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finnish 1942 M39 sako

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Re: finnish 1942 M39 sako

Postby farmerboy78 » Fri Apr 12, 2013 6:58 pm

Thank you very much, I hope its another laser shooter... This one has better rifling than my two 28/76's I'm working on... Anxious to be able to put a few rounds down the tube in the future.
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Re: finnish 1942 M39 sako

Postby farmerboy78 » Mon Apr 15, 2013 7:58 pm

I decided to take the timney from my 28/76 and put in this build since the bluegrass stock will come inletted... Hope to have more progress soon...
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Re: finnish 1942 M39 sako

Postby farmerboy78 » Sun Apr 21, 2013 8:27 pm

Hey guys have a small update, have been emailing my smith, he is going to bead blast the entire barreled action, thread the crown 1/2x28, and give it a black ceramic coating for $200 plus tax... Seem like a decent price?
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Re: finnish 1942 M39 sako

Postby biggorillagunworks » Mon Apr 22, 2013 2:18 pm

Sounds reasonable to me...
Precision threading (to within .0002) concentric to the bore usually runs about a bill by itself...so another bill for bead blast and paint sounds fair to me.
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Re: finnish 1942 M39 sako

Postby 0933 » Mon Apr 22, 2013 3:06 pm

$200 for a barrel cut-down, re-crown, threading, and bead blasting/ceramic re-finish sounds about right.

I'm curous though... are there any .30 cal QD suppressor mounts threaded for 1/2-28?? It seems like most of them are 5/8-24.

I'm definitely looking forward to seeing the finished rifle! :thumbup:
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Re: finnish 1942 M39 sako

Postby farmerboy78 » Mon Apr 22, 2013 3:51 pm

Yep, I was on yhm website and they offer one, I currently have one for .22 cal that I'm going to have bored out to fit a .310 projectile.
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Re: finnish 1942 M39 sako

Postby Shepard » Mon Apr 22, 2013 4:41 pm

Have you ever put a 1/2x28 thread on a 30 caliber before? I just did the math and it leaves .0945 wall thickness if you didn't thread it --- so threading that will leave you about .070 wall support. You just might be blowing of the end of your barrel. I never did the math before and now that I did it is kind of frightening how little material is holding your brake on your barrel.
I would recommend you stop and re-evaluate what you doing. It's in my opinion creating a unsafe situation that could lead to someone getting hurt.
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Re: finnish 1942 M39 sako

Postby 0933 » Mon Apr 22, 2013 7:16 pm

Shepard, I've been thinking about this for a while now... ShootnMathews first started the wheels turning late last summer when he was wanting to put a brake on his Mosin.

The problem is that the stock Mosin barrel is around .700" in dia where you could feasibly cut the barrel. I believe 'normal' thread specs for .30 cal muzzle devices is 5/8-24... if you threaded a (stock) Mosin Nagant barrel with that 5/8 thread, you'll be left with a very small shoulder to torque the device onto.

With a 1/2" thread, 1/2-28 would be conveinent because of the multitude of AR devices that you can open up, there is a 'decent' shoulder to torque the muzzle device onto.

Know thinking about pressure/dwell time that this portion of the barrel is experiencing... Here is a graph showing the pressure vs. bullet location for the 5.56.

Image

Now, the 7.62x54R is not going to be exactly the same... but it will be similiar. The ratio's of the bore volume to case volume are very similiar with these two calibers. So what we can gather from this is that by the time the bullet travels 20" down the barrel, the pressure inside the barrel has dropped to between 10,000-15,000 psi.

Another factor, is the 'dwell' time... the time that barrel will have to 'hold' that pressure. At the muzzle, the bullet is traveling at pretty much the muzzle velocity... so say 2600 fps. The dwell time will be .2 milliseconds. This is just the time that a 1/2" portion of the muzzle will have to hold that 15,000-10,000 psi.

Now, burst (continuous) pressure of pipes...

P = (st)/(d) s=material strength t=wall thickness & d= the O.D.

Taking s=120,000 psi (chrome molly steel) t=0.070" and d= 0.440"

The max pressure the threaded portion (1/2-28) can take would be around 19,000 psi. Since it won't be a continuous pressure, but rather a short duration pressure, I have no doubt that it would hold.

Also, ShootnMathews brake is 1/2-28... he hasn't had a problem with the barrel holding at that point. viewtopic.php?f=5&t=3458 I'm also theading the muzzle 1/2-28 for a flash hider on the (stock) barrel from my 43 Izhevsk.

Good thinking Jerry! :thumbup: And I'd definitely opt for a 5/8 thread if the barrel allowed it!
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Re: finnish 1942 M39 sako

Postby 6.5x47 » Mon Apr 22, 2013 8:17 pm

Yeah, been puttin the 9/16 24 on the gi bbls. Brakes commercially available up to 3/4 24, and some kinda 1". Been gettin alot of stuff from muzzlebrakesandmore, and cnc warrior.
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Re: finnish 1942 M39 sako

Postby Shepard » Mon Apr 22, 2013 9:33 pm

I've re-thought what I was saying and come to the conclusion that -- a flash hider produces zero forward torque -- as a matter it may increase recoil pushing backwards. Now install an energy absorbing device like an effective muzzle brake or a silencer, you now have pressure and forward motion torque. A silencer is an effective energy absorbing device just like a gill brake. I don't have the math skills -- I use past experience and basic understanding of steel. I don't trust a half inch diameter circle of steel .070 thick to hold and transfer the torque of say a 75% recoil reducing brake or silencer.
Also remember -- accidents happen. Take your rifle -- standing it on the recoil pad -- lean it to the side till the muzzle brake or silencer is 6-8 above the chair seat in your kitchen and drop it on the brake simulating a fall --- would you take it out and shoot it?

T -- I'll put 2 -- 5/8x24 jam nuts in the box with your other parts when I send them.
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