Accurate A1680 data for Surplus ThunderBird T680 for 7.62x39 in SKS

[DonMountain]

I bought a Chinese SKS rifle in 7.62x39 maybe 35 years ago when they were cheap, and discovered it didn't shoot very accurately. So, it's been in a storage vault all these years. I had also purchased an 8 pound jug of T680 powder about that time to use in an M1 carbine, and I still have maybe 7 pounds of it left. Recently I resurrected that old SKS (it was brand new when I purchased it), and replaced the magazine since the follower was missing on the original 10 round magazine. So, now it shoots ok, but with very poor accuracy with Winchester factory loads of full metal jacket 123 grain bullets. I bought a box of Hornady 123 grain jacketed bullets with lead tips for potential deer hunting bullets from Grafs Reloading, which is a nice motorcycle ride from my farm on a nice day. Which brings me to the point of this request. Is reloading data for Accurate A1680 close enough to ThunderBird T680 powder to start a little bit lower than their starting load before progressing to higher loads reasonable? And I have a Lyman mold for the pointed 129 grain bullet that I use in the M1 Carbine, sized to 0.309". If I size them to 0.311" can I make them work in the SKS? And with what powders to make it function properly? Or is this strictly a jacketed bullet rifle?

[knitepoet]

Lots of different points. I'll try a couple

T680 data: Everything I can find online says it's similar to AA1680. That said, it IS a surplus powder, so you're pretty much stuck with "winging it" Start low and work up.

Lead bullets: Not to be a smart "donkey", but you can load lead bullets in just about any cartridge you can get the correct diameter bullet for. Some will work better than others though.

Lyman CBH4 lists the same 7 powders for Lyman 311359 (115gr) and 311410 (130gr)
Unique
SR-4759
IMR4227
5744
IMR4198
Rx7
AA2230

[DonMountain]

That 311359 is the mold I have and it works very well in the M1 carbine. What sort of trouble with the gas system on an SKS will there be? And will the T680 powder work here also?

[Der Gebirgsjager]

Just in case-- the 7.62x39mm is a .311", so if you're shooting .308" diameter bullets in the SKS you can expect poor accuracy. If you're going to shoot jacketed bullets buy .311, but if casting I'd try .312.


DG

[DonMountain]

I do have a .312 sizing die for my RCBS sizing machine. I will have to check the 311359 as cast and see if they measure that large. I wonder if those Winchester factory 123 grain rounds (which I bought years ago just to get the brass) used 308 bullets? I will have to pull one to check. And now it trying to figure out if the T680 will work with the 311359?

[knitepoet]

I've given you all the T680 data I can find.

[jdgabbard]

That 311359 is the mold I have and it works very well in the M1 carbine. What sort of trouble with the gas system on an SKS will there be? And will the T680 powder work here also?

So, I can give a little input here...

Not about the T680 or the 311359...I don't know what powder that is. But I did recently start casting for the 7.62x39, using the Lee 155gr Mold. This is for a Chinese "Paratrooper" style rifle, same SKS but with the barrel cut to 16" and the front sight block moved back against the gas block. It has a REALLY short dwell time, and I was concerned this would be a problem for cycling. I was using 4227, I don't have charge data on hand but I can look if you want me to. I found that the very first load I tried allowed the rifle with the short dwell time to cycle reliably. To the point I would actually rather back off the charge to save brass, as it was still flinging it rather far away.

With that I concluded that SKS rifles have a VERY GENEROUS gas profile. At least mine do... I wouldn't be worried about these cycling.

[DonMountain]

Thanks jdgabbard for the info. I have been test firing my SKS with 22.0 grains of this T680 powder I have, and it is still throwing the brass a mile away and hard to find. And I am still trying to get some Hornady 123 grain jacketed, led tipped bullets to shoot before I switch to trying out the cast 311359's in it. Probably with a different powder. So, maybe I will start shooting reduced farther loads to see what it will do. As I reduce the suggested load of 25.0 grains of T680 in the ThunderBird's loading data I received with the powder.

My intent was to use this load for deer hunting. A reduced velocity 311359 might not be wise for deer hunting.

[405grain]

Though I haven't used T680 powder before, Accurate 1680 is an excellent powder for cast loads in the 7.63x39. I have an SKS which must have been a mistake that slipped through the factory because it is unusually accurate (on occasion 2" groups at 100 yards) There are many powders that perform really well in the 7.62x39 with cast loads. My input here is in regards to the bullets. I have tried loads with the SAECO #302, a 120 grain round nose designed for the 30 carbine, and the results were less than stellar. In the SKS (mine anyway) the rifle shoots significantly better using heavier bullets. You might get better performance using bullets like the Lee C312-155-2R or the CTL312-160-2R. Mine really likes the RCBS 308-165-Sil, powder coated, gas checked, and sized to .312"

An interesting feature of the SKS is that it's chamber has a throat that looks like a long cone going from the case mouth to the rifling. This was done to insure the most reliable feeding under rough conditions, but it has an added benefit. You can load ridiculously long and heavy cast bullets in the SKS. I've shot loads using up to the 215 grain Lyman #311284 in mine, and it feeds and shoots fine. Here's an article about shooting heavy bullets in the SKS. https://www.castbullet.com/shooting/sks4.htm (part of the excellent "Frugal Outdoorsman" website by the late Junior Doughty) Basically what this means is that you can shoot most any cast bullet that's sized .312" (or .313") in a SKS.

