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shalafi4
Feb 20, 2011

another medical bills avatar

Herr Tog posted:

sorry it needs to go to the home man, all the gun money is going to Ars because

awwwwww..


oh well... had to attempt to spread the 9x39 bug

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bulletsponge13
Apr 28, 2010


Just make a 9x39 AR.

E- smart rear end post, sorry. I realize what a giant project that would be.

Javid
Oct 21, 2004

My sole partiality is to that delectable spiced meat. Any additional confederation of vegetables shall not compromise the pie as I see it.

It wouldn't be TOO difficult to appropriately thread one of these barrels and screw it into an existing 7.62x39 AR setup.

B4Ctom1
Oct 5, 2003

OVERWORKED COCK


Slippery Tilde

The hardest part once you had the chambered barrel, would be deciding gas tube length and port size. Since the 9x39 is meant to be a big heavy bullet going slow then following the lead of 300 BLK could be a starting point. pistol gas etc.

Having the barrel threaded to accept an AR barrel extension and pin shouldn't be too terrible. Since this is how the headspace would be set anyways.

shalafi4
Feb 20, 2011

another medical bills avatar

bulletsponge13 posted:

Just make a 9x39 AR.

E- smart rear end post, sorry. I realize what a giant project that would be.

458 socom exists


B4Ctom1 posted:

The hardest part once you had the chambered barrel, would be deciding gas tube length and port size. Since the 9x39 is meant to be a big heavy bullet going slow then following the lead of 300 BLK could be a starting point. pistol gas etc.

Having the barrel threaded to accept an AR barrel extension and pin shouldn't be too terrible. Since this is how the headspace would be set anyways.

Again, thinking more the .458 socom end instead of a 300 blk.

Yes we've thought about doing this quite a bit. AND the wierdo AR 7.62x39 magazines *should* work pretty well with the 9x39.


Using this as a serrogate

http://www.aimsurplus.com/product.aspx?item=F1RF762GFS12&name=Radical+Firearms+7.62X39+FGS-12+Rifle&groupid=5387

Doctor Grape Ape
Aug 26, 2005

Dammit Doc, I just bought this for you 3 months ago. Try and keep it around for a bit longer this time.


shalafi4 posted:

oh well... had to attempt to spread the 9x39 bug

Might be an easier sell if you make an effort post as to what else is required in terms of gun/parts/tools/skills.

Roundboy
Oct 21, 2008


This would require custom/ handloaded ammo, correct?

Javid
Oct 21, 2004

My sole partiality is to that delectable spiced meat. Any additional confederation of vegetables shall not compromise the pie as I see it.

Yeah. 9x39 isn't really available in the US so this is essentially a wildcat project.

shalafi4
Feb 20, 2011

another medical bills avatar

Doctor Grape Ape posted:

Might be an easier sell if you make an effort post as to what else is required in terms of gun/parts/tools/skills.

Been slowly getting one together. The 80 hour weeks recently have left me scatterbrained, I'll get it out tonight or tomorrow.


Roundboy posted:

This would require custom/ handloaded ammo, correct?

Javid's correct. It's a wildcat in the US.

shalafi4
Feb 20, 2011

another medical bills avatar

Maximum effort post!! ( chimichanga's optional)

Here's a few routes to go for building 9x39 platforms.


Probably the easiest route.

A Savage bolt action as a base.

Savage rifles are probably the easiest of the bolt action rifles to re chamber to a different caliber. The vast majority of them have the same barrel threads so finding a suitable action becomes fairly easy. The larger magnum calibers have slightly different threads, If you're in question as to which you have contact Savage with your serial number and they can confirm which thread type you have. Generally you'll want one with a short action. Theoretically a long action will work but I'm not sure how well it'll feed from the magazine.

IF you can manage to find one of the 7.62x39 Savages skip ahead to the barrel changing portion.

If you have any other Savage you'll need a couple parts. (I'll be walking through what I need for mine but any other short action savage *should* be very similar if not identical)

Mine is a Savage Axis II in .308 (stock photo)



The different parts we'll need are a Barrel (obviously), A new bolt face for the 9x39, and a new magazine.

The new barrel will need threaded for the action with the appropriate threads. Which are 1.055"-20 (talk about custom threads)

The bolt face is a touch trickier. Savage discontinued their 7.62x39 bolt action a few years ago and I never got a reply from them asking if I could get a replacement bolt face.

However,
http://pacifictoolandgauge.com/sava...lignment_cut-no

The PPC bolt face is identical to both the 7.62x39 and 9x39 case heads.

