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Thread: Build planning for CETME - Modelo G Hypothetical Design Ideas

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    Senior Veteran r.erichsen's Avatar
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    Build planning for CETME - Modelo G Hypothetical Design Ideas

    Modelo G

    I originally wanted to build a hypothetical "Modelo D", but my desire for a picatinny rail on the top and bottom of the receiver placed me in a time period no earlier than 1995. Since this is a hypothetical exercise to speculate on what might have been, there is probably no wrong way of doing it and I can try a few things that suit my fancy.

    What if the CETME line had continued to include a 7.62x51 mm rifle until the end of the 20th century? Perhaps if Spain had found itself in a major conflict on it's home territory, it might have found it needed the reach and penetration of the older rifle and caliber even after the Spanish military had already largely phased-in the 5.56x45 mm L/LC/LV rifles. In such a circumstance, they may have dusted off the the surplus Modelo C rifles and used them to equip a section with a couple of DMRs, something the US did with the old M14. The refit and upgrade program might have been similar to the approach countless militaries have used for any number of military rifles over the years, perhaps most relevant are the upgrades performed on mid-60s G3 to bring them up to date for a somewhat modified role.

    If we could presume that the proper role of a 7.62x51 mm rifle in a modern section consisting of lighter 5.56x45 mm chambered carbines is as a DMR support weapon, what does that role demand in terms of changes to the weapon? The DMR configuration tends to differ from that of a battle rifle - it could be several kilos heavier due to optics, barrel length, stocks and so on. It might even be fitted with flip-up or removable sights given it would primarily be used with optics to cover ranges beyond typical assault rifle range, but below the typical range of a sniper rifle system.

    To reduce weight a bit, a rifle like this might use shorter/lighter magazines, and rather than a fixed bipod, the bi-pod might be removable so that it might be fitted only when needed. To avoid applying weight on the barrel or cocking tube attachment, the attachment of the bipod could be on a support bracket welded to the front of the magazine well away from the barrel.

    The buttstock may be longer and/or of adjustable length to better adapt to variously sized shooters or to the differences in LOP experienced when shooting prone vs. kneeling, standing or firing over obstacles. It will probably have a raised cheek rest to line up the eye better with optics, though to use the iron sights, it should be easy to remove, or be adjustable so that it falls away when using the backup iron sights. It would probably fire heavier than typical ammo for a 500-600 meter/barrier penetration role. Would CETME have continued to use wood stocks decades after the transition to polymer? Maybe, but probably not. Part of what gives CETME it's looks and old-school charm are those wood stocks and I would like to preserve some aspects of that character.

    This is a list of ideas I'm throwing around.

    * Polygonal or 4 groove cut rifling with 1:10" twist, medium-contour 20" barrel with threaded muzzle and radiused target crown.
    * Front hand guards fabricated in aluminum (probably 7075) - essentially a simple ventilated tube sectioned to fit the cocking tube at it's top and closed off at the front where the barrel and cocking tube protrude. To this hand guard will be applied a relatively thin wood veneer in two 180 degree sections, seamed at the bottom. Diameter. length and vent holes will reproduce the overall lines of the Modelo C hand guards.
    * Receiver will be fitted with strengthening ribs, brass deflector, ferrule and block reinforced rear section for buttstock push-pins, with long picatinny rail atop receiver from rear edge at interface to stock backplate extending to the front edge of receiver or perhaps for a few centimeters along the cocking tube
    * Rear sight base is picatinny interface with dual apertures, windage and elevation adjustments mounted atop this rail to render sight removable and position flexible to user needs (co-witnessing with compact 1x-4x scopes or red-dot sights as needed)
    * Stiffen charging tube as necessary with ventral ribs to to better stabilize tube for affixing front sight mount with less deflection and wobble. Sight base is formed as a single ring around the cocking tube terminus with a single slot picatinny rail section for flip-up BUIS type iron sights of hooded fixed front post type. Like the rear, sight is fully removable as needed.
    * Fit Adjustable buttstock with length and comb height adjustment, may be of a commercial type with minor modifications or a custom job in aluminum square tubing fitted with wood vaneer identical to the hand guards.
    * Pistol grip with short shelf, likely custom fabricated as no type appears to match what I'd like to use - wood easier than plastic which is fine as it will be made to match the hand guards and buttstock
    * Fit enhanced 2 stage recoil buffer assembly to better dampen recoil
    * Fit compact muzzle brake - a few to choose from, none selected yet
    * Swap CETME FCG for HK type FCG and fit ambidextrous extended reach selector (top is safe, middle semi), Fleming Firearms ambi-selector
    * Magazine release flapper with anti-rattle spring as found on later HK weapons
    * Bottom picatinny rail on support for fitment of bi-pod, support will be fabricated to weld to front of magazine well and further stabilized by bolting to bottom of the rear section of the hand guard. Goal is to keep the weight of the weapon off the barrel when bi-pod is used, but to move the bi-pod several centimeters away from the magazine to improve balance and avoid clearance with magazine manipulation when fitted

