This was sent to us by a customer who did some extensive testing.
Leades and Ogives and Pressures, Oh My!
(“Lions and Tigers and Bears….”)
August 31, 2023
Dear Friends:
As I enter 6th Decades Studying the Way, I am still learning. What follows is of interest to the Reloading Nerd but also has some valuable information for every gun owner as it pertains to “stubbed” cartridges wherein the bullet is seated deeper into the case because of repeated chambering, etc.
SUMMARY:
A 0.060” increase in depth of seating caused a 125 fps increase in velocity with my given load, and short or long throats (leades) made no difference as the bullet did not contact the leade. With my load and barrels, pressures remained Safe, albeit in the +P range. Part of the forgiveness in pressure increase may have been to the relative short length of the 124 NUKE projectile.
Definitions:
OAL: Cartridge over-all length.
Ogive: The shape of the bullet towards the front that will come into contact with the rifling of the barrel.
Throat (or leade): The distance in the chamber between the end of the case and the start of the rifling.
Facts: (Please note that this discussion pertains to 9x19mm 124 grain JHP’s.)
Bullet length:
124 XTP: 0.575”
124 Gold Dot: 0.565”
124 RMR “Nuke:” 0.550”
Hornady stated in one of their reloading manuals in regards to loading the 9mm cartridge that, “an increase of 0.030” in seating depth can more double the pressures.” They cite an increase from 23K psi to 62K psi, but did not give the particulars as to projectile, shape, weight, powder charge, powder type, actual oals, etc.
A different problem with bullet seating and oal is that a substantial pressure spike is expected if the bullet contacts the leade when chambered (before firing.) This is possible in a barrel with a short throat and especially with a bullet with a fat ogive such as is found on the 124 NUKE. More often the cartridge simply will not chamber. This phenomenon did not occur in our testing.
Hornady Factory loads their 124 XTP cartridge to 1.060” oal so that it can chamber and function in all 9mm barrels regardless of leade. (SMART!)
Hodgdon’s on-line manual lists the 124 XTP at 1.060” oal with 4.5 grains of Universal (Burn Rate 33) at 1126 fps from 4.0” barrel.
Alliant’s on-line manual lists the 124 Gold Dot at 1.120” oal with 5.8 grains of Unique (Burn Rate 33) at 1180 fps from 4.0” barrel.
Certain 9mm pistols have barrels with short throats. These tend to mostly be European pistols and include the CZ’s and notably Gen5 Glocks. (Also Glock 43X and 48, and several aftermarket Gen3 G19 barrels.)
A gentleman on-line determined the distance at which different shaped 9mm cartridges would stand slightly off the rifling (Leades) in a CZ-75 pistol. (“The plunk test.”) His findings were:
124 NUKE: 1.067”
147 XTP: 1.096”
124 and 147 RMR FMJ: 1.136”
124 Gold Dot: 1.142”
Now for my Data:
Method:
Two nearly identical pistols were used. Both had a 4.0” land-and-groove barrel but “Pistol S” had a short Leade/Throat and “Pistol L” had a longer Leade/Throat.
124 NUKE bullets were loaded into brass cases at an oal of 1.060”. Increasing 0.2 grain increments of Unique powder were loaded into two cartridges starting at 4.8 grains and ending at 5.8 grains.
Findings:
Previous experience showed that 124 NUKES loaded to 1.120” oal would not chamber in Pistol S.
Previous experience proved that 124 NUKES loaded to an oal of 1.120” loaded with 5.8 Unique in Pistol L gave (only) 1075 fps. Please note that based upon data from published reloading manuals with a 124 Gold Dot bullet we expected this load to generate 1180 fps! I attribute the lower velocity to lower pressure as the NUKE was 0.015” shorter than the Gold Dot and thus the volume below the bullet was greater with the NUKE.
As we’ll see below, the “same load” of a 124 NUKE with 5.8 Unique but loaded to a shorter oal of 1.060” gave 1200 fps, a gain of 125 fps compared to when it was loaded to 1.120”. (This is the most significant finding of my brief study.)
RAW DATA, 124 NUKE loaded to 1.060” oal. 08/30/23, Cloudy temperature in high 70’s.
Cartridges 1-12 and 15&16 were fired through Pistol S with a short throat.
Cartridges 13&14 were fired through Pistol L with a longer throat.
Unique Powder and WSP primers were used for all (except 15&16)
Cartridges 15&16 were 115 FMJ loaded to 1.150” and loaded in bulk with 5.8 Unique and GINEX primers.
#01 4.8 1.059” 1102 fps
#02 4.8 1.062” 1079 fps (average of 2 at this weight was 1090 fps)
#03 5.0 1.059” 1092 fps
#04 5.0 1.060” 1107 fps (average of 2 at this weight was 1099 fps)
#05 5.2 1.059” 1129 fps
#06 5.2 1.059” 1116 fps (average of 2 at this weight was 1122 fps)
#07 5.4 1.062” 1129 fps
#08 5.4 1.060” 1178 fps (average of 2 at this weight was 1153 fps)
#09 5.6 1.058” 1181 fps
#10 5.6 1.060” 1182 fps (average of 2 at this weight was 1181.5 fps and very consistent!)
#11 5.8 1.060” 1226 fps
#12 5.8 1.059” 1173 fps (average of 2 at this weight was 1200 fps)
#13 5.8 1.060” 1220 fps
#14 5.8 1.060” 1180 fps (average of 2 at this weight was 1200 fps)
#15 5.8 1.050” 1148 fps
#16 5.8 1.050” 1210 fps (average of the 2 FMJ cartridges at this weight was 1180 fps)
Noteworthy:
The 5.8 NUKES loaded to 1.060” gave the same velocities regardless of leade. (Pistols S and L.)
There were no significant pressure charges as measured by observation of abrupt velocity changes or flattened primers. One of the 5.8 primers showed minor flattening.
image0.jpeg
Fired cases. Only one of the 5.8 Unique cases (second row, second from right) showed minor primer flattening and was still well within the acceptable range.
Discussion and Final Impressions:
The short length / fat ogive 124 NUKE can be safely loaded (in the two barrels tested) with up to 5.8 grains of Unique powder at an oal of 1.060’ but this is a +P load. Based upon these findings I think the optimal load is 5.6 grains as it still gives us the desired target velocity range (1150-1200 fps) and is very consistent. Loaded to 1.060” the 124 NUKE cartridges may be used in all barrels regardless of leade.
Perhaps the reason that we did not get as great an increase of pressure as feared by loading the bullet 0.060” deeper is that the length of the 124 NUKE bullet itself is short and thus its lower edge is not seated as deeply as a longer bullet such as the 124 Gold Dot or 124 XTP? Supporting this supposition is the fact that we obtained only 1075 fps when this cartridge was expected to give 1180 fps using published data for the longer 124 Gold Dot.
In regards to dangerously high pressure due to bullet set-back during repeated chambering, etc, we cannot conclude that we would have similar results to the experiment above. In the case of bullet set-back (shortening of oal) with a cartridge that is already at full velocity, ie: 1180-1200 fps, we should expect the pressure to be unacceptably and dangerously increased.
I would not shoot a factory cartridge that was noticeably shortened. Many admonish against repeatedly chambering the same 1-2 rounds for fear of set-back. I make it a point to mark the position of the bullet as it exits the case with a thin black Sharpie to monitor for the possibility of set-back. Personally I have found that set-back is rare. If I should notice any shift of bullet as evidenced by the Sharpie mark, I would shoot it off during a practice session.
Respectfully Submitted,
Doc
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