Gunco Forums banner

308 ak

49K views 321 replies 44 participants last post by  1biggun 
#1 · (Edited)
0001
 
#127 ·
Here's a link to the pdf article on the cup/psi conversion if you want to take a look at it.

www.shootingsoftware.com/ftp/psicuparticle2.pdf

I'm not an engineer, don't play one on tv, and didn't stay at a Holiday Inn Express last night, so take the above info with a grain of salt. Bert01's engineers may say that everything is BS. I know that there is software out there that the engineers can use to test stress and how a metal will hold up over a certain number of duty cycles. Maybe we can get some help in sorting all this out.

Looking at the different calibers:

The 5.45 pushes a 60 grain bullet at around 2900fps. Surface area is around .120 square inch.

The 7.62 pushes a 123 grain at around 2350fps.

The .308 pushes a 147 grain at around 2800fps.

These are the figures for the 7.62 and .308 are from PCM, UMC, Winchester white box, and American Eagle as these are probably the ammo that someone would just walk in and buy at the store. If we could find the pressures that these rounds are running then that might give us a chance to compare apples to apples. Does anyone know the data on the Yugo .308 ammo?
 
#128 ·
Here's a link about the CIP and SAAMI standards for 9mm. It goes into some detail about the two. The CIP lists their loads as MPa (which 1 MPa = 145.0377psi), but the post states that you should not convert the two.
 
#130 ·
sorry for the long post just trying to get it easy to read, got some of the info from www.thegunzone.com/30cal.html trying to do everything on the safe side hence the max proof pressures for the 308 stuff and the bolt head diameter instead of the true case head diameter

i got some good solid works 3D models of a romy trunnion today trying to run the force application on it as we speak (test how the lugs will hold up under different pressures applied from the bolt thrust)

not having much luck the software im using doesnt allow for heat treated steel so even the opperating pressures of the 7.62 x 39 arent giving safe results in the solid model stuff

ill keep trying and let you know what happens


Bolt thrust= area x psi

Area = 3.146 x ( (case head diameter / 2)^2)

Above is from http://www.riflebarrels.com/articles/custom_actions/bolt_lug_strength.htm


7.62 x 51 NATO

"Proof" pressure = 67,500 psi
Bolt head diameter = .475

3.146 x ((.475 / 2)^2) = .1772

67,500 x .1772 = +/- 12,000

7.62 x 51 NATO = +/- 12,000 lbs bolt thrust max

308 Winchester

"Proof" pressure = 83,000 psi
Bolt head diameter = .475

3.146 x ((.475 / 2)^2) = .1772

83,000 x .1772 = +/- 14,800

308 Winchester = +/- 14,800 lbs bolt thrust max

7.62 x 39

Max "reload" pressure = 45,000 psi
bolt head diameter = .458

3.146 x ((.458 / 2)^2) = .1647

45,000 x .1647 = +/- 7,420

7.62 x 39 = +/- 7,420 lbs bolt thrust

6.5 Grendel

Case head diameter = .445
 
#131 ·
okay putting the force application stuff off till tomorrow

but i was doing some figuring with the formula for bolt shear strength from the lilja website. i used the small lug on a romy bolt.
the height i used was .27, length .423, 2 lugs, and 100,000 psi yield strength for hardened 1050

.27 x .423 x 2 x 100,000 = 22,842 then divide by a safety factor of 2 and you get 11,421 psi of bolt thrust before shear occurs

the 100,000 yield strength nums are for 1050 hardened to rc 30, i got 1050 from a post on another site, but as for the rc number im not sure, the psi num drops pretty sharp as hardness goes down

C:\Documents and Settings\ba\Desktop\Ruger Investment Casting - Steel.htm

BG can you get the measurements from a m70 bolt?
 
#132 ·
I will compare the yugo and the VEPR. 1st dim. .405/.537 2nd. .621/.722 Bolt face .452/.483 Interesting difference is the bottom front .424/.422 The Bulgy 5.45 bolt is .333. The VEPR is a small stem bolt with a spring loaded firing pin. Lightning cuts are the same from the 5.45 to the VEPR. Bolt heigth from the 5.45 to the VEPR .839/.926. The yugo is .917. Bolt length yugo 3.335 vepr 3.438 bul 3.439 Trunion lugs are the same as the yugo on the VEPR.
 
