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308 ak

49K views 321 replies 44 participants last post by  1biggun 
#1 · (Edited)
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#241 ·
Hello 1biggun,
You aren't the only one who sucks at math !!! My math has a big fat error in it !!!

The radius of a 30'06 case head is as you say about .25 inches. My figures are for a .50 BMG shell !!! Darn !!!

So... .25 x .25 = 0.0625

0.0625 x 3.14 = 0.1964 square inches area

0.1964 x 63,000 = 12,370.02 lbs force on the bolt face.

Not only is that correct it is also reasonable !!! Sorry about the screw-up.

VD
 
#245 ·
can you get those into the US?? and if so how much????? love the stock can you take some pictures of of the rod in the back of the stock that adjusts elevation????

Also is there any way to get any three lug bolts out of russia???????


1st question is how much bolt thrust will a 2lug bolt & trunion take on a yugo truniuon?? followed by how much bolt thrust will the 308 saiga handel. I want to get to ask the first Question Please please please. :)
 
#247 ·
Answers to all the questions above is YES, but it has to make financial sense for both myself and the Russians otherwise no one will do it. That is the biggest problem....5 or even 10 guys that say they want .308 bolts probably isn't enough to justify all the paperwork and hassle unless they all bought several. I may be able to add on an order of some parts to one of my shipments to help with the paperwork costs etc. but it would still have to be worth it for everyone involved.

Ok here are some specs on these:

Caliber: 7.62x54R

Factory Acceptable Accuracy Standards:

Extreme spread from three groups of four shots each at 100m is not to exceed 30mm
**Of the rifles that are here in country currently the average is 17.71mm at 100m shooting military grade ammo which is 30-40% less accurate than the best recommended ammunition (EXTRA)**Also note 1MOA at 100m = 29.08mm**

Deviation of mean point of impact from aiming point when firing from 100m is not to exceed 25mm

Adjustable butt plate length and height

Adjustable stock comb

Adjustable trigger pull 2.2 - 3.31 lbf

Adjustable trigger travel

10 round magazine

Barrel length = 650mm

Weight = 12.1 - 12.8 lbs

Cost ~$5.5-6.5k

Available in EXTREMELY limited quantities in 7.62x54R, .308, and .338LM
 
#251 ·
1biggun, would a psl be a better platform to do a larger cal conversion. i ask only because i saw a psl receiver with trunnions really cheap. got me wondering after reading this thread if this would be a better alternative. i found somewhere the x54 chamber pressures are in the upper 50k psi range. kind of makes it consistent with the 308.

given i have recently gotten into building my knowledge base in comparatively small compared to many here.

man a 338 lapua or 7mm mag would be wicked shoot.
 
#252 ·
it can be done likely on a psl how ever you will still need to lengthen the mag well as well as also deal with a much larger bolt face. It all depends on what x54 ammo your looking at some is really hot. If you can get a reciver and trunion cheap go for it you will still need a carrer and bolt. it may be possable to mod a standard bolt and trunion to work. Im not really sure if there are any real streangth gains over say a m70.

IMOO a ak 74 bolt on a Yugo trunuion should give the most streangth possable with standard AK parts. that are not super hard to find. Im thinking a AK 74 trunion would possably in second place.


If I had no parts lying here Id buy a bulgy ALK 74 kit as a doner kit and go from there. I have yet to see any documented cases of a trunion failure in any calibur or conversion. it seems the bolt would be the weak link. untill some one actualy has a failure its hard to say.

My 243 build is back on the bench and I hope to unt with it next month. after that I plan on some hot load testing and care full measure ments of head space changes.
 
#255 ·
biggun sorry about the trip down geek lane. question 1, do you want to calc just the thrust. this is easy given there are only 2 defined variables, case head diameter and chamber pressure. the original code i was working with was a bit more complex in the sense that it requires you to provide more info (some that may be difficult to obtain) such as # bolt lugs (easy), width of one lug (not as easy), diameter of bolt lug (not so easy). the payoff is getting calcs for lug strength lug shear and lug flex.

given the formula info from lilja barrels, it was somewhat easy to write an app to handle the calcs.
 

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#257 ·
i can handle the math and the program as long as its simple. like you said there are so many variables that cannot be accounted for. at this point you almost have to make assumptions based on what ever info is available. it really difficult to predict to the gnats-ass whats really happening. the best way to handle the data is take a safe approach and build in a fudge factor based on the assumptions. the idea is to get a reasonable prediction of what the forces will be. i used the formula supplied on dan lilja's web site. after looking at his calculations there are some questions i have asked regarding some of the numbers used in his formula.

now something simple like thrust is straight forward enough to do. adding flex and lug shear make things a tad more difficult. if you have some particular data caliber, case head diameter, chamber pressure) you want to see send it to me. i will try to get you a chart showing the thrust.

i am a complete noob with gun building, even tho i have been around them all my life. i have just started this as a new hobby and have a shitload to learn.

cheers
scott
 
#258 ·
How about pooling together and investing in some cheap romy trunnions and bolts and doing some real world proof testing I'm sure a bolt and trunnion could be bought for about 40 bucks I'd buy a set for the cause. I think we could step up the loading on say a .308 untill we have failure see how a couple sets compare and it gives us some good real world results which I think would be well worth the pooled cost, biggun, let me know if you're interested in doing a real proof test and I'll send you a spare romy trunnion and bolt.
 
