New brass - different velocities than fire formed?

[Pdvdh]

It's a nice luxury having 3 velocities recorded for each bullet fired. I was shooting 60gr .223 Rem loads over the chronos last weekend. I was too lazy to put the skyscreen shades over the skyscreens and as the sun got higher in the sky, I had a couple instances where one chrono might not record a velocity, but the other two still gave comparable readings. So I still recorded valid velocity data with the two remaining chronos.

Also, I hadn't used the chronos for a year, and the PACT PC2 then shut down on me and I missed a velocity over that unit. Turns out the 9V battery was finally weak enough that the unit wouldn't function. But the two Oehlers still recorded velocity so that shot wasn't wasted. Simply replaced the battery in the PACT and then recorded additional MVs from another load.

It's a little more hassle to set up my triplicate chronos than a single chrono, but very nice and confidence inspiring, once they're all up and running.

The greatest thing since sliced bread in bullet measuring devices is the MagnetoSpeed Chronograph, according to many who own them. It straps to the muzzle of your rifle and uses electromagnetic sensors to detect the bullet speed. Current cost is about $400 Chronographs | MagnetoSpeed

I don't own one and have never even seen one in use. But many Forum members are tickled pink with theirs. The serious drawback for my rifles, is that if you shoot lighter contour barrels like I do, the weight of the MagnetoSpeed on the muzzle can and most likely will alter your POIs and group sizes. Meaning I couldn't expect to be able to use the MagnetoSpeed while developing accurate loads for my rifles. That's why I haven't, and won't, purchased a MagnetoSpeed. Not a good match for my #3, #4, and #5 lighter contoured barrels.

 

[gohring3006]

It's a nice luxury having 3 velocities recorded for each bullet fired. I was shooting 60gr .223 Rem loads over the chronos last weekend. I was too lazy to put the skyscreen shades over the skyscreens and as the sun got higher in the sky, I had a couple instances where one chrono might not record a velocity, but the other two still gave comparable readings. So I still recorded valid velocity data with the two remaining chronos.

Also, I hadn't used the chronos for a year, and the PACT PC2 then shut down on me and I missed a velocity over that unit. Turns out the 9V battery was finally weak enough that the unit wouldn't function. But the two Oehlers still recorded velocity so that shot wasn't wasted. Simply replaced the battery in the PACT and then recorded additional MVs from another load.

It's a little more hassle to set up my triplicate chronos than a single chrono, but very nice and confidence inspiring, once they're all up and running.

The greatest thing since sliced bread in bullet measuring devices is the MagnetoSpeed Chronograph, according to many who own them. It straps to the muzzle of your rifle and uses electromagnetic sensors to detect the bullet speed. Current cost is about $400 Chronographs | MagnetoSpeed

I don't own one and have never even seen one in use. But many Forum members are tickled pink with theirs. The serious drawback for my rifles, is that if you shoot lighter contour barrels like I do, the weight of the MagnetoSpeed on the muzzle can and most likely will alter your POIs and group sizes. Meaning I couldn't expect to be able to use the MagnetoSpeed while developing accurate loads for my rifles. That's why I haven't, and won't, purchased a MagnetoSpeed. Not a good match for my #3, #4, and #5 lighter contoured barrels.

I suspected a change in harmonics with this chrony so I also won't be buying one I just don't see a use for something that I can't use in accuracy development

 

[Pdvdh]

Re: Dented brass MV much higher than undented brass

Well I had a learning experience yesterday that surprised me, and it was in line with the subject of this original Thread. Except it wasn't virgin brass versus once fired brass. My experience was with dented .223 Rem brass versus undented brass. All brass was once-fired in someone's chamber and resized in my Forster resizing die.

Some background information. I purchased a couple thousand rounds of once-fired Lake City .223 Rem/5.56 brass several years ago. In addition, I've also picked up hundreds of once-fired .223 brass (range pickups) over the past few years. Some of these cases have dents in them and others have been bent and deformed by tire traffic. I clean all the field pick-ups by ultrasonic device with a citric acid/water solution, prior to resizing. Resizing often removes the damage with bent cases, but resizing the case with will not remove focused impact dents.

Two weekends ago I was recording MVs from my 16" barreled AR15. Hornady 55gr VMax bullets over 26.6gr Hodgdon BL-C(2) powder. My chronograph setup includes 3 separate chronographs. All 3 chronographs concurrently record the velocity of each bullet fired. The 3 chronographs consist of: Oehler 35P, Oehler 33, and PACT PC2. I recorded these MVs for three shots:

Oehler 35P ^ Oehler 33 ^ PACT ^ Average fps
1) 2801 . . . . .2786 . . . . No Rec . 2794
2) 2916 . . . . .2901 . . . . 2913 . . 2910 > Abnormally High MV
3) 2753 . . . . .2748 . . . . 2753 . . 2751

The MV for the second shot was excessively high. I didn't think I'd mismatched reloads, but I tentatively concluded I may have mistakenly fired a reloaded cartridge with a different powder or powder charge.

