Broken Charging Handle

#116

I love the physics of structures and moving objects!

If MCARBO wants to make a really strong charging handle they would need to modify the counter weight from a round cut to a rectangular cut and have a greater contact area for a charging handle with a higher center of gravity.

@ChrisNelson how about a modified MCARBO counter weight? Should be relatively easy to machine!

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#117

This is what I learned Brother @Dred

Just spoke with Adam @MCARBO for up to date info, he was very helpful, in fact just awesome. There is a presently a newly released design of the RCH. I just ordered and recently received mine mid November. He suggested I measure mine with a caliper to determine if I received the new RCH .043 or old stock .064.

Explained-
The depth of the milled in steel on the old version is .064, the newer improved stronger charging handle is .043 and spring notch is shallower which should provide more strength to the RCH and prevent the failures of the past.

He required pics of my RCH, but the measurements are so close it’s hard to determine by pics sent. I will measure with calipers and let Adam know my findings.
Hope this info helps brothers!

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#118

@Patriot1 that would help, but the shaft (judging from previous pics) is failing at the point of contact with the base of the charging handle.

From a physics point of view that makes perfect sense and to be expected.

A rectangular cut shaft mated to the base would distribute the inertia of the charging handle over a greater area by using an inherently stronger structure. (It would also allow MCARBO to make their own heavy counterweight to slow down the cycle rate.)

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#119

I guess only time and use will tell John, we’ll see. :+1:

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#120

@Patriot1 I completely agree with you! And I do think MCARBO is going in the right direction with the new RCH.

I like the RCH, it is what I mount on my game gun, and it along with the polished feed ramp solved the problems of first round loads with the polymer coated ammo we are required to use in competition.

The down side is it is shaving metal from the leading edge of the counterweight due to increased drag and down-force.

I would just hate to lose a stage due to a structural failure.:hushed:

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#121

No I have never slapped it. I always clear the notch and let it slide forward on it’s own.

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#122

Many S2K shooters are seeking to do two different things: 1. They want to improve the grip length of their OEM charging handles 2. They want to change the mechanical impulse (recoil) of the weapon.

All shooters want reliability!

A charging handle such as this, cut from flat bar stock, and mated to a heavy counterweight and possibly a shorter spring would do all of that and solve the failure issues by being a stronger structure and having a low CG (putting the mass where it belongs in the counter weight and in-line with the bolt).

It would also positively index with the spring eliminating the turning to “find the flat spot” issue.

Since it is cut from flat stock the machining would be simpler and result in lower production costs.

The heart of the charging handle problem is that “round is not strong” in the manner in which it is being employed. The solution lays with changing both the structure of the charging handle and the cut in the counterweight.

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#123

@ChrisNelson Better picture…

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#124

@Johnksg I think you are correct with the physics and have identified the pertinent issues but believe your focus on the charging handle in a way overlooks the real issue. The problem is the one you have identified. If you put a substantial amount of weight at the end of a small circular shaft that is subject to repeated mechanical force, you virtually guarantee an eventual fracture at the point you have identified and where the fractures have in fact been occurring. One way of working around that is what you have suggested but why are we doing this in the first place?

As you noted, shooters are looking to do two different things: 1) They want to improve the grip [ease of use] of their OEM charging handles; and 2) They want to change the mechanical impulse (recoil) of the weapon. But they can do the first without creating the problem discussed above in any meaningful way. A longer, fatter or more easily controlled charging handle does not necessarily have to be a heavier charging handle that imparts undue stress upon a potential fracture point. It could be a total redesign like you suggest but it does not have to be if it is lightweight. (Even without added weight, the sheer leverage from the added length of the two finger charging handle and the reports of breakage suggest it should at least be “skeletonized” to reduce the added force imparted by that leverage). Such a lighter handle will not in any way achieve the second objective, but it should be far less prone to failure.

As for the second objective, you seem to have already decided as have I that the charging handle is a poor tool with which to manage recoil. There are simply too many downsides with fracture being only one of them. And there are many other tools available to reduce recoil. One is a heavier bolt but that is a balancing act that has to consider a number of factors. What I have not seen considered and what is well beyond my ability to estimate is the potential impact of increased weight at different areas of the bolt . With today’s metallurgical processes and computer controlled milling equipment a manufacturer could readily manipulate and control the weight at varying points along the length of the bolt. I really would like to know the impact on recoil of additional weight at the rear of the bolt; the front; the middle; etc. That is an area probably worth researching. In any case, that seems a more productive place to focus on reducing recoil than the charging handle where adding weight solely for that purpose seems like a plan guaranteed to eventually cause fractures.

That’s my two cents worth for you to think about.

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#125

@JoeFridaySays I think you have some very good insight and I agree with you.

I posted some pics of the additional wear the RCH is causing on the bolt/weight against my other S2K for comparison.

The structure of the modified charging handles is the problem, not how they are made, and not what they are made of. :+1:

If we want a real solution, one that will not interfere with the balance of inertia on a blowback action, and be more user friendly I would suggest a slotted rail.

