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Thread: LMT Enhanced Bolt Question

  1. #1
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    LMT Enhanced Bolt Question

    I am currently waiting for my LMT 16in upper to arrive.I ordered it with the full auto enhanced bolt carrier group.Now i have been reading that I may be better off with the regular bolt.I was just trying to get the best I could get.Other than maybe overspending, did I make a mistake?This is my first AR so bear with me.Are there any downsides to the enhanced bolt?

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    Quote Originally Posted by markdeerhunter
    I am currently waiting for my LMT 16in upper to arrive.I ordered it with the full auto enhanced bolt carrier group.Now i have been reading that I may be better off with the regular bolt.I was just trying to get the best I could get.Other than maybe overspending, did I make a mistake?This is my first AR so bear with me.Are there any downsides to the enhanced bolt?

    The enhanced bolt might work just fine, but they tend to be picky on ammo. If you only shoot mil-spec ball then you will most likely be ok.



    C4

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    I'd would just go with a Colt/FN/LMT or CMT M16 carrier and a regular bolt CMT MP tested bolt. I haven't seen a LMT 'enhanced' carrier work in anything but a 14.5" full-auto w/M855. It's a solution is search of a problem.
    FFL/SOT armorer

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    Quote Originally Posted by gotm4
    I'd would just go with a Colt/FN/LMT or CMT M16 carrier and a regular bolt CMT MP tested bolt. I haven't seen a LMT 'enhanced' carrier work in anything but a 14.5" full-auto w/M855. It's a solution is search of a problem.

    I run two in two different 16 inch weapons and both cycle fully using everything from Wolf to M-193 spec ammo. And I run a heavy MGI RRB buffer in both.

    Perhaps they have fixed the issues in the later production.

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    I'm slow. What were these bolts supposed to "enhance?"

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    My LMT enhanced has run very well so far on mixed ammo.
    Stick


    I have been asked to point out that I am Magpul's photographer. I have also done work for 95 or so manufacturers within the firearm community, my work has been used for web, catalog, banners, magazines, covers, etc. I have also shot work for the US Military where it has been used in training aids. I am prior service and a full time LEO.


    I also shoot and write for Military Times. My primary focus is weapons, accessories and related equipment reviews. Manufacturers can reach me through any of the boards. If you have something new, let me know.



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  7. #7
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    Quote Originally Posted by Dport
    I'm slow. What were these bolts supposed to "enhance?"

    They are supposed to be more resistant to breaking lugs due to design features in both the bolt and carrier among other things.

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    I thought the enhanced since it is chromed would be smoother cycling and easier to clean.Maybe I'm dense but what could cause a bolt upgrade to be finnicky pertaining to ammo?

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    I am very much a fan of the LMT Enhanced Bolt and Bolt Carriers; especially in full-automatic fire. I have LMT Enhanced Bolt and Bolt Carriers in all four of my M4 (Class 3, full-auto) carbines. Functionality and reliability is 100-percent in both semi-automatic and full-automatic fire.

    The oldest and highest round count I have on one of my LMT Enhanced Bolt and Bolt Carriers is now approximately 34,000 rounds; and, I have never experienced a stoppage or malfunction. This last weekend I went shooting and fired 2,000 rounds, mostly on full auto, without any problems.

    I especially like the idea that the LMT Enhanced Bolt and Bolt Carrier were designed to solve the functionality and reliability problems in the SOCOM M4A1 carbines. If it good enough for SOCOM, it is good enough for me!

    I highly recommend a LMT Enhanced Bolt and Bolt Carrier for your weapon!

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    The "enhanced" bolt has less extractor tension than the new USGI copper washed 5coil spring & a Crane oring. So it might not be the deal for a 10-11.5" shortie m4. It sure is pretty though.

    The enhanced carriers run cleaner(more/different porting), have less bearing surface, and slowed cam timing. I've played with some on 14.5 & BCM & Armalite midlengths... wolf, m855, and mk262 w/o drama. I would put one on a 14.5 or 16" carbine gas system w/o worries. Do use a standard recoil spring & buffer though.

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    It bears mentioning here that there are two specific different "enhanced" pieces that LMT offers.
    The "enhanced" bolt uses a whale-tail shaped extractor with two springs and has a relief on the lug opposing the extractor to equally load the remaining 6 lugs.
    It also has the sand cuts on the lugs.
    Then there is the "enhanced" carrier.
    This has a re-timed cam slot to allow for a slower un-locking of the bolt, an extra exhaust port, re-located gas vent behind the bolt tail and additional metal up at the front where the carrier hits the extension in normal use.

