Mini-30 Asymmetrical Case Stretch - Shooting Sports Forum


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Old 03-11-2010, 23:56   #1
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Mini-30 Asymmetrical Case Stretch

I've recently begun reloading for my Mini-30. I'm finding that most of the expended cases have asymmetric vertical expansion around the circumference of the shell near the base. Or, to put it another way, the cases wobble when spun in a drill, from a point very close to the extractor groove.

I initially thought I was using too much powder. The problem persisted even after reducing the loads to the point they would barely cycle the action. FYI, I have installed a smaller diameter gas port, but the rifle still throws brass about 10 feed with a normal load.

Then I thought maybe the problem was that the powder I was using, IMR4198, burned too quickly. So I tried AA1680 and H335. While the frequency of the problem was reduced, it did not disappear.

Finally, I ran some Remington Express ammunition through the rifle to see if the problem persisted with commercial ammunition. Sure enough, the problem does occur with commercial loads.

I've decided to settle on the following load as a good compromise between case distortion, accuracy, and velocity.
Winchester brass
Winchester LR primers
26.9 grains of AA1680 (Speer Reloading manual calls for 26 - 28 grains)
Speer 123 grains .310 soft point bullet for 7.62x39
2.195" OAL
Crimped with a Lee Factory Crimp die
Chrono shows velocity to be around 2320 fps.
For comparison, my unknown brand cheapo steel cased 7.62x39 123g FMJ ammunition runs around 2340 fps out of my rifle.

The rifle's action, barrel, and bolt are all stock.
Serial number 196-97965. 18.5" barrel.

All rounds were created using new Winchester brass casings.

Running warped expended cases through an RCBS full length sizing die does not straighten them out. Running them through multiple times, rotating to a new position each time, has very little effect.

Is this stretching normal for a Mini-30?
Is there anything I can do to straighten the cases?
Is there anything I can do to reduce or eliminate this problem, short of purchasing Lapua or Norma cases?
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Old 03-12-2010, 02:45   #2
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I load for my M30 but have not noticed that 'wobble' when I chuck the cases in the Lee trimmer for trim to length. I haven't had much luck with Win cases the neck splits after 3-4 loadings if make it that far. Lapua, IMI, K-P, and PMC last longer.
I load 25gr of 680 under 123gr slugs and use the 4198 for some 150gr I've been working on.
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Old 03-12-2010, 05:41   #3
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Brass Cases fired from auto-loaders do stretch due to the slight amount of chamber pressure when the round is extracted. Stretched, not crooked.

If your cases are truly coming out crooked, then I would think the chamber has issues. That said, I'm not sure chucking a brass case in a drill is an accurate way to check concentricity.

I check my concentricity with one of these.
http://www.sinclairintl.com/prod_det...tricity-Gauges
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Old 03-12-2010, 08:34   #4
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Originally Posted by steve4102 View Post
Brass Cases fired from auto-loaders do stretch due to the slight amount of chamber pressure when the round is extracted. Stretched, not crooked.

If your cases are truly coming out crooked, then I would think the chamber has issues. That said, I'm not sure chucking a brass case in a drill is an accurate way to check concentricity.

I check my concentricity with one of these.
http://www.sinclairintl.com/prod_det...tricity-Gauges
I use the drill for trimming. The concentricity problems are severe enough to become readily apparent during this process.

Last edited by Strake; 03-12-2010 at 08:36.
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Old 03-13-2010, 03:46   #5
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Your saying that one side of the case has a bulge, near the base? Bad chamber (egg shaped) Try placing a fired case back into the chamber, if it only drops in, in one position, than you've confirmed it.
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Old 03-13-2010, 13:02   #6
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Make sure the chuck is completely clean, I will see the same affect on my 223 if the chuck is not clean. Roll the cases on a flat surface after you load them and see if the bullet shows a wobble when you roll them. It could be the chuck is over sized and giving the illusion of wobble.
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Old 03-13-2010, 15:45   #7
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Chuck something you know is straight in your drill and see if it wobbles. Many hand drills and most all cheap drill presses have some/a lot of runout. Your problem may be your dril and not the cases.
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Old 03-13-2010, 17:08   #8
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Thanks, Tailgunner, I'll give that a try. What are the most common causes of a messed up chamber?

I know hand drills have a lot of runout or whatever you call it. I've trimmed a lot of cases using the drill, including other calibers, and know what I should generally expect. There is something out of whack with these shells.

I'm going to experiment with higher quality brass and steel casings. If I don't experience the same problems with those, I'm going to assume that Winchester brass in this calber sucks. I've had other indications this might be the case.
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Old 03-13-2010, 17:23   #9
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This may be a stretch, but I noticed in my Mini .223 (from 1977) the cases didn't last more than 2 or three reloads. They split mid-case and stuck in the chamber, which was remedied by cycling an empty case in behind it and pulling the stuck half out.