As for how far the SKS flings it's empty brass, I have a theory; It's a military rifle, so I suspect that it was designed to fill dual roles - as you shoot at bad guys the rifle doubles as an anti-aircraft gun, sending spent brass skyward to knock down enemy airplanes.

[DonMountain]

So, 405grain, do any of these bullets, when seated at the crimping groove, fit in the magazine? My intent is to use it for woods deer hunting and I always prefer having a second round loaded with these small caliber firearms. Although for the last 20 years I have been using a Browning 1885 in 45-70 successfully without a need for a second round. Unless I have several deer to shoot at the same time? Out in the soy beans?

[Maven]

Two suggestions: First, slug the bore of your SKS as they vary widely (different nations made them; different factories within the same nation produced them). Second, call NOE and ask if he'll cut a copy of the C.E. Harris designed CB for the SKS that will fit your bore. The photo below shows the NOE/Harris CB on the right and a Lee 175gr. 8mm CB sized to fit my gun. Also, I let the action determine the OAL, 2.125" in my SKS, and I don't crimp the CB's ever.

[405grain]

DonMountain: I didn't worry about the crimp groove as neck tension was more than adequate for proper ammunition function. The max cartridge overall length for the 7.62x39 is 2.205", but if I remember correctly I seated the bullets to fit the magazine instead of just going with the OAL specs. (I made up a dummy round and seated the bullet long. Then I would try it in the magazine and increase the seating dept until it would fit the magazine, load into the chamber, and then eject properly. Once I got the cartridge short enough to do all this I seated the bullet .010" deeper and then used that dummy cartridge as a gauge to set up the seating die for making live rounds)

I have loaded up ammunition for the SKS using heavier than usual cast bullets like the Lyman #311041, the RCBS 30-180-FN, and the Lyman #311284, and have had no issues with the rifle cycling or firing. Though I have used several powders in these loads, it seems that most of the data for using heavy cast loads in the 7.62x39 is with Leverevolution. A good resource for these loads can be found in the collection of posts by Larry Gibson found here; https://castboolits.gunloads.com/sho...92s-load-tests Just look for the posts regarding Leverevolution in the 7.62x39. I also used GRT to develop some load data. Powders that I've used besides Leverevolution are Shooter's World Blackout, Accurate 1680, and IMR-4198.

In cast bullet loads with my with "normal" weight bullets I try to keep the gas check at or above the case shoulder, but with the heavies this isn't always possible. However, with a properly crimped on gas check I have never had any issues with the SKS having the checks below the shoulder. The trend of using heavy for caliber cast bullets in the SKS was started several years ago in articles in the website "The Frugal Outdoorsman", specifically in the "hunting", "shooting", and "reloading/casting" sections.

[Rockindaddy]

I load 7.92 x 33 Kurtz Patrone. The cartridge is very close to the Com-block 7.62 x 39mm 22 grs driving a 125gr Hornady soft point is super accurate. Start around 20 grs if loading a jacketed boolit or a powder coated hard cast boolit.

[jdgabbard]

It's a military rifle, so I suspect that it was designed to fill dual roles - as you shoot at bad guys the rifle doubles as an anti-aircraft gun, sending spent brass skyward to knock down enemy airplanes.

You might be onto something there... They do eject up and forward.

[Rapier]

If you have an AR -15 and want a cast bullet shooter, Sota Arms has 7.62x39 barrels in 16" for sale right now at $100. They are .308 and 1-10 twist, work with 1680. You just change the expander ball in the 7.62x39 die set, in the sizing die to a .308 expander. You have a 30x39. Like having a box mag fed 30-30. Iit uses the 7.62 mags and the bolt. It does shoot the 220 grain cast Cruise Missle into 1/2" groups or the 150 grain onto 1/2" groups. Advantage of reloading, making something useful from nothing much. It makes a very good hog rifle.

[rickt300]

If you have an AR -15 and want a cast bullet shooter, Sota Arms has 7.62x39 barrels in 16" for sale right now at $100. They are .308 and 1-10 twist, work with 1680. You just change the expander ball in the 7.62x39 die set, in the sizing die to a .308 expander. You have a 30x39. Like having a box mag fed 30-30. Iit uses the 7.62 mags and the bolt. It does shoot the 220 grain cast Cruise Missle into 1/2" groups or the 150 grain onto 1/2" groups. Advantage of reloading, making something useful from nothing much. It makes a very good hog rifle.

How did you know the bore diameter is .308. Doesn't say anything on the site. Very interested in a .308 bore diameter 7.62x39 barrel.

[Rockindaddy]

I load 7.92 x 33mm Kurtz Patrone shooting 123 gr Hornady soft points. Down to around 60 pounds of WW680 ball powder left. Ya use what is available! 22.5 grs shoots an 1 1/2" group at 100 yards with open sights. The Russians developed the 7.62 x 39mm round from the WWII 8mm Kurtz round. I would start around 20grs of WW680 and see if it works the gas system.

[GONRA]

Rockidaddy - GONRA's not really sure about 7.62 x39 Soviet cartridge development:
BUT.........
Even MY modest cartridge collection hasa Berdan primed MT case + 123 gn. boolit
from 1930's that closely (micrometer) matches components from today's 7.62 x39 Soviet cartridge.

Never read a good story on all this BUT
supposedly all such specimens can be traced back to a box(s)
imported (looong ago) from Switzerland by a US&A cartridge dealer.

Between the wars, all sorts of retarded blowback
and delayed blowback actions along with
"intermedient caliber cartridges" were experimented with in Europe.....

WHO NOS? ????