Ever had flatter primers with lighter loads than heavier loads?

[tonysnoo]

Same day...same conditions...same powder...same primers...same everything?????

I was out at the range fire forming brass in my 6 Fatrat. Running cfe223 w 87s wolf primers and was at the low end of my test loads. Brass was flying forward so couldn't pick up till we had a target brake. Primers were a little flat but nothing crazy. Fired three more groups .3grains hotter each step. Next break picked them up and and found they showed minimal and some no signs at all...nice and rounded.

Sound familiar??? What did I experience?

 

[LCazador]

Fire forming anything is unpredictable. I look for a load that fully forms the case with a low attrition rate. Nothing more 8)!

 

[dkhunt14]

Sometimes when a barrel is really clean the first couple rounds through a barrel have higher pressure because of more friction in the bore; no fouling. Matt

 

[VinceB]

I posted a similar question last weekend. First couple of rounds were higher pressure with marks on the brass and hard bolt lift. It turned out to be due to solvent left in the chamber. Cleaning the chamber with acetone solved the issue.

There's your answer Tonysnoo - because of you low fire forming load, the brass isn't gripping the chamber - putting all the load on the bolt face. Oil or solvent in the chamber produces the same effect.

 

[tonysnoo]

Thanks guys, I have a sneaking hunch I had a combination of both. I may have left some lube on the cases from sizing.

 

[TEXMAG]

You don't think you could be having a light charge detonation? Never seen it on a 223, but I have seen it on a 257 Weatherby.

TEXMAG

 

[tonysnoo]

You don't think you could be having a light charge detonation? Never seen it on a 223, but I have seen it on a 257 Weatherby.

TEXMAG

I have never heard of that condition. Ths round is a bit bigger than a 223. Its basically a 6mm grendel with a 40 degree akley style shoulder. I am definitely down at the slow end of what some guys are running for this round powder bullet combo.

 

[amamnn]

light charge "detonation" is a buzz word for double charging that people with egos that will not accept their mistakes like to use--

assuming that this FF was done in a bolt gun and not an AR--what would the problem be with waiting until brass could be recovered, since it can't have fled far--or--remove the ejector from the rifle--if the brass was ejected from an AR----and it was--be honest---or other semi auto-- ---the question is nonsensical

 

[CatShooter]

Flat primers without any other signs of pressure are a sign of headspace issues.

Smokeless powder cannot "detonate" under any circumstances - if it could, you could not buy it without a federal explosives license... and it could not be shipped as a class "B" solid propellant.

 

[tonysnoo]

light charge "detonation" is a buzz word for double charging that people with egos that will not accept their mistakes like to use--

assuming that this FF was done in a bolt gun and not an AR--what would the problem be with waiting until brass could be recovered, since it can't have fled far--or--remove the ejector from the rifle--if the brass was ejected from an AR----and it was--be honest---or other semi auto-- ---the question is nonsensical

I guess I am not following what you are saying. This is an AR. I was working with a crony...nothing abnormal in the readings. 10 shots 5 each .3grains apart before I could retrieve the brass. All were alittle flat but no other signs 15 more shots 5 EA .3 grains apart. Had to wait again to pick up brass. 5 looked similar...10 looked way better...unknown exactly which loads were which brass. All were single loaded so brass catcher was left home.

This as accurate as I can say.

 

[37Lincoln1]

You can single load and use a brass catcher. It just adds more steps to load/unload but for tracking pressure signs in your brass don't you think it's worth it?

 

[Bindi2]

Secondary explosion is a light charge of powder that reaches high pressure before the projectile moves. Common in pistols useing fast powders and light loads. In rifle cases it occurs when the powder volume is less than 75% of case volume. Each rifle, case and powder type used will have a different danger point. Worst case senario blown revolver reels (seen 4 ) Semi autos pistols lost count destroyed, target rifles stuffed cases from ruptures to blown primer pockets one cracked bolt. All done by shooters with limited reloading knowledge. Just because your method worked for you does not mean it is a safe method.

 

[Syncrowave]

Smokeless powder cannot "detonate" under any circumstances - if it could, you could not buy it without a federal explosives license... and it could not be shipped as a class "B" solid propellant.

Actually, straight nitrocellulose OR nitrocellulose+nitroglycerine powders can, and will, cross over from deflagration to detonation if given sufficient heat/pressure, such as with a big squib, as will many nitrated materials such as film and lacquer. They just won't do it in rifle chambers.

And yeah, you can get flattened primers from light loads. It's caused by the primer having a chance to "balloon" before the case head gets slammed back against the bolt, which then pushes the primer cup back into its pocket and causes some flattening at the edges. (This is different from flattening caused by excessive pressure.)

 

[bigedp51]

Catshooter called it headspace, I call it head clearance, your shooting a over gassed AR15 and using reloads that do not have crimped primers.

Headspace technically isn't the problem, but over resizing the case and excessive shoulder bump creates "head clearance" or the air space between the bolt face and the rear of the case. At certain pressure levels head clearance can cause the primer to mushroom and appear to be flattened more.

