Ok, so finding no information on Cor-Bon's magic 338 LM subsonic load, and the fact that loading large cases to subsonic velocities is dangerous due to the likelihood of a detonation/explosion, how hard would it be to make special brass for large calibers with a decreased internal case volume? Just make a 338 brass with really thick walls to have same volume as 300 blackout or something a little more like a 308. Pushing 300 gr pills subsonic would be awesome especially with a can and this seems like the easiest solution. Someone should make a special run of 338LM/.50/.300WM etc subsonic specific brass.
- Thread starter ahhshoot
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I would be interested in hearing your actual load, if you have done this successfully.
Dogtown,
When you get a chance if you could post that data I'd be interested as well. I am running a 25" tube so it might put me past subsonic velocities if all the powder is not burnt and you are on the ragged edge. Does anyone have any input as to whether 50% case fill is safe?
I've never used TB but I understand that it doesn't like to be compressed or loose. Am I correct about it not liking extra room in the case?
TrailBoss looksl like little flat donuts, so it's bulky and fills the case quickly. I did my initial development on a 26" barrel, starting with the case filled at 70% and I had to go quite a ways down to get to subsonic speeds, where I wasn't all that comfortable. Moving to the 18" barrel I found a load fairly quickly, but I like I said, I haven't gone back and revisited it since I started shooting 12.7x48mm.
I have a 308 SS load with 10 g of trail boss with one of my cast and coated 150's, the case is over 50% full of powder.
There are people who have machined reduced capacity cases but I would just buy or build another gun and I have CNC equipment. Anything can be made, how much do you want and how much money do you have? If you want 20 low volume cases they are going to cost a lot more each that of you want 20,000 but no matter what they are going to be more expensive and likely not last as long as struck cases.
There are people who have machined reduced capacity cases but I would just buy or build another gun and I have CNC equipment. Anything can be made, how much do you want and how much money do you have? If you want 20 low volume cases they are going to cost a lot more each that of you want 20,000 but no matter what they are going to be more expensive and likely not last as long as struck cases.
Just roll up another barrel for the .338 BR. Its a cartridge based on the .308 1.5" case used for lots of silhouette shooting in the dark ages in 7mm and 30 cals. Now its being used in 6mm for very accurate shooting. We use the 6mm BR or the 7mm BR cases necked up to .338 and launch 300gr SMK's at 1050 with great accuracy and no issues with short powder charges bouncing around in a huge case. 16" barrel works great and its the only real hollywood quiet round I've fired.
As for making cases with reduced capacity its a great idea and has been done for a long time. Some guys have used fillers like epoxy or cast lead that are then drilled out at bullet diameter to whatever depth is needed for the powder being used. It works much better than huge cases with powders that aren't all that great. The BR uses a wide range of powders for subsonic instead of just trailboss. You can also get someone to machine up cases from scratch with short capacity .
Frank
As for making cases with reduced capacity its a great idea and has been done for a long time. Some guys have used fillers like epoxy or cast lead that are then drilled out at bullet diameter to whatever depth is needed for the powder being used. It works much better than huge cases with powders that aren't all that great. The BR uses a wide range of powders for subsonic instead of just trailboss. You can also get someone to machine up cases from scratch with short capacity .
Frank
50% case fill is dangerous and can cause secondary ignition, you need at least 70% fill to be safe. With a 338 mag you're going to have to run a filler regardless of what powder you run.
That is a pretty blanket statement. Lots of factory loads and load data in many books are under a 50% fill. I am not sure how many years it has been since I loaded a 38 SPL with a powder slow enough that I filled it more than half way.
I understand Trail Boss is likely to be the best powder for full case capacity loads in a 338LM for subs, I just don't know what an appropriate filler would be. I have looked online for some insight into Cor-Bon's 338 subsonic loads but no real data, at least nothing solid or reputable enough for me to put my face behind. And another barrel would be great but I want to keep the gun able to shoot the Lapua full power loads and I don't have a switch-barrel rig, I have a custom 700 action, so I'm really looking at a way to use my current setup to run subs with full size brass whether it be done by decreasing internal case volume or using a filler, I am up for the easiest solution here as the subs will just be a novelty for plinking pigs and stuff around my house. The cast lead idea Frank mentioned might be a good one, does anyone have any reason this wouldn't work? Seems like a filler might still be the best way to go though as it might get tricky keeping case volume constant once you start playing with the cast lead/drilling idea. I'm not familiar with the subsonic world but I'd like to be, so any help on a filler idea would be good.
Filling the case with the bullet may work out great for safety but it won't help at all with accuracy. Having the bullet an inch or two off the lands isn't always the recipe for success in that area. Trailboss apparently works safely but I've not heard anyone who shoots subsonic 308 or .338 LM say that they're getting sub moa accuracy out of it. Most guys are happy that it doesn't ping the suppressor so a 4 inch group is no big deal. If you have a switch barrel gun or really want to get into the subsonics build a barrel to shoot one that works with more than just trailboss. There are lots of choices out there that work well and are accurate.
If you are really set on the idea of using full length cases get a local machine shop to make up some cases with the same neck thickness as your standard round but with a powder chamber that is the same diameter as the bullet and not full depth in the case. This allows you to use a wide range of powders so you can find one that is accurate and also keeps your face from being removed by a round that doesn't do what you think it should. There are drawings all over the net for chamber dimensions and case dimensions so getting that info is simple. Do a google search for the one you want and give the drawing to the machineshop. Do a google search for "cat sneeze" loads which is what the europeans used to call these subsonics. Thats where I got the info on casting lead or plastic inside the case to reduce capacity.
Lots of info out there if you want to look.
Frank
If you are really set on the idea of using full length cases get a local machine shop to make up some cases with the same neck thickness as your standard round but with a powder chamber that is the same diameter as the bullet and not full depth in the case. This allows you to use a wide range of powders so you can find one that is accurate and also keeps your face from being removed by a round that doesn't do what you think it should. There are drawings all over the net for chamber dimensions and case dimensions so getting that info is simple. Do a google search for the one you want and give the drawing to the machineshop. Do a google search for "cat sneeze" loads which is what the europeans used to call these subsonics. Thats where I got the info on casting lead or plastic inside the case to reduce capacity.
Lots of info out there if you want to look.
Frank