Savage bolt disassembly isn't too complex. Just don't loose the little wave washer, they're a pain to find replacements for.

The small parts for the bolt head you can either strip off of your existing rifle or buy new ones. (this might not be a complete list, I'm posting from work and going off of memory)

https://www.midwayusa.com/s?userSearchQuery=savage+extractor

https://www.midwayusa.com/product/194256/savage-arms-ejector-spring-top-loading-all-calibers

https://www.midwayusa.com/product/782010/savage-arms-ejector-retaining-pin-top-loading-all-calibers

If you really want to go hog wild, Midwayusa also has entire savage bolts for ~$100

The magazine is a bit harder to find since it's out of production. Although places do get them in stock periodically

https://www.cheaperthandirt.com/product/savage-model-10-11-12-magazine-762x39-4-rounds-black-55221-011356552211.do

One thing to keep in mind that I found out. Savage model 10/11/12 magazine bodies are identical to Axis bodies.. HOWEVER they use different floor plates. IE if you swap them off your existing Axis magazine it'll plop right in.


Barrel changing instructions.

There's a few tools you'll need to change the barrel out on a Savage.

Biggest things are a sturdy vise to hold the action in and a barrel nut wrench.

I'm sure you could fabricobble a wrench that would work perfectly well however.

https://www.midwayusa.com/product/288765/wheeler-engineering-barrel-nut-wrench-savage-10-110

From there it's,
Tighten the receiver down,
spin the barrel nut loose.
Unthread the barrel,
Thread the new barrel in with the PPC bolt and a 9x39 GO headspace gauge in till it's snug. Put the barrel nut back on and tighten. Double check that both the GO and NO GO gauges function properly.

There's some conjecture on whether or not the barrel nuts can be reused or not. Generally from reading around if you don't go 400lb gorilla on it you should be fine.



Next Option an AR

*Disclaimer* I haven't actually done a full blown barrel swap personally so please point out any errors and I'll correct them.


You'll need a barrel that's threaded the same as an AR barrel extension (which acts like a front trunion in most rifles)

Here's where a good gunsmith comes in. The barrel extension needs headspaced to the chamber and the bolt. IE the chamber needs to be cut to the proper depth after it's threaded into the barrel extension. Which is either a LOT of guess and check on a good lathe or a whole crapton of measurements to make the cut once. (I kind of know how to do it since it's similar to cutting a chamber on a fully threaded bolt action but I'm not sure if there's some AR specific monkey wrench involved.)

Once the barrel extension is properly timed the trunion pin needs drilled/pressed in place and the gas port drilled

Once you have the barrel extension on and gas port drilled here's a pretty descriptive set of instructions

http://www.thenewrifleman.com/ar15-barrel-installation-guide/


*To be continued...*

Shaocaholica
Oct 29, 2002

Fig. 5E


Final option(?): get the full blown 9x39 AK from shalafi4 co.

Bummey
May 26, 2004

you are a filth wizard, friend only to the grumpig and the rattata


bulletsponge13 posted:

Just make a 9x39 AR.

E- smart rear end post, sorry. I realize what a giant project that would be.

Why bother when 300 blackout exists to do basically the same thing?

Javid
Oct 21, 2004

My sole partiality is to that delectable spiced meat. Any additional confederation of vegetables shall not compromise the pie as I see it.

Bummey posted:

Why bother when 300 blackout exists to do basically the same thing?

shalafi4
Feb 20, 2011

another medical bills avatar

Bummey posted:

Why bother when 300 blackout exists to do basically the same thing?

The same reason a .300 blackout exists when a 7.62x39 can do the same thing as well

shalafi4 fucked around with this message at 19:24 on Oct 3, 2016

Bummey
May 26, 2004

you are a filth wizard, friend only to the grumpig and the rattata


shalafi4 posted:

The same reason a .300 blackout exists when a 7.62x39 can do the same thing as well

300 blackout and 7.62x39 do not do the same thing

shalafi4
Feb 20, 2011

another medical bills avatar

Bummey posted:

300 blackout and 7.62x39 do not do the same thing

7.62x39

220gr ~1050fps

125gr 2300~2400fps depending on manufacturer



300 blk

220gr ~1025fps

125gr ~2225fps



300 blk exists so people can subsonic AR's that use normal magazines and don't match the ballistics of a .380 acp (subsonic .223) without having to go to a .458

edit: 7.62x39 subsonic is a bit of a snowflake but not more so than 300blk/whisper was 10 years ago.

shalafi4 fucked around with this message at 00:01 on Oct 4, 2016

Monocled Falcon
Oct 30, 2011


I'm still in for a barrel but this is a little overwhelming. Basically, you listed off all the things that I need to convert a Savage Axis II into a 7.62X39mm from any of the currently available models, excepting of course that the barrel will be for the 9x39mm.

shalafi4
Feb 20, 2011

another medical bills avatar

Monocled Falcon posted:

I'm still in for a barrel but this is a little overwhelming. Basically, you listed off all the things that I need to convert a Savage Axis II into a 7.62X39mm from any of the currently available models, excepting of course that the barrel will be for the 9x39mm.

