7.62x39 subsonic custom prototype

[Gigs]

Here's some drawings I made for my attempt at a super heavy 7.62x39 subsonic that might actually cycle a gas gun.

One design is tumble, and the other is standard grooves. I've never designed a bullet before so let me know if I messed up, because I'm probably going to get custom molds on these.

http://www.gigstaggart.com/pics/Gigs_7.62-260GR-GC.Jpghttp://www.gigstaggart.com/pics/Gigs_7.62-260GR-GC-S.Jpg

260 grain, rounded meplat. There's 0.2 inches of flat bearing surface behind the ogive before the first groove, seating depth should be around the middle of that.

[Bloodman14]

DANG!! If I can get the right one in .316, my Enfield would be in love!

[runfiverun]

probably wanna leave a little room in front of the gas check.

[Pat I.]

I think if you don't throat the barrel with a shallow angle taper or taper the heck out of the bullet itself there's going to be a lot of bullet hanging below the case neck. You could also do away with a few grease grooves. Probably run one groove for the print on the right, might get you closer to your wanted weight too. Don't know if it would matter for the tumble lube. I have 1.425 long 260 gr and 1.385 250 gr, in WWs, Mos moulds I shoot in a .30 PPC. The throat on that barrel is .310x45 min. included and long enough so only a little past the check is in the neck when chambered after the bullet's been tapered in a die made with the same throating reamer . The 260 gr bullet has two grooves and the 250 gr bullet has one. I shoot them around 1700 fps in a 10 twist Shilen barrel and never had a problem with leading.

I know we're talking apples and oranges about what we use gunwise but I think if you want to shoot a bullet that long without doing anything special to the throat you'd be a lot better off going to a bore ride design.

[Gigs]

The goal is to hit the SAAMI overall length for 7.62x39 so they will fit in a magazine. That's the reason they are .313 all the way up to the relatively short ogive (designed to emulate the stubby ogive of 7.62x39 commercial), and don't have a separate top band.

They will be way down in the case, but since this is intended to be a subsonic load anyway, I don't think the loss of case capacity will matter. Are there issues with extremely deep protrusion in the case other than loss of case capacity?

Thanks for the advice on the grease grooves. I'll check the lube volumes on the tumble grooves vs the standard groove.

[RU shooter]

What rifle are you planning on using these in? If its an AK you maybe suprised how light you can go with something lighter in weight like a 200 gr. bullet. As most AK's are way over gassed.

[stubshaft]

If you are making it subsonic, why is there a gas check?

[wlc]

If you are making it subsonic, why is there a gas check?

You beat me to it. If you are loading it SS only then really no need for the GC. Does the barrel you plan to use have a fast enough twist to stabilize that pill? I'd be interested to hear your use and which rifle this is going in. I love messing with subsonic stuff especially with a suppressor. I'm planning on a 357 Max barrel for my Encore just for such a purpose. It will have a 1:12 twist to stabilize up to 300 grain boolits. I plan on using mostly 250 grainers though and from what a friend has told me it will be very accurate with that twist, or at least it is in his rifle.

[Bullet Caster]

Excuse my dumbness, but why such a heavy boolit??? I reload 155 grainers for my AK-47 (which sank to the bottom of a lake) with a case full of IMR 4895. I know that's not SS but it works. I would think a 260 grainer would be too massive and the boolit wouldn't stabilize in shorter shots. Can't you just lighten the load on a regular boolit? Seems like that would work better for a SS load. BC

[Gigs]

Czechpoint vz.58 pistol, I'm going to SBR it and get a supressor. 1:7 twist .310 grooves .300 lands.

I did the calculations on this boolit and it's going to need every bit of 1:7. If I can shave off 0.080 or so by eliminating one of the lube grooves then it'll have a little more margin.

Regarding the gas check, I've heard that gas check bases seem to work better when attempting cast lead in gas operated guns, regardless of speed. Don't know if there's anything to it or not. I figure I don't have to actually put the check on there.

I probably should at least tweak the gas check base to put a chamfer on the first ring to make them easier to seat without a check and without belling.

[Gigs]

Excuse my dumbness, but why such a heavy boolit???