#260 ·
Hmm you bring up some interesting thoughts, I was thinking the same as you that there's no need for a full gun in fact just a trunnion barrel bolt carrier fcg and like a tapco flat.

I was thinking maybe a .243 might be better for tested and if possible load in steps all the way to 125% unless of course we have failure before, you're right as we could test with x39 but while we could get some high pressure I think it would be easier to get very high bolt thrust levels without worrying as much about case failure..

I like your yugo barrel idea as it would kill 2 birds with one stone like you said. Also if the thin yugo barrel romy trunnion and bolt are able to fair well with some serious proof loads then I think it would give more confidence in caliber conversions. The math is great but some things just need to also be proven in real tests as well. I also might be able to dig out a yugo bolt and trunnion for testing as well ;)
 
#262 ·
Yeah I agree with you about using romy parts for testing., that spare yugo trunnion and bolt are for my someday .308 build but I'm more leaning toward a 54r yugo with m76 barrel parts and psl bolt and carrier.

If we discover ak (especially yugo) bolts and trunnions can safely handle some high thrust levels then I think I might build my long time idea of a 5.6x57mm ak based system (though that might be best for my m14 reciever ;) )

There are a few ways I can think of testing headspace or atleast locking lug deformation creating a longer headspace, one method I can think of would be adding thin shims to a go gauge maybe like .001 or even .0005 shims but holding them in place might create inaccuracies another method could me micing the distance between the lugs and breech face. My preference though might be a combination of micing the lugs for deformation along with measuring the bolt tail end play, it could be zeroed on part of the trunnion and endplay could be measured with go and no go gauges originally used and thus be a quick way of seeing if the lugs are deforming and the bolt is moving back. Also the breech face could be measured for forward movement of the barrel which I used to think was a non issue untill I had my initial hs problems with my m76.

Maybe we could send bolts and trunnions to zteknik if he's able to use to magflux machine at his work ;)

Sound like decent methods bg? You're right for testing it would be easiest to load rebated rim .308's also I think I can round up a .308 take off though I've also thought a lot about a .243 from reading your threads ;)

I know another way to kill two birds with one stone, like your .308 yugo barrel idea, if I can get enough machine time from my buddy I might buy a psl bolt and try testing with a 54r wildcat, I'm thinking 6.5x54r

Sorry I've been rambling let me know if any of it gives you ideas lol
 
#263 ·
biggun

i have an web page for you check out. i wrote this to plot thrust vs chamber pressures. let me know if this will do.

there are 3 basic parts. on the left is the fields that default to 12 random calibers with pressures and thrust values. these will plot on the chart as is. if you want to compare just overwrite the fields with what ever data you have and refresh the chart.

on the right is the "math" part. the upper block allows you to fill in a caliber the pressure and the case DIAMETER (i do the math for you).
hit the "GET YOUR THRUST" label and the fields will populate. you can cut and paste into the chart fields on the left side and replot.

i included a table of common pressures from saami. what i did not have was the case diameters.
 

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#264 ·
Wow that is so awesome I saved it on my blackberry ;) I want to build a .308 ak more than ever now since I just got back from the range with my m76 I must have done something right as it groups a ragged hole regularly now that I'm getting used to the trigger.

Bg, are you ready to do some testing with my spare romy bolt and trunnion?
 
#265 ·
i have debated a civil lawsuit against hcpookie and biggun. they have given me nothing but mental anguish since i joined this board. everytime i turn around they come up with something so damn cool that my head explodes. i have enough to do around the house without the barrage of new "ideas". god my head hurts!

that being said, and in complete jest, i am seriously contemplating a 6.5x55 swede on a psl platform. i think the x54 mag will just be able to hold the swede. it very well may work out to a barrel swap with some tweaks. so the question is. do i sell my saiga 308 to fund this project. or beg the wife for some of my money back (which is btw why she keeps my money i have zero impulse control) .
 
#266 ·
For a 6.5x55 do what pookie did and use those french lmg mags they look like they worked well, I have 3 of them I got from ima if you want to trade them for something I got em for 5 bucks a piece (4 for 20 bucks) but I'm not going to use them.

But I agree with you bg and hc do too many cool things that make me want to spend even more money ;) by the way is your siaga modified or stock trim? If you converted it it might make it hard for you to let it go so you might as well keep it and build another hehe
 
#267 ·
yes its converted and tore apart again to get new furniture.

this is the mock up



i know it will be tough to get rid of so i will not even seriously try. i will most likely start collecting more parts. i havent even started the x25 build yet. wife's had me on a marathon honey do list. i think i have just about knocked the list out. MAYBE i can focus on some builds.
 
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