This case problem doesn't occur with my AR and I think the Mini's problem was it had a larger chamber. This same difference exists between the chambers of my .30-06's and 7.7 Japs (Which are entirely different rounds, dimensionally). I use old '06 cases to trim and reform into 7.7 rounds, but when fired will exhibit the same slight off-center "bulge" you describe. This has no noticeable effect on performance or accuracy in the Jap rifles, nor on the life of the cases I made.

The only problem that could arise with your cases is if you use them in another 7.62 X 39 Mini which may have a tighter chamber unless you full-length resize. I doubt that any Kommie platforms would have difficulty digesting them though. Those things could eat gravel, burp then just continue firing.

Last edited by hoplophile; 03-13-2010 at 17:26.
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Old 03-13-2010, 19:36   #10
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Originally Posted by Strake View Post


I'm going to experiment with steel casings.
Good luck with that.
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Old 03-13-2010, 21:33   #11
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Originally Posted by steve4102 View Post
Good luck with that.
What problems do you think I'll have?
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Old 03-14-2010, 05:40   #12
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Without starting another debate(war) on the reloading steel issue, loading steel can be a bad idea.

Brass is much more "malable" than steel. i.e. can be stretched more with out weakening than steel. If you weaken the case the pressure may crack or burst the case. Yes it will also be hard on your dies. It isn't worth it.

I won't reload nickel cases anymore either, the particles stick to the die, and scratch the cases. I had to dissamble the die many times to clean/buff the particles off the die walls.

Besides some steel cases are Berdian primed. Most dies are for Boxer primers. Every steel cased ammo I've seen says "So not reload" on the factory box.

"The brass case is like a fuse in an electrical circuit. It is the first thing to react to high pressures and give you a warning.

The steel case is not going to give you that degree of luxury or rather protection. Unlike brass there will be little difference from when the steel case fails and the rifle is in danger of being damaged along with the shooter."

You will aslo find those that feel loading steel is OK. If you are one of those, then as I said, "good Luck".
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Old 03-14-2010, 06:31   #13
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as stated before steel cases are Berdan primered which is nigh on to impossible to find in the USA, and difficult to remove. if the ammo was really scarce then maybe it would be worth it, as an antique firearm or one that would shoot that ammo isn't made for any longer but the steel cases I've seen are all for modern guns which ammo is avaulable for.
save the time and trouble and buy some brass cased ammo to reload.
Cabela's has a sale on MFS (Hungarian made) X39 brass, boxer primered ammo. about 8$$ bx/20. good reviews of it on THR forum.
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Old 03-14-2010, 07:10   #14
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Reloading brass is the way to go, I like using Remington but you can try some premium stuff to see you get better groups. I just bought 100 pcs for my 6.8 in Hornady, I have SSA I have been working with. I measured all the lengths and they are exactly the same.
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Old 03-14-2010, 08:46   #15
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Every thing you said in your original post, especially this:

Running warped expended cases through an RCBS full length sizing die does not straighten them out. Running them through multiple times, rotating to a new position each time, has very little effect.

points to drill runout. If the die does not straighten them out, then likely they are not crooked. Why do you doubt the RCBS die and not the drill? If you have the case chucked into the drill so that you can still see the extractor groove then run out is guaranteed. You cannot get the case chucked straight with just the base in the chuck.

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Old 03-14-2010, 10:51   #16
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Originally Posted by yrralguthrie View Post
Every thing you said in your original post, especially this:

Running warped expended cases through an RCBS full length sizing die does not straighten them out. Running them through multiple times, rotating to a new position each time, has very little effect.

points to drill runout. If the die does not straighten them out, then likely they are not crooked. Why do you doubt the RCBS die and not the drill? If you have the case chucked into the drill so that you can still see the extractor groove then run out is guaranteed. You cannot get the case chucked straight with just the base in the chuck.

ljg
Yup, kinda like chucking a finish nail and using it for a drill bit, works, but wobbles.
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Old 03-14-2010, 15:58   #17
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Drills, Steel

I am absolutely sure the problem I'm seeing is real, not caused by poor tolerances in a drill. Continued insistence to the contrary will not change my mind. If you are adamant, and want to prove yourself right, I can mail you a few sample cases to measure.

