I have found little specific information for loading this even after cruising the forums for 2 months. I'll post what I've decided to do and execute some loads today with all the background information both as a record for me, and for others who may be working up their own loads.
Background: I've got about 140 rounds through my DTA HTI so far, about 70 rounds of DTA munitions 352 grain, about 50 CheyTac 350 SMKs and about 20 Cheytac 350 grain "balanced flight projectiles". Without getting into gory details, the 350 SMK from Cheytac shoot the best (very close to 1/2 MOA) and I'm interested in a long range hunting load, and even though these don't perform very well on deer past 1000 yards, I decided to go with the SMK because of their accuracy, their field confirmed velocity of 3150 FPS, and the fact that I got 500 of them from CTD for $350. I await an AMAX or an Accubond offering that will have a similar or better BC.
I tore apart a factory CT load with 350 SMK and found that whatever powder is inside weighs 136.5 grains. I think it's Retumbo. The OAL of the cartridge is 4.100". I consulted Quickload with all my cartridge and gun specifics, and if this is Retumbo, its not at max pressure, although this depends critically on your "Shot Start Pressure" which I left at default because these are seated deep and are not on the lands. You can barely hear the powder when you shake these loads so it's just under compressed.
BRASS: I got 100 Jamison from CT for about $2 each. I hand chamfered the inside and outside of the case mouths because my motorized RCBS thingie sucked at the job on these large brass. This brass does not appear to be annealed. I'm not sure if this is worth it because I have been told by a trusted guy at DTM that the primer pockets will be the rate limiting factor for my brass life. The DTM Bertram brass does appear to be annealed, however. I do not have a reloading tray that will accommodate the case head of the 505 Gibbs based 375CT round, so I used the box the brass came in. I cannot find a tray yet that is stated to accommodate this case head.
RESIZING: I used a 50 BMG RCBS press with the adapter (product number 88715) for the #47 shellholder, and I'm using Dave Viers Viersco dies with a diameter of 1.5". They're quite nice. I found that the expander ball was difficult to run through the neck on the first couple of brass. Subsequently, in addition to generously lubing the case body with RCBS case lube, I lubed the inside of each case neck individually with RCBS case lube applying it with a Q-tip. This made the first full length resizing much easier. The case length is 3.030 +/- 0.005. I tested an empty case and it chambers easily. I have the press mounted to a hand made bench that I made using 2 layers of 3/4" plywood 4'x4' glued and screwed togehter as the top with a 2x6 skirt that is bolted to 4 4x6s for legs with a bottom shelf (only one layer of 3/4" plywood on the bottom shelf which also has a 2x6 skirt for bolting to the legs) fastened together with 7" 3/8 bolts, 2 per level per leg. It is SUPER solid and loaded with equipment weighs over 400#. It is UBER-OVERENGINEERED-SOLID and I'm glad it is because this press for this cartridge puts a lot of stress on the bench. I noted minimal flex. I built this for 50 BMG reloading that I have never got around to doing yet. But the press is perfectly adapted for 375 reloading.
PRIMING: I used an RCBS bench mounted automated priming thingie. I have been told to worry about primer pocket expansion with multiple reloadings. I deprimed a factory CT shot case and reprimed it. The primer seated with mild-moderate force. I'm guessing that after just one firing the primer pocket is indeed expanded a bit, especially after comparing to priming the new Jamison brass. The Federal 215M primers seat "stiffly" in the new brass, but not as stiff as new Nosler brass in my 300 RUM. Those pockets seem tighter, from the factory.
POWDER CHARGING: The RCBS powder hopper maxes out at 120 grains of Retumbo. Fortunately I have 3 of them. So I maxed out one and set the other at about 10-12 grains and threw 2 charges, one at 120 grains, the next at 10-12 grains and then hand trickled the rest of the charge onto an RCBS ammomaster electronic scale (which is excellent and WAY better than the Lyman offering I previously used, BTW). I then used a Q-tip to push the few grains of powder that were stuck to the residual lube in the case necks down into the rest of the charge in the case. Note in the photo the powder dispensers: the one in the center has the plunger fully unscrewed and the one on the right nearly fully inserted.
I reloaded 12 shells to start, 3 each of 134.0, 135.0, 136.0 and 136.5 grains.
BULLET SEATING: I used a factory CT round to crudely adjust the the seating depth to 4.100". I then seated the bullets. The Viersco micrometer (an option that I selected on his dies) works SPOT ON for an individual round, meaning that if you seat and it's 4.105, and you adjust the micrometer 0.005, it brings it right down to 4.100. This is better than my Redding dies do. In spite of this, the OAL of the loaded cartridges varies by 0.015 to 0.020, probably because of the meplat of the SMKs which are irregular and which I did not uniform. I then noticed that I don't have a .375 anvil for my Hornady OAL gauge, so I cannot measure base to ogive for uniformity. I ordered the anvil and this will have to wait for a subsequent reloading session. I'm going to wager that the base to ogive is far more uniform than 0.020
I used a Hornady concentricity gauge to check run-out. They are all within 0.0025". Usually I will strive for 0.001, but I found that this piece of equipment does not "true" the round as well as it does on smaller calibers, so I said "it's good enough" and let it rest. The Viersco dies have a sliding sleeve that aligns the bullet and guides it up the die like Redding Competition dies, so maybe that's why they were relatively concentric right out of the seating die.
