308 Secondary Explosion Effect (handloading)

[brad96nm]

Hello,
I have recently found a new issue with ammo I built apx. 3 years ago. Reading around the web I've found that the leading cause of S.E.E. is below minimum charge. I run near max loads, and I've always used the same components. I keep the ammo in a cool/dry place, and I'm meticulous about my loading process.
This happened three times today at the range. I started shaking the ammo to see if I can hear lose powder, but didn't and didn't have an issue either.
After the long introduction, my question is; has anyone experienced this from or in theory think it could be due to age of powder or primer.
Recipe.
BLC2 46 gr.
168 gr A-max
Winchester brass
CCI primers.
This problem has yet to cause my bolt gun any issues in accuracy or reliability.
The Powder/primer is blowing a hole near the base of my brass and it is always on the ejector/port side.

brass PIC at:
http://www.facebook.com/media/set/?set=a.2726627805811.2115606.1260642955&type=1

 

[RoosterShooter]

Re: 308 Secondary Explosion Effect (handloading)

WOW .... the charge it too hot! That's a dead giveaway.


You're lucky that only your brass is blowing out! That's not the primer blowing out the brass. It's due to the fact that this is where the gas is escaping! Again, you are extremely lucky you aren't damaging your rifle.

I took a double take of that brass. Is that a .308 cartridge? At any rate ... the base of the cartridge is 'belled' out. Look towards the bottom right side of the photo. Also, the light brass ring around the base of the cartridge, before the sidewall meets the rim, is stretched brass! You're damn lucky friend!

I'd pull every bullet and reload with a lighter load. Max is NEVER a good place to start!

 

[RSA-Raven]

Re: 308 Secondary Explosion Effect (handloading)

Maybe have a smith look at your chamber, I wonder if it could be un-supported area that fails...

G'luck & hope it's a minor issue,

Rgds

R-Raven

 

[crshep]

Re: 308 Secondary Explosion Effect (handloading)

How many times has that case been reloaded?

 

[Greg Langelius *]

Re: 308 Secondary Explosion Effect (handloading)

I concur with the RoosterShooter, your load is at least 2 full grains above what I would consider to be a reasonable max.

While some rifles will tolerate this (for awhile), the load performance becomes less predictable, and small influences can have serious effects at such charge weight levels.

The problem with rifles which appear to tolerate such treatment is that the more serious consequences of such treatment are cumulative. Repeated overpressure events decrease the MTBF (Mean Time Between Failures, an engineering/design term which relates directly to stress cycles and mechanism lifespans). Metal parts exceed their maximum designed stress levels and frequently suffer metal fatigue-related failures well before their intended life span expires.

Even when the excessive stress levels are discontinued, the overall lifespans of the critical parts remian compromised, and could just as easily fail later with a 'reasonable' charge, leaving no immediate evidence of their cause.

As for secondary explosion effect; no, I've never experienced or witnessed any instances that can be traced directly to the phenomenon. In any case, the lore suggests it would be taking place with sub-published-minimum charges of slower powders, while your data suggest a potential overcharge with a faster powder.

I think the circumstances would suggest a diagnosis of a basic overpressure excursion. Your summation clearly suggests that the conditions needed for a secondary explosion effect are not clearly present.

There may not be any way to conclusively determine whether the rifle has been compromised. This hidden compromise is one of the reasons why published maximums exist at the levels they are published, and may appear lower than is possible to achieve without glaring pressure indications. This is why I personally hesitate to purchase used rifles from any other than well known sources.

Greg

 

[Ulakhan]

Re: 308 Secondary Explosion Effect (handloading)

According to my computer program your load in a standar chamber and with standard brass is very close to SAAMI max pressure. It takes very little fiddling with case volume and seating depth to go above.

