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Rifles, Reloading, Optics, Equipment
Reloading
New brass - different velocities than fire formed?
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<blockquote data-quote="Pdvdh" data-source="post: 990866" data-attributes="member: 4191"><p><strong>Re: Dented brass MV much higher than undented brass</strong></p><p></p><p>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.</p><p></p><p>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.</p><p></p><p>Two weekends ago I was recording MVs from my 16" barreled AR15. Hornady <u>55gr</u> 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:</p><p></p><p>Oehler 35P ^ Oehler 33 ^ PACT ^ <strong>Average fps</strong></p><p>1) 2801 . . . . .2786 . . . . No Rec . 2794</p><p>2) 2916 . . . . .2901 . . . . 2913 . . <strong>2910</strong> > Abnormally High MV</p><p>3) 2753 . . . . .2748 . . . . 2753 . . 2751</p><p></p><p>The MV for the second shot was excessively high. I didn't <em>think</em> I'd mismatched reloads, but I tentatively concluded I may have mistakenly fired a reloaded cartridge with a different powder or powder charge.</p><p></p><p>Yesterday I again chronographed .223Rem loads. These four shots consisted of Hornady <u>60gr</u> VMax, Federal 205s, over 26.5gr Hodgdon BL-C(2):</p><p></p><p>Oehler 35P ^ Oehler 33 ^ PACT ^ <strong>Average fps</strong></p><p>1) 2786 . . . . 2777 . . . . .2786 . . 2783</p><p>2) 2913 . . . . 2902 . . . . .2911 . . <strong>2909</strong> > One <strong>large Dent</strong> on Case Shoulder</p><p>3) 2771 . . . . 2762 . . . . .2768 . . 2767</p><p>4) 2799 . . . . 2790 . . . . .2797 . . <strong>2795</strong> > Two smaller Dents on Case Shoulder</p><p></p><p>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... <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite11" alt=":rolleyes:" title="Roll Eyes :rolleyes:" loading="lazy" data-shortname=":rolleyes:" /> 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 <strong>Mikecr</strong>'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.</p><p></p><p>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? </p><p></p><p>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?</p><p></p><p>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.</p></blockquote><p></p>
[QUOTE="Pdvdh, post: 990866, member: 4191"] [b]Re: Dented brass MV much higher than undented brass[/b] 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 [U]55gr[/U] 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 ^ [B]Average fps[/B] 1) 2801 . . . . .2786 . . . . No Rec . 2794 2) 2916 . . . . .2901 . . . . 2913 . . [B]2910[/B] > Abnormally High MV 3) 2753 . . . . .2748 . . . . 2753 . . 2751 The MV for the second shot was excessively high. I didn't [I]think[/I] 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 [U]60gr[/U] VMax, Federal 205s, over 26.5gr Hodgdon BL-C(2): Oehler 35P ^ Oehler 33 ^ PACT ^ [B]Average fps[/B] 1) 2786 . . . . 2777 . . . . .2786 . . 2783 2) 2913 . . . . 2902 . . . . .2911 . . [B]2909[/B] > One [B]large Dent[/B] on Case Shoulder 3) 2771 . . . . 2762 . . . . .2768 . . 2767 4) 2799 . . . . 2790 . . . . .2797 . . [B]2795[/B] > 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... :rolleyes: 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 [B]Mikecr[/B]'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. [/QUOTE]
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