Apologies if it's a bit scatterbrained.


It's mainly a list because other than the barrel work Savage rifles are pretty plug and play in terms of changing parts out. I can go more in depth on specifics what it takes to change the bolt/magazine if you want.

Monocled Falcon
Oct 30, 2011


This would be my first gun purchase, so I'm certainly a little nervous, but it does seem simple.

Ive always been a bit of a one gun kinda guy, so the savage would actually be a great choice. Is converting back and forth advisable?

JRay88
Jan 4, 2013


Monocled Falcon posted:

This would be my first gun purchase, so I'm certainly a little nervous, but it does seem simple.

Ive always been a bit of a one gun kinda guy, so the savage would actually be a great choice. Is converting back and forth advisable?

If you want to go the one gun/multiple barrels Route get an AR. They are stupid simple to change calibers. With a bolt action you could do it, but the process is completely different and it takes a lot of work. With an AR you simply push two pins, pull the upper off, put a new one on and push pins back in.

Wa11y
Jul 23, 2002

Did I say "cookies?" I meant, "Fire in your face!"

Edit: ^^That would be a better "one rifle" option, assuming you can use a semi-auto for everything you want, and can get parts for it. With a Wildcat like the 9x39, you'll have some growing pains in a semi-auto that you wouldn't have in a bolt action.

Monocled Falcon posted:

This would be my first gun purchase, so I'm certainly a little nervous, but it does seem simple.

Ive always been a bit of a one gun kinda guy, so the savage would actually be a great choice. Is converting back and forth advisable?

Converting a Savage is really easy. I bought a Cabela's Prairie Dog Hunter, which is just a .223 Remington Savage 11. Blind magazine, crappy plastic stock, ball bolt handle. Ended up converting it to .22-250 with a barrel and barrel nut from Blackhole Weaponry, a recoil lug from The Barrel Outlet (which I sent to BHW to have them shot peen and blacken to match the barrel and barrel nut), Sharp Shooter Supply's upgraded extractor and extractor (after I had piss-weak ejection), Tactical Works tactical bolt handle, .308 bolt face and bottom metal for AICS magazines from PTG, and an HS Precision M24 stock. I called Northland Shooter Supply, and ordered their action wrench and barrel nut wrench, and .22-250 headspace gauges from Midway. I ordered the PTG bottom metal and bolt from Midway, as I've heard PTGs customer service sucks, though their products are great. When I was contemplating a 6.5 Grendel bolt rifle, the PTG PPC bolt face came highly recommended for that application, and the 7.62x39 uses the same bolt face as the 6.5 Grendel, so if you don't already have a 7.62x39 bolt face for your Savage, you may as well get the PTG (if it's time to replace, may as well upgrade it!).

Swapping out all of the parts was pretty easy, nothing was particularly difficult, but I wasn't doing anything particularly wildcat, and it was all by the book. I'd imagine if you already have a 7.62x39 Savage with magazines to match, it'll be a piece of cake. Only hard part might be headspacing, but if shalafi4 gets headspace gauges made, it should be easy. I understand you CAN set the headspace with a resized case, but I'd be concerned about crushing the case with the barrel, and having your headspace be too short, so I opted to use a real headspace gauge. Ain't to way I'm crushing that solid little chunk of precision machined steel.

I think the hardest part was getting the old barrel nut off. It was torqued on pretty heavy and there was also some sort of blasting media in the threads, but once you break the nut loose, you can unthread the barrel from the action, and then just spin the nut down toward the chamber and off the barrel, then clean out your threads with a wire brush.

