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michiganflyer
07-01-2013, 02:32 PM
Guys,

Been reloading many years and I have a problem I cannot figure out.
Worked up some loads 2 weeks ago.
2400 14, 14.5, 15G with the 155G lee cast.
IMR 4198 18-21 grains.
All seemed to shoot fine, but the 2400 would not cycle the bolt.
I only loaded 2 or so of each so while it hit a 9 inch pie plate at 25 yards, I didn't have great or bad accuracy.
Not really enough to focus on, I was watching for pressure changes, and cycling issues.

This week-------

7.62x39 reloads in sks.
20G IMR 4198 155g lee cast sized .311 with check.
4 power scope on rifle.
Missed target at 50 yards (9 inch pie plate)
Moved up to 25 yards and got some cardboard behind it.
Almost spraying one shot 10 inches high, one 10 right, one left, one low.
(from a bench rest no less here).

So I thought scope must have come loose. Nope.
Got out some reloads of 125G jacketed.
3 shots in about a 1/2 in group.

Shot 3 more cast, and spraying. (20G 4198)

I had 3 rounds left of IMR 4198 at 20.5 grains. (loaded 2 weeks ago)
Shot those - one inch group at 25 yards.
I had 3 more of the 20G 4198 left and I shot them and back to spraying????
What the heck?

Did some more jacketed, and put some bullets in bullets.
5 shot group of an inch at 50 yards

All bullets were cast, then tumble lubed with Lee Alox, then dried, then gas check and thru lee push thru .311 sizer.
Then tumble lubed again, dried over night (or a week ) and then loaded.

Each charge was weighted.
Primers out of same 100 box.
Power out of same bottle.

What was different between 20.5 grain load that is accurate and the 20G that sucked:

20.5 grain loads, bullets didn't seem to have as much lube on them
20.5 cases were tumbled in media before loading
Bullets not wiped clean of lube of sticking out bullet after loading.

20G sucky loads -
.5 grains less powder
Didn't tumble cases, just wiped them off, since I only had 10
Wiped bullet sticking out of case

That's all I can think of.

Ideas?

gwpercle
07-01-2013, 08:01 PM
It's your rifle's " sweet spot " . That magical amount of powder that makes all the boolits huddle together on the target. Don't fight it, no one can explain it , it is the load your gun likes.

If I could explain this phenomenon and how women think , I would write a book and become rich...but, sadly, I haven't a clue. Especially how women think.

runfiverun
07-01-2013, 08:34 PM
yep it's like shooting a ladder test and watching the groups make a figure 8 on the paper.
tight/loose/tight/loose/tight again.

Larry Gibson
07-01-2013, 09:22 PM
Have you slugged the bore of your Yugo?

Larry Gibson

44man
07-02-2013, 10:00 AM
Throw out the Alox.

mdi
07-02-2013, 12:19 PM
The most important item for shooting lead bullets is bullet to barrel fit. Have you slugged the barrel of your rifle?

tyeo098
07-02-2013, 01:36 PM
Cast some soft lead, ram it down the barrel, mike it and get your number. Desirable is .001-.002 over bore size.
This will ensure an effective seal (stops leading and gas cutting) and allow you to retain accuracy.

Check this first! Otherwise you're trying to repair a car who's problem is its out of gas :P

michiganflyer
07-02-2013, 01:41 PM
I have not slugged the barrel.
how do you do that again?
Drive a piece of lead down the muzzle part way, then back out again? Or all the way to the breach?

If the bullet was undersize then why would one load be good?

Thanks guys, I do appreciate the help.
Ron

jhalcott
07-02-2013, 01:47 PM
It's the "sweet spot" where pressure causes the bullet to swell into the rifling. Have you chronoed this load and can you add more powder to see IF that gives even better groups? Alox is easy to apply and quite effective, but there ARE other equally good lubes around. I'm lazy and use it often. I do NOT like the way it goobers up the seater die though! I do wonder WHY you use such a heavy bullet in the 7.62x 39! It was designed for a good bit lighter bullet.

michiganflyer
07-02-2013, 02:00 PM
I have not chronnoed it yet.
I know maybe too heavy, but I have had great luck with LEE molds and it seems many on here, say it makes a good bullet for SKS.
All the other molds were OOS and impossible to find.
I have used tons of LEE pistol molds over many years so figured it would work.
I also use it in my 30-30 and it works great.
For Pistol I use my RCBS sizer luber, but for this, I figured this was easier and a bit cheaper.
So you think faster?
I am going to load up more this week.
So maybe 20.5 and 20.7 and 20.9.
I think 21G of imr 4198 is max in my book.
I don't use it to hunt, just mess around with.
I know the jacketed bullets are 125 at .311 and work great.
But man getting expensive at 25 bucks a hundred if you can even find them.

truckjohn
07-02-2013, 02:04 PM
Remember that the Military Spec Minimum for 7.62x39 barrels was 0.312"....

Most likely, your cast bullets are too small for the barrel... If I had to make a prediction, my guess is that cast bullets in the 0.313" range would run best...

Thanks

Pb2au
07-02-2013, 02:41 PM
Remember that the Military Spec Minimum for 7.62x39 barrels was 0.312"....

Most likely, your cast bullets are too small for the barrel... If I had to make a prediction, my guess is that cast bullets in the 0.313" range would run best...

Thanks

+1234 on the bullet fit. I would be willing to bet that your boolit is simply undersized. Where you are seeing some success is simply a sweet spot as stated before. It probably has just enough bump to swell the boolit a bit to seal the bore.
Slug the bore and let's work from there. Find a soft lead sinker/slug that is a bit over sized to the bore, clean the bore and lube the sinker. Start it at the muzzle with a soft mallet and then send it all the way through. I use a .25" brass rod I cut into 6" sections and simply chase one after the other as I tap it down the bore.

1Shirt
07-02-2013, 03:35 PM
Suggest you try .314, or possibly even larger.
1Shirt!

mdi
07-03-2013, 11:06 AM
Normally, if you intend to shoot lead bullets .002", or so, over groove diameter is desirable. Without knowing groove diameter, how ya gonna know what +.002" is gonna be? Drive a soft slug all the way through the barrel (your bullets are going to travel the whole length of the barrel, right?). Finding groove diameter variations/constrictions can come later if problems are encountered shooting +.002" bullets...

Cane_man
07-04-2013, 12:16 AM
the "sweet spot" is called the Optimal Barrel Time, it can be calculated

leadman
07-04-2013, 01:08 AM
My Norinco SKS has a barrel that measures .3135"+. I use a hi-Tek coated .314" Lee bullet designed for the 7.62X39 and it weighs just over 170grs. I think Lee is cutting them on the large size these days.

One thing the heavy boolit may help with is getting the action to cycle correctly at a lower velocity. I tested H4895 last week in it and it worked great. As I was also testing the HT coating I took it all the way to 1,950 fps. Would be a good hunting load as far as power goes, but might need part of the nose filed off. Probably will try a different powder for other loads.

To the OP: Were all the boolits cast from the same alloy at the same time? If one batch was feshly cast they might not have hardened up enough yet.

michiganflyer
07-08-2013, 08:45 PM
Thank you all for the info. I will try some new loads and see what I come up with.