mooredj
Well-Known Member
Doesn't this negate some of the reason behind the short action? Doesn't cutting out that much bottom metal reduce the stiffness of the action that precision shooters want?
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7 SAUM Seating Heavies Long
- Thread starter Rijoh
- Start date
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Not enough to even notice in a hunting rifle.
Benchrest shooters aren't shooting the same action, bullets or in most case cartridges that we are as hunters. And they aren't using a DBM either.
Hawk in WY
Well-Known Member
This has been my experience almost exactly with the 7 SAUM and other calibers except I start from what I found to be an accuracy node.
Loading longer and adding powder to get back to the same accuracy node didn't seem to be a benefit.
I will admit that loading longer and reaching a high node would be of benefit but that has not been my experience.
mooredj
Well-Known Member
I have found this to be true and the only way to improve on the velocity is to pick a different powder. For instance, in GRT modeling for the 7 SAUM, I can get to 2900 FPS with H1000, but If I use 4831 or 4350, I can only ever get to 2850 or so holding the pressure (60000psi) constant. I set up the freebore out to 0.218 with 1.5 degree throat angle to allow shooting the Berger 195. You have to get more powder behind the bullet in order to get there. I shoot a LA in order to do this.
A little modeling below for the 7 SAUM and 195 Berger. The freebore is actually 0.218 the way most everybody understands it. I show 0.236 in the title because I add in the chamber to bore transition (0.018) right before the freebore so 0.018+0.218-0.236. Just noting so I don't cause confusion with what is shown. This is using H1000 with a compressed load. Currently shown with a 0.030 jump and the bullet seated with the boat tail slightly above (0.022) the case neck junction. I can get to 2900fps with 62.3 grains of powder. The issue I will run into is seating the bullet less over time due to throat wear and eventually getting close to running out of enough neck to adequately hold the bullet. Depending on how often I shoot it, that could be a long time from now.
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mooredj
Well-Known Member
Just some data I put together since I am jumping into the 7 SAUM arena. I am really working on getting the heavies to work. I wanted just a bit more powder capacity to makes sure I can get to 2900fps. As noted in the previous post, I have set this up with a 0.218 freebore as designated by the column noted in green. The arrow on the bottom left points to the bullet seating depth. The arrow on the right is what I have settled on for shooting the Berger 195 EOL. I have been told what you need is bore diameter bullet seating and that is shown at 0.284. The cartridge neck length is 0.311. The bullet is seated in the case of the seating depth at 0.311 so that the bearing surface starts right at the case neck junction with the boat tail below that point. The boat tail is slightly up the neck when the bullet is seated at 0.284. I am taking a page from Brian Litz on seating depth for the Berger hybrids and assuming I will find accuracy at a jump of 0.025 with a seating depth of 0.284. If what he says holds true, I will keep shooting the same load with the same bullet seating depth until accuracy falls off at some point. In the meantime I will keep measuring the throat to see how fast it moves. Pay attention to the COAL on the far right. I will be shooting this out of a Zermatt Arms TL3 long action so no issues for me but a short action will be a problem. You really need a long action to stretch out the legs on the 7 SAUM with heavies. If I want to shoot the 180 Hybrids, I will not be able to seat to bore diameter. It can be done but I will probably need to single load to make sure the bullet stays concentric during loading. Okay for target and not ideal for hunting loaded in a magazine. This design does open up lots of possibilities using some of the other heavies.
You can also see what the SAAMI design looks like with the 0.90 freebore using a 1 degree throat angle. You can see how the 180 hybrids work but where using the heavies becomes an issue since you can't get the powder capacity you need to get them to shoot inside the 180 hybrids. You can shoot the 195 EOL out of a SAAMI chamber but you will need to load them long in order to make it work. If you look in the column under SAAMI and look at the bottom box in that column you can see that with no jump to freebore you are already seating part of the bearing surface below the case neck junction. Adding in jump will just require more seating below the case neck junction. This is where you begin to take the powder hit and can't get the speed you really want for the 195 EOL. With the SAAMI chamber and the 195 EOL seated close to the lands, I figure you can maybe get 2700-2750 fps. I would need to verify this with actual loads at the range. I am guessing others already have the data.
You can also see what the SAAMI design looks like with the 0.90 freebore using a 1 degree throat angle. You can see how the 180 hybrids work but where using the heavies becomes an issue since you can't get the powder capacity you need to get them to shoot inside the 180 hybrids. You can shoot the 195 EOL out of a SAAMI chamber but you will need to load them long in order to make it work. If you look in the column under SAAMI and look at the bottom box in that column you can see that with no jump to freebore you are already seating part of the bearing surface below the case neck junction. Adding in jump will just require more seating below the case neck junction. This is where you begin to take the powder hit and can't get the speed you really want for the 195 EOL. With the SAAMI chamber and the 195 EOL seated close to the lands, I figure you can maybe get 2700-2750 fps. I would need to verify this with actual loads at the range. I am guessing others already have the data.
