Subsonic load for 6.5BR

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NormB

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I am planning a 6.5mm BR to shoot 140 gr. jacketed bullets subsonicaly. The case capacity is around 35 gr of water but the bullet will take up 5 grains of that. I have no experience with reduced loads so I am looking for advice from those that do. I was thinking of 5 gr of Unique as a start. Any advice???

NormB
 
Trail boss. Check out the IMR website they have loading directions for it.
The trail boss fills the case up really well. I'm using 9 grains of TB in my 308 and it fills the case up about 3/4 of the way.
 
The 140 grain bullet is long in a 6.5mm. You will have to be careful about sticking a bullet if you are trying to get a sub-sonic load. While a load that shoots the bullet out a 1000 fps is unlikely to stick a bullet, working up may have you at a starting velocity much less, and that could result in stuck bullet. You would be better off with a cast bullet, with less friction, and less potential for sticking a bullet if you get down too slow.
What velocity do you anticipate with 5 grains of Unique?
 
What velocity? I don't know.. maybe 800fps. What do you think? Paperslayer has a good point. The twist is 1 in 8, quite fast, and that is more friction/resistance. So the combo of jacketed plus fast twist may require 8 gr unique???

The barrel is 30" long. Ideas.

NormB
 
I have not done this with this particular cartridge, but in my experience with sub-sonic loads in rifles I have only used cast bullets. I have not had a problem in shooting long rifle bullets at 800 fps, but they were cast.
In your case, you are compounding the issue with a long barrel, and the intention of using jacketed bullets.
I would suggest that you need to have a chronograph, and start high, and work down. If you start low and try to work up you might end up practicing getting jacketed bullets out of a barrel.
I have no recommendation for a starting load, as I am not familiar with the cartridge. In a .257 Roberts, about 5 grains of Red Dot and a 100 grain cast bullet gives me around 1200 fps.
 
Well I did some load testing today with 139gr Scenars in 6.5 BR Lapua brass. I settled on Lil Gun Powder. It is slower than pistol powders, but is in the fast range of rifle powders. I started with 9 grains thrown by an RCBS Chargemaster. Listening to the report it sounded like a 22 long rifle. I could hear the sonic crack. Having no chrono I would estimate velocity around 1100-1200 fps given my next tests. I loaded 7 grains and could just faintly hear the bullet fly.. maybe 900-1000 fps . I tried 6 and 6.5grs. No bullet flight noise and bullets hitting much lower. I had a block of exotic hard wood.. 4 inches+ thick in front of the back stop. 9 grains penetrated the block and 7 grains almost at 50 yds. The noise of the bullet hitting the block was a large part of the report. No signs of pressure, and the cases sized easily in a small base die.

NormB
 
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