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Thread: receiver flex

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    Gunco Regular smartbomb's Avatar
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    Default receiver flex

    biggun, hc and the rest of you seasoned builders

    one of the issues with ak precision is too much flex on the stamped receivers, right? is it possible to weld stiffening plates to the receiver or bend thicker (>2mm) flats to minimize the flex?

    curiosity is getting the best of me. the wife has agreed to get me a psl kit for christmas. my option is to get a nodak receiver or try something stiffer. the plan is to ditch the x54 barrel and go the biggun route and try something outside the norm. i like the 6.5 swede, or if the kit will handle it a 7mm-08. this and the x25 parts i have should get me thru the florida winter.
    al gore is full of carbon enriched shit

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    I guess a fair comparison would be an ordinary AKM vs. a Yugo.

    My best guess is that receiver flex isn't hurting much, since it's consistent.

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    No Hope For Me 1biggun's Avatar
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    well i can tell you this the most accurate AK that I have seen or heard of is sitting here on my bench and it has a un tempered Tapco flat as the reciver. It will shot sub 1/2' groups so Im finding it hard to buy into the whole reciver flex causing accuray issues. If any thing its possable the reciver is dampening the barrel harmonics ( no proof of any kind ) I think the before you can even think of factoring in reciver flex to the equation you need to remove the slop from the bolt to reciver, the slop from the carrier to bolt, the loose chamber and and then make sure the bolt is true to the bore and centered. then and only then would I worry about reciver flex. the only thing it might affect is when a scope is mounted to the reciver and then it becomes a issue. I can litteraly twist my reciver by hand and with good ammo its well under 1" all day long and has been for the last 4000 rounds or so.

    Im not saying it wont afect it but you have a lot of other issues infront of it. I saw were one of the US reciver or barrel makers did a test and they claim there milled wil shoot better than a stamped the only problem was that neither guns were very accurate to begin with. saying one is better than the other when they were both shooting a 3" or bigger group tells me little.

    The barrel makes all the differance my varmint gun in reality is nothing more than a good barrel and some mild mods. the reciver is the least modifed part of the gun.

    what differance will it make if the reciver flexes a thousands when you can raise and lowere the carrier/bolt assembly close to 3/16 of anch in the reciver??


    If your going to build a 6.5 swede or 7mm-08 or any other round that uses a 308 win size bolt face then i would not use a x54 based kit. I would use a m70 kit or even a AK 74 kit and open the bolt up. If you want to do some thing with a x54 kit I would be looking a rounds that use a simular larger bolt. There is a 6.5x54 that was used in Bioatolon compitition that would be a barrel change only as awell as several wild cats based on the 7.62x54 round one of them would be the way to go IMOO.

    If you were going to do a 7mm-08 i would just get a used 308 Saiga and rebarrel it. then you should be safe with any factory load.

    I need to get one of those PSL kits to play with a wild cat based on a WSSM case would be cool. again the million dollar question is what will the bolt and trunion handel pressure wise?????????? What is the chamber pressure of the ammo that was original used in the PSL????? abolt face extention like a sagia shot gun might work to reduce it. I would not weld it up under any circumstances.

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    BANNED nalioth's Avatar
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    The receiver's got nothing to do with accuracy.

    Any "flex" that shows up, does so long after the bullet has left the barrel.


    The sights are mounted on the barrel (fore and aft), so you can't pin any sighting issues on it, either.

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    No Hope For Me 1biggun's Avatar
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    the reciver on any rifle can affect accuracy to some degree as it affects the harmonics of the barrel perticulary were the barrel attaches to it as well as many times the scope is mounted to it. driving a pin in on one side of the barrel cant be good as it surly will induce some stress also. however as nalioth said the bullet is long gone before any recoil induced flexing is going on.