Yesterday I again chronographed .223Rem loads. These four shots consisted of Hornady 60gr VMax, Federal 205s, over 26.5gr Hodgdon BL-C(2):

Oehler 35P ^ Oehler 33 ^ PACT ^ Average fps
1) 2786 . . . . 2777 . . . . .2786 . . 2783
2) 2913 . . . . 2902 . . . . .2911 . . 2909 > One large Dent on Case Shoulder
3) 2771 . . . . 2762 . . . . .2768 . . 2767
4) 2799 . . . . 2790 . . . . .2797 . . 2795 > Two smaller Dents on Case Shoulder

Prior to firing the 2nd shot, I noticed a deep dent in the shoulder of the case. I didn't intend to used dented brass for recording MVs, however this one slipped through my QA/QC control... I was dumbfounded to record another excessively high MV, 126fps higher than my first shot. All 3 chronographs recorded comparable velocity for shot #1, and shot #2, just that shot #2 was much higher MV. So I was recording good data. I tentatively concluded Hodgdon BL-C(2) powder may be responsible and made a mental note that perhaps I should stick with Varget powder. I examined the 3rd round for case dents prior to firing - saw no dents. When the 3rd shot yielded a MV in line with the 1st shot, I remembered this Thread and wondered if the deep dent on the shoulder of the 2nd case could be responsible for the excessive MV. I recalled Mikecr's Posts in this Thread. I examined the 4th casing for dents and sure enough, another resized case slipped past my QA/QC inspections. The 4th case had two smaller dents, both located on the shoulder joint of the case. Much smaller dents, together maybe 1/4 the volumetric displacement of the single dent observed on the 2nd case fired. So I'm saying to myself - ah hah - if the dents are responsible for the increase MV, perhaps I'll see another increase in MV on the 4th shot over the chronographs. Bingo! Sure enough, the 4th casing provided a notably higher MV than the MV recorded on the two cases with no observed dents.

I'm a college-educated engineer, and have spent a career practicing engineering. No way could I convince myself that these dents in the relatively thin portion of the cases up by the shoulder joint could create increased pressure sufficient to increase MV by up to 125fps. The case walls are too thin up there by the case neck to my reasoning. I think the internal case pressure would instantly blow the dents out to conform with the chamber walls. Hmmmm... so I visually examined the two cases more carefully. I observed significant blackening / carbon deposits on the shoulders of both fired cases where the dents had been located. The casings were now dent free, but sometime during the firing of the shells, combustion products has leaked past the case necks and filled the voids where the dents had been located at the shoulder joints. This observation led me to my current, tentative conclusion: combustion gases leaked past the case necks and filled the voids where the case dents were located, which reduced the effective volume inside the cases during powder combustion. This, perhaps, could cause higher internal case pressures and yield these higher observed MVs. Maybe this what caused the abnormally high velocity in the one round I fired 2 weekends ago?

This is by no means exhaustive testing that proves anything beyond a shadow of doubt. This level of testing doesn't rise to any defensible scientific standards. And I may be reaching an errant conclusion. But..., anyone else ever observed something similar?

In the mean time, I will avoid using either virgin brass or dented cases, for any serious MV measurements and load development. My AR15 is mostly a plinking rifle, and I was less cautious with these reloads.

 

[HunterGreen]

Remember to always use photo grade batteries. Avoid using anything else.

 

[Don Titus]

Re: Dented brass MV much higher than undented brass

Well I had a learning experience yesterday that surprised me, and it was in line with the subject of this original Thread. Except it wasn't virgin brass versus once fired brass. My experience was with dented .223 Rem brass versus undented brass. All brass was once-fired in someone's chamber and resized in my Forster resizing die.

Some background information. I purchased a couple thousand rounds of once-fired Lake City .223 Rem/5.56 brass several years ago. In addition, I've also picked up hundreds of once-fired .223 brass (range pickups) over the past few years. Some of these cases have dents in them and others have been bent and deformed by tire traffic. I clean all the field pick-ups by ultrasonic device with a citric acid/water solution, prior to resizing. Resizing often removes the damage with bent cases, but resizing the case with will not remove focused impact dents.

Two weekends ago I was recording MVs from my 16" barreled AR15. Hornady 55gr VMax bullets over 26.6gr Hodgdon BL-C(2) powder. My chronograph setup includes 3 separate chronographs. All 3 chronographs concurrently record the velocity of each bullet fired. The 3 chronographs consist of: Oehler 35P, Oehler 33, and PACT PC2. I recorded these MVs for three shots:

Oehler 35P ^ Oehler 33 ^ PACT ^ Average fps
1) 2801 . . . . .2786 . . . . No Rec . 2794
2) 2916 . . . . .2901 . . . . 2913 . . 2910 > Abnormally High MV
3) 2753 . . . . .2748 . . . . 2753 . . 2751

The MV for the second shot was excessively high. I didn't think I'd mismatched reloads, but I tentatively concluded I may have mistakenly fired a reloaded cartridge with a different powder or powder charge.

