7mmsaum info

[drdtmd]

hi guys i'm new here and wanted to say hi and have a few questions on a build i'm doing. first of a few is this will be a mag gun(badger bottom metal)so i will be bound by length and my question is what is the largest coal this will be?also the three bullets i will be most interested in using right now are the 168 berger,162 amax,and the 160 accubond.with that selection and coal what realistic velocity's should i be able to see out of a 26" tube?thankyou very much

 

[HammerDown]

If you are using a long action and AICS 338 LM magazines you can seat out the projectiles as long as you want ;-)

 

[offgrid]

Guessing you are going with a short action, take a look at these mags to get you a longer OAL.
http://www.alphaindmfg.com./store/index.php?route=product/product&path=35&product_id=52

 

[drdtmd]

Hey thanks guys. I got some info from Chris at alpha( very nice guy) and he said that the max I can load in his mag is 2.975 . With this in mind what kind of velocity am I looking at with these bullets? I also talked to Dave kiff ( another real nice guy ) and it looks like we are going to go .315 neck, .080 Freebore and 1.5 degree lead. How this sound?

 

[pmarauder]

Im running a .313 neck with .101 freebore and a 1.5 degree. Shooting the 175 XLD. If your shooting the smaller bullets with a shorter bearing surface, you should be ok with a shorter freebore

 

[drdtmd]

pm thanks.are you using a mag that restricts you to a coal of 2.975? also are you using rem brass? thanks

 

[Tondar15]

I'm in the same boat... my project has been on hold for a while but I am trying to get back to it. I plan to shoot the 168 bergers as well. Haven't made my dummy rounds yet. Have you given any thought to having seating depth flexability? If you load to the max coal and are not touching the lands at that length you won't have the ability to experiment with touching or jamming into the lands. Please let me know what you decide.

Thanks
Tony

 

[drdtmd]

tony I here ya. I'm not sure myself because I don't have my dies to make a dummy rd. I explained what I was building and bullets I was going to use to Dave and this is what he recommend for a chamber. I'd love to hear from guys that have already chambered for a mag gun. Thanks

 

[pmarauder]

i believe if you are only going to shoot the shorter bullets you may be ok with a .080 freebore, but with the saum, you will be taking up case capacity due to your bullets being seated further into the case, especially if you are limited by your mag length... what is your mag length?? To give you an idea, i have a .101 freebore and when i seat a 175xld .015 into the lands.... that puts the bearing surface/BT junction right at my Neck Shoulder junction in the case. 3.045 OAL (trimmed and pointed) and if i were to use any more powder charge than 64.5, i would be crunching powder when i seat the bullet.

 

[drdtmd]

Pm my max I can load them out to to still work in the mag is 2.975 . How would you build your chamber with this in mind and how much less powder will my cases hold vs yours with the bullet seated .070 deeper? Thanks

 

[offgrid]

If you are going to be just shooting the 162 Amax and 168vld, your Max OAL of 2.975 should be OK.

I'm gathering up parts for a 7MM build. Looked at a few options including a 7saum on a short action. Borrowed a 7saum seater, and seated a 168vld, 162 Amax and 175vld. Seated the 168 @ 2.970 which gave me 2.2675 to the ogive. Seating a 162amax to 2.2375 gave me a a OAL of 2.944. Figuring I would maybe seat the VLD 10 thou into the lands and the Amax 20 thou off to start. The Amax boat-tail is right at the neck shoulder junction, the VLD above it. Seating a 175vld 2.2675 to the ogive gave me a a OAL of 3.0675.

Not sure how these numbers equate to freebore?

Had I choose the 7saum SA, would have sent Dave Kiff a dummy round with the 168vld to make a custom reamer.

 

[drdtmd]

Offgrid thank-you for all the great info. I wish I knew alsoo how that relates to Freebore maybe someone else will chime in and answer that.

 

[drdtmd]

Hey guys I think I have this figured out. If I make my chamber for a 160 accubond to touch the lands with a oal of 2.975 I can use the mag for hunting and this will give me more Freebore for single loading and possible use the 180 hybreds am I thinking right? Offgrid would you possibly have a 160 accubond you could seat out to 2.975 and let me know what dimension you get off the ogive? Thanks again guys for the help

 

[pmarauder]

The Ogive of a given bullet is not a precise universal spot from which to measure..... You can take a comparative measurement at some point on the ogive, but you would need to make sure that your comparator and the person taking the comparative measurement also, are identical if your going to be making a precise determination of your seating depth and freebore.

If i were you..... I would purchase the Sinclair comparator insert. It measures the most consistant.
As far as figuring out your freebore to work with your mag length, Call Dave at PTG and tell him your mag length and tell him what you want to do.... He will get you set up.

 

[drdtmd]

ok talked to Dave and we came up with this .315 neck, .160 Freebore, 1.5 degree lead. I should be able to touch the lands with a mag feed 160 accubond and single feed 180 hybrids. I laughed when Dave told me once the throat starts eroding I can push the 180's out further. I told him and maybe the accubonds will like a jump. Anyway I think this will be the perfect setup for me. One last question if I turn my remmy brass to .314 will .015 thick neck be ok? Thanks

 

[pmarauder]

The 160 accubond has a longer bearing surface than does the 180 hybrid. However, it is much shorter than the 180 Hybrid.
Accubond is 1.403 oal and the Hyrbid is 1.521. Looks like that .160 FB will work.

You will need to turn your necks to .014 thick.
.014+.014=.028+.284= .312 loaded round. That gives you .003 chamber clearance.
Use a .309 or .310 Sizing bushing

 

[drdtmd]

pm thankyou for all your help. is .014 a good neck thickness? did i go with the right chamber neck size?

 

[skyking]

I am building a 7saum AI on a Big Horn action. Sent Dave a dummy round with the Berger 180's in it. That way I can shoot both the 180's and 168's. You can go with Seekins Precision bottom metal. It will give you an OAL of 3.14. Just waiting on the reamer. Ordered it back in December. Driving me crazy.

 

[drdtmd]

Skyking thanks for the reply I already have my a5 that has been setup for the badger bottom metal. What brass are you using and what neck are you going with? Thanks