Putting on the new barrel should be easy, just run the nut up on the threads, slide the recoil lug on the threaded shank (the recoil lug should have a pin that indexes to a notch in the bottom of the receiver), and start twisting the barrel into the action. The assumption, of course, is that you already have your action mounted in your action wrench, and the wrench held in a vice securely, but in such a way that you can still get to the ejection port, and can feed the bolt in (I suppose you could use a barrel vice, and lock the barrel in place and just twist the action on by hand until you get it set where you want. Just make sure it doesn't spin on you until you can get the barrel nut snugged). Take the extractor and ejector out of the bolt head, which is really easy to do. One pin in the body of the bolt head, and the ejector pops out; push the extractor out with a punch, while covering it with your thumb so you don't lose the ball bearing and spring, and set them aside. Since you'll already have them out, it's a good time to upgrade them, unless you know they're good. Once you get the barrel most of the way threaded in, drop the go headspace gauge into the chamber, and close the bolt on it, then continue threading your barrel down until it stops. Open the bolt, twist the barrel down...eh, quarter turn to half turn, and try to close the bolt. If you can't close the bolt, back the barrel out until the bolt closes smoothly without much resistance. It's really a "by feel" at this point. Once you can get the bolt to close smoothly without any resistance, snug the barrel nut down by hand so nothing can move, and swap the go gauge for the no-go gauge (you might need a wooden dowel to push down the bore to push out the gauge, since you won't have the extractor in the bolt). Make sure the bolt can't close more than 1/2 way on the no-go gauge (at least, that's the rule I read, and it seemed to work pretty well. As long as your bolt can't close on the no-go gauge, but can close without resistance on the go gauge, you should be good. I ended up backing my barrel out just a touch after I'd had it set initially, because I had it set too tight. Chambering loaded rounds was very difficult). Setting it up this way made it so that fired cases barely have their shoulders blown out, so there's not much resizing that will need to be done when reloading it, which should mean longer brass life.

Shockingly, the PTG bottom metal needed barely any fitting in the HS Precision M24 stock, just a little on the sides near the tang behind the trigger, and it works just find feeding .22-250 out of a 7.62 PMAG AC. I know that's not much help for the 9x39 conversion, as I don't know if the 9x39 cartridges will fit or feed from the 7.62 PMAG AC, and it sounds like 7.62x39 magazines for a Savage might be tough to find. So you're kind of on your own for recommendations for stocks, bottom metal, and magazine, but you might be able to call Savage and explain what you're looking for, and get the right bottom metal, and possibly magazines, if they still make them.

As for being a one-rifle guy, and just swapping calibers, I wouldn't really recommend it. You COULD mark your barrel so you can index it to the same place ever time, but then you'd have to worry about making sure your headspace is set the same every time, so you can use your loaded ammo and resized cases in it without hurting accuracy or brass life. And it is a pain in the rear end to disassemble the bolt and swap bolt heads if you're going to change that too. I can't speak for Savage magazines, but AICS magazines that feed .223 and .308 will work fine in the same bottom metal, so if you go that route, it's no big deal as long as you have cartridges that feed in the AICS magazines. Honestly, one of my first rifles was a T/C Encore, and for the same reason. One rifle, easy swap barrel, that'll be awesome and a huge savings! But then the Encore is a single shot break action, so while swapping the barrels is easy, the rifle action kinda suck, and you have to manually cock the hammer, and break the action open between shots, so you have to break from your shooting positions, and the barrel isn't free floated since the handguard attaches to the barrel. The Savage barrel swap is nowhere near as quick or easy to swap, and it'll be harder to make sure it's set to the same every time, so unless you're really dedicated to only having one rifle, I'd recommend away from it. Remington actions are so available, even after market ones, and the barrel nut option is also available on them, so it's not like you have to be tied to a Savage action either.

I already have a suppressed .300 BLK AR-15 SBR and a .458 SOCOM AR-15 carbine, and don't really have the money for another rifle and suppressor (because what's the point of big heavy subsonic bullets if you're not suppressing them?!), but if I had the money, I'd be tempted to get in on this. With the Savage barrel nut twisting on from the chamber side, it'd be easy enough to turn a Savage barrel into an integral suppressor, even if it's fatter than the standard barrel profile. You'd just need to open the stock for it, and make sure the integral body tube attaches to the barrel past the threads for the barrel nut.

Monocled Falcon
Oct 30, 2011


When I get down to it, I just find shooting to not be a hobby for me.

What would be the best options for someone like me with no prior firearm ownership?

Bummey
May 26, 2004

you are a filth wizard, friend only to the grumpig and the rattata


Monocled Falcon posted:

When I get down to it, I just find shooting to not be a hobby for me.

What would be the best options for someone like me with no prior firearm ownership?