I don't intend to reload fired steel cases. I intend to cannibalize existing rounds for my experiments. The goal is to see if steel cases will exhibit the same problems I'm seeing with my brass cases. So no problems with berdan primers, no hacking cases to try to make a boxer primer fit, no drilling out the anvil, no worries about weakened steel blowing out.
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Old 03-14-2010, 18:10   #18
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Originally Posted by Strake View Post
I am absolutely sure the problem I'm seeing is real, not caused by poor tolerances in a drill. Continued insistence to the contrary will not change my mind. If you are adamant, and want to prove yourself right, I can mail you a few sample cases to measure.

I don't intend to reload fired steel cases. I intend to cannibalize existing rounds for my experiments. The goal is to see if steel cases will exhibit the same problems I'm seeing with my brass cases. So no problems with berdan primers, no hacking cases to try to make a boxer primer fit, no drilling out the anvil, no worries about weakened steel blowing out.

PM sent.
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Old 03-14-2010, 19:03   #19
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By your tone, I don't think you would believe me if I measure them and it's not going to do me any good anyway. And that's all right, I'm not putting you down for that.

Try one thing. Take one of the case that wobblies the most and set it base down on a kitchen counter (smooth). If there is enough wobble for you to see in the drill, the case will lean one way or the other on the counter top. Like the Tower of Piza. Take and post a picture.

But I can quarantee you that if your chucking those cases in a drill using only the bases inside the chuck you cannot get them straight and they will appear to wobble. Are you doing this??????

I also am not saying that your drill is bad, or has a bad chuck. .003 inch runout is a good chuck. Even a $300.00/$500.00 chuch for a lathe used in a small shop will be speced at about that. To get a lathe chuck with better spec's that that you'll have to go to a 4 jaw or an adjustable. Three jaw chucks are just not very precise, not do they repeat well.

But again, until you tell me different, I think you are chucking only the base in the chuck. That's the only way you could see "the wobble" at the extractor grove. There is just no way on God's Green Earth you or anyone else can chuck them straight. Even if you chuck the whole thing in the chuck the case is tapered and you cannot get it straight. Just like the finish nail mentioned.

None of this is going to profit me one way or the other. My only agenda is to make sure no one else tries to measure wobble (run out) this way. If you're chucking those cases some other way, please advise and I will shut up.

By the way, if a case were crooked and you run it through a full length resizing die three times turning it each time, it would be physically impossible for the die not to effect the case in some manner.

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Old 03-15-2010, 01:00   #20
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Well Gosh Darn. Paint me stupid and call me a clown. :wacko:

Tools:
Dewalt hand-held electric drill
Lee lock stud and cutter for trimming cases, #90110
Lee case length gauge and shell holder for 7.62x39, #90133

The Lee lock stud is chucked into the drill, and left there for the first four observations. The shell holder screws onto the stud. Cases are inserted into the shell holder, then the shell holder is screwed down to tighten the grip on the case.

Observation 1:
Unfired Winchester 7.62x39 brass, when placed into the shell holder and spun in the drill, shows "wobble". This is probably from drill "runout" or whatever it is called. The amount is quite visible. Trimming is easy.

Observation 2:
Complete, unfired Remington Express 7.62x39 round, when placed into the shell holder and spun in the drill, shows "wobble". This is probably from drill "runout" or whatever it is called. The amount is quite visible. Wobble is visually equivalent to that of the unfired Winchester brass.

Observation 3
Once fired 7.62x39 Winchester brass case, from a light load, is placed into the shell holder and spun in the drill. The shell visually "wobbles" noticeably more than those in observations 1 and 2. Repositioning the case within the shell holder does not bring the level of wobble into line with observations 1 and 2. Trimming the case is easy in spite of the wobble.

Observation 4
Once fired 7.62x39 Winchester brass case, from a medium-to-full power load, is placed into the shell holder and spun in the drill. The shell wobbles an alarming amount. It is obvious something is wrong. Repositioning the shell in the holder does not eliminate the problem. Trimming the case is difficult because the wobble, combined with a stiff grip on the cutting head, tends to cause the shell to leave the holder. The shell holder must be tightened significantly more than is required in observation 3. The feel of the wobble of the trimming head in the hand is obvious.

Remaining observations are made without the shell holder, and are suspect.

Observation 5
A new Winchester shell is chucked into the drill up-side down and spun. There is wobble. Most likely "runout" or whatever in the drill. But, to the naked eye, all appears to be even and OK. The edge where the ejector groove meets the main vertical portion of the case appears consistent (even, straight) while spinning.

Observation 6
The same as observation 5, but with a fully loaded, unfired Remington Express round. The results are identical.

Observation 7
The same operation as in observation 5, but with the shell from observation 4. Most of the case appears to rotate slightly "funny". Hard to describe. The head appears to be more out of whack than the rest of the case during rotation. The edge where the ejector groove meets the main portion of the case body appears to move up and down as the case is rotated, in a manner suggesting the case head does not align on the same axis as the remainder of the case.

