Mysterious overpressure

[BoyGlock]

Its 38sc. Pf 170 in my 2011. 125 head, winch spp, 10.2gr ziira 7 powder. These are my usual load data but for no apparent reason exhibited this signs of primer flow and piercing clearly due to excessive pressures. The only thing i changed in the reloading bench was increase considerably the crimp for feeding reliability issues.  But Chronoed again and have same 170pf as previous same loads. In 100 rnds had 6 primers pierced and 4x my big stick mag fell while being shot. What have i missed?

[Shadyscott999]

Why is your crimp now? 

 

[bowenbuilt]

Your considerable increase in crimp is most likely under sizing your bullets and causing some setback. A lot of crimp only decreases the diameter of your bullets and reduces neck tension. This is what I would be looking at since it's the only thing you changed.

[superdude]

Do you have a source of load data using ziira 7?  I can't find anything via Google.

[BeerBaron]

Yeah what is ziira7? Never heard of it. Those pierced primers are scary!

[Hi-Power Jack]

I can think of only a few possibilities:

 

1.  bullet setback (not on all - but just 6/100)

2.  more powder dropped into 6 cases than you intended

3.  there was something stuck in those 6 cases before you dropped the powder,

     reducing the case capacity.

 

Good luck with it     

[Yardbird]

Or the rounds were a touch long and the bullets were in the rifling...

[BoyGlock]

I have not yet mic'd my crimp but I can say its much more than my normal crimp but not very much its gonna deform the bullets. Also I checked there were no keyholing in all the hits on paper. 

Ziira 7 is a brand used locally but not made in my place and I dont know what its branded in US and Europe. But Im sure its branded different there. Also Googled it but didnt find anything. Its very fine and a bit inconsistent to meter but not enough to cause excessive pressure and @ 10.2gr for for 170 major pf it can easily be compared to other powder brands in your place. 

Those pics showed only the pierced primers. All other primers were very much flattened with raised craters around the fpin indentations indicating all were overpressured. 

Ammo length is same as my previous loads, 1.235" in thousands of rounds. I think it does not touch rifling. 

The mystery began when I decided to use this powder again. In 2014 I decided to stop using it because I could not make my loads feed reliably in all my guns. Some rounds would not chamber completely. After lots of tests I stopped and returned to vv 3n37, my usual powder. Recently the cost of vv powder became a bit unbearable and a club member and I decided to give it a try again. Looked for my old recipe at 10.2 and loaded a hundo. Again there were ftf. But no overpressure signs. My friend whose crimp were more than mine had no ftf. But he is loading minor at 9 grn.  I copied his crimp but before doing so, checked my powder settings and found it throwing 9.6! I was very surprised and baffled. I adjusted it to 10.2 then went for a day-break. When I returned, checked it and found its at 9.9! I initially thought my digital scale was the culprit so I unboxed my old beam scale and another new digital scale to be very sure. All were giving the same readings. Readjusted again and went to load a hundo again. In the course of reloading I spot checked my powder loads and some were throwing 10.3 so I adjusted it a few more times during the 100 I loaded. I used the 3 scales simultaneously for every weight checking, readjusted, repeat, and took me more than an hour to do the hundred ammo! I even disassembled and cleaned the powder mechanism in the mid course to check for the inconsistencies. But I was confident a .1 or .2 grn more would be safe. Still I adjusted a number of times midcourse to 10.2 just to be very sure. Testfired and serious overpressure signs appeared in all 100 rounds with pierced primers in 6. In the middle of the session I chroned a few rounds and showed 170 pf, same with those I loaded in 2014. So I thought the additional crimp did not affect much the load pressure-wise. 

I intend to reduce the load to 10grns and chrono again. But will load some beforehand in 10.2 and test them in my other 2011s to be sure its not the gun. Im as very much concerned to know the cause as solving it. 

By the way, the  misfeeds were cured by the additional crimp. All 100 fed and ejected without any hiccup. 

Thanks for the inputs. Will recheck everything based on these. 

Edited April 20, 2017 by BoyGlock

[racer-x]

Are these compressed loads? 

I ask since you had FTF's and a round longer than your chamber/throat would cause that as well.

Compressed loads can elongate without the correct case tension. Have you verified all OAL's after loading? I've heard of people discovering their compressed loads had grown some after a few weeks/months, but were OK right after loading. 

 

Can you do a plunk test with your bullet and brass to determine the longest OAL before bullet contacts the throat?

Should be able to fully insert, spin and fall freely from your barrel. If not, cartridge is too long or something else is wrong with case.

 

Also, I really recommend working up to your load in steps. It is possible that you are well past safe pressures, even though you are only at 170PF. 