If MCARBO was making uppers it would be very possible to attach a slotted rail to the bolt, thus moving the charging handle forward of the receiver. It would assemble in a similar manner to a rail on a shotgun.

The drag of the rail could in effect take up some of the burden of the counterweight, resulting in a lighter bolt group, and thus less mechanical impulse.

Plus if forward you would not need a very big charging handle as mechanical advantage would be in the users favor.

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#126

@JoeFridaySays You know as I ponder and mull around your points there could be some merit in distribution of weight forward of the bolt group on a charging handle rail. (Think of a pull in addition to a push force). With a properly increased spring tension it should be possible to maintain cyclic timing while at the same time reducing mass of the weight which would lead to less mechanical impulse.

Of course it would require a new receiver to do properly. But a blowback receiver is basically just a pipe…easy peasy!

I do hope Chris makes a new receiver with a detachable pistol grip lower. From there the PCC could be bundled and configured to how the user wants it.

There would be no limiting the concept then. It would be the new AR of the firearms world for PCC. :grin:

#127

@Johnksg You are way beyond my firearms knowledge or comprehension but the folks who should know hopefully are listening. :exploding_head:

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#128

@JoeFridaySays I think you bring up some valid points regarding physical force and simple machines. I think you absolutely have a place at the table.:+1:

Here is the often overlooked beauty of the S2K. The block of plastic and the barrel/chamber are basically isolated from the mechanical impulse of the cycling action. This makes the S2K surprisingly accurate to most!

Take it a step further as you suggested, fix both the problem of the location of charging handle and redistribute the weight…

Theoretically you could have a very short, even lighter carbine, with less felt recoil!

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#129

I’ll jump in here a bit, yes the small shaft and the big weight will always break, it’s just a matter of time. It’s making me doubt installing my RCH.

I’ll toss in an idea, I know kel-tec has a heavier brass bolt, but is there any heavier metal that could be used? Or ovalize the shaft of the CH to help spread the load? Only other option could be a non-reciprocating CH, but don’t know how possible it could be.

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#130

@CatFood yeah your right, the RCH and the 2FCH are not the answer. An oval shaft could improve the strength of the shaft but is the higher CG of the CH that is causing the problem. (CG is moved outwards either through increased length or increased weight).

They are breaking at the point were the shaft meets the handle.

The other problem as @JoeFridaySays points out is the ergonomics of the location and the short charging handle.

A rectangular cut base as I sketched out earlier would work, but Brian’s idea to redistribute the weight takes it a step further…

It can improve the ergonomics, give greater mechanical advantage, and lighter weight!

It would require a different receiver, but that is just a simple tube. Easier to recut that than almost any other part.

The original Thompson submachine gun (back when it was named the Annihlator) used a friction design that used some of those principles.

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#131

Other companies make lathe turned charging handles (they all look like MCARBOs) but i think their ignoring the strength of the billet in touting their process.

Plus the cost is higher.

And it looks like their still snapping off at the base!

I think the solution lays with an MCARBO receiver…from there so many things can be improved. :grinning:

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#132

I’ll throw this out, just a rough concept. Using the cz scorpion CH as inspiration. Non reciprocating CH, don’t know if it could ever be made. Would be able to HK slap the heck out of it. CH would never experience repetitive impacts besides initial bolt drop, but my scorpion is functioning perfectly.

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#133

@CatFood @Johnksg
WOW! I understand most of the physics and mechanical concepts you guys are discussing but you exceeded my firearm knowledge right after “You pull the trigger and it goes Bang.” Maybe most are getting it but could you dumb the explanations down a bit for me and anyone else that is similarly slow but won’t admit it?

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#134

My two finger charging handle from Twisted Industries broke recently. It broke where the shaft is flattened and recessed for the recoil spring with a hole drilled though the flattened area. I have since replaced it with the M-Carbo version and no problems so far. I also keep the OEM charging handle in my range bag just in case.

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#135

@JoeFridaySays lol. Sorry!

I have never built/designed a weapon in my life, but I have spent a lifetime studying the evolutions in design in doing evaluations. I also taught physical science. So I apologize for my poor explanation since I must rely on mere words and not the great graphics you can produce! :grin:

To put it simply…take a popsicle stick and break in half. Easy right? Now break in half again. Difficult. Try to break it again. Impossible. This is the problem with the longer 2FCH is the length of the structure and where the CG point is.

You also get the same result by matching a large mass, such as the RCH, outside of the bolt group. It moves the CG outwards and the charging handles predictably break in the same location.

You could use a different shape as I originally suggested, put the greater mass of the charging handle, with a lower CG, back into the bolt unit.

Or just simply use the OEM part…I don’t think I have heard reports of them breaking?

But as you pointed out ergonomics is an important issue and the location and use of the OEM charging handle stink!

You made the comment about changing the distribution of the mass of the bolt group. Thats what got me thinking about changing the location of the charging handle completely to solve both problems at the same time! :+1:

@CatFood yes a non reciprocating charging handle would do the trick. HK makes some finely engineered equipment and they also charge HK $$$!

Also to do so you would need to redesign the existing receiver & bolt group. It is an interesting idea though! :grin:

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