Take a beginner class. Say what horrible things you will about the NRA, and many of us will agree with you, they've got some good classes.

shalafi4
Feb 20, 2011

another medical bills avatar

Bummey posted:

Take a beginner class. Say what horrible things you will about the NRA, and many of us will agree with you, they've got some good classes.

^ this

Monocled Falcon
Oct 30, 2011


I kinda misspoke there? I was thinking more what caliber should I order a Axis II for a noob?

MazeOfTzeentch
May 2, 2009

rip miso beno


Probably .223 or .308

Bummey
May 26, 2004

you are a filth wizard, friend only to the grumpig and the rattata


Monocled Falcon posted:

I kinda misspoke there? I was thinking more what caliber should I order a Axis II for a noob?

Ha. Uhh. Depends on what you want to do with it.

Monocled Falcon posted:

When I get down to it, I just find shooting to not be a hobby for me.

What do you mean by this?


Edit: Whoa wait what thread am I in?

Wa11y
Jul 23, 2002

Did I say "cookies?" I meant, "Fire in your face!"

Monocled Falcon posted:

When I get down to it, I just find shooting to not be a hobby for me.

What would be the best options for someone like me with no prior firearm ownership?

I really sounds like you should be reading and posting in the Newbie Question Thread not in a thread pretty much dedicated to completely non-newbie things, like building a custom gun from scratch for a wildcat cartridge.

Shaocaholica
Oct 29, 2002

Fig. 5E


Wa11y posted:

I really sounds like you should be reading and posting in the Newbie Question Thread not in a thread pretty much dedicated to completely non-newbie things, like building a custom gun from scratch for a wildcat cartridge.

Herr Tog
Jun 18, 2011



Grimey Drawer

Monocled Falcon posted:

When I get down to it, I just find shooting to not be a hobby for me.

What would be the best options for someone like me with no prior firearm ownership?

I'll see you in the newbie thread

shalafi4
Feb 20, 2011

another medical bills avatar

Hey all,

I'm not dead just been swamped with work class and a bunch of interviews. I graduate in December so I've been doing a bunch of interviews and will hopefully know where I'll wind up in the next few weeks. Sadly with my financial situation at the moment I probably won't be able to order the barrels till after I start whatever job I wind up at. (probably mid January)

Shaocaholica
Oct 29, 2002

Fig. 5E


It's kind of ballsy as it is starting a project like this in school but then again having access to school resources helps a lot. It's like the best/worst.

shalafi4
Feb 20, 2011

another medical bills avatar

Shaocaholica posted:

It's kind of ballsy as it is starting a project like this in school but then again having access to school resources helps a lot. It's like the best/worst.

Mine's kind of a weird situation over the past 8 years.

Work mostly full time (student position) take classes part time

Work full time (full time position at the university) take one or two classes

Classes full time

Work full time (non university position) take part time classes.


This really got off the ground when I was working full time at the university position. I got to use the baby CNC mill in my shop to make parts.


The one thing I'm really going to miss is not being near having access to a high end EDM. I have a crazy knife project I want to get done before I leave that involves T-15 tool steel cutting edges.

shalafi4
Feb 20, 2011

another medical bills avatar

double posting for status update.


Just submitted my signed offer letter for a pretty lucrative engineering position. The project is back from sitting on the shelf collecting dust.

Now to find a new apartment, finish finals, pack my entire apartment up and deal with Christmas holiday shenanigans in the next 2 weeks.

shalafi4 fucked around with this message at 04:41 on Dec 14, 2016

bulletsponge13
Apr 28, 2010


Not sure if this has been covered, but how did you decide your gas hole size?

shalafi4
Feb 20, 2011

another medical bills avatar

bulletsponge13 posted:

Not sure if this has been covered, but how did you decide your gas hole size?

Honest answer? I haven't done the math for the exact size yet.

There may be a better way to determine it (any ak expert gunsmiths out there chime in!) But what I was going to do is a kind of empirical comparison.

Here's an example of the process I was going to use.

Lets assume we have an AK 47 gas port diameter and distance from the chamber. lets call it 3mm in diameter and 250mm down the barrel. (not actual numbers but it's just an example)

Here's where the assumptions come in.
lets assume that the round hits full pressure right when the bullet is at the edge of the case mouth. This will let us use published case volumes.
That's not the case in reality but I don't want to break out multi variable differential equations
We're also going to ignore any surface effects from the gas port not being "round" on the interior profile of the barrel. (Again comparing several examples the same way should reduce any irregularities)
Also we're going to assume that the interior of the barrel is a cylinder (ignoring the volume of the rifling)

So here are our knowns.