#133 ·
Bert, I think there is a mistake in your figures. LS=(LxLLxNLxYS)/2

L is the length of the arc segment not the height of the lug. Finding the radius of an AK bolt is a little tough. I'll measure a trunnion in a while and see if we can get a radius.
 
#134 ·
if i understand your deminsions correctly, the height of the lug is .405, length .621 for the yugo m70

so using the same yield strength and 2 lugs

.405 x .621 x 2 x 100,000 = 50,031 divide by safety factor of 2 = 25,150.5 lbs of thrust before shear occurs. this is well under even the calculated bolt thrust with proof loads from above (14,800 lbs of thrust)

does this sound right?
 
#139 ·
There is nothing in the ROBARMS manual resticting use of any .308 ammo. Guys these VEPR rifles have been thoroughly tested in Russia. If there was an issue of strength, ROBARMS would definitely identify it for liability purposes. I think as long as you use a bulged trunion in your build there shouldn't be a problem.
 
#141 ·
Ok, I've spent most of the day getting his program to run. I've got it all working now. So, I'll see about getting some numbers run. It will probably be tomorrow before I can get things run.

Just a quick run of the .308 proof round of 83,000 psi.

Using an AMD 65 bolt because it was handy.
Bolt Dia=.654
Small lug length=.404
Small lug width=.256
Bolt Yield strength=100000 (using the figure for the 1050)

His program says:

Bolt Thrust=9667
Bolt Lug Shear Strength=10630
Lug Shear Area=.213
Lug Flex=.004
 
#142 ·
If anyone else wants to run the program, let me know and I'll post where to get GWBASIC, how to get your program in, and a few things that needed changed to work with this version of GWBASIC.

We still don't know the type and RC hardness of these bolts/trunnions. If someone had a RC tester we could find out at least that much. The numbers below are based on a main bolt body of .635. Since the AK bolts aren't the same as a bolt action, it's a little hard to get a good measurement. The AMD bolt was the best to get this measurement from.

Also we are just using that the AK bolt has 2 of the small lugs. It would be hard to get a good number with the cut out for the extractor on the large lug. Since the large lug is longer it should be stronger according to Lilja's program.

I'm not saying that any of the numbers listed below should be taken that it is safe to build that type of rifle. We are using numbers taken off the net and Dan's program. I'm not saying anything bad about Dan, but I'm not an engineer and I can't look at his formulas to say that yes they are correct. We are assuming that everything is correct, that the yield pressure of the steel is 100,000psi, and the ammo is loaded to SAAMI max specs.
 
#143 ·
So, lets look at a 7.62X39 loaded to SAAMI max of 45,000.

AMD Bolt
Dia. =.635
Small lug length=.404
" " width=.256
Yield= 100000

Bolt thrust=4484
Bolt shear=10649
Flex=.0018

Now lets look at the Saiga bolt in .308 loaded to the SAAMI max of 62,000.

Dia.=.635 (I'm just guessing at this figure)
Small lug length=.645 ( from rbthntr64 post)
" " width=.256 (I didn't see this posted, so guessing)
Yield= 100000

Bolt thrust= 7222
bolt shear= 16998
Flex=.0018

The Vepr bolt at .308 loaded to 62,000.

Dia.= .635 (guessing)
Small lug length=.537 (from rbthntr64 post)
" " width=.256 (guessing)
Yield=100000

Bolt thrust=7222
Bolt shear=14153
Flex=.0022

Yugo Bolt with .308 loaded to 62,000

Dia.=.635 (guessing)
Small lug length=.405 (from rbthntr64 post)
" " width=.256 (guessing)
Yield=100000

Bolt thrust=7222
Bolt Shear=10675
Flex=.0029

How about a 8mm on a AMD bolt loaded to SAAMI max of 35,000psi. Surplus 8mm could be loaded way higher than 35,000psi.

