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paulbrasky
This will be a brief report. First, as I still don’t have a powder on hand that’s recommended for the SKS* so I’ve been experimenting with Blue Dot (started at 10.5gr. and worked up to 12.2gr.). I’ve also focused on the NOE 316-GC-SP, and have tried different a different seating depth (2.215″ v. 2.125″), as well as a “factory crimp” via a Lee FCD. Here’s what I’ve found:
(1) Factory crimp (moderate) v. no crimp: My initial impression that even a moderate factory crimp degrades accuracy was correct. While the crimped rounds were accurate enough @ 50 yd., and some clustered close to one another, the uncrimped ones grouped 6 in 1″ and 3 in
/4″ (twice).(2) OAL, 2.215″ v. 2.125″ (all lube grooves in case): Not much difference here, but I need to retest this one. Crimping made more of a difference than OAL from what I could see.
(3) Blue Dot, 11.7- and 12.2gr. today. Not a lot of difference in accuracy that I could see, but I only had 10 of the 12.2gr. loads. None of my Blue Dot loads has been inaccurate. However, none operated the action either. I’ll try 12.5- and 13.0gr. hoping for some joy in that respect, but the 13.0gr. charge is 50% of the 7.62 x 39mm case’s capacity and I don’t want to exceed it. RL-7 would make my life so much easier!
(4) Purchased 20 rounds of “Silver Bear” steel cased jacketed SP to see whether they would operate the action. Did they ever! Accuracy wasn’t gilt edged, but I managed to put 5 (out of 10) in a 1 .5″ x 1.5″ group. Even with the rear sight at its lowest setting, the Silver Bears went ~6″ high and 3″ to the left of point of aim. Were I to use factory ammo more frequently, I could easily adjust the front sight for both elevation and windage.
paulbrasky
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“OAL, 2.215″ v. 2.125″ (all lube grooves in case): Not much difference here, but I need to retest this one. Crimping made more of a difference than OAL from what I could see.” …Maven
I retested those OAL against each other using 12.5- and 13.0gr. [weighed] charges of Alliant Blue Dot. The results were by no means clear since the longer OAL grouped better with 13.0gr. B. Dot while the 2 1/8″ loads did better with 12.5gr. B. Dot. Additionally, neither load, regardless of OAL operated the action reliably: perhaps 3 full ejections; the rest were battered to the point of uselessness. Btw, 13.0gr. B. Dot occupies 50% of the 7.62 x 39mm’s case capacity and I’m hesitant to go beyond that.
As you know from my earlier posts, I’ve had difficulty finding a suitable propellant locally. (By suitable, I mean one which will operate the action.) Yesterday, just for grins, I decided to see how many grains of IMR 7383 a FL sized 7.62 x 39mm case would hold when topped with the NOE 316SP-GC CB seated to 2.125″. Using Jim Conner’s method,* repeated 5X for reliability, I came up with 22gr. In spite of dire warnings from several people on other boards, I loaded 3 such cartridges with that load and with great trepidation, fired them earlier today. I was also able to chronograph those 3:
22gr. IMR 7383 (uncompressed) + NOE 164gr. CB @ .3155″ & 2.125″ OAL -> 1,389 fps +- 26 fps.
There was no sign of excessive pressure; all 3 cases ejected and cleared the rifle; and accuracy @ 50 yd. was good (3 in 1.5″). Btw, there was little unburned powder left behind and the cases weren’t smudged in the least. I’ll next try 21.5gr. 7383 with the same OAL v. 22gr. and 2.215″ OAL, but I’m beginning to think the shorter OAL is more accurate (see below).
The remainder of my testing today (at 50 yards) was with 12gr. Blue Dot (11.8 -11.9grs. in fact) and the NOE CB seated to 2.125″. 6 of the 10 went into 1″ and 4 of those into 3/8″! The remaining 4 grouped into 1″, but 1″ higher than the others. That was probably the best accuracy I’ve obtained so far with this particular SKS. Here’s the chronograph data:
11.8 – 11.9** gr. B. Dot + NOE CB @ .3155″ & 2.125″ OAL -> 1,531 fps +- 30 fps
*Drill out the primer pocket on a FL sized case; seat CB to OAL you’ll be using; fill case to origin of primer pocket (tap the case to get a proper fill); weigh and repeat to get an accurate reading.
**what my Lyman pistol powder measure throws with rotor 10L
steveleonard
Maven, I just ran into a problem that could lead to disastrous results for you! I found that without crimping, my boolit was pushed back into the case when loading from the magazine. Wouldn’t that over compress that IMR 7383 to the possible point of being a dangerous load? I don’t have any experience with IMR 7383 and might be full of beans!
Is it possible for your boolit to be pushed back when feeding?
I got a Lee universal expanding die and a NOE expander plug .313″x.318″. I adjusted it so the case neck would barely fit all the gas check into it. I sized my HT’d boolits to .314″ using 2500+ lube. I’m currently working with dummy rounds to get the length right. At 2.115″ the boolit is pushed back to 2.090″ and engraving. I’m thinking about lightly crimping at 2.095″ to take advantage of just a little engraving without the boolit being pushed back on me. Still thinking…
The OAL’s I use, 2.215″ and 2.125″ (with NOE 316-160) were obtained by partially seating that CB in an empty FL sized case, putting in the carrier, and then allowing the bolt to slam forward and seat the CB: 2.215″. Once in a while, I do get a CB pushed back with that OAL. However, I experienced none of that with the 2.125″ OAL, and that’s the one I used with 22.0gr. IMR 7383. If it wasn’t so sunny today, I’d be at the range chronographing the 22.0- and 22.5gr. 7383 loads. Moreover, I’m starting to think the shorter OAL produces greater accuracy with less nose engraving* and a lower chance of the CB being pushed back into the case.
Btw, thanks for pointing this potentially dangerous problem out. While 7383 can be compressed, it’s best to tread gingerly when using it. The 3 shots I fired the other day averaged only 1,389fps +-26fps, with virtually no pressure signs. I’d like to get 10 more readings @ 22gr. and 22.5gr. before deciding whether to continue using 7383.
*This may be heresy, but it’s not the first time a non-engraving, i.e., shorter OAL has produced stellar accuracy for me.
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