Yesterday I again chronographed .223Rem loads. These four shots consisted of Hornady 60gr VMax, Federal 205s, over 26.5gr Hodgdon BL-C(2):

Oehler 35P ^ Oehler 33 ^ PACT ^ Average fps
1) 2786 . . . . 2777 . . . . .2786 . . 2783
2) 2913 . . . . 2902 . . . . .2911 . . 2909 > One large Dent on Case Shoulder
3) 2771 . . . . 2762 . . . . .2768 . . 2767
4) 2799 . . . . 2790 . . . . .2797 . . 2795 > Two smaller Dents on Case Shoulder

Prior to firing the 2nd shot, I noticed a deep dent in the shoulder of the case. I didn't intend to used dented brass for recording MVs, however this one slipped through my QA/QC control... I was dumbfounded to record another excessively high MV, 126fps higher than my first shot. All 3 chronographs recorded comparable velocity for shot #1, and shot #2, just that shot #2 was much higher MV. So I was recording good data. I tentatively concluded Hodgdon BL-C(2) powder may be responsible and made a mental note that perhaps I should stick with Varget powder. I examined the 3rd round for case dents prior to firing - saw no dents. When the 3rd shot yielded a MV in line with the 1st shot, I remembered this Thread and wondered if the deep dent on the shoulder of the 2nd case could be responsible for the excessive MV. I recalled Mikecr's Posts in this Thread. I examined the 4th casing for dents and sure enough, another resized case slipped past my QA/QC inspections. The 4th case had two smaller dents, both located on the shoulder joint of the case. Much smaller dents, together maybe 1/4 the volumetric displacement of the single dent observed on the 2nd case fired. So I'm saying to myself - ah hah - if the dents are responsible for the increase MV, perhaps I'll see another increase in MV on the 4th shot over the chronographs. Bingo! Sure enough, the 4th casing provided a notably higher MV than the MV recorded on the two cases with no observed dents.

I'm a college-educated engineer, and have spent a career practicing engineering. No way could I convince myself that these dents in the relatively thin portion of the cases up by the shoulder joint could create increased pressure sufficient to increase MV by up to 125fps. The case walls are too thin up there by the case neck to my reasoning. I think the internal case pressure would instantly blow the dents out to conform with the chamber walls. Hmmmm... so I visually examined the two cases more carefully. I observed significant blackening / carbon deposits on the shoulders of both fired cases where the dents had been located. The casings were now dent free, but sometime during the firing of the shells, combustion products has leaked past the case necks and filled the voids where the dents had been located at the shoulder joints. This observation led me to my current, tentative conclusion: combustion gases leaked past the case necks and filled the voids where the case dents were located, which reduced the effective volume inside the cases during powder combustion. This, perhaps, could cause higher internal case pressures and yield these higher observed MVs. Maybe this what caused the abnormally high velocity in the one round I fired 2 weekends ago?

This is by no means exhaustive testing that proves anything beyond a shadow of doubt. This level of testing doesn't rise to any defensible scientific standards. And I may be reaching an errant conclusion. But..., anyone else ever observed something similar?

In the mean time, I will avoid using either virgin brass or dented cases, for any serious MV measurements and load development. My AR15 is mostly a plinking rifle, and I was less cautious with these reloads.

Very interesting...I wonder how much of a difference it would make had those dents been on the main body of your cases? Probably the only definitive way to evaluate your hypothesis is to run tests on equipment designed to measure pressure.

 

[Mikecr]

It don't matter where the dents are, and Phorwath's dented cases did fully expand to the chamber & springback. That there was some blowby is the nature of semi-auto chambers(loose). The gas would come & go where it logically would(least resistance). It could have gotten trapped, but it didn't in this case.

It's all about initial confinement.
If this is hard to picture capacity-wise, think of it as simple load density. The dent increased load density a little bit and a lot of times it don't take much.

If your cases were at ~90% fill(for real) you could run a test to see the same thing without dents.
Load a gun while it's pointed downward, ease it up to fire through a chronograph.
Then load the gun pointed up, and ease it down to fire across chrono.
The second shot will be higher in velocity, because relative load density has increased nearest ignition source. You've altered initial confinement.

Sure the cases expand to chamber dimensions. Hell it's takes little more than 100psi to do that. Brass might as well be tinfoil to a normal ~55Kpsi pressure peak.
And a charge laying very slightly tighter against a flash hole will blow forward **** quick.
But neither is fast enough to negate their affect by then. The powder ignition that causes these things was affected FIRST, and this can't just undo itself.
Most of what matters happens way before bullet movement.

 

[Canadian Bushman]

Mike i read your post and wonder where i'd be if i knew these things years ago!

 

[Pdvdh]

I preferentially read Mike's posts, as I've learned a thing or two (maybe more ) from him over the years.

 

[LoneTraveler]

Same lot of powder, same lot of primers. Here is 3 more things that could cause change. Is neck tension changing as the case is fired and resized in loading. Is the same set of dies used adjusted the same. Is the case sized till it goes a few thousands further into the chamber. The prime is not getting the same exact hit. Or check the primer pockets, Did the first primers anvil make small dents in the bottom of the primer pocket, Now the primer is not getting the exact same crush. Is it possible the cases have thin metal at the bottom of the primer pocket and it being crushed in slightly not allowing a complete primer crush. Food for thought. Good Luck.