204 bullet setback ar

[04whtrubicon]

I destroyed my dpms 204 upper. I loaded some 30 gr bergers on top of 28gr of Benchmark.I shot 20 or so rounds, with good groups. Brass looked good, crono was 3650 or so. The load was soft shooting and then boom. My only idea is that a bullet set completly back into the case. Any thoughts or experiance with this load?

 

[counterclockwise]

Sure would like to see some photos. Did you keep any of the reloads from the lot that did the KaBoom? If so, inspect a few and see if the bullet is tight in the neck. Also check the COAL before and after retention load testing. To put things in perspective, the MilSpec for the 5.56 x 45 M193 is 35 pounds prevailing retention force, and for the M855 is 45 pounds prevailing force.

Some reloaders believe that bottle neck destructive set backs or set forwards are nonexistent. So, you will have to make the post-KaBoom forensics prove it.

Do you have any sized cases that were not seated? Measure bullet OD, neck OD and neck thickness, compute Neck ID; or measure Neck ID direct. Theoretically you only need .001 interference on the diameter, but .003 interference covers a multitude of tolerance stackups going the wrong way.

I am going to guess at a bullet/case retention force target of 30/55 x 35 = greater than 19 lbs. Find a 1" board, drill a hole with a flat head screw prep bit so the board hole gloves over and rests on the bullet ogive of the assembled round. Lower the board onto the round (round vertical and standing on a flat surface). Very gently (using a pillow or other cushion of necessary) lower a 20 lb weight onto the top of the board. IF the COAL maintains its preload position, the neck tension is good.

Welcome to the forum.

 

[counterclockwise]

I notice that 28 grains of benchmark is listed as filling the case, so overcharging with powder is low on the list of possibilities.

You could have under-filled a preceding round and fired into a squib.

 

[04whtrubicon]

My first thought was that I fired into a sqib, but the round before it was in a fresh target and was just about where I wanted it. After the kb I loaded about 20 rounds into another 204 and racked them through the action as fast as I could, and 1 of thos did set full back into the case. My guess is that 28 grains only fills the case to about 95 pecent, alowing those short little bullets to almost disapear. I have pictures, Ill put them up in a little while. My camera is thawing.

 

[04whtrubicon]

some pics
http://picasaweb.google.com/tipton1974/Ar204Kb?feat=directlink

 

[rcmodel]

According to Hodgdon, 28.0 grains Benchmark & a 32 grain V-Max is a MAX load, and gives 4,047 FPS @ 57,100 PSI!!!

That is the highest pressure load they list for that bullet with any powder.

Maybe you were running a MAX load in conjunction with bullet setback.

That would easily exceed acceptable pressure limits!

rc

 

[04whtrubicon]

Thanks counterclockwise, I will have to do some measuring and testing, but setback makes complete sense to me. There is so little bearing surface on these bullets when oal is 2.24 or 2.25. I am going back to the boat tail 32's and up because they are way easier to seat, and are longer.

 

[04whtrubicon]

Rc Model, That may be true. I started with that 32 grain data for the 30grainers thinking I was pretty safe. I could not find much data for the 30 gr bergers I wanted to use. The primers and the chrono showed no signs, with only 3600 fps, but that doesn't mean my pressures wern't up there. Anyone have decent 30 grain Berger data?

 

[Kernel]

04whtrubicon,

Do you apply a crimp to your handloads? I was seeing some set back issues in a Mini-14 chambered in 6x45. I added a crimp step, separate from bullet seating, and the problem went away. Never had a KB, but due to the likelihood of set back, I’m now a firm believer in crimping all my handloads used in self loading firearms.

 

[Blackrock]

++ on that Kernel

I was shooting some Lee collet neck sized loads in my 6mm Rem and had an overpressure from a bullet that slipped back. I had loaded 3 rounds in the magazine and the last one must have slipped back under recoil. I now fire all my neck sized rounds as single loads only.

 

[counterclockwise]

Thanks for the photos. Looks like a typical case head structural failure from overpressure, followed by hot plasma tunneling back into the bolt through the extractor channel and exploding, bolt, bolt carrier, and upper housing from the inside out.

Did you find the remains of the case, and what did it look like? Was the magazine damaged at all?

