View Full Version : 7.62x39 cast load work-up
May 10, 2010, 02:50 PM
All righty then. I've finally had a few minutes to start working up a load for my 7.62x39 hand casts. First Test shown.
Try as I might, there is limited info to be found with regard to load data on the 7.62x39 using cast bullets. I have several, but out of the half-dozen sets, only one had powder I currently use---a case stuffed full of IMR4895. Well, I'm not big on using more powder than necessary, so I had to develop something not on the books. My .32 Win SP uses hand casts of nearly identical weight with a light load since that one isn't a GC bullet. The case volume is larger, but by comparing load data between that case and the ratio of volume increase/pressure, etc, I settled on a starting load with a powder I have plenty of and already use in multiple loads.
---7gr Red Dot.---
The low flyer is entirely my fault. It was the first shot and I am always a little flinchy firing a new load that doesn't have any supporting data. After confirming everything was still in one piece, the following 4 shots went right where they were suppose to.
Just in case you can't make out all my writing on the photo...
173gr TL GC bullet sized to .311
7gr. Red Dot
DID NOT CYCLE (rifle is a Norinco Mak-90 all milled)
No leading found
Additional not written down---Bullets are water dropped WW. BHN hitting around 16.
I didn't expect the pressure to be high enough to cycle the action--and that was intentional. Now that I've established the starting load and everything else checks out, I can increase pressures. I'll keep things posted as I work up to a fully-functional load. So far--so good.
Next I'll go up in grains by .5 till I get reliable cycling with everything else the same. Then I'll start working on POA/POI adjustments for distances. But that's all for the moment. ;)
May 10, 2010, 03:51 PM
Looks to me like a great start. Good job!
May 11, 2010, 01:57 PM
All right, here are the next set of details.
8 through 9.5 grains of Red Dot produced very little change in performance. Still no cycling. Grouping DID tighten up a bit. Higher velocities are bringing faster stabilization. 9-9.5 grains produced touching groups---low of POA by about 2", but center. No test targets to display, thanks to the wind ripping them out from under the rock I was holding them down with right before leaving---If you live east of Colorado, keep an eye out. :D
At 10 grains I started to get partial cycling---about 1/3 bolt travel. Still no signs of pressure at all---in fact I compared against a factory mil surp and the muzzle blast and felt recoil were considerably greater. So there seems to be no reason at all not to continue stepping up the load a bit more.
For velocities, I should add before the question comes up anyway. I don't currently have a functional chrono, so MV is anyone's guess until I can rectify that little problem. So far--so good.
Next step is through 11 grains.
FYI---the mold is a LEE 312-160-2R (dropping consistant 173gr as finished with crimp-on gas checks and liquid alox tumble lube).
May 11, 2010, 02:21 PM
Red Dot is an awfully fast powder for the x39. 2400 is the king for cast x39. Be safe, and I'll watch for your targets in Nebraska.
May 11, 2010, 07:42 PM
I use Alliant 2400 start with 11 grs. and increase by .5 grs. until you get reliable cycling do not exceed 15.0 grs. as stated by C.E. Harris. You can work similarly within the range of 13-18 grs. of 4227, 16-22 grs. of 4198, 18-24 grs. of RL-7 or just stuff the darned case with all the 4895 it will hold if you are lazy.
The TL GC bullets were cast from straight WW alloy and water quenched bullets dropped at .312.5 dia and 165 grs. before GC is applied,lubed once with Lee Alox that has been thinned with mineral spirits 1 oz. to the 4 oz, bottle of Alox and allowed to dry overnight,gas checks were then seated with a Lee .314 sizing die with no sizing applied to the bullet. Then TL once more and allow to dry before loading. No sight adjustment was made on first firing in the Chinese,hence the group is low and to the left,on the Yugo I adjusted the rear sight leaf to 400 meters as i ended up doing with the Chinese and it shot high,it seem the Yugo shoot a bit flatter.
The 12.5 gr. 2400 load drops the brass right at my feet and cycles the bolt every time,a load of 14.0 grs. shoots just as accurately but throws the brass about 20+ feet away.
Lee GC TL 165 gr. RNFP .312.5 dia.
Primer CCI #34
12.5 grs. Alliant 2400
May 11, 2010, 07:52 PM
Nickles>> How right you are about Red Dot burn rate---it is very fast. The main reason I went with it though was because not only am I already using it in several other cartridges, I'm using it in one rifle cartridge that made it easier to calculate case volume ratios and determine starting load. The trick is going to be building up the load to get the right pressure for cycling the action without exceeding pressure inside the case--fast powder complicates that for sure with very little tolerance. 2400 seems to be the overall favorite and I have the load data for it, but that would mean adding another powder to my stock---do-able, but not preferred. It would either become a dedicated powder, or I would have to rework loads with it in other cartridges to justify it.
One might respond.... "And the down side to that is...WHAT?" And while I agree, reworking new loads to accommodate 2400 just means MORE SHOOTING!! Yes--it does. No down side there. But I'd like to use all my Red Dot supply first, and I like versatility in my load capabilities. And, if I can add new load data to an otherwise limited base for 7.62x39 cast bullet data, all the better! More options for all of us!
Thanks for keeping an eye out for my targets, BTW. If the jet stream hooks back north, they'll likely be right in your neighborhood by now---freaking wind is making it really difficult to do much of anything here lately...