I've experienced a point with a few powders where increasing the powder charge will not increase velocity, and then increasing even more the velocity goes down some. For example, it would be good to chrono 9, 9.2, 9.4 & 9.6 gr charges all at same OAL.

 

And lastly, can you verify the actual weight of your bullets? If they are heavier than you think...

 

[ShortBus]

You don't *think* they are hitting the rifling and you adjusted your taper crimp a considerable amount but didn't bother to measure? 

 

Imcould be way off, but reading your posts I am  not surprised you have issues. 

[BoyGlock]

Sorry if I appear to be so careless in my process but I take my reloading seriously and observe all neecssary safety precautions that I know of. Will check again COL to see if it changed with the crimp. 

Its not a compressed load. Ive used this exact recipe in 2014. I log all my reloading data since I started about 12yrs ago so I can have them as reference for safety's sake. 

Thanks again for your inputs. Made me think and review all my reloading process and habits. Pls keep them coming. 

 

[BeerBaron]

I also think in this case velocity through the chrono is not an indicator of pressure. At some point in loads you can find pressure goes up but velocity does not. That is why even though you're at 170pf you are getting nasty pressure signs. 

 

My personal view is I would not keep shooting that load. I would not even have shot the complete 100 rounds. After the first pierced primer I would have stopped and pulled the rest. Those pierced primers are venting seriously hot, high pressure gas onto your breech. No wonder the magazine was blown out of the gun 4 times!!

[BeerBaron]

What projectile are you using?

[BoyGlock]

127gr coated .356" heads. Scheumann 4 popple holes barrel. 

 

It could very well be unsafe to shoot. But it did not feel harsher and with remarkably lesser dot flip to shoot, isnt that the holy grail open shooters are searching no end??  

[Hi-Power Jack]

3 hours ago, BeerBaron said:

  I would not keep shooting that load. I would not even have shot the complete 100 rounds. After the first pierced primer I would have stopped and pulled the rest.

 

 

That pretty much summarizes this adventure.

 

STOP.

 

Sounds very possible that this powder is NOT intended to safely make Major

with these bullets.

 

Pierced Primers mean    .....     STOP.

[BoyGlock]

Could it be the gun?

 

This just came in sent via net. Im out of town now and my club mate got one round from my hundo batch. Found lying on the ground where I shot a day before. Not 100% sure its the same load but most probably it was as we two are the only ones shooting open 38sc in that range and most probably in the whole country. Besides mine is always clean and polished brass. Its the one on the right in the pic below. The 5 on the left he loaded HOTTER in 10.4 gr. Z7 with same heads, shells, crimp, COL. Only his brass are mighty dirtier than mine hahaha!. They were all shot in HIS open 2011 with kkm no holes barrel. There were primer flows in all but not much. The primer edges in all 6 are still very prominent vs mine which were scaringly flat in the previous pic. 

Im not holding my breath so much but if its the gun, whats in the gun that could spell such drastic differences in chamber pressures?

[Hi-Power Jack]

chamber length ....   OAL.

20 minutes ago, BoyGlock said:

  whats in the gun that could spell such drastic differences in chamber pressures?

OAL - chamber length.

[M1A4ME]

And powder can change lot to lot, year to year.  The same brand/type of powder you just bought can be different than what you bought/used a few years ago.

 

Have you asked your buddy to shoot some of your loads in his pistol (to rule out some issue with your pistol?)

 

Same, thing, shoot some of his loads in your pistol and compare the brass/primers from each gun with the same loads.

 

Good luck with it.  On, if that brass was mine, I probably wouldn't use it again.  It looks, from the primers, like it was stressed pretty good.

 

One last thing, primers - using the same brand?  Can you try some different primers?  Another brand of small pistol primers, or small rifle primers even, just to see if they are different/causing the problem.  A few years back when I was shooting M&Ps and having bad (really bad - like 3 to 5 failures to fire per magazine) I was checking my primers.  I took some brand new primers apart (carefully - its funny how easy the anvil and priming compound pop loose from the cup with a nice sharp dental pick) and was measuring/comparing the cup metal thickness from one brand to another.  I also loaded up a batch of 9MM ammo with small rifle primers after buying a different brand of pistol (my first CZ) as another comparison between pistols to see if both would have the same issue.

 

Again, good luck with it.

[racer-x]

11 hours ago, racer-x said:

Can you do a plunk test with your bullet and brass to determine the longest OAL before bullet contacts the throat?

Should be able to fully insert, spin and fall freely from your barrel. If not, cartridge is too long or something else is wrong with case.

 

Also, I really recommend working up to your load in steps. It is possible that you are well past safe pressures, even though you are only at 170PF. 

