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Posted: 2/18/2015 3:09:12 AM EDT
| I am relatively new to reloading and have what may be a dumb question. I would like to load some subsonic rounds for a .338 Fed using some extra heavy bullets (300 grain hawk custom) Is there any major danger from loading a bullet like this deeper into the cartridge to maintain COAL. My thought was that by having it a little deeper into the cartridge it would take up some extra space helping to keep my case volume used higher decreasing the risk of a detonation. Does anyone have any experience with loading like this? |
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Moving the bullet into the case will greatly increase pressure so you will have to lower powder charge volume. If you are only going a few thou deeper you may be alright but if you are talking about .030-.060" or more you are asking for trouble. Here is a test I did moving the bullet into the case. YOU CANNOT USE THIS TO DETERMINE HOW MUCH PRESSURE INCREASES IN RELATION TO SEATING IN YOUR SETUP. The effect will be the same but the amount will likely be different with different powder/bullet combos.
This load was designed for this test to work through the range of depths. If you load is already near max pressure or near max case volume smaller amount deeper seating may cause pressure to increase more than this shows. 
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In response to the second post - yes, it is true that seating a bullet deeper into the case can under some circumstances create higher pressures.
But as the OP indicates, he is trying to launch long, heavy 300 gr bullets in a .338 Federal cartridge at sub sonic velocities, essentially trying to get .338 Whisper performance levels. The .338 Federal however is a .308 necked up to .338 that normally uses 180 gr to 225 grain bullets at velocities between 2300 and 2700 fps. Loading a 300 gr bullet down to sub sonic levels would still be a light load. The OP also rightly expresses concern over the resulting low load density and the potential for pressure spikes due to that low density. He's got good reason to do so as the .338 Whisper is based on the 7mm Bench Rest case, which has similar body dimensions to the .308/.338 Federal, but it is a half inch shorter. That extra volume in the case can be a major problem with a light load, and sub sonic loads in rifle cartridges are one of the general areas in reloading where detonations are a major concern. The OP is right to be concerned about it, but while seating the bullet deeper in the case will help, it may not be enough to prevent the problem. I have no data for subsonic loads for the .338 Fed or the roughly similar .338 Marlin, and I suspect you'll largely be in test pilot territory on this one. The absence of any reliable load data for a similar weight bullet in a similar volume case in the same caliber is probably going to a barrier that you may not want to attempt to overcome. Unless you have access to Quick Load and can use it to develop a potentially safe starting load, I'd advise strongly against trying to develop a subsonic load for the .338 Federal Even then I'd strongly advise against it as it's very advanced reloading and not something to take lightly. If you have access to Quick Load and want to pursue it, there are however a couple of general principles that apply and you might be able to borrow some ideas from cast bullet shooters in developing a workable and safe subsonic load. 1. fillers One approach that is used in some light cast bullet loads is to use a filler material to take up some of the extra space. This is fairly common in black powder era case like the .45-70 where the velocity is well in excess of what is needed to get black powder era velocities with smokeless powders. I'll use Unique or Win 231 in 405 gr .45-70 loads but I use a piece of 1/4" thick polyester quilt batting cut in a 1" square and then placed in the case on top of the charge. This takes up some of the volume in the case, holds the powder back against the rear of the case, and unlike a solid wad, won't cause issues with ringing the bore if there is any airspace between it and the bullet (which their isn't anyway). I do the same think in .38-55 loads with Unique using a 5/8" square wad. 2. Powder choice If you do venture into test pilot territory, powder choice is extremely critical. For reduced loads, in high capacity cases, Unique (a double based, disc shaped powder) has been an old standby for cast bullet shooters seeking lower velocities as it is not prone to detonation and pressure spikes in low density loads. Consistent with that, low velocity cast bullet loads for the last 30-35 years have most frequently used powders like Unique, Red Dot, 700X, and Green Dot and Win 231, all of which are fast to medium fast disc shaped double base powders. The common thread here is that these double base disc shaped powders all burn through convective ignition, where the entire surface ignites at once, as opposed to conductive ignition where the powder ignites progressively through the use of holes in the powder and retardant coatings on the exterior. The use of nitroglycerine in these double base powders is by design, as it burns hotter and produces more gas than nitrocellulose, which aides in consistent ignition and ensures all the other grains are quickly and consistently ignited. The disc shape of the grain is also intentional as disc shaped powders won't pack like ball powders will, so again the entire surface area of the powder is available for rapid and consistent ignition. In general these powders perform much better with standard primers, and magnum primers tend to increase the standard deviation in velocity. Personally, I like Win 231 and Unique for reduced loads in my .45-70 as it is very clean, efficient, easy to measure and it produces very low SDs in the single digit range from a 32" barrel. The take away here is that when it comes to low load densities (reduced charges in large capacity cases) it's very hard to beat the double based powders for safety as they are consistent and help avoid the pressure excursions and spikes that have been known to blow up rifles shooting reduced loads. The same thing applies to light loads in large capacity pistol cases. A target load in a .38 Special for example fills less than half the case, but Red Dot, a double base flake powder, works very well in this caliber, and it's my preferred choice for .38 Special target loads. ---- At the other extreme, wildcat cartridges, (with the exception of those designed for subsonic use) by default are seeking maximum case capacity AND high load density. Consequently, a progressive burning single base powder, using deterrent coatings, high thermal conductivity and high mass grains makes sense. These powders will ignite primarily, through grain to grain contact (rather than by flash ignition of the entire charge) and will burn from the back of the case to the front, with the exposed area of each grain remaining fairly constant as it burns. This combination of traits helps produce a nice smooth increase in pressure and a longer pressure curve with a lower peak pressure, helping the cartridge gain peak efficiency from the charge without excessive pressure. But in their large case capacity application, with these burn traits, a high load density is essential to avoid the potential for detonation |
| Thanks for the great information. I knew when I got into this that most of the project would involve some pioneering as the cartridge is relatively new on the market and I can can find precious little information about anything other than factory loads. I figured I might have a vicious cycle of loading the bullet deeper but then having to decrease the charge in order to maintain subsonic speeds so this may not work out at all but seems like a fun and interesting challenge to me. And yes I know that any information I find here or elsewhere is not gospel and the only real proof is my own testing so I am holding no one responsible for my crazy experiment. |
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Quoted:
I am relatively new to reloading and have what may be a dumb question. I would like to load some subsonic rounds for a .338 Fed using some extra heavy bullets (300 grain hawk custom) Is there any major danger from loading a bullet like this deeper into the cartridge to maintain COAL. My thought was that by having it a little deeper into the cartridge it would take up some extra space helping to keep my case volume used higher decreasing the risk of a detonation. Does anyone have any experience with loading like this? In the old days, seating the base of a bullet below the neck/shoulder junction, so it protruded into the powder space, was regarded as not a good idea. (Bad juju) I think now, it is common, but I don't do it. |
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Quoted:
So then he should fine with sub-sonic rounds and the associated low pressure? I don't have enough information so I cannot say. I will play it safe with FACTS, decreasing case volume by deeper seating with a given charge WILL raise pressure unless there is already an effect from seating on lands in which case it may drop some and rise again. Too many variables and too little info to guess the amounts. I would guess running subsonic the pressures would be lower but I don't know. Posted Via AR15.Com Mobile |
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