May 12, 2010, 09:56 AM
Today's results are in! So here's the scoop---there is NO sweet spot using Red Dot that will cycle and not over pressure. It's just too fast. At 10gr I started to get cycling. At 10.5gr. we see the beginnings of a pressure spike. The case consistently expanded just enough to negate the previous bolt motion seen at 10gr. and make the bolt a little sticky ejecting manually. At that point, stepping to the 11gr loads just really wasn't that interesting---they got pulled and tossed back into the melting pot fr the next casting session.
Now, as the late and great Paul Harvey use to say, for the rest of the story...
After digging a lot, I found several references to using Red Dot in cast 7.62x39 loads. They list 4-5 grains, 5 being max. After doing some math and logical comparing, I came up with my own conclusions that differed. I use Red Dot to push a near-identical flat-nose bullet through my .32 Win Special. The case volume averages 40gr of H2O--same as a 30-30 since it's just a necked up 30-30 case. Case volume on 7.62x39 averages about 35 gr. of H2O up to about 35.4 depending on brand and wall thickness. With only 5 gr. or less in volume differences, there should be some overlap. I've run the .32 all the way up to 10.5 within documented load data, and have settled in with a nice little 7gr load for plinking. Logic says 7.62x39 should run well somewhere on the lower end of that, but shouldn't need to go all the way down to 5gr. My rifle did indeed run well right up through 9.5gr, and actually liked 9gr. the best. Keep in mind that it IS a milled receiver, however. So, my adjustments to the available (though deeply archived) 7.62x39 Red Dot data using the .312-160-2R Lee TL mold with gas checks are as follows:
4 grains archived as a subsonic load
8 grains as a safe max load (still hand cycled, but enough leg to reach out a bit)
Step beyond that with caution, and do NOT exceed 10.5 ever. Cycling will NOT occur. Keeping that in mind, YES---Red Dot can safely run through a 7.62x39 for light-duty plinking. One might say "What's the point if it doesn't cycle?" KNOWLEDGE--pure and simple. If it needs to be done, it can be. I'm kinda goofy that way ;).
Guess I'll start reworking a few other cartridges for 2400 now... :D
May 17, 2010, 01:57 PM
Try as I did, I just couldn't make myself NOT try developing a load for 7.62x39 using powders I currently burn... Probably a good thing, too---because I've got a winner!
Bullet weight, type, etc. is all the same:
Lee mold CTL312-160-2R
Tumble Lube bullet (Liq Alox) with Gas Check finishing at 173 grains using water dropped WW at a BHN of 16 average.
Load is 15 grains of H335
I started the ladder at 12.5 grains and .5 gr ladder. It was pretty sluggish through 13.5gr but started to cycle at 14 grains. 14.5gr smoothed out more, and at 15 grains cycling was 100% and smooth --and it really started acting like an AK should. Brass lobbed a reliable 5-feet to my right. The bore stayed bright and shiny--no leading or fouling in the slightest.
We'll run some groups with this load just to verify it, and then stretch it out to see where the POA adjustments need to be. I still don't have a functional chrono, so velocities are a wild card right now. But so far, this load combo shows some real promise!
May 17, 2010, 02:26 PM
Lookin' Good! :cool:
May 18, 2010, 01:07 PM
More tests today---Now I'm getting things worked in with the minor details.
These were fired from prone flopped out in the gravel. I'm sure they would tighten up quite a bit with a nice bag rest and a bench--just didn't feel like trucking the whole set-up out for a couple quick shots before the rain caught up to me.
25 yards 5-shot group
OAL 2.13 no crimp
The brown spot is because my coffee cup likes target shooting as much as I do ;)
50 yards 3 separate 3-shot groups
Group 1 is the three in the bottom of the circle.
OAL 2.13 no crimp
Group 2 in the three just high and right.
OAL 2.16 no crimp
Group 3 is the two center and low right flier--(my fault on the flier--bad rest).
OAL 2.16 with slight roll crimp
What I've found so far:
Cycling is great all the way through. However, seat as far out as your magazine and lands will allow, then finish with a slight crimp. Without the crimp I noticed just a hint of incomplete burn occurring. WITH the crimp, burn appears more uniform, complete, and the bullet seems to prefer it as well. Sight slide was set at 100 for all groups. On a side note, H335 meters extremely well with a Lee dipper. 1CC dipper pulls a consistent 15 grains. I still weighed them individually just to confirm, but every dip came up even-money. From here out, I'm thinking it's going to be straight dipper for me on this load.
May 28, 2010, 03:07 PM
All right guys (and gals?), finally had a few minutes to get out today and give this load a fair accuracy test. I can't post a photo at the moment because I'm at work, and the camera is at home. BUT... For the moment, I'll just say that I really like where this load is going. I stretched out my seating depth just a tad more, from the previous 2.16 to 2.18, and took a good bag rest for a 50 yard group. Results were 6 clean holes within a golf ball size area, and still good cycling all the way through--pressures are great, so I may step it up just a little more to see where things go (15gr to maybe 16gr with a half step). Load is accurate and consistent. It's definitely a go for anyone looking for alternate load data on 7.62x39 firing hand cast bullets.
(picture still to come though ;) )
May 28, 2010, 09:25 PM
Thanks for the data! I've been using AA#1680 for my Lee TL 160 mould, but I have some H335 left over from 303 rounds, might try it with your recipe for starters. Mine are shot in a bolt action CZ 527.
May 29, 2010, 11:29 AM
All right, as promised, the above-mentioned target. So it's grouped just a touch bigger that a golf ball, but I'd like to think it's a good reflection where the H335 experiment is going. I'll post more as I dial things further. Till then, enjoy!
May 29, 2010, 07:16 PM
Same mould, same lube. Thanks, gonna have to get the pot melting in the morning, make some more...
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