BHuij
Active Member
So I have run into the problem of "not enough pressure for efficient or consistent burn" a few times as I've worked up light loads for various firearms, especially rifles. This most commonly happens when I'm working well below the reloading manual recommended minimum powder charges for jacketed bullets. It appears to be more severe with slower powders than faster powders, presumably because pistol powders more quickly reach "optimal pressure" for a good burn than rifle powders (side note; is this why magnum pistol powders are often used for mouse fart loads in milsurp rifles?)
Inconsistent and inefficient burns lead to inconsistent velocities which = vertical stringing. Also can lead to really dirty ammo which can be problematic with direct impingement gas guns like ARs, although that particular problem hasn't affected me (yet).
So there appear to be three traditional solutions to fixing this problem:
1. Increase the charge. Obviously this isn't super viable if your goal is a light gallery load.
2. Use a faster burning powder. This is probably fine in bolt guns (indeed it appears to be the standard recommendation), but quickly leads to short-stroking in gas guns, particularly ones with mid- or rifle-length gas systems. I myself couldn't get IMR 4227 to cycle in my carbine-length .223 AR-15 with a 16" barrel without loads that had me worried on chamber pressure spikes (and weren't accurate anymore).
3. Use a filler such as Dacron.
Seems like with cast bullets, having too much pressure up front (i.e. too fast of powder) will deform bullets before they clear the parts of the chamber where there's room for riveting and the like, which leads to poor accuracy. If you can get the peak pressure to occur AFTER the bullet is well into the rifling, and your bullet design doesn't have a big honkin' bore rider or otherwise unsupported nose (looking at you Lee 185gr .312"), deformation can be kept to a minimum and you have one less thing trying to ruin your accuracy. Meanwhile, anything you can do to help the bullet resist deformation before fully engaging the rifling is a plus. Seating out as far as possible during loading, using a gas check, and maximizing the hardness of the bullet all seem to help. Indeed, my best and most accurate cast bullet rifle loads are all seated to the max OAL I can chamber, and use the slowest powders I have yet tried. Also my best results with cast .223 in my AR were bullets heat treated and measuring at a surprising 35 BHN.
So after all that rambling, I guess I have two questions:
1. Would increasing neck tension for the purpose of upping chamber pressure cause more harm than good? Seems like it could give me a more consistent burn with ball powders like H335 or slowish stick powders like IMR 4895, but also seems like it would increase the chances of having a pressure spike to deform the bullet before it's "safe" in the rifling.
2. Is there any reason not to shoot the absolute hardest bullets I can make in a high-pressure rifle round? I have gotten 35 BHN with HT/Q on COWW alloy and that performed better with the same near-jacketed loads of IMR 4895 than 26 BHN bullets. Only reason I've ever heard cited about too hard of alloy is failure to obturate and get a good seal in the barrel, but it kinda seems like the less obturation, espeicially at the base, the better shape the bullet will be in when it leaves the muzzle. The reason I ask is because I have about 20 different loads of .223 loaded up and ready for my next range trip, ranging from "probably won't cycle" to "hot jacketed load" territory. If NONE of them perform even with 35 BHN bullets, I want to look at trying out some weird stuff like adding babbit or copper to my alloy to exceed 35 BHN.
Oh, and bonus question, is there really no better option for modeling loads before physical testing than Quickload? Seems outrageously expensive for what it is.
Inconsistent and inefficient burns lead to inconsistent velocities which = vertical stringing. Also can lead to really dirty ammo which can be problematic with direct impingement gas guns like ARs, although that particular problem hasn't affected me (yet).
So there appear to be three traditional solutions to fixing this problem:
1. Increase the charge. Obviously this isn't super viable if your goal is a light gallery load.
2. Use a faster burning powder. This is probably fine in bolt guns (indeed it appears to be the standard recommendation), but quickly leads to short-stroking in gas guns, particularly ones with mid- or rifle-length gas systems. I myself couldn't get IMR 4227 to cycle in my carbine-length .223 AR-15 with a 16" barrel without loads that had me worried on chamber pressure spikes (and weren't accurate anymore).
3. Use a filler such as Dacron.
Seems like with cast bullets, having too much pressure up front (i.e. too fast of powder) will deform bullets before they clear the parts of the chamber where there's room for riveting and the like, which leads to poor accuracy. If you can get the peak pressure to occur AFTER the bullet is well into the rifling, and your bullet design doesn't have a big honkin' bore rider or otherwise unsupported nose (looking at you Lee 185gr .312"), deformation can be kept to a minimum and you have one less thing trying to ruin your accuracy. Meanwhile, anything you can do to help the bullet resist deformation before fully engaging the rifling is a plus. Seating out as far as possible during loading, using a gas check, and maximizing the hardness of the bullet all seem to help. Indeed, my best and most accurate cast bullet rifle loads are all seated to the max OAL I can chamber, and use the slowest powders I have yet tried. Also my best results with cast .223 in my AR were bullets heat treated and measuring at a surprising 35 BHN.
So after all that rambling, I guess I have two questions:
1. Would increasing neck tension for the purpose of upping chamber pressure cause more harm than good? Seems like it could give me a more consistent burn with ball powders like H335 or slowish stick powders like IMR 4895, but also seems like it would increase the chances of having a pressure spike to deform the bullet before it's "safe" in the rifling.
2. Is there any reason not to shoot the absolute hardest bullets I can make in a high-pressure rifle round? I have gotten 35 BHN with HT/Q on COWW alloy and that performed better with the same near-jacketed loads of IMR 4895 than 26 BHN bullets. Only reason I've ever heard cited about too hard of alloy is failure to obturate and get a good seal in the barrel, but it kinda seems like the less obturation, espeicially at the base, the better shape the bullet will be in when it leaves the muzzle. The reason I ask is because I have about 20 different loads of .223 loaded up and ready for my next range trip, ranging from "probably won't cycle" to "hot jacketed load" territory. If NONE of them perform even with 35 BHN bullets, I want to look at trying out some weird stuff like adding babbit or copper to my alloy to exceed 35 BHN.
Oh, and bonus question, is there really no better option for modeling loads before physical testing than Quickload? Seems outrageously expensive for what it is.
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