Thank goodness, no one was hurt.

Neck tension only is OK for autoloaders, if and only if you apply the QC to back it up. I agree that the bullet barrel section or shank is very short for the 30 gn FMJ-FB. The rule of thumb is one caliber contact length between bullet and neck if possible.

Earlier, I was referring to data I had found for 32 gn Hornady projectiles in the Ruger .204listed as "case full". So, any accidental double charge would result in powder all over your loading bench (don't ask how I know). Your chrono data does not show "hot" load velocities.

 

[04whtrubicon]

I was not using any crimp, but I think I should have. I use the lee factory crimp die in my 223 ar loads, and will now in 204. I The pmags follower broke, and the mag release too. No injuries, just expensive lessons. It looks like I have .127 bulet contacts in the case, not all that much. The part of the case that was left in the barrell looks fine, the other part was in pieces inside the bolt face. One of the pieces is an exact mold of the extractor claw.

 

[243winxb]

204 Ruger - Bridging

Bridging of powder on loading could be the cause. When you lube the inside of the neck, the expander ball pulls most of the excess out. But with undersize brass neck wall thickness like yours, the expander leaves some lube. More if using a QTip instead of a proper nylon brush. If you work the measure fast "dumping " the powder instead of "trickling" it, powder will handup on the lube. This can give you one round with 80% of the powder charge, the next case gets 120% KABOOM. If your lucky it will be 20% to 180% and the case will overflow. The smaller the caliber, the bigger the problem like in 17 caliber. I found this out loading 223rem. Check the diameter of your measures or Dillon drop tube area, a .224" bullet will not pass thru it. So, clean your necks after lubing, work the measure a little slower. Do this simple test,(photo) see how your powder flows. Do a dump, then trickle. The dump may just bridge. Then put a case with lube in the mouth, see how that works. I need proof on set back causing it, anyone have links to proof?

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[243winxb]

Don't try to match factroy velocity as the factory uses a proprietary powder composition specially formulated for the .204 Ruger, and not currently available to handloaders as far as i know. Hornady is doing a dangerous thing IMO producing ammo with high fps with special powder not availibe to the public. The American Rifleman, Jan. 2010 has an article on page 54 about "Superformance" using special powders. Hornady covers there butt by putting in disclaimers like this at the end.

Under no circumstqnces should a handloader attempt to blend propellants. Always follow handloading data from reputable resources exactly.

P.S. Change your title to "KABOOM 204 RUGER" you will get more readers, lookers.

 

[Walkalong]

Speer .22 TNT bullets have very little full diameter to them. The ogive is so long and tapered that there might be .010 worth of full diameter base to them. (I am not where I can check it) It is hard to get good neck tension with them. They would definitely be unsuitable for an autoloader. I tried them in 5.7 X 28 and it was a total failure as far as feeding without severe bullet setback. Singly loaded they worked as well as could be expected for a 50 Gr bullet in that caliber.

How about those 32 Gr V-Max's?

 

[04whtrubicon]

I could never prove that setback was the issue, unless I could get a few donated ar 204's as test beds. I'll return them when finished. I proved that my combination will setback a bullet when cycled through another 204. I just filled a case with Bechmark until the bullet would touch the powder. It was 30.0 grains, after that I would be crunchin. I wonder what type of pressure 30 grains of benchmark would give me

 

[243winxb]

I just filled a case with Bechmark until the bullet would touch the powder. It was 30.0 grains,

Would be nice to know for sure, but for now , have to go with the set back i guess. Sure wish i knew more about setback. After a few loadings, my 223 can turn out a few with light bullet pull. Testing showed that most all take 35 to 45 lbs to push the bullet into the case. The ones that went in under 20lbs have me worried now.

 

[04whtrubicon]

I have about 80 rounds loaded, I going to figure out the setback pressure on all of them and log it. Then i'm going to pull all of them and weight the powder and bullets. I'm going to pick up another ar 204 upper Saturday, and I plan on keeping this one a long time. Up until then my biggest reloading mistake was to seat some bullets to long and a few of them stuck in the lands and left the bullets and powder sittin in the chamber.