Dia.=.635
Small lug length=.404
" " width=.256
Yield=100000

Bolt thrust=4079
Bolt shear=10649
Flex=.0017
 
#144 ·
these numbers look in line with the numbers i came up with

i would like the info on the gw basic stuff, post or pm me

i wasnt doing this to debate different cartridges on different actions, i would just like to have some idea of how to figure and compare differences for my own knowledge

this is great stuff guys, i appreciate the all the info in this thread
 
#145 ·
Here is the website that I downloaded GWBasic from:

http://www.geocities.com/KindlyRat/GWBASIC.html

I just checked it and it said that the site was down due to it exceeding it's data transfer limit. Are all you guys downloading it?:brows: Maybe it will be back up. My virus software didn't find anything, but any time you download something there is a chance. So, use at your own risk, blah, blah ,blah. GW Basic is old school.... no mouse, black screen, and you have to type commands in.

Download the GWBASIC.EXE zip file to your computer. Exract the zip to a folder and remember where you stored the folder.

Go here:

http://www.riflebarrels.com/articles/custom_actions/bolt_lug_strength.htm

and go to the program code. Left click, highlight all the code (line 10 to line 330), right click, and copy.

Now on your computer go to start, programs, accessories, and open notepad.
In notepad paste the program. Now we need to do some work. When the program was loaded to the web, any line that was to long was dropped to the next line. Fine for a web page, but bad for a program. So we need to fix this. Between line 40 and 50 it says BMG";QHS. We need to stick that back at the end of the line above it. Go to the end of line 40, hit delete twice, then the space bar once, and that should bring the code back into one line. Do this to every line that ran over. When done it should read 10 to 330 on the left side without any breaks.

After line 280 replace the rest of the program with this:

281 U=(THRUST/10+.5)*10
282 Z=(LS/10+.5)*10
290 PRINT"":
291 PRINT"THE APPROXIMATE BOLT THRUST IN POUNDS IS:";U
300 PRINT"THE APPROXIMATE BOLT LUG SHEAR STRENGTH IN POUNDS IS:";Z
310 PRINT"THE LUG SHEAR AREA (SQ. INCHES):";:pRINT USING".###";SA
320 PRINT"THE AMOUNT OF BOLT LUG FLEX FOR THESE CONDITIONS (INCHES):";:pRINT USING".####";FLEX
330 END

It does the same as his orginal program but this version of GW Basic wouldn't print as he had it written. Also if the webpage drops some of the lines down you will need to do as above to get it back on one line.

Now we need to save it. At the top left click File and click Save As. Change the Save As Type box to All Files. Then name the file whatever you want .bas. I called it lug.bas. Then save the file. Remember where you saved it or save it right to the GWBASIC.EXE folder. If you saved it someplace else, go to it and copy it. Go to the folder with the GWBasic exe and paste it into the folder. Now we are ready to give it a try

Click the Basic.exe icon and the program should start. Windows will ask you if you want to run it. Click Run. It should open a black screen that has some words and then says OK. Type Load "whateveryoucalledit" and this will load the program. I called it lug.bas so I type Load "lug". It should come back with OK. Then type Run and the program should start and ask which size of cartridge. Input the values and it should list the results.

If you want to add the 7.62X39 instead of the Magnum in the list of cartridges then replace these two lines in the program.

40 INPUT"1=.222; 2=PPC; 3=.308; 4=7.62X39; 5=378 WBY MAGNUM; 6=.50 BMG";QHS

and

150 IF QHS=4 THEN HS=.356

This will give a close inside diameter of the case head. As before if the webpage drops any lines you will have to put them back on one.

If you need to edit the program after it is saved, then click on it twice. Windows will want to know what you want to open it with. Check "Select from a list" and "Open". Windows will pull up a box. At the bottom by default "Always use the selected program to open" is checked. UNCHECK it and then select notepad from the list above. Click OK and do your editing. When done just click save. If you have it in a different folder than the GW Basic folder, you will need to move the new saved program to the folder and overwrite the old one.

Once you run one set of numbers you have to type Run again to do another set. When finished type system and hit enter. The window should close.
 
#149 ·
Ive gotten a couple fal barrels, mags and yugo kits. waiting to finish my designs for a reciever, milled to fit over the front trunion, have the correct magazine opening and release for fal mags, and using AR grips and fcg. Not sure about a stock style yet (any suggestions). Im like everyone else i assume, too many projects too little time
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top