I'm aiming for the same type of thing as 300 blackout subsonics that are 220-240.

I think the ones above calculate out at about 255gr with 20:1 alloy.

[wlc]

That should be pretty cool. Good luck and document your build here for us to follow.

[AggieEE]

How do you guys think it would work in a 7.62x54R Mosin? Although I think 200gr might be better? I don't know.

[stubshaft]

I just started working up loads for the 7.62x39 in a 1 in 9 twist on an Contender pistol platform. I used some of the Lee 309-230-5R's last week and was getting 1.25"-1.5" groups at 50yds. out of a 15" barrel. The slowest load was 5.5 Green Dot (didn't bother to chrono it) and boolits showed no signs of instability. Used mule snot for lube and no GC.

[Gigs]

I thought 309-230-5R was going to be my ticket. The problem is that if you want to seat to SAMMI OALs you are putting the driving bands right at the bottom of the neck. And the only part of the boolit that comes out .311 are those tiny driving bands by the microgrooves.

I had pretty bad leading problems with them in my .310 bore. I think the very small bearing area that's over .310 meant that any imperfections were leading to gas cutting.

The rest of that bullet is designed as a .300 or so bore ride from the end of the ogive down to the microbands.

For a contender, especially one with a 308 bore and a long throat, they'd work fine.

One concern I have about my design above is that the "bore ride" is full groove diameter, so I'm not sure how well they are going to align when entering the throat. I wanted to have a smooth ogive-boreride-driving band transistion so they can have almost the exact same nose profile as a jacketed load for feeding purposes in autoloaders.

Good information though that your 1:9 stabilized a bullet that is nearly as long as my design and shaped similarly, thanks.

[Gigs]

There's some advice floating around on the internet that you can use 44mag loads as a starting point for heavy 7.62x39 subsonic. This is terrible advice. My hand has a lot of little holes in it now, and I need to order a new bolt for my gun. Figured I'd post this here as a caution. Yes, I was stupid for not cross comparing with similar 300 aac heavy loads first. H110 @ 21gr under a 230gr bullet in 7.62x39 = boom. The gun is OK other than the bolt.

http://www.gigstaggart.com/pics/IMAG0297.jpg

[runfiverun]

dude...
h-110 is not a low pressure powder, it has some uses in large rifle cases with cast but the powder isn't really worth the trouble.
you can do the same thing with waaay more stable and predictable powders.
but you know that now.

[blikseme300]

dude...
h-110 is not a low pressure powder, it has some uses in large rifle cases with cast but the powder isn't really worth the trouble.
you can do the same thing with waaay more stable and predictable powders.
but you know that now.

Agree. Had blown primers in my AR-15 in 300blk when I went from 15 to 16gn of H110 under a 165gn boolit. The 15gn charge did not display any over pressure signs. Lil Gun is better but accuracy was nonexistent. Switched to H335 and accuracy as good as jaxeted.


Bliksem
Sent from my iPad using Tapatalk

[Harter66]

D I've used a 200 gr full spire point in an S K S long,since passed on, w/good results after curing the leading beyond the gas port. I achieved 1800 fps but those were a single feed load. My boolit was seated below the shoulder to get into the magazine. Mine had a generous throat and bore. The best accuracy was w/ the top loads and single fed. My last load that fed and functioned well was 22.0 IMR 4350 for a blazing 1200 fps ,that is the upper limit of case volume in Win and FC brass.

As a side note weigh matched brass was needed to ensure hits. Out at 100 7-8 would stay in 5-6" w 2-3 making their own group a foot away.

[Silvercreek Farmer]

Glad you are all right! Kinda late, but feel free to post any experimental loads here before you light them off, lot of experience out there.

[lawboy]

I think if you don't throat the barrel with a shallow angle taper or taper the heck out of the bullet itself there's going to be a lot of bullet hanging below the case neck. You could also do away with a few grease grooves. Probably run one groove for the print on the right, might get you closer to your wanted weight too. Don't know if it would matter for the tumble lube. I have 1.425 long 260 gr and 1.385 250 gr, in WWs, Mos moulds I shoot in a .30 PPC. The throat on that barrel is .310x45 min. included and long enough so only a little past the check is in the neck when chambered after the bullet's been tapered in a die made with the same throating reamer . The 260 gr bullet has two grooves and the 250 gr bullet has one. I shoot them around 1700 fps in a 10 twist Shilen barrel and never had a problem with leading.

