This is intended for people interested in the subject of military guns and their ammunition, with emphasis on automatic weapons.
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A small update, but first, a warning.
The following operations were safe because before shooting the cartridges into real weapons, we fired them into an EPVAT barrel (Electronic Pressure, Velocity & Action Time) to check that the pressure and internal ballistics were in line with the AOP 4172.
Please, don't try to duplicate those tests if you don't have access to a proof barrel.
First, we selected a lot of IMI 5.56 mm M855 ball ammo, removed the bullets with a bullet puller (not the inertia hammer type) and saved the powder for later use.
Left to right, 4 SS-109 / M855 cartridges made by various manufacturers, one LC M855A1 and our shortened and reloaded 5.56 mm.
The 5.56 mm family, from left to right, one M193; 3 SS-109 / M855; one M855A1 and the second version of our test bullet.
The test bullet is a solid copper-alloy bullet, based on the design of the Mle1898D bullet, but with a slightly secant ogive (Rt/R = 0.75). On the second version we changed the boat-tail to a more conventional conical design instead of the original long & truncated ogive BT.
The ogive length is around 16.7 mm so we will need to trim the case length at a maximum length of 40.7 mm in order not to exceed 57.4 mm COAL.
The bullet length is around 26.9 mm, with a weight of 4.15 g (64 gr).
The primed cases were cut with a saw (don't do this at home).
The small saw used to shorten the brass.
The shortened case, the case mouth is rough and impractical at this stage.
After this rough cut, the primed case is trimmed to the proper length.
The trim length was supposed to be around 40.5 mm, but the crimping groove on the bullet second version was deeper and longer than expected, so we had to adapt and tried 40.2 mm and 40.65 mm case length.
After trimming the case to the proper length, we removed the external burrs on the case mouth. Since we used "never fired" cases, there was no "donuts" inside the case.
From left to right, case mouth after the first cut, after trimming, and after removing the burrs.
Powder saved during the initial bullet extraction phase was partially put back in the case, and the test bullet was seated.
During the first test, the bullets were crimped with a hydraulic tool which heavily deformed the case mouth, so we didn't crimp the bullet during the second test to check if some issues with bullet accuracy observed during the first test were not caused by improper bullet placement.
The final cartridges were then checked.
During our first test, we removed some powder from the original IMI load to stay well below 100% of loading density (the effect of the solid bullet was unknown), then the EPVAT tests revealed that the MAP was only ~300 MPa with the improved bullet (equaling to a MV of 900 m/s from a 20" barrel and 815 m/s in a 14.5").
During the second round of tests we increased the loading density step by step to reach a MAP of ~340 MPa and then ~360 MPa.
At this later pressure, the measured MV was above 930 m/s in a "pseudo Mk12" AR-15 with a 18'' barrel, duplicating the MV of the M855 bullet when fired from a 20" test barrel.
Super cool work man. I really hope these come to fruition.
Great results, even more so when pressure is ~52k psi.
Congratulations to you and your team!