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Thread: Bolt fails to stay open on PMAG M3 but ok with Lancer L5 AWM mag

  1. #31
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    Rainier-Arms just got back to me.

    There are two uppers and the same one lower.
    #1 Rainier-Arms 16" mid-length gas with port size =0.090 brass ejection at 4:00 [Woks great]
    #2 Lilja 16" carbine-length gas with port size =0.080 brass ejection at 1:00 [Over-gas situation)

    Does the observations make sense for #2 being over-gassed?

  2. #32
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    #1 actually seems large, too, but yes, .080 makes #2 at least .017 oversized.
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  3. #33
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    Quote Originally Posted by SPQR476 View Post
    #1 actually seems large, too, but yes, .080 makes #2 at least .017 oversized.
    Agreed. Rainier was kind enough to respond with the following "The gas port diameter on our Medcon barrels are .09".

  4. #34
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    Quote Originally Posted by patrick0525 View Post
    Rainier-Arms just got back to me.

    There are two uppers and the same one lower.
    #1 Rainier-Arms 16" mid-length gas with port size =0.090 brass ejection at 4:00 [Woks great]
    #2 Lilja 16" carbine-length gas with port size =0.080 brass ejection at 1:00 [Over-gas situation)

    Does the observations make sense for #2 being over-gassed?
    Based on the port sizes, barrel length, and gas system lengths, yes, it makes sense to me.

    Joe Mamma
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  5. #35
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    #2 is definitely overgassed at .080"/CAR

    #1 would be almost as overgassed IF the port were acutally .090"/MID

    I had a 16" mid with .093 port that would rip the rims off steel case wolf and throw everything to 1:00

    Have you actually measured the Rainier gas port?

    I suspect the port is actually ~.080", or their is a huge leak somewhere.

    In either case, #1 appears to be working fine, so I wouldn't worry about it too much.

    Quote Originally Posted by patrick0525 View Post
    Rainier-Arms just got back to me.

    There are two uppers and the same one lower.
    #1 Rainier-Arms 16" mid-length gas with port size =0.090 brass ejection at 4:00 [Woks great]
    #2 Lilja 16" carbine-length gas with port size =0.080 brass ejection at 1:00 [Over-gas situation)

    Does the observations make sense for #2 being over-gassed?
    Black River Tactical
    BRT OPTIMUM HFCL Barrels - Hammer Forged Chrome Lined 11.5", 12.5", 14.5"
    BRT OPTIMUM Barrels - 16" MPR, 14.5" MPC, 12.5" MRC, 11.5" CQB, 9" PDW
    BRT EZTUNE Preset Gas Tubes - CAR and MID
    BRT Covert Comps 7.62, 5.56, 6X, 9mm
    BRT MarkBlue Gas Tubes - BRT EXT, EXC and PDW Lengths
    BRT MicroPin Gas Blocks - .750" & .625"
    BRT MicroTUNE Adjustable Gas Blocks
    BRT CustomTUNE Gas Ports

  6. #36
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    Quote Originally Posted by Clint View Post
    #2 is definitely overgassed at .080"/CAR

    #1 would be almost as overgassed IF the port were acutally .090"/MID

    I had a 16" mid with .093 port that would rip the rims off steel case wolf and throw everything to 1:00

    Have you actually measured the Rainier gas port?

    I suspect the port is actually ~.080", or their is a huge leak somewhere.

    In either case, #1 appears to be working fine, so I wouldn't worry about it too much.

    I have not measured #1 or #2 since both gas blocks have been pinned to the barrel.
    More likely to buy an adjustable gas block or use a gas port insert and then measure #2 port's diameter size.

  7. #37
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    Range update:
    I built a new lower for the upper in question;

    the new lower
    Joe Bob billet lower
    Three Bravo Company parts: carbine spring, H Buffer 3.8oz, and mil-spec buffer tube

    Result: PMAG M3 magazine locked back properly after the last round (tried a total of 50 rounds)
    I asked someone to observe the brass ejection. It was 2-3 o'clock.


    the original lower
    Mega Arms billet
    Sprinco blue spring
    Spikes Tactical ST-T2 Buffer 4.1 oz
    POF USA mil-spec Buffer Tube, Anti-Tilt carrier

    Any comments? Still an overgassed condition. I think the sprinco spring was responding faster than what the PMAG M3 can react to.
    Last edited by patrick0525; 02-01-14 at 17:16.

  8. #38
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    I think all the answers have been provided. In addition since you changed springs and buffers you changed the variables.

    Quote Originally Posted by patrick0525 View Post
    Range update:
    I built a new lower for the upper in question;

    the new lower
    Joe Bob billet lower
    Three Bravo Company parts: carbine spring, H Buffer 3.8oz, and mil-spec buffer tube

    Result: PMAG M3 magazine locked back properly after the last round (tried a total of 50 rounds)
    I asked someone to observe the brass ejection. It was 2-3 o'clock.


    the original lower
    Mega Arms billet
    Sprinco blue spring
    Spikes Tactical ST-T2 Buffer 4.1 oz
    POF USA mil-spec Buffer Tube, Anti-Tilt carrier

    Any comments? Still an overgassed condition. I think the sprinco spring was responding faster than what the PMAG M3 can react to.



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  9. #39
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    This weekend I removed the Geissele super gas block and measured the gas port. The diameter is 0.080"
    I am planning to install a Wilson adjustable gas block.

  10. #40
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    Went to the range and tested with the Wilson adjustable gas block. It went well. The brass was ejecting at 3 0'clock and the PMAG M3 did not have any issues.
    I also lucked out. The barrel dimples done by my gunsmith for the Geissele gas block matched perfectly with the Wilson gas block.

    I even got to play around. With one round in the magazine, and me tuning for more gas restriction, I even got the bolt to lock back with the brass failing to eject. The brass was extracted but still in the ejection area. It was loose and in front of the locked bolt. Adjusting for more gas solved that issue.

    Thank guys for all your help.

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