Friday, June 18, 2010

Reloading Challenge

Some of you (esp those on GBC) are aware of my reloading saga ... for those not familiar with it, the story to date is:

Shooting buddy and I split 5000 proji (125gn conical, 356dia) & 5000 (federal) primers.

He reloaded these in 9mm cases first and had tumbling issues. I've been using these proji & primers for years and never had a problem. However, when I eventually got around to reloading some I also had tumbling issues.

He increased his crimp, went up to 4.1grns of AP70N (which is what I'm using) and used only winchester brass and the tumbling stopped. I put some of his loads through my gun - great grouping and NO tumbling.

I used winchester brass, 4.1grns of AP70N and still had tumbling issues. On Monday night I reloaded 50 or so with more crimp, took them to the range on Tuesday and they still tumbled.

So back to the drawing board. OAL of his & mine are 5 1000's of an inch different. However, there is a marked difference in the width of the case at the base. So I got him to run 50 through his press doing the first stage only (primer out, resize) and then loaded them last night with different crimps.

I backed the crimp right off and then increased it by a quarter turn and loaded 5 at each point, taking it harder than it was originally.

Took them to the range today, and saw a marked difference in grouping but not in tumbling. I will now set the crimp to the best grouping and start looking at length as being the issue.

We tested the gun and the max length that I can load is 1216 OAL, his rounds are 1143, mine were 1138 (not sure what units these are - it's whatever his calipers measure!).

So I guess my next challenge is:
a) measure the rounds in mm on my calipers
b) load different test loads at 5mm increments from 1140 to 1210, using the best grouping crimp above and see if we can solve the tumbling issue.

If it's not this then I'm not really sure what to do next. (Oh, we pulled some rounds apart and double checked the powder - mine was exactly 4.1, his varied between 4.3 and 4.5, so maybe I could increase my powder just a touch).

It's been an interesting and educational challenge - but I really would like to find a solution :)


ZerCool said...

The OAL is likely in inches, and

What bullet material? Jacketed, cast, etc?

Is it possible your barrel is leaded up? Do other loads still shoot well?

Julie said...

HI ZC, it is probably inches, but I don't understand them :)

Lead coated with teflon? Same proji that i've been using for the last 3 years.

Barrel doesn't appear to be leaded up - my mate's rounds work fine ... and yes, I could get him to do all my reloading but that would be mean :)

Crucis said...

Tumbling, I've found, is a mismatch between the rifling, turns per inch, and bullet velocity. I've only had this issue with reloading .223. I've two rifles, one with a 1 in 9" twist and the other in 1 in 14 inch. If the bullet weight is high for the caliber and the velocity is slower, the reload works fine in the 1 in 9" but will tumble in the 1 in 14. Contrawise, what works fine in the 1 in 14 may shed its jacket when fired in the 1 in 9 inch rifle.

I suspect you will have to tweak velocity (powder weight), OAL (affects chamber pressure) and bullet to resolve this. Faster burning powders vs. a slower powder can also attribute to the situation.

Just some areas to investigate...

Julie said...

thanks Crucis, stay tuned :)

Anonymous said...

Hiya, Julie.
Finally got a chance to pop something in here.
Max OAL for the 9mm is 1.17 inch (29.70mm) So, you're not too far off.
You've loaded that combination in the past, with no stabilization problem.
I suspect there may have been a change in bullet alloy or construction.
I'll guess they are swaged soft lead, rather than hard-cast.
My suspicion, stripping on engagement with rifling.