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Thread: XCR-M Bolt and Carrier?

  1. #11
    Rifleman popups's Avatar
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    Gas System

    Quote Originally Posted by kolob View Post
    Let me try to answer some questions here. The bolt and carrier are different. There's lots of reasons and not enough room to discuss here. It has nothing to do with the caliber. I like the .308 design a little more because it's more efficient.

    [b]The gas system is very much like that of the M-14. It works almost exactly like that of the M-14. The M-14 had a shutoff located on one side (I think it was for launching grenades). Instead of a shutoff, we have a gas valve with five settings (one is for a suppressor). Unfortunately we could not use the stock M-14 parts so we designed our own.
    Doesn't the XCR funnel gas through the gas tube like the Kalashnikov? Wouldn't just having another setting for low power on the gas regulator be enough for low pressures or very adverse situations such as mud?

    Does the M need to build pressure with a plug? So is that why the gas block extends an inch (from what I can tell) under the receiver? Would that mean the "gas tube" is no longer needed?

    Why wasn't the original design viable in the M? Was it because it would require a certain distance from the chamber, which would limit flexibility?

    With that type of design, doesn't it change from: relying on gas to continuously move the operating rod to the rear, to a design that relies on initial momentum provided by the pressure that builds within the plug?

    I am intrigued, so, sorry if I ask too many questions. I figure that it is better to ask in the forum -- than send emails -- for my understanding of the engineering done for the XCR system.

  2. #12
    Marksman AEnemaBay's Avatar
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    Re: Gas System

    Quote Originally Posted by popups View Post

    Doesn't the XCR funnel gas through the gas tube like the Kalashnikov? Wouldn't just having another setting for low power on the gas regulator be enough for low pressures or very adverse situations such as mud?
    Don't have an answer for your other questions, but I just wanted to point out that the Kalashnikov doesn't funnel any gas through the gas tube. All of the gas needed to work the action is used on the piston head while it's seated in the gas block. After that the remaining gases (like the gas that makes it into the tube) is useless.

    The same operation is carried out in the XCR-L, where the "gas tube" is just a place for the carrier/piston to travel and guide itself into the gas block hole.
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  3. #13
    XCR Guru MickeyC's Avatar
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    Re: XCR-M Bolt and Carrier?

    The gas tube is more of a piston/oprod guide and has some venting for excess gas.

    It does look to be similar to the M14 system as Alex has stated. Without a schematic it's just supposition on my part but it looks like the elongated gas plug provides an expansion chamber that generates a longer and gentle ramping push stroke rather than a snappy impulse.

    Judging by some of the powder marks on some of the pictures we've seen it looks like the design may still use the floating piston to control gas flow, which is a pretty good system. This controls flow into and out of the expansion chamber. Again, I could be wrong as I haven't seen the schematics.

    If the design does follow the M14 design then dwell time will be greater than other designs and bolt velocity will be slower to build, resulting in less violent operation. Lower stresses and pressure should also provide greater life expectancy of the parts. Also if this is the design used the lack of a bend in the op-rod and the M14 style gas system should result in less wear when using hot ammo.

    It wil be interesting to see what this has alloowed in terms of a bolt and carrier design. Hopefully someone will post some pictures soon after getting their rifle.
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  5. #14
    Rifleman popups's Avatar
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    Re: Gas System

    Quote Originally Posted by AEnemaBay View Post

    Don't have an answer for your other questions, but I just wanted to point out that the Kalashnikov doesn't funnel any gas through the gas tube. All of the gas needed to work the action is used on the piston head while it's seated in the gas block. After that the remaining gases (like the gas that makes it into the tube) is useless.

    The same operation is carried out in the XCR-L, where the "gas tube" is just a place for the carrier/piston to travel and guide itself into the gas block hole.
    I was figuring that the Kalashnikov system still uses the gas that is left over to maintain the momentum of the carrier. I understand it isn't necessary for the AK, as it doesn't have a regulator, but it is for a Saiga shotgun correct? That is why I used the name "Kalashnikov".

    Quote Originally Posted by MickeyC View Post
    The gas tube is more of a piston/oprod guide and has some venting for excess gas.

    It does look to be similar to the M14 system as Alex has stated. Without a schematic it's just supposition on my part but it looks like the elongated gas plug provides an expansion chamber that generates a longer and gentle ramping push stroke rather than a snappy impulse.

    Judging by some of the powder marks on some of the pictures we've seen it looks like the design may still use the floating piston to control gas flow, which is a pretty good system. This controls flow into and out of the expansion chamber. Again, I could be wrong as I haven't seen the schematics.
    I can see how delaying the operation cycle is an improvement for the envisioned use of the M. If I think of the adjustable gas regulator, I can understand why, it now extends under the forearm. However, wouldn't having the gas block extend into the receiver affect the barrel's harmonics, whether that is for the good or the bad, especially the thin barrel?