    You can get these features seperately, ie: enhanced bolt with a regular carrier or an enhanced carrier with a regular bolt, OR you can get a complete enhanced bolt carrier group.

    The enhanced carrier is NOT recommended for barrels shorter than 14.5" as it extends the unlocking time and those barrels have sufficiently short dwell times that can cause problems when you extend the unlocking time.

    I recommend the enhanced carriers on 14.5" and especially 16" carbines.
    I don't feel that the bolt is really worth the extra money, but some people like them because they are electroless nickel plated and have that cool extractor...
    Randall Rausch
    AR15 Barrel Guru
    California Precision Rifle Club founding member

  12. #12
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    Let us perhaps be a little more precise with regard to the details of the LMT enhanced bolt and carrier system. As shown the details are very often misinterpreted.

    In the first instance one must understand why the system exists, more particulaly in the context that the design is brilliant in its execution, but as reported frequently on the errornet is not always reliable. The design basis for the assembly is specifically to enhance the durability of the M4 configuration as currently issued. This gun is to some extent unbalanced. Port pressures running military grade ammunition are well in excess of the design levels which leads to very high carrier acceleration rates (+22 f/s/s). this combined with chamber pressure drop often creates the undesirable condition that the bolt commences to unlock while still subject to a degree of head thrust from the cartridge case. The result is that the lugs are subject to a biaxial loading of both shear and bending.

    The LMT system being both the carrier and the bolt seeks to operate directly in this gun and elleviate symptoms. The carrier is set up with a longer delay during the initial portion of its movement. To facilitate this longer cam path and movement of the bolt forwards in the carrier, the front edge of the carrier is extended such that it still continues to retain the extractor pivot pin. Additional exhaust vents act to drop the piston pressure faster and to relieve any blowby at the tail of the bolt.

    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.

    When considering wether to use the LMT parts one must consider the weapon. Correctly ported guns will derive little or no benefit from a carrier that is specifically set up to absorb excessive port pressures and some degree of residual case pressure. If not sufficiently gassed the reliability will suffer. This is not a fault of the carrier rather a mistake made in the application so be careful with simple substitutions. The bolt itself is exemplary. If not constrained by a $ value the bolt is a worthy addition to any rifle and will do nothing but enhance the durability of this part of the system.

    Bill Alexander

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    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.

  14. #14
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    Quote Originally Posted by Dano5326 View Post
    I noted the decreased tension of the extractor (in comparision to the current SOCOM 5coil copper washed extractor spring, black insert, and Oring)
    When you say '5 coil' do you mean the 3.5 coil Colt spring? Or is there some 5-coil spring that is used by SOCOM? Do you have a photo of one?


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    Further to Bills excellent description of the Enhanced Bolt, you can see from the picture the generous radius and stress relief cuts



    I don't use my ARs for work so I don't feel I need a super duper bolt like this. Having said that I have broken 2 DPMS bolts in my 7.62X39 AR. The only bolt that keeps chugging away in this upper is the LMT Enhanced 7.62X39 bolt

    You would think the lobster tail extractor would more tension but it does not ( for the reason Bill outlined above )

    It would be be wrong however to assume it has insufficient tension. See pic below of a stuck 7.62X39 case that I managed to pull out using the charging handle...and a block of wood ! The extractor had no problem holding on to this case. As you can see the build up from the laquer coating grabbed on to this case

    Last edited by trg42; 07-28-10 at 10:39.

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    Would the LMT enhanced bolt be good to go in a BCM 16" recce middy?

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    I have the Enhanced Bolts and they run great on all ammo and even when I put them in "other" carriers. From everything I have read, Bottom line, you did buy one of the finest BCG available. You did good.

  18. #18
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    so if the LMT enhanced bolt was designed to counter the imbalances of the carbine gas system would it be correct to assume there is a diminished advantage using it in a midlength system?

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    Not for use with barrels less than 14.5" according to LMT.

    http://www.lewismachine.net/product....0a3dcdc25c31c5

  20. #20
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    Quote Originally Posted by ForTehNguyen View Post
    so if the LMT enhanced bolt was designed to counter the imbalances of the carbine gas system would it be correct to assume there is a diminished advantage using it in a midlength system?
    You are confusing the carrier with the bolt.
    The CARRIER is designed to counter the problems of the carbine gas system.
    Randall Rausch
    AR15 Barrel Guru
    California Precision Rifle Club founding member

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