    Comments? Suggestions?

    R

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    holescreek's Avatar
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    Sounds a lot like the GHG1 with iron sights and a lower pic rail like I used on the PSG1 clone.

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    Senior Veteran r.erichsen's Avatar
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    Quote Originally Posted by holescreek View Post
    Sounds a lot like the GHG1 with iron sights and a lower pic rail like I used on the PSG1 clone.
    Holes,

    Nicely done sir. Would you be willing to share additional information on this build of yours? I like many of the features you've done here. Could I get a closeup of the bottom rail for the bipod? Did you fabricate that buttstock out of alu? How is the center section articulated and locked? Can you adjust the length, or just the cheekrest on the buttstock above? I see the picatinny rail, I would extend mine all the way to the backplate and as far forward as I could go without getting in the way of the charging handle. I see your tube locks downard, not upwards. Did you fabricate that tube, or did you get one of the tubes that is built that way?

    For the front sight, I wanted to use an adaptation of Matt's "double frame" (reduced to "single frame" in my case) to mount the front sight to the tube instead of the barrel. To increase rigidity I might increase the diameter of the cocking tube to the next size up, a few mm and fashion the fixture from a section of tube a further diameter larger to slip over the tube where I would tack weld this on and then the single slot of rail would be tacked on to supply a picatinny base front BUIS.

    I'm not sure yet how I want to build the support bracket for the lower rail for the bi-pod, I just know I want to fit it to the front of the magazine well. Did you reinforce this area first with a couple mm of plate and then weld the bracket to that? There isn't a lot of room for a vertical support that won't intrude into the bottom of the handgrips, but if I relieve the tube for that vertical support it would just "slot" into place. How does yours fit?

    Thanks Holes,

    R

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    holescreek's Avatar
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    Are you on Weaponsguild yet? There is a 26 page build thread on the "GHG1" (Ground Hog Gun 1) from 2009/10 that goes into painful detail on all of the parts machined for it.

    There are some more photos on this site, but nothing showing the trunnion extension to hold the handguard, AR grip adapter or the stock articulation. Two of the 3 sections move on an acme screw and the butt extends. Probably too heavy for what you are planning anyway.
    http://www.militaryfirearm.com/Forum...me-on-my-hands.

    If you are on WG, the original build thread is here. It was essentially my first build thread on WG and got off topic a lot towards the end as more people got involved. What I'm saying is look at the pictures!
    http://www.weaponsguild.com/forum/in...p?topic=7560.0

    When I made my 7.62x39 cetme just about the same time, I made a front folding BUIS out of a cetme triple frame. You can kind of see it on the last page here:
    http://www.militaryfirearm.com/Forum...consider/page6

    but again, there is a detailed build thread on WG.

  5. #5
    Senior Veteran r.erichsen's Avatar
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    Quote Originally Posted by holescreek View Post


    Are you on Weaponsguild yet? There is a 26 page build thread on the "GHG1" (Ground Hog Gun 1) from 2009/10 that goes into painful detail on all of the parts machined for it.

    There are some more photos on this site, but nothing showing the trunnion extension to hold the handguard, AR grip adapter or the stock articulation. Two of the 3 sections move on an acme screw and the butt extends. Probably too heavy for what you are planning anyway.
    http://www.militaryfirearm.com/Forum...me-on-my-hands.