I've experienced a point with a few powders where increasing the powder charge will not increase velocity, and then increasing even more the velocity goes down some. For example, it would be good to chrono 9, 9.2, 9.4 & 9.6 gr charges all at same OAL.

 

Do the plunk test. You need to 'know' your cartridges are fitting correctly in the chamber.

 

I absolutely agree with the comment to STOP.

I would not fire another one of these loads in your gun.

[BoyGlock]

Think I got the culprit. Though its not yet 100% sure, found the powder measure body has a small crack. Dont know yet how it increases the thrown powder but didnt not see the crack when I disassembled and cleaned the parts. When I loaded another set of test loads at 10grn Z7, crimp .375" (previous was .369) the chrono pf went up to 175! When I checked the powder throw it read 10.4grn! 

Having run out of possible suspects, decided to replace the whole powder measure assy with my reserve unit. Its when I saw the small crack adjascent to the bolt holding the whole assy together. 

Calibrated the reserve unit to 10grn 2 nights ago and will load some test loads and chrono them tomorrow. Will see if it has resolved the issue. 

[Youngeyes]

10 minutes ago, BoyGlock said:

Think I got the culprit. Though its not yet 100% sure, found the powder measure body has a small crack. Dont know yet how it increases the thrown powder but didnt not see the crack when I disassembled and cleaned the parts. When I loaded another set of test loads at 10grn Z7, crimp .375" (previous was .369) the chrono pf went up to 175! When I checked the powder throw it read 10.4grn! 

Having run out of possible suspects, decided to replace the whole powder measure assy with my reserve unit. Its when I saw the small crack adjascent to the bolt holding the whole assy together. 

Calibrated the reserve unit to 10grn 2 nights ago and will load some test loads and chrono them tomorrow. Will see if it has resolved the issue. 

Did I read this correctly? Did you load up a bunch and shoot them before you checked the powder throw? Especially after those disastrous rounds? Please stop continuing to load until you check everything. IMO you should have known that the powder throw was off before you fired those test rounds. Just sayin 

[BoyGlock]

3 minutes ago, Youngeyes said:

Did I read this correctly? Did you load up a bunch and shoot them before you checked the powder throw? Especially after those disastrous rounds? Please stop continuing to load until you check everything. IMO you should have known that the powder throw was off before you fired those test rounds. Just sayin 

 

If 200 rnds is a bunch, yes! And at 175pf its not supposed to be disastrous in my book. It normal major load pf. I expected the pf at 166's as my previous data say so with 10.0 grns Z7 with same head and coal but the crimp is now looser at .375". When my chrono showed 175pf from the 2 ammo boxes, I decided to practice with it instead. It was very accurate and lesser and slower muzzle flip that I can call the dot more precise than usual. After awhile I considered sticking with this load. But it may be too harsh for the gun.

 

Thanks for the concern. Im still ok. 

[Hi-Power Jack]

Hope you don't get hurt ....   

[M1A4ME]

8 hours ago, Youngeyes said:

Did I read this correctly? Did you load up a bunch and shoot them before you checked the powder throw? Especially after those disastrous rounds? Please stop continuing to load until you check everything. IMO you should have known that the powder throw was off before you fired those test rounds. Just sayin 

Absolutely.  I charge 50 cases.  Then I look in them with a bright light to confirm they all have powder.  Then I pick 5 of the 50 that look different to me, or just random picks if none look high or low, and weigh the charges on the scale.

 

Sometimes things get loose, sometimes something changes and the random scale checks keep me (and my guns) safer.  Extra time?  Sure.  But I feel better about it and that's important.

[racer-x]

Final thought here...

 

Your cases with very flattened primers, primer flow and peened head stamp markings is a direct indication of a dangerous CHAMBER PRESSURE.

PF is irrelevant to whether or not the load is safe.

- these pressure signs indicate you are very close to a destructive event... maybe a case separation or rupture, maybe something much worse.

 

PF (does not equal) CHAMBER PRESSURE

 

PF is (velocity x projectile weight).

CHAMBER PRESSURE is the pressure exerted within the chamber when the cartridge is fired.

 

Within normal / safe operating ranges,  these two usually increase together while increasing powder charge

        (i.e. increased powder charge=increased velocity=increased PF=increased CHAMBER PRESSURE). 

However, as you continue to increase the powder charge within the same cartridge volume, at some point this may not hold true (lots of variables).

Increased powder charge may result in no increase or a reduction in velocity (same or reduced PF).

CHAMBER PRESSURE is most likely to increase.

 

It seems that you may be in this region based on what your primers look like, or that the batch of powder you have is not a good match for your requirements.

 

Either way, the safest course of action is to step your powder charges down 10-20% and work up the load in this gun again with this batch of powder.