 

[45ACPUSER]

I do not think set back is as much of an issue with rifle rounds as it is with hand gun rounds. Think about this a straight walled cartridge with a tubular bullet is just akin to packing a minnie ball in a flintlock. And, you reduce the operating space the powder has to expand bleed off gases from powder ignition.

When you get set back into shoulder cartridge the bullet shape with way less bearing surface will allow for blow by of the expanding gas to a certain degree before the bullet gets headed down the bbl. And, one would expect to see a soot covered case because the case was unable to expand to the extent of the chamber walls...... and possibly a projectile lodged into the bbl with the first round as a result of setback. Then when the subsquent round is fired, the kaboom happens.

Another thought is an over length cartridge case not COAL is loaded into the chamber,
the case mouth engages the chamber and effectively crimps the bullet and causes a spike in pressure and possible kaboom. Saw that in a 243 of fellow who never seemed to grasp that you need to trim brass. The brass flowed into the bolt face and sort of welded he case head into the bolt face. The gunsmith had to use a cheater bar to open the bolt....... The gun was sent back to Rem for bolt and it seemed to suffer no gross damage.....
Overworked brass from FL sizing weakens the brass......and using a crimp die is a band aid for covering up shot brass. I have shot thousands and thousands of 308, 3006, and 223 in auto loaders for highpower competition. I never had an alibi related to ammo, in many years of competition. With good brass management with quality brass and prudent reloading practices never had a bullet set back.

But, of course if I was to make ammo to go to war with I would use a crimp die for bullets with a cannalure or not.

 

[counterclockwise]

I could never prove that setback was the issue, unless I could get a few donated ar 204's as test beds. I'll return them when finished. I proved that my combination will setback a bullet when cycled through another 204. I just filled a case with Bechmark until the bullet would touch the powder. It was 30.0 grains, after that I would be crunchin. I wonder what type of pressure 30 grains of benchmark would give me

Quickload shows 59,000 psi max press at 28 grains of benchmark at 2.250 COAL with the 30 gn berger. 103% powder fill

Quickload shows 75,000 psi max press at 30 grains of benchmark at 2.250 COAL with the 30 gn berger. 110% powder fill.

Of course, many handloaders do not accept Quickload's predictions for more powder and/or reduced case volume using bottleneck cartridges in the model.

"Set forward" is something I have been thinking about. With the short 30 gn berger, could the bullet dislodge when the round slams against the shoulder and get cocked in the leade so the meplat hangs up on a land and presents a very high resistance to the plasma upon firing?

 

[Doug b]

04whtrubicon could I ask here what resize die and resize method you used and what your brass situation is.As is it varied head stamp varied number of fires or same head stamp same number of fires.

 

[04whtrubicon]

Set forward is an interesting idea, I have only thought of that in revolver. 75000 is definately hot. Won't be tryin that. Doug b, this was new Remington brass, FL sized with a lee die.

 

[Tim the student]

Anyone have decent 30 grain Berger data?

Berger does. Call them up, and they will email you a spreadsheet.

 

[243winxb]

Counterclockwise, what pressures does Quickload show when reduced case volume or set back happens in this bottleneck cartridges? Proof loads(M197 HPT) for 5.56mm are said to run 70,000 psi , i would guess they don't KABOOM http://www.inetres.com/gp/military/infantry/rifle/556mm_ammo.html

 

[counterclockwise]

243,
I only rely on QuickLoad 3.5 for parametric studies. Their absolute values, for the most part, have never agreed with my experience over the chronograph. Part of their error has to do with making educated guesses about bullet friction in the bore, start pressures, burn rates, things like that.

To be conservative I adjusted start pressure down to about 1800 psi for the data I posted. It may be even lower for the rounds the OP was using because of the apparent neck tension problem.

Anyway, I am not sure I understand your last query exactly. The HPT round generates 70,000 psi. I think those are used for checking integrity of the chamber/bolt/barrel structure (proof load). I may be wrong but the back of that cartridge does not fall apart, probably because it is designed not to at some pressure even above 70,000 psi.

If I keep all other parameters the same that I used to do the initial calc.s, 28 gns of Benchmark, and just vary the COAL, QuickLoad says:

2.200 61,000
2.150 63,000
2.100 65,000
2.050 67,000
2.000 70,000