When you pull the trigger the firing pin pushes the case forward into the chamber until the shoulder of the case contacts the shoulder area of the chamber. The cartridge goes "bang" and the primer is the first thing to move to the rear and out of the primer pocket. The amount the primer moves to the rear and "how much" the brass stretches to the rear effects how the primer looks. If you have ever seen a case that had the primer crimped removed with a deburring tool and the primer pocket over beveled you would understand better. These cases look like a large rifle primer was used in a case designed for small rifle primers because the primer mushroomed.

Bottom line, at lower pressures in the AR15 the primer will look like a mushroom and flattened more when removed. At higher pressures the case is forced back against the bolt face and this reseats reseats the primer. At lower pressures the case does not contact the bolt face causing the primer to flatten and mushroom outward.

Question, on your "flattened" primers and lighter loads how much of the primer is protruding above the base of the case? On your higher pressure loads how far is the primer sticking up or is it flush with the bottom of the case. The answer to these two questions will explain the flattened primers, which has nothing to do with detonation.

A over gassed AR15 rifle will let the bolt to start moving to the rear while there is still pressure in the barrel. Please note that the shorter the barrel on the AR15 the higher the port pressure which governs when the bolt starts to move to the rear. This can effect how the primers look and if you have loose primer pockets this pressure can also cause the primer to be pushed out of the primer pocket and jam the trigger group.

 

[bigedp51]

And yeah, you can get flattened primers from light loads. It's caused by the primer having a chance to "balloon" before the case head gets slammed back against the bolt, which then pushes the primer cup back into its pocket and causes some flattening at the edges. (This is different from flattening caused by excessive pressure.)

Syncrowave, after I posted I reread your posting and saw I missed your above remarks, sorry you hit the nail on the head before I did.

This just shows you must be almost as smart and good looking as I am.......did I mention humble?

 

[bigedp51]

Catshooter, the three photos below show what excess headspace is.

Catshooter, from the level of the beer to the top of the glass is called head clearance. :

 

[CatShooter]

Smokeless powder cannot "detonate" under any circumstances - if it could, you could not buy it without a federal explosives license... and it could not be shipped as a class "B" solid propellant.

Actually, straight nitrocellulose OR nitrocellulose+nitroglycerine powders can, and will, cross over from deflagration to detonation if given sufficient heat/pressure, such as with a big squib, as will many nitrated materials such as film and lacquer. They just won't do it in rifle chambers.

Actually, it cannot - have you tried it? I have.

Take a few pounds of smokeless powder and put it in a cardboard tube - end cap it with a Tetryl booster charge and shoot it - you will have smokeless powder all over the place... but no detonation.

 

[CatShooter]

Catshooter, the three photos below show what excess headspace is.

Catshooter, from the level of the beer to the top of the glass is called head clearance. :

Ed... now that's a hellova lotta headspace.

You definitely have the best artwork on any shooting forum.

There is "H"eadspace (the stuff of which SAAMI speaks), and "h"eadspace - the amount of space between the head and bolt face... but it is semantics, cuz we both know what we are speaking about.

Some 15-ish years ago, I was speaking with Richard Diaz at Remington about your and my favorite subject, "wet" (oiled) cases, and bolt lug strength. Some things that were (and still are) interesting is that the modern, two piece bolt (Rem and Winchester, maybe others), is capable to holding 100,000 pounds without any problems.

That is NOT pounds per square inch, but plain ol' pounds of raw force (which is why the new military M-24's are rated at 70,000 psia as a working pressure).

But in the conversation came up an interesting face - the primer exerts ~700 pounds of force on the case, driving it forward (like a "Ramset" cartridge), so the case is jammed forwards, and the primer is now extruded against the bolt face, holding the whole thing in place - when the powder lights, the pressure pushes the case back, causing the edges of the primer to flair out... looking flat, even though the chamber pressure can be below <45,000 psia.

An interesting demonstration of this is to take a primed revolver case and pop the primer - it will be difficult or impossible to revolve the cylinder again, as the primer against the recoil plate will lock it up - you will have to pound the case back with a rod and hammer to re-seat the primer, to free up the revolver.

 

[Syncrowave]

Those 50-ton bolt lugs must be made of unobtainium.

Let's say they're roughly 3/8" x 3/8" (.14 sq in) and there are two lugs for a total of .28 sq in. If they didn't yield until the force was 100k # then their yield strength in shear would have been 100k/.28 sq in = 357,000 pounds / sq in.

Since shear is typically 75% of tensile strength, that means the tensile strength of those lugs would have to be at least 357k/.75 psi = 476,000 pounds per square inch.

I've never heard of any steel with a tensile yield strength exceeding maybe 230ksi, and that's some pretty exotic alloy steel, certainly not something used in a rifle. Yet those bolt lugs were apparently made of something more than twice as strong (476ksi). (Common structural A36 mild steel yields at around 36ksi.)

Any idea what they were made of?

 

[CatShooter]

Nope.

I do know that I have Rem bolts that have seen 15,000+ rounds of oiled cases and show no signs of it on their faces - which is all I care about.