I know we're talking apples and oranges about what we use gunwise but I think if you want to shoot a bullet that long without doing anything special to the throat you'd be a lot better off going to a bore ride design.

You are going to run into problems seating a gas check below the case neck. Some of the checks will be stripped off the bullet as the base moves through the /shoulder/neck juncture. Ask me how I know... With SS loads, the danger that a gas check will end up lodged in the barrel unbeknownst to you is increased and you DO NOT want to fire a shot with a gas check obstructing your barrel.
Throating to long seat is a very effective option for a bolt gun but I know you want to run these from a magazine. You can likely design a 185 to 200 grain bullet that will allow you to seat within the short Ruskie neck and still fit the cartridges into a box magazine, depending on the magazine you are using. I use a 185gr Saeco bullet in my CZ527. with a little barrel throating I am able to run them through the magazine just fine and seat the gas check even with the base of the neck. I am not running these SS but full bore.
Good luck!

[Gigs]

Based off of 300 blk subsonic loads and a few reports of 7.62x40 subsonics, I think I may try the following:

7.62x39 230-240gr UNTESTED EXPERIMENTAL LOADS
Accurate 1680 - 10 grains
IMR4198 - 10 grains

Secondary combustion is a concern with these lighter loads of slow powder, but it seems that people are working with them in the 300BLK OK. Thinking of picking up a strain gauge pressure transducer setup so I can detect the beginnings of secondary combustion.

[Gigs]

You are going to run into problems seating a gas check below the case neck. Some of the checks will be stripped off the bullet as the base moves through the /shoulder/neck juncture.

Thanks, that's good advice. From my calculations I think you can only go up to about 140 gr without extending into the shoulder, assuming a tangent ogive, unfortunately.

[HotGuns]

Interesting thread.

I just built a 7.62x39 rifle from a Mauser action. I'm using a 1in 8 twist barrel from Green Mountain, but its a .308 barrel,not a .312. and its a 1 in 8 twist to stablize it.
My plan is to use if for the 247 grain cast bullet, the 6 cavity mold got from here about a year ago. The barrel is threaded for 5/8-24 and it is 16 inches long.

Its being reblued right now and I'm putting it a Boyds walnut stock.

http://i18.photobucket.com/albums/b130/HotGuns/1893Mauserintheraw.jpg

[Gigs]

Nice looking gun. Glad to know I'm not the only one working on x39 heavy. The information out there is pretty sparse, but I think the cartridge has potential if you have the barrel to do it.

[HotGuns]

We'll see. My plan is to go with the 247 around 1000-1050 FPS and shoot it suppressed. Right now all of my cans are sealed units, but I plan on getting one of the user friendly designs out there just so that it can be cleaned.

I have no reason to beleive that it wont work well, as I've built a multitude of .300 Blackouts, and they are basically doing the same thing, in fact if you look at the Blackout cartridge and stand it beside the 7.63x39 there really isnt a whole lot of difference other than the rim.

Post your progress and I'll do the same. Maybe we can help each other out...

[HotGuns]

I plan on using AA #5. I've tested dozens of powders and charges on the Blackout, for some reason this powder shoots obviously quieter than everything else.

I mean, its really noticably quieter to others that are near by. I'm thinking that the 247 grain bullet ought to be quite a thumper.

[Harter66]

Here's a thread that has a couple of thoughts.....

http://castboolits.gunloads.com/showthread.php?95523-Subsonic-Roosky-(7-62x39)

[thehouseproduct]

I used the Lee 200gr boolit in my AK subsonic with 14.6grs of Xterminator. Dropped the brass in a nice little pile about 3 feet away.

[lawboy]

Here is a thread that details my efforts. It may be useful or interesting to you.
http://castboolits.gunloads.com/showthread.php?81943-7-62x39-Happiness-finally!&highlight=

[Diegokid]

This is a old thread but here is some info on subsonic loads I've been reading about.