    If you are on WG, the original build thread is here. It was essentially my first build thread on WG and got off topic a lot towards the end as more people got involved. What I'm saying is look at the pictures!
    http://www.weaponsguild.com/forum/in...p?topic=7560.0

    When I made my 7.62x39 cetme just about the same time, I made a front folding BUIS out of a cetme triple frame. You can kind of see it on the last page here:
    http://www.militaryfirearm.com/Forum...consider/page6

    but again, there is a detailed build thread on WG.
    Holes,

    You've compelled me - I'll join Weaponsguild to get the full thread on the builds you've mentioned. Much to be learned from what you've done here.

    Any chance of a repeat performance of the 40 degree CETME LPs sometime in the near future? I'd really like one or two of those.

    R

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    Senior Veteran r.erichsen's Avatar
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    I haven't done the math, but a tube diameter increase of some 10% or so should increase charging tube rigidity while maintaining the same wall thickness - more suitable for a place to attach a sight. In addition to a larger diameter, some form of fluting or splines to crease along the length and add more lateral stiffness in the process might be appropriate. I've looked at bicycle tubing, but nothing appears to match these characteristics - perhaps it's unnecessary and the increase in diameter or use of a somewhat stiffer alloy should suffice?

    R

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    holescreek's Avatar
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    Which platform are you building from, HK or Cetme? It will make a difference on material acquisistion. With some exceptions, Cetme parts can be made to work in an HK but HK parts cannot work in a Cetme. For example, the cocking support in a cetme is .007" smaller in diameter than the HK. I can buy tubing that will work with the Cetme off the shelf but I could not find any sized for the HK and didn't want to try to hone that much material out in the length required.

    I would not put a sight on a cocking tube unless I had to if I ever thought I'd need to rely on it. If you are going with an aluminum forearm secured to the receiver, attach it to that.

    Most of this is covered in other threads.

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    Senior Veteran r.erichsen's Avatar
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    Quote Originally Posted by holescreek View Post
    Which platform are you building from, HK or Cetme?
    Holes,

    I'm building two rifles: One HK and one CETME - the list earlier in this thread is all for the CETME - my hypothetical "Modelo G" build.

    It will make a difference on material acquisition. With some exceptions, Cetme parts can be made to work in an HK but HK parts cannot work in a Cetme. For example, the cocking support in a cetme is .007" smaller in diameter than the HK. I can buy tubing that will work with the Cetme off the shelf but I could not find any sized for the HK and didn't want to try to hone that much material out in the length required.
    Good to know, I wasn't aware the cocking handle support was a bit smaller.

    I would not put a sight on a cocking tube unless I had to if I ever thought I'd need to rely on it. If you are going with an aluminum forearm secured to the receiver, attach it to that.
    I'll look for a thread on attaching the sight to the forearm - I hadn't considered that. I suppose if it's a tight fit it shouldn't shift when removed and re-attached. I'll think that one through.

    R

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    Quote Originally Posted by holescreek View Post


    Are you on Weaponsguild yet? There is a 26 page build thread on the "GHG1" (Ground Hog Gun 1) from 2009/10 that goes into painful detail on all of the parts machined for it.

    There are some more photos on this site, but nothing showing the trunnion extension to hold the handguard, AR grip adapter or the stock articulation. Two of the 3 sections move on an acme screw and the butt extends. Probably too heavy for what you are planning anyway.
    http://www.militaryfirearm.com/Forum...me-on-my-hands.

    If you are on WG, the original build thread is here. It was essentially my first build thread on WG and got off topic a lot towards the end as more people got involved. What I'm saying is look at the pictures!
    http://www.weaponsguild.com/forum/in...p?topic=7560.0

    When I made my 7.62x39 cetme just about the same time, I made a front folding BUIS out of a cetme triple frame. You can kind of see it on the last page here:
    http://www.militaryfirearm.com/Forum...consider/page6

    but again, there is a detailed build thread on WG.
    Holescreek: You should really have a show on discovery channel replacing sons of guns.

  10. #10
    Senior Veteran Windy's Avatar
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    Quote Originally Posted by silverbear View Post
    Holescreek: You should really have a show on discovery channel replacing sons of guns.
    Amen to that! I would then go back to watching Discovery channel then On a related note Holes, should you want to adopt a middle aged 'son' I would throw my name in the hat! :lol:

    r.erichsen, looking forward to your build(s) with much interest.

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