Anybody seen this? I am interested in what the hive thinks, I am concerned about the affects of severely reducing the face of the bolt as far as structure of the lugs, wear, and the ability to strip rounds.
Wouldn’t practically removing the impact area have serious implications? I would like to see some slow motion videos to see if it would have any affect on bolt bounce as well.
Sako does this with their bolt guns. As long as there’s enough meat to strip rounds I don’t see a problem. It just looks like someone needed an OER bullet. That or they were having issues with the bolt guiding into the barrel extension.
Bolt bounce is a misnomer. This will have no effect that I can see on “bolt bounce” which is actually carrier bounce.
Justin
thanks for correcting me, I always knew that spring tension and buffer weight were the biggest factors for “bolt bounce” but for whatever reason when I saw this my mind went there, maybe just thinking of it’s ability to lock.
It does not appear that way. One of the features of the modified bolts is heavy filleting at the lug roots. This filleting (radius) helps to eliminate any stress risers that are caused by the 90 degree (ish) sharp joint where the lugs meet the bolt body. This area basically propogates cracks, which is one reason the M4 experiences a lot of broken off bolt lugs (relatively speaking).
This bolt does not appear to have any filleting at the base of the lugs, and if I remember, somebody may have actually patented that design aspect (KAC or LMT maybe?)
Additionally, an advanced bolt design would have a relief groove cut at the rear of the lugs (the side that touches the barrel extension) which would allow a fillet in this area also, for the same reasons. This bolt does not appear to have a radius at the rear base of the lugs but it’s hard to say from the pic.
I still think the coned bolt is to guide the bolt into the barrel extension. I think this because I have designed a bolt this way for the exact same reason. Look at how the bolt is not only coned, but each lug is rounded at the leading edge.
Also I am curious if that is an actual roller cam pin or just a regular pin with a round top. If it’s not a roller, it may mean they cheaped out as that pin would be an easy lathe turned part vs a lathe turned and milled part on a standard M4. Or maybe they just thought it was a better design.
Justin
They say “The lugs curved shape seek the raceways on the barrel extension if the firearm comes slightly out of time due to supression, carbon build up or any other issue.” so yes part of it’s to guide the lugs in. They also say that it is in fact a roller cam pin, I guess like LWRC has been selling that everyone says is a waste of money
They are actively responding to questions on TOS if anyone is dieing to know something.
It looks like roughly 30% of the lug has been deleted from the original bolt lug design. The Bolt locks on the BACK side of these lugs when it is in battery. When the weapon is fired, this area is what sees the high chamber pressure.
The firing pressures on the bolt are divided between 7 lugs. The pictured design has aprox 30% less material per lug but the firing pressure has not changed. It remains the same. The potential for wear/fatgiue/break appears greater than a stock bolt. It simply has less material than a stock design.
From a purely observational standpoint, I don’t see a drastic increase in bolt failures as a result of the ramped lugs.
The barrel extension lugs seem to hold up well with about that much ‘squared’ section and ramps behind them at the throat of the extension.
I know there are most likely some metalurgical differences between barrel extension and bolt, but beyond that, the revised shape shouldn’t be too much of a factor as barrel extensions seem to outlast bolts by a pretty fair margin AFA outright breakage.
Comparing the bolt lugs to the extension lugs is apples to oranges.
The barrel extension lugs are wider (more overall mass/strength) than the bolt lugs.
Barrel extensions are not made from the same material as mil-spec bolts.
I’m not sure if the ramped lugs is a issue or not. I use this example for comparason/illustration:
If you removed 30% of the material from your car or pick up truck frame, would you drive it??
Or, If you removed 30% of the load bearing material from a bridge you cross daily, would you continue to drive across it?
It’s been happening all over the forum for a day or two now.
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Lemme expand just a bit on the angled lug vs rectangular with an anology of my own:
You build 2 shelves completely out of 1x6 pine
The supports are cut to 6" along the side that is going against the wall while the 6" of the width of the board is used to hold the shelf portion and that shelf upon it is 6" deep.
Both shelves are the same length, anchored to the same wall in the same fashion on studs and have the same number of supports.
One shelf will hold no more weight than the other if the support is cut with its corners all at 90 degrees into a square shape than it will if cut as a right triangle as the very great majority of the load is being carried in shear by the side along the wall.
The triangle is a 50% reduction in size along one axis, yet the load support is the same.
In the instance of the revised bolt, the ‘shelf’ is on the rear side of the lugs where they abut the barrel extension lugs after lock, the portion in shear is where the lugs meet the bolt body proper.
**
Honestly I believe one of the reasons the lugs still retain the rectangular shape is ease of manufacturing, not extra stength.
Slots can be broached easily enough, which is currently how the lugs are machined for the long axis, but there are extra steps that would be needed to broach then taper, which would likely be done before broaching but still represent ‘extra’ processes, then radius the top outermost side of the ramp on each of the lugs.
The KAC version with the radiused lug and bolt areas would actually be easier to produce than the one this thread is about if for no other reason there are really little to no more machining processes involved with broaching the KAC shape vs standard square cut lugs. It’s simply a different shaped cutter.
I would not, but I would trust that an engineer doing a proper structural analysis can determine what areas can have material removed without adversely affecting the structural performance, or can be done by making a proper material selection.
Without seeing the stress loading calculations on the front of the bolt lugs to back up the assertion the front of the lugs is actually aiding in resisting the shear loads, that material up front may very well be “dead weight”
We also don’t know what grade of steel or heat treat is being used, which can very much play into the ultimate load resistance capability of the material and design.
From the picture, it appears the shape of the bolt lugs can come from a regular bolt profile, minus some material. I fail to see how removing material can make it stronger or better in any way.
Other designs, like KAC or LMT enhanced have additional material at the base of the lugs in the form of a radius. This shape makes them stronger.
‘Stronger’?
Unlikely unless there is a materials change.
‘Not weaker’ would be about the limit using the default standard material.
‘Better’?
Gray area.
On very low scale levels, the rounded noses and taper of the lugs could allow for easier barrel extension engagement and the lighter weight could allow for faster lock/unlock times and higher BCG cycle speeds.
Again, very incrementally small %-ages of change, but certainly plausible.
Whether that is actually better or worse :shrug:
Other designs, like KAC or LMT enhanced have additional material at the base of the lugs in the form of a radius. This shape makes them stronger.
I totally agree that a radiused transition is far superior to a sharp angled transition. Sharp corners are where failures generally begin.
Adding material or not to accomplish it is questionable though.
Certainly if the radius is quite large there would have to be significant material increase and the weight associated with it, but is that large a radius actually neccisary compared to smaller radii?
ie: does it need to really be that large with all that extra material, or would it be as mechancially sound if the curves were smaller?
Dunno.
But I do know that adding material isn’t always the answer to make something stronger.
Sometimes a subtle shape change with no change in mass, or different engineering techniques and/or materials allow for significantly lighter end results that actually have superior strength over thier ‘mass is master’ counterparts.