Sincerely

 

[SIG700]

Re: 308 Secondary Explosion Effect (handloading)

Take a picture of the head stamp (with spent primer still in brass) and put it up. Flat primers/letters would be a dead give away that your loads are too hot. Also, what is your C.O.A.L.? (Like Harald said, seating too deep can spike pressures, especially if you're running hot to begin with)

 

[brad96nm]

Re: 308 Secondary Explosion Effect (handloading)

Thanks to all that replied,
I'm going to pull all my ammo apart and start over close to minimum. My first thought is that I was running under minimum and causing the S.E.E. but thinking it is over pressure due to over max load after reading these comments.
I plan to run the .308 to a smith with spent brass (factory and handloads)
Thinking back when these were being made I used a manual dispenser and weighed every 5th round, which has been corrected with a Hornady electric dispenser and scale.

My COAL is 2.800 case lengths are all measured to the same length 2.015 +/- .001

3rd reload on the cases.
44 to 47 grains is the window per Hodgdon data.
usually what I do is split the difference between min and max and move up never reaching max. in this case I'm looking at 45.5 grains
Looks like I will start back over at 44.5 grains and not exceed 45.5.
Also it will help extend the life of my brass.

Agreed I have yet to buy a used firearm, and if this is trashed beyond repair it will become a Man-Cave wall decoration.

I will update with my findings on the weight of the loads and see how far off I am.

 

[Greg Langelius *]

Re: 308 Secondary Explosion Effect (handloading)

I would no be completely committed to sidelining the rifle as long as you can count these experiences on the fingers of two hands. The key issue here is that they still add up to ten.

If the loads were significantly higher, or the number of instances started to need toes to count on, my confidence would be lower. Everybody gets a free pass once in awhile, and design margins allow for some smaller mea culpas. Just don't be makin' a habit of such behaviors...

Man caves and decorations? I wish...

Greg

 

[brad96nm]

Re: 308 Secondary Explosion Effect (handloading)

All digits are accounted for.
I only had two tell tell signs.
1. obviously the case, which ejected fine.
and
2. (I over shot my target)which is when I started looking at the case. No extra recoil, and the it wasn't any louder than normal.

It will be a lot of work to rebuild all the ammo, but worth it. The weapon isn't going on the Man Cave wall till it is proven to be more cost to fix than to replace.
Which new is a problem because I'm going to be outfitting my arsenal with a new .338 later this spring, and I can't go without a .308 very long.

 

[Ratbert]

Re: 308 Secondary Explosion Effect (handloading)

There's the pic for those who prefer not to click on links.

 

[brad96nm]

Re: 308 Secondary Explosion Effect (handloading)

Thanks for the assistance with the pic. and everyone's advise.


Issue has been found "theoretically speaking" "User error while using a mechanical scale which has been replaced by a good digital scale" I pulled the first 5 apart in the batch and measured the powder. (electronically).
Min=44 max=47 for BLC2 using 168 gr. pills
1. 39.5
2. 38.4
3. 45.9 we have a good one. 20% is bad.
4. 39.2
5. 40.1
Even if one or two flakes didn't make it to the scale I'm still way to far off.
I'm leery of taking one that is at 38 or 39 grains and firing it to prove my theory, but I think this is substantial, unless anyone has a .308 I can borrow for testing

or safe suggestions are always welcome.
This would explain why I didn't blow the bolt out of the gun, or "wreck the gun/barrel."
I have read where people are trying to make subsonic .308 rounds, and having problems due to the powder they are using doesn't burn fast enough.
With so few grains and slow burning powder such as BLC2 it may smoulder in the case and then explode, instead of a steady consistent burn that creates pressure and pushes the pill out the barrel. Still a theory but I think it is feasible.
Pistols and shotgun powders will shake like a salt shaker, but at the same time the powder they use has a much faster burn rate than your large cal. rifle powders. "statement/question"

I shoot oldest to newest, and once I found the recipe that works with my rifle, I stick with it. This means that every round I made prior to my digital scale/dispenser will need to be pulled apart. I'd say about 350-400 rounds.

 

[Arbiter]

Re: 308 Secondary Explosion Effect (handloading)

I've seen very similar case failure from factory ammo that had been stored in suboptimal conditions for ~10-15 years, with no visibly negative effects upon the rifle or downrange performance. 3 loadings seems far too few to cause an issue, but it's not outside the realm of possibility that you found a bad piece of brass somehow.