    Do you think with the bolt, carrier and gas block being redesigned, the XCR be more functional in mud? The only tests I have seen was a water test from Mr. Rob and Martens' Youtube tests. Or was the failures from the tight tolerances of the upper receiver and the operating system?

  6. #15
    Marksman BADDFROGG's Avatar
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    Re: XCR-M Bolt and Carrier?

    I would really love to see photos of these parts...prior to me pre-ordering it. It is pricey but probably very well worth it. I really like the new stock. Just wondering how strong it is? Still on the fence between the .308 or the .260 Remington? Like I have previously posted before: I really love my RobArms XCR-L 6.8. It is my favorite rifle, shoots great, and does not kick. I love the design and the engineering. Thinking about ordering the XCR-M in green,heavy barrel,muzzle break,sixteen inch barrel,and still undecided in the caliber.Common sense would dictate .308/7.62x51 but I will not compromise. I am seeking maximum performance at the greatest distance. Cost of ammunition not being factored into the equation. Cheers.

  7. #16
    XCR Guru MickeyC's Avatar
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    Re: XCR-M Bolt and Carrier?

    Technically the expansion chamber doesn't have to be in front of the gas port, it simply needs to exist, but there are some packaging benefits.

    As to reliability, tight tolerances aid accuracy but sand cuts and reasonable operating system energy should be enough to aid reliable operation.

    The water test is really simply a demonstration of the benefits of piston over DI in wet conditions. Basically the pressure caused by a DI system massively increases pressure in the reciever and if water is present over pressure occurs and this can cause structural failure. In a pisotn gun excess pressure is liited ot the piston head and water in the reciever is less of an issue.

    BADDFROGG - Based on your comments I'd look at .260, with efficient bullets it wil have longer effective range than a .308, but essentially they wil be close.

    With a 100 yard zero a .308 with a 168g MatchKing doing around 2550 FPS gets you approx 2437ftlbs at the muzzle and at 1000 yards it dropped 481 inches and has 412ftlbs and is doing 1050fps

    With a 100 yard zero a .260 with a 120g MatchKing doing around 2700 FPS gets you approx 1950ftlbs at the muzzle and at 1000 yards it dropped 442 inches and has 313ftlbs and is doing 1085fps

    The .308 has more energy, but suffers more drop and wind deflection. A .260 will give you higher velocity at range with less energy but with the potential for better accuracy as the transonic point is further out than with a .308. But you also have to understand the limits of the platform in allowing you to leverage that accuracy. A 1.5 MOA 100 yard gun is going to have issues at 1000 yards. Ammo consistency is a much bigger deal at range as is consistency from the platform and shooter ability.

    Do you handload?
    Semper in excremento sum, solum profunditas mutat. 'Always in the shit, only the depth varies'

    The problem with socialism is that you eventually run out of other people's money.... Margaret Thatcher,

    Among the many misdeeds of the British rule in India, history will look upon the act depriving a whole nation of arms as the blackest.
    Mahatma Gandhi

  8. #17
    XCR Guru variablebinary's Avatar
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    Re: XCR-M Bolt and Carrier?

    Quote Originally Posted by cjt50 View Post
    I am assuming that it is not like the 3 lug design of the -L. M-60ish 2 lug design maybe? (just the lug part, not the entire bolt) I'm just curious :ninja:

    When you say "like" the M-14 gas system, does it have a seperate piston?

    Guess we'll just have to wait until it hits the street to know for sure......
    The bolt uses a 3 lug design, but the bolt and carrier are very different. As was said many moons ago, the -M is not a scaled up -L in terms of operation.

    The XCR-L is generally regarded as a long stroke piston and AK47 like, but the -M has a passing resemblence to the M14 and SCAR
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  9. #18
    XCR Guru MickeyC's Avatar
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    Re: XCR-M Bolt and Carrier?

    The M14 is a short stroke floating piston design. The SCAR is a more simple short stroke gas system. They operate differently with the only similarity being the short stroke and gas powered operation.
    Semper in excremento sum, solum profunditas mutat. 'Always in the shit, only the depth varies'

    The problem with socialism is that you eventually run out of other people's money.... Margaret Thatcher,

    Among the many misdeeds of the British rule in India, history will look upon the act depriving a whole nation of arms as the blackest.
    Mahatma Gandhi

  10. #19
    Marksman BADDFROGG's Avatar
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    Re: XCR-M Bolt and Carrier?

    Thanks MICKEYC for the valuable information. I truly appreciate it. I do not reload at this time. Because I dont shoot enough. I am a gun collector. You have answered my question and the doubt I had. I will go with the .308. My hobby of weapons is thirty-one years. Currently waiting to see if Bushmaster will come out with the ACR version 2 6.5 Grendel. And also the Beretta ARX-160/5.56. Then, hopefully my addiction of purchasing guns will be over.
    I enjoy the design and engineering of these fine weapons. Thank-you.

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