Finally, the shell in observations 4 and 7, when stood on a flat surface, does appear to lean.

All observations are consistently repeatable.
Yes, there is a great deal of runout in the drill.
Yes, there is probably no way of seeing small variances in concentricity in a case by spinning it in a drill.
This does not, however, mean that all observations made with a drill are irrelevant. There are differences in how my shells look and feel in the drill. And, given the obvious runout or whatever of the drill, the differences must be significant to consistently stand out.

One other thing...
I don't experience the same problem with my .243 or .308 shells.

yrralguthrie, -1.

Last edited by Strake; 03-15-2010 at 01:17.
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Old 03-15-2010, 04:55   #21
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Great report, thanks. Observation #4, trimming question, is this attempt at trimming of a once fired case or a once fired case after resizing? How much if any did the "wobble" reduce after resizing?
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Old 03-15-2010, 07:02   #22
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wobble

John Wayne said in one of his movies, "Your fault, my fault, nobodies fault..."

You need to verify the "wobble" by some means other that using the drill. Did you place a case on a flat surface and see any tilt one way or the other?

Resizing the cases in the RCBS full length sizer completely contradicts the results you get with the drill.

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Old 03-15-2010, 08:57   #23
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Originally Posted by steve4102 View Post
Great report, thanks. Observation #4, trimming question, is this attempt at trimming of a once fired case or a once fired case after resizing? How much if any did the "wobble" reduce after resizing?
Once fired case after resizing. No noticeable change in wobble before and after resizing.
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Old 03-21-2010, 17:16   #24
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I got your cases and ran them across my concentricity gauge. All cases both fired and resized measured true and without issue from the extractor groove forward to the neck. But, from the extractor groove back to the rim was a different story. It appears that the rim is bent, thus the wobble when spun in a drill/shell holder. This is why your sizing dies cannot fix the wobble.

The Factory brass and the steel cases had very little bend to the rim. About the same as I have from my fired handloads. You handloads on the other hand were bad. The one with the "X" was way bent as were many of the other handloaded cases.

Why do you think your handloads are bending the rim so bad? I have a guess, but it is only a guess. Pressure. Your loads are running on the high side for Speer and over max according to Hornady 123gr 23.9gr Max, Sierra 24.8 .308 and 23.7 .311 Diameter bullet, Accurate 25.5gr Max and Lyman 48 25.7gr Max. Speer is the only data that runs the 7.62x39 with more than 25.7gr of 1680 as max.

I think your loads may be over pressure and the rim is getting bent or pulled away from the extractor groove when the action is yanking the over pressure swelled up case from the chamber. Similar to the "sticky bolt lift" one get with an over pressure round in a bolt action.

Try loading a few new cases at 25-25.5gr of 1680 and compare the wobble to some of your 27.9gr loads and see if there is any difference.


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Old 03-22-2010, 00:43   #25
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Thanks Steve4102. I'll give your suggestions a try. I think pressure is the most likely answer, but need to rule out case quality. I'll run some comparisons using higher-quality brass to make sure that my problems aren't being caused by crappy brass.

I appreciate your information, measurements, and suggestions.

I asked Speer to verify that their load data was correct and "safe", given the apparent discrepancies.

Some of the load data for 7.62x39 within Reloading Manual #13 seems
aggressive when compared to load data from other sources.

Speer:
125g #2213 bullet
26-28 grains AA1680
24-26 grains IMR4198
29.5-31.5 grains H335

Accurate Arms:
125g Speer SP
23-25.5 grains AA1680

Hogdon:
125g Speer SP
24 grains IMR4198
31.5 grains H335

Lyman:
Hornady Soft Point .310 123g #3140.
23-25.7 grains AA1680
22-24.6 grains IMR4198
30.5-34.5 grains H335


Speer's starting load for AA1680 is greater than the maximum loads
listed by other sources.
Speer's starting load for IMR4198 is the same as the maximum load listed
by Hogdon, and 98% of the maximum load listed by Lyman.
Speer's load data for H335 seems to be in line with recommendations from
other sources.
Is the 7.62x39 load data within Reloading Manual #13 for AA1680 and
IMR4198 powders "safe"?
Speer's response?
I have attached our current load data from Speer #14 manual. Linda

Linda Olin
CCI/Speer Technical Services
The attachment was a PDF of the 7.62x39 section of their 14th edition reloading manual, which is pretty much the same as what is contained within my copy of the 13th edition so far as I can tell.

The PDF looks like a scan of a printed manual, with the section about primer selection bracketed.

There was nothing to indicate they thought anything was wrong with their data. No direct answer to my question either. Odd.
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