 

[Greg Langelius *]

Re: 308 Secondary Explosion Effect (handloading)

I had misread your original description to indicate the leakage was occurring around the primer. I did not realize there was a case rupture in the sidewall. The picture set me right.

A case rupture in that vicinity should not be occurring, most cases have a radiused interior bottom contour that should put extra brass where that rupture occurred. The illustration suggests a case manufacturing anomoly, or some sort of chamber protrusion issue that's leaving the case unsupported in that area. If the case weights are light for these failed cases compared to the rest of the batch, that might be a clue.

Now I'm wondering if this rifle and barrel are original, or if there was a barrel replacement sometime in its past.

Some replacement barrels get shipped with a short chamber to allow a final chamber reaming that refines/reduces the protrusion spec., allowing the chamber length to be adjusted as the shoulder gets cut for headspacing. If that final reaming doesn't get performed, a chamber can end up with excessive case protrusion, leaving too much of the case length unsupported at just about that portion of the failed case wall.

This is a crucial gunsmithing step, and inattention to detail can result in a situation similar to what might be happening here. If my memory serves, the only barrels that are shipped reliably chambered to a final protrusion spec are the ones that are designed to be used with a barrel nut system.

Greg

 

[LawnMM]

Re: 308 Secondary Explosion Effect (handloading)

Quite a range of charge weights there. Did you weigh each one or set a dispenser and go?

 

[JuniperEyes]

Re: 308 Secondary Explosion Effect (handloading)

Looks to me like it was just an odd piece of defective brass. There was likely a void or air pocket of some type that causes such a rupture in the case.

I would dissect the case and know for sure.

 

[brad96nm]

Re: 308 Secondary Explosion Effect (handloading)

I purchased the rifle new, and it is a savage 10fp .308.
Looking through my spent brass this morning I found two more that have burned a hole in the base of the brass. This area looks to be where the bolt ejector is or just forward of the ejector lever in the bolt head, also the side of my barrel where what looks like the head of the bolt on both sides has a small hole for gas to escape maybe..
When I set the brass casing in the bolt and spin it, the burn hole shows up well where the ejector in the bolt head is.

I will cut a case apart tonight and see what it going on with it.

How I measured back then is not how I do it now. I'm very consistent measuring every charge today. These rounds are also in my youth with hand loads, and I'm going to say I probably weighed every 5th to 10th charge that came out of my mechanical dispenser.

 

[LawnMM]

Re: 308 Secondary Explosion Effect (handloading)

Those dispensers are woefully inaccurate. Fine for plinking, not safe for dispensing at or near max, definitely not for over book max recipes.

Live and learn, we all goof something, especially when we are new.

 

[i_Adam_i18]

Re: 308 Secondary Explosion Effect (handloading)

My first thought when I saw 46gr of BLC2 was "man that sounds hot".

 

[brad96nm]

Re: 308 Secondary Explosion Effect (handloading)

I can't find any issues with the rifle, and will run it down to a smith next week.
But in the mean time.
I sat down tonight and made 6 rounds of each of the following.
BLC2 min=44 and max-47
Hornady A-max 168...
2.800 OAL
2.015 case length
44.5 gr
45 gr
45.5 gr
46 gr
46.5 gr
I packed up an extra 12 rounds of 45 and 45.5 to warm up with.

Range this weekend, with all tools to check spent brass.
I weighed all the brass primed 186 +/_ .5gr, bullets 168 +/_ .1 gr, and powder electronically.

 

[264shooter]

Re: 308 Secondary Explosion Effect (handloading)

Isn't the trim to length 2.005 on a 308 case?
I know that a long piece of brass is a very quick way to run up the pressure.

 

[zmann]

Re: 308 Secondary Explosion Effect (handloading)

2.015 is the MAX...trim those down and try that.

 

[mattr25]

Re: 308 Secondary Explosion Effect (handloading)

+1 on the trim length. It is 2.005"

 

[brad96nm]

Re: 308 Secondary Explosion Effect (handloading)

thanks for the information on the max case length.
I've taken all ammo apart and starting all over.