    Bench rest shooters go to great lengths to make sure that there recivers are stiff and very very percise. They mount there scopes on them so any distortion from heat, stress or bolt fit will affect the inharent accuracy of the gun. Untill you are getting well under 1/2" groups you would be hard pressed IMOO to show me accuracy gains or losses of a .045 vs a .060 or even a milled especialy if the scope is mounted on the RSB an not the reciver. if the scope mount is touching any part of the recver then flex will affect it as how even holding it on the bags VS holding it to your shoulder will affect point of aim. If i was going to mount a scope on a side rail then IMOO a milled reciver would be the best. I can litteraly twist my reciver by hand so if the scope mount was touching it any up down or side pressure would easly affect the point of aim. since my scope is on the barrel it affects it very little. it light affect the bolt position slightly and how it locks in but I havent got one that accurate to really be able mess with seeing if side loads or down pressure will affect how it shoots. I likelywould never be able to proove it to myself at any rate. some thing to think about is a thein reciver cools off faster than a heavy one so while it may flex faster during rapid fire it will also cool off and go back to normal if shooting slow like in a target situation.

    tighten the carrier to reciver fit as well as the bolt to carrier fit and also remove up and down play and it will do far more than any recvier material or thickness will ever change.

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    Gunco Regular smartbomb's Avatar
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    see this is why i ask the questions. i do not know these things i am starting the learning curve. rumor has it that flex is the achilles heel of the ak platform (look at the comments on any ar discussion board).


    as far as chamber pressure and bolt thrust are concerned, i used the web app i wrote to compare. based on the info i could get of the www,

    the x54 has a cham press of 57000 and a thrust of 10617 psi
    the 7mm-08 has a cham press of 61000 and a thrust of 10583 psi
    the 6.5 swede has a cham press of 55000 and a thrust of 9047 psi

    all 3 are very close and most likely well within the tolerance of the bolt and chamber. i assumed the x54 psl kit would be a better starting point for a large caliber/long range rifle.
    al gore is full of carbon enriched shit

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    No Hope For Me Coils's Avatar
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    rumor has it that flex is the achilles heel of the ak platform (look at the comments on any ar discussion board).
    First mistake, listening to AR people talk about something other then ARs

    Most AKs are fairly accurate, and a lot of them are more accurate then people think. A couple of the main things I noticed that can cause problems; 1-Ammo, most people shot surplus or low quality ammo. 2-The trigger can make a big difference, a gritty or hard trigger (plus the long travel) can cause people to move around before the shot is fired. 3-The shooter, yes the person holding the firearm can be the cause as well.



    i assumed the x54 psl kit would be a better starting point for a large caliber/long range rifle.
    Your assuming right, at least that's my opinion too.
    "Government is not the solution to our problem, government is the problem" Ronald Reagan

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    GuncoHolic Rahatlakhoom's Avatar
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    Here's a slow motion clip of the AK.
    I can see barrel flexing going on.
    The large bolt also racks the entire rifle.

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  9. #9
    No Hope For Me 1biggun's Avatar
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    all 3 are very close and most likely well within the tolerance of the bolt and chamber. i assumed the x54 psl kit would be a better starting point for a large caliber/long range rifle.
    the problem is the bolt face on the x54 is to large for the non rimed rounds like the
    7mm-08. now if you start looking at some of the magnum cases you might find something you like. I was also thinking of a 458x2 on one of those kits. that round uses a cut down 458 mag or any mag case in that class. the rim is still a little small but it likely can be done and the length would work. the WSM an remington short mags are really close. the 6.5 remington short mag would be a great longrange shooter.

    rumor has it that flex is the achilles heel of the ak platform (look at the comments on any ar discussion board).
    have any of those so called experts actually tried to shoot a AK accurately??? IMOO the loose chamber and poor ammo quality are the biggest issue. followed by the lousy sights and crap trigger. the loose tollerances of the bolt and carrier also factor in as they are responsable for consistant round placement in the already loose chamber.

    this gun that I litteraly threw together with no other changes to the reciver ( un tempered tapco) has a decent barrel and a good trigger and a scope mount that dont touch the reciver. it shoots one inch 3 shot groups at 100 yards with handloaded softpoint hunting ammo and I havent even started working up a load for it yet. the action is as slopy as hell. Im sure with better bullets and a properly worked up load it will do 3/4" or better.
    its a 308x39 BTW.
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    Gunco Regular smartbomb's Avatar
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    Quote Originally Posted by Coils View Post

    Most AKs are fairly accurate, and a lot of them are more accurate then people think.
    coils i agree. i have a norinco hunter (milled) that is phenomenal. i can bust tennis balls all day long on the iron sights. once i got the saiga 308 dialed in it shoots 11/2'-2" groups, even with a few stringers i am still center mass. i could care less about tack driving, my eyes arent that good. i just want the round to go where i point it within the limits of the system.
    al gore is full of carbon enriched shit

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