesn’t sound right. My new gas rings measure .5105. Did you measure inside the carrier where it steps down for the gas rings?

[Quib]

I measured as far in as my digital calipers would reach. Anything deeper would require a t-gauge which I do not have here at home.

ETA: I measured 4 separate carriers. All fell into the same window.

[Eric]

I measure .5375"
Same ballpark on the two I had sitting here. .530" and .532" per the Lyman dial.

[Quib]

Same ballpark on the two I had sitting here. .530" and .532" per the Lyman dial.

Thanks Eric for checking the dimensions as well. [:)]

If I understand 5pins correctly, he's wanting a measurement farther down within the carrier? Possibly within the area of the cam pin slot? And what I gather from his follow-up response to my measurement, is that this area is reduced in diameter (stepped down) in comparison to the mouth of the opening? Is this correct?

If the carrier inner diameter tapers towards the rear, this is new to me. All these years, I always was under the assumption that the dimension remained constant throughout, from front to rear.

[5pins]

If I understand 5pins correctly, he's wanting a measurement farther down within the carrier? Possibly within the area of the cam pin slot? And what I gather from his follow-up response to my measurement, is that this area is reduced in diameter (stepped down) in comparison to the mouth of the opening? Is this correct?


Yes, just past the cam pin slot the diameter is reduced. This is the area where the gas rings are squeezed down when the bolt is inserted into the carrier. My calipers will not reach down far enough either. I have looked all over for a blueprint or machinist drawing but can’t find one.

[Quib]

Yes, just past the cam pin slot the diameter is reduced. This is the area where the gas rings are squeezed down when the bolt is inserted into the carrier. My calipers will not reach down far enough either. I have looked all over for a blueprint or machinist drawing but can’t find one.

I never knew that was the design of the carrier. Good to know, can always learn something new!

I tried looking myself for blueprint, production or assy drawing........no luck. :(

[Eric]

Yes, just past the cam pin slot the diameter is reduced. This is the area where the gas rings are squeezed down when the bolt is inserted into the carrier. My calipers will not reach down far enough either. I have looked all over for a blueprint or machinist drawing but can’t find one.
Correct. I have no evidence to support it, but my theory is that this area may be the cause of damaged gas rings on some carriers. If the machining is rough or too pronounced, I believe it is reasonable to assume that it might be an issue.

I have no way of measuring the area with my calipers.

[Quib]

I've been out in my shop trying to devise a way to get an accurate measurement. I can't come up with anything off the top of my head, short of cutting the bolt carrier open to get a measurement.

I feel like a big dummy, LOL....... after studying the carrier more closely to try and get a measurement, I can't believe that I didn't recall the reduction in size internally. [BD]

[Quib]

In the name of Weapon Evolution, I sacrificed a bolt carrier in order to get an accurate measurement.

Behold my new bolt carrier training aid.....


http://farm5.static.flickr.com/4024/4672574499_6eca9dfd93_b.jpg

[5pins]

In the name of Weapon Evolution, I sacrificed a bolt carrier in order to get an accurate measurement.

Behold my new bolt carrier training aid.....

You’re a bigger man then me.[wow]

Thanks for your sacrifice.

[Quib]

Well, at least we now have somewhat of a good idea what the dimension in question really is.

[Quib]

More can be seen here: http://www.weaponevolution.com/forum/showthread.php?2362-BOLT-CARRIER-CUTAWAY&p=21196#post21196

[5pins]

That’s perfect Quib. This is the reason I asked the question, I was interested in how much the gap closed when the bolt was inserted in the carrier. And as Quib’s pictures show the closure is substantial.

http://generalcartridge.net/images/4675366713_82c688b3b2_b.jpg
http://generalcartridge.net/images/4675989680_34816ed41e_b.jpg

Excellent job!

[Quib]

Thank you Sir.

I kind of had a feeling this was the direction you were going with that question, and it's a question I myself have often wondered about......"Exactly how much do the gas ring gaps close up once the bolt is inserted into the carrier?"

I thought about the cutaway last night while laying in bed, and early this morning when I got up.

I decided after a couple cups of coffee, with some extra cutting I could easily illustrate just how much that gap does close up!

[Specialized Armament]

Nice photos Quib. Have we finally laid to rest the value of a one piece bolt ring?

[Quib]

Thank you Sir.

[Quib]

I've done some more cut-away work tonight. Updated pics will be posted in the next few days.

[Skintop911]

Thanks for doing that Quib. Very useful information, and a visual to go with it to boot.

[Quib]

Thank you Sir. [:)]

As I mentioned above, I did some more cut-away work yesterday, and I hope to get some new pics shot and posted here soon.

[TehLlama]

Between your front-end cutaway and ADCO's side-on cutaway, it's really easy to tell what's going on; great stuff!

[Quib]

I wasn't aware ADCO had cut-aways. Do you have a link?

[TehLlama]

From AR15.com (http://www.ar15.com/forums/topic.html?b=2&f=130&t=165511)

As above, the sectioning on yours combined with this give the most complete picture of the dimensions, relative size, and how the parts interact.

[Quib]

Ah, ok, thanks.

I was looking on ADCO's web site.

[Quib]

New photos are up.

http://www.weaponevolution.com/forum/showthread.php?2362-BOLT-CARRIER-CUTAWAY

[Eric]

Quib,
Are you able to gauge what the gap is at the ends of the compressed ring? Maybe .025" or so? Obviously is will vary somewhat between carriers and rings.

Outstanding info presented and great work on the cut-away.

[Quib]

Quib,
Are you able to gauge what the gap is at the ends of the compressed ring? Maybe .025" or so? Obviously is will vary somewhat between carriers and rings.

Outstanding info presented and great work on the cut-away.

Thank you Sir.

I'll see if I can drop a feeler gauge down into the gap. Stand by.......

[Quib]

Ok Eric....

With the ring inserted, I get about .017" gap....


http://farm5.static.flickr.com/4041/4693435054_302e0c993a_b.jpg





With the ring standing free, I get about .050"....


http://farm5.static.flickr.com/4023/4692800775_de463b8032_b.jpg