If I get a chance before SHOT, I will test these rounds at the range and report back, hopefully with photos.
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Background: I've got about 140 rounds through my DTA HTI so far, about 70 rounds of DTA munitions 352 grain, about 50 CheyTac 350 SMKs and about 20 Cheytac 350 grain "balanced flight projectiles". Without getting into gory details, the 350 SMK from Cheytac shoot the best (very close to 1/2 MOA) and I'm interested in a long range hunting load, and even though these don't perform very well on deer past 1000 yards, I decided to go with the SMK because of their accuracy, their field confirmed velocity of 3150 FPS, and the fact that I got 500 of them from CTD for $350. I await an AMAX or an Accubond offering that will have a similar or better BC.
I tore apart a factory CT load with 350 SMK and found that whatever powder is inside weighs 136.5 grains. I think it's Retumbo. The OAL of the cartridge is 4.100". I consulted Quickload with all my cartridge and gun specifics, and if this is Retumbo, its not at max pressure, although this depends critically on your "Shot Start Pressure" which I left at default because these are seated deep and are not on the lands. You can barely hear the powder when you shake these loads so it's just under compressed.
BRASS: I got 100 Jamison from CT for about $2 each. I hand chamfered the inside and outside of the case mouths because my motorized RCBS thingie sucked at the job on these large brass. This brass does not appear to be annealed. I'm not sure if this is worth it because I have been told by a trusted guy at DTM that the primer pockets will be the rate limiting factor for my brass life. The DTM Bertram brass does appear to be annealed, however. I do not have a reloading tray that will accommodate the case head of the 505 Gibbs based 375CT round, so I used the box the brass came in. I cannot find a tray yet that is stated to accommodate this case head.
RESIZING: I used a 50 BMG RCBS press with the adapter (product number 88715) for the #47 shellholder, and I'm using Dave Viers Viersco dies with a diameter of 1.5". They're quite nice. I found that the expander ball was difficult to run through the neck on the first couple of brass. Subsequently, in addition to generously lubing the case body with RCBS case lube, I lubed the inside of each case neck individually with RCBS case lube applying it with a Q-tip. This made the first full length resizing much easier. The case length is 3.030 +/- 0.005. I tested an empty case and it chambers easily. I have the press mounted to a hand made bench that I made using 2 layers of 3/4" plywood 4'x4' glued and screwed togehter as the top with a 2x6 skirt that is bolted to 4 4x6s for legs with a bottom shelf (only one layer of 3/4" plywood on the bottom shelf which also has a 2x6 skirt for bolting to the legs) fastened together with 7" 3/8 bolts, 2 per level per leg. It is SUPER solid and loaded with equipment weighs over 400#. It is UBER-OVERENGINEERED-SOLID and I'm glad it is because this press for this cartridge puts a lot of stress on the bench. I noted minimal flex. I built this for 50 BMG reloading that I have never got around to doing yet. But the press is perfectly adapted for 375 reloading.
PRIMING: I used an RCBS bench mounted automated priming thingie. I have been told to worry about primer pocket expansion with multiple reloadings. I deprimed a factory CT shot case and reprimed it. The primer seated with mild-moderate force. I'm guessing that after just one firing the primer pocket is indeed expanded a bit, especially after comparing to priming the new Jamison brass. The Federal 215M primers seat "stiffly" in the new brass, but not as stiff as new Nosler brass in my 300 RUM. Those pockets seem tighter, from the factory.
POWDER CHARGING: The RCBS powder hopper maxes out at 120 grains of Retumbo. Fortunately I have 3 of them. So I maxed out one and set the other at about 10-12 grains and threw 2 charges, one at 120 grains, the next at 10-12 grains and then hand trickled the rest of the charge onto an RCBS ammomaster electronic scale (which is excellent and WAY better than the Lyman offering I previously used, BTW). I then used a Q-tip to push the few grains of powder that were stuck to the residual lube in the case necks down into the rest of the charge in the case. Note in the photo the powder dispensers: the one in the center has the plunger fully unscrewed and the one on the right nearly fully inserted.
I reloaded 12 shells to start, 3 each of 134.0, 135.0, 136.0 and 136.5 grains.
BULLET SEATING: I used a factory CT round to crudely adjust the the seating depth to 4.100". I then seated the bullets. The Viersco micrometer (an option that I selected on his dies) works SPOT ON for an individual round, meaning that if you seat and it's 4.105, and you adjust the micrometer 0.005, it brings it right down to 4.100. This is better than my Redding dies do. In spite of this, the OAL of the loaded cartridges varies by 0.015 to 0.020, probably because of the meplat of the SMKs which are irregular and which I did not uniform. I then noticed that I don't have a .375 anvil for my Hornady OAL gauge, so I cannot measure base to ogive for uniformity. I ordered the anvil and this will have to wait for a subsequent reloading session. I'm going to wager that the base to ogive is far more uniform than 0.020
I used a Hornady concentricity gauge to check run-out. They are all within 0.0025". Usually I will strive for 0.001, but I found that this piece of equipment does not "true" the round as well as it does on smaller calibers, so I said "it's good enough" and let it rest. The Viersco dies have a sliding sleeve that aligns the bullet and guides it up the die like Redding Competition dies, so maybe that's why they were relatively concentric right out of the seating die.
If I get a chance before SHOT, I will test these rounds at the range and report back, hopefully with photos.
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