Case volume for a 7.62x39 = 2.31 cm^3
Max pressure for 7.62x39 = 355MPa
gas port diameter 3mm so the area of it is 7.065 mm^2

Now to dust off our chemistry hats.
https://en.wikipedia.org/wiki/Ideal_gas_law

go down to the isothermal reactions table (I'm ignoring gas cooling inside the barrel. not that dedicated)

so from the formula we have
P1/P2 = V1/V2

Pressure 1 (chamber)
Pressure 2 (gas port)
Volume 1 (Chamber)
Volume 2 (Chamber plus barrel up to gas port)

We know P1 and V1. We're looking for P2 and we can calculate V2

the barrel volume up to the gas port would be ((7.92mm/2)^2)*3.14 * 250mm = 12310mm^3
converting the case volume to mm^3 = 2310mm^3

Solve for P2

P2 = P1/(V2/V1) --> (P1*V1)/V2

P2 = (355MPa * 2310mm^3)/12310mm^3

mm^3 cancel out

P2 = (355MPa*2310)/12310

P2 = 66.61MPa (that's about 9500 psi for comparison)

Now that we have our pressure at our gas port we need to figure out the force of the gas through the port. (again ignoring any wall effects, effectively the gas port is smaller than it's actual size due fluid dynamics)

P= F/A

F= P*A

the area of our gas port is 7.065mm^2

F= 66.61Mpa * 7.065mm^2

units cancel out to leave Newtons

F= 470.59N or 105.79 lbs


Now that we have that pressure we re-run the calculations for a 9.3mm bore and an unknown gas port size


Back to the P1/P2=V1/V2 (9x39's have effective the same chamber pressure as a 7.62x39)

P2 = P1/(V2/V1)

P1 is the same
V1 = I don't have the volumes I measured on hand but lets call it 3cm^3 or 3000mm^3
V2 = ((9.3/2)^2)*3.14*250 = 16973mm^3

Plug everything in

P2 = 59.211MPa


Back to the P= F/A

we have our new pressure and our target force rearrange for Area

A= F/P

A= 470.59N/59.211MPa

A= 7.947mm^2

convert that back into radius

7.947/3.14 = 2.53

sqrt(2.53)= 1.59mm radius so 3.18mm

english comparison on gas port diameters orignal one 0.118in dia the calculated 9x39 port came out to 0.125in dia


As always if there's any questions let me know!

Shaocaholica
Oct 29, 2002

Fig. 5E


Ah chem equations. Did you factor in any pressure drop between the bullet leaving the case and when it passes the gas port? Seems like a bubba method would be to just undersize the hole and do a binary style search for the right practical size. You only have so many drill sizes anyway unless you use a taper reamer.

B4Ctom1
Oct 5, 2003

OVERWORKED COCK


Slippery Tilde

I like all these equations. Out of curiosity, I checked to see how AK's that likely have stock gas ports, cycle various subsonic 7.62x39 ammo

https://www.youtube.com/watch?v=2vy4FgpxSKU
https://www.youtube.com/watch?v=DxfAPYKi9ps

this doesn't sound very subsonic
https://www.youtube.com/watch?v=3tSLIDiFfps

There is some interesting cycle/load discussion here
http://www.theakforum.net/forums/19-ammunition-reloading/110677-subsonic-7-62x39.html

Doctor Grape Ape
Aug 26, 2005

Dammit Doc, I just bought this for you 3 months ago. Try and keep it around for a bit longer this time.


Too much work, just open the hole up progressively with number drill bits until it runs, if you make it too big then that just means you now get to create/incorporate an adjustable gas block to your design

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shalafi4
Feb 20, 2011

another medical bills avatar

Shaocaholica posted:

Ah chem equations. Did you factor in any pressure drop between the bullet leaving the case and when it passes the gas port? Seems like a bubba method would be to just undersize the hole and do a binary style search for the right practical size. You only have so many drill sizes anyway unless you use a taper reamer.

Yup it's V2 in the giant pile of equations. (going to edit the post to make that more clear)




Also in regards to the subsonic 7.62x39's wether a stock gas port will work depends on if they're using more bullet weight to slow it down or lightening the powder charge.

It doesn't *quite* come out the same because your functional case volume changes but if you're using a heavy bullet (and appropriate powder charge) in theory your pressure curve should be similar to a normal supersonic round.

shalafi4 fucked around with this message at 20:00 on Dec 23, 2016

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