LMT Enhanced Bolt Question

[Tyrantresister]

The bolt itself is of particular interest. The function of the dual spring extractor is frequently misinterpreted as an attempt to add spring force to the extractor claw. Rather it reduces the fatigue that the extractor spring(s) undergo by allowing the use of longer springs with lower K values; the % relative compression during the movement of the extractor is reduced. Remember that additional extractor force is not required now that the carrier is slowing the extraction cycle. The mitigation of stress in the bolt is accomplished in several ways. Material is the least visible change but is important to the design. The traditional Carpenter 158 is abandoned, being replaced by a significantly tougher grade from a different manufacturer. The lugs themselves are generously radiused between lugs and at the rear the diameter is actually reduced to allow a larger transition radius to be machined. The incorrectly identified sand cuts on the lugs are stress relief cuts. These allow any individual lug to elastically deform and give a smoother load over the contact patch. While this type of feature is very difficult to calculate and even more difficult to implement it helps to place the lug in a true shear load rather than amplify the bending moment. As noted the lug opposite the extractor is relieved. This feature prevents the unequal transfer of load to the two opposite lugs but I would argue that the stress relief groove already in place largely accomplishes this purpose. This is a academic quibble so I will bow to LMT in this respect. There is one additional feature that can be found in the bolt, but I am not at liberty to disclose the detail.

Bill Alexander

Bill, I only have one question for you. How do you think LMT's enhanced bolt compares to Denny's Super Duty bolt?

[Thomas M-4]

It's elctroless nickle.

This^^

[Tyrantresister]

How does electroless nickel compare to nickel boron?

[Mr blasty]

How does electroless nickel compare to nickel boron?

It's a good finish but in no way does it come close to the performance of NIB. I doubt you would be dissatisfied with electroless nickle though. If it wore off or you don't like it then just get it coated in whatever you want. It's still better than phosphate.

[Tyrantresister]

I think the main benefit of the enhanced LMT bolt is the mechanical design and not the coating. Things like the stronger steel, and the stress relief cuts, etc. are what makes it that much better / stronger.

[AR15barrels]

That's what I was thinking. I was thinking that I could compensate for that by using the AR-15 BCG rather than the M16 BCG (lighten it up) and go to a carbine buffer vice the 'H' buffer (further lighten the mass). But in the long run I may just go with the bolt and forget about the carrier.

The difference between M16 and AR15 carriers is so slight that it can be ignored, perhaps 1/3 ounce.

You should already be running a standard carbine buffer with a 14.5" midlength so there's nothing to be gained from switching from an H buffer to a standard carbine buffer.

[Waylander]

Sorry for the slight necropost but since this discussion seemed to revolve primarily around the use of an enhanced bolt in 5.56 (with the exception of a 7.62x39 post) I though I'd raise the question of how much this design would benefit the 6.8 platform?

If I'm not mistaken, LMT uses this BCG exclusively on their 6.8 rifles and I don't think they would be a company that would use it if it weren't warranted when they could use a less expensive BCG if possible. They seem for the most part no-nonsense IMO.

I know it's hardened steel but does anyone know if it's Carpenter 158 or 9310?

[TacticalSledgehammer]

What's the advantage of the enhanced bolt itself? Only the extractor and the cuts on lugs? Other than that would you say it's about equal to a quality bolt itself?

[Waylander]

What's the advantage of the enhanced bolt itself? Only the extractor and the cuts on lugs? Other than that would you say it's about equal to a quality bolt itself?

It's also hardened, nickel plated, and has less material taken out under the extractor like a standard bolt. Pics with the extractor removed are here.

https://www.m4carbine.net/showthread.php?t=1130

[PatrioticDisorder]

The LMT "lobster tail" extractors do not appear to increase spring tension, nor have I heard of anyone suggest they do.

I noted the decreased tension of the extractor (in comparision to the current SOCOM 5coil copper washed extractor spring, black insert, and Oring) on the LMT bolt, as it may be of concern if tried on the usual 10-11.5" uppers with their increased speed of recipication, esp with cans.

I really would've liked to see a lobster tail that used two standard AR extractor springs (captured) perhaps a wee deeper well to minimize spring compression.

Given the chance I would like to play around with this bolt, in a standard carrier, on a shorty.

I have a LMT enhanced F/A bolt group that was milled down similar to the Smith Ent "lightweight" chrome ones... just playing with ways modify the recoil impulse. It's really pretty, hah.

On an actual m4, with milspec ammo, the enhanced BCG appears to be a big plus. Two guys told me they had 35K and 50K+ on their BCG w/o issue.

I've been trying to research the LMT enhanced bolt, I'm strongly considering buying one for my DDM4V1 LW (carbine length), I'm strongly sold on the utility of the bolt, but what about the carrier, do you think the DDM4V1 would benefit from the carrier or would it potentially cause issues?

Also of relevance, Hornady TAP 75gr. .223 pressure is what I have for defensive ammo.