Help me understand freebore. 7 SAUM 180 ELDM

[Tyler75]

So go .180 rather than .090? That won't be too much?

 

[can1010]

So go .180 rather than .090? That won't be too much?

that would be fine. if you switch bolt stop .225 is even better on a long action. mine is .228 and with the 162 eld I am at 3.1 at .030 off

 

[MarkTheFark]

Good info in here, guys. Thanks to all who have shared.

I have an XM action ready for a 7 SAUM and my barrel is being cut soon. My smith only has a SAAMI reamer and I have been hesitant to go through the hassle of having a custom reamer built. (I'm also a bit impatient as I'd like to have this rifle for spring bear.)

I know I'll be giving up some case capacity and room I have for extended OAL in the XM action with the SAAMI chamber, but I think I'll still be able to get the speed I need out of 150 and 160 class bullets with 4350-range powders. Looking at 168 VLDs and 155 Hammers primarily.

 

[can1010]

you will enjoy your 7saum they really shine with 160 class bullets at 3000 fps in a 24 inch barrel while keeping the oal under 3.0 inches.

 

[Tyler75]

My Tikka started as a Remington 7 mag so with the long action bolt stop maybe I'll just have it at .225 free bore.
Thanks for your help, I'm real excited for this caliber. What powder are you using for the 162 eld?

 

[drdool]

Great thread and advice here. Tagging in

 

[Sending156s]

Good info in here, guys. Thanks to all who have shared.

I have an XM action ready for a 7 SAUM and my barrel is being cut soon. My smith only has a SAAMI reamer and I have been hesitant to go through the hassle of having a custom reamer built. (I'm also a bit impatient as I'd like to have this rifle for spring bear.)

I know I'll be giving up some case capacity and room I have for extended OAL in the XM action with the SAAMI chamber, but I think I'll still be able to get the speed I need out of 150 and 160 class bullets with 4350-range powders. Looking at 168 VLDs and 155 Hammers primarily.

Recommend you put together dummy rounds for your gunsmith.
1. Pick the bullet & case you will use.
2. Seat boattail bullet with junction of boattail/bearing surface even with the junction of case shoulder/neck. On a flat base bullet seat the base at the shoulder/neck junction.
3. If any doubt go to YouTube and search for Greg Tannel, one of top GS in world. He has a video showing how to make the dummy rounds.
4. Your gunsmith will cut the chamber and without moving the barrel he will switch out to a throat reamer for your custom throat (Freebore).
5. I have 2 6.5 PRCs built on XM actions with the throat cut for the 156 Berger EOLs. Don't buy the XM and not make use of your extra room. Make those dummy rounds. If your gunsmith has a problem with this he probably is not the person you want building your rifle.

 

[fightthenoise]

Alex Wheeler has a post on accurate shooter about making a dummy round. That's the process I followed.

1. size a case with a bushing die. The bushing only sizes the neck partially, so you measure the sized portion. I used a lighter to black the neck, then measured where the bushing rubbed off the black. Call it .250

2. Back your seating die way off. Run your sized case and bullet up in there. Dial your seating die down until it touches the bullet. If you want to jump the bullet .020, dial down 0.230 (0.250 from above minus .020) and seat the bullet. You now have a dummy round with the bearing surface 0.020 above where the neck sizing ends.

3. Gunsmith throats barrel so that your dummy is touching lands. When you back off .020 for your jump, your bearing surface is lined up with the bottom of the sized portion of your neck.

 

[mn_hntr]

Great thread, this is answering several questions I have for a potential Tikka build.

 

[Sending156s]

The OP's original question of help me understand freebore (throat). See pic from Bison Ballistics. For farther info go to thier site to find an educational section that is very well written.

 

[SteelBanger]

Not to get too far off the topic, but if you look at the Sherman lineup the 7SS and 7SST cartridges are slightly improved 7 SAUM cases. I have the 7SST and if I remember I'm right the freebore on it is .110, I have no problems fitting 180 hybrids in an accurate Mag but I'd have to go look at my notes for the COAL, I want to say CBTO is at 2.103 to the lands but again would have to check my notes.

 

[JakeC]

I just wanted to thank folks again for the encouragement. I now have the barrel and brass and have fitted a few bullets. The max COAL is longer than I anticipated, by a fair bit but I think it'll work. I don't have my notes in front of me but the jump from mag length is going to be a lot longer than I anticipated, but by no means is there going to be any spacewalking. I think the 180 ELDM and 168 ABLR are a .090 jump or something, the 175 ELDX is around .030. I might have those swapped around, but two were long and one was normal ish. I can get the details from the basement is anyone would find it helpful. Some of that might not work with those soft bullets but the fun is in the trying.

I'd have results to share but I ran into a final snag: my Gunwerks brass (from a community member here, I like this place) ranges from .016 to .019 in neck thickness meaning some loaded cases do not fit in the chamber. I've wanted a neck turner for a long time and finally have the excuse. The Bigger half of the snag? It's in shipping purgatory. Brownells got it out the door in hours; it's been at the distribution center ten miles from my house for 9 days. Oh well.

I just wanted to say thanks again and offer to share results in the future if anyone gets stuck where I was.

 

[clemmy]

Can I tag in for a question!
I'm building a 7 saum also. It's on a Tikka t3 and I'm having struggles with figuring the free bore. I can't make a dummy round because I can't find bullets. I want to shoot 155 gr Fed terminal ascent, 162 hornady eld-x, or maybe 155 gr hammer. The barrel will take 4 months so I want to get it ordered. Should I go .090" fb? Or stick with saami?

Dredging up an old thread. I'm also going with a 155 or 169 hammer hunter in a short action using max 2.95 (mag length). What did you end up going with for freebore, COAL, etc? Were you able to run close to mag length?

 

[JakeC]

Dredging up an old thread. I'm also going with a 155 or 169 hammer hunter in a short action using max 2.95 (mag length). What did you end up going with for freebore, COAL, etc? Were you able to run close to mag length?

I know you're not asking me but I started with hammers last year. I'd have to go look up my freebore but the generally accepted wisdom is that hammers don't care about freebore. This is what I read and what I've backed up with my own experience. I am shooting the 140 Absolute now alongside the 180 ELDM and I just loaded it to the length where I'd crimp into the first groove and let it rip. I found pressure, backed off a little, and I'm shooting around a quarter minute out to 600. I tried crimping inthe second groove and gained powder for 50 more FPS but I just didn't like it as a hunting round with less in the neck. Pretty sure my COAL is around 2.83. I could fine tune for speed deviation but it's so accurate I just don't feel the need. I'm not going to shoot animals past 600 anytime soon and a steel plate doesn't care if you hit it in the high half one shot and low the next. My 180s are jumping a full tenth of an inch and they're under half a minute too. COAL 2.925. I just started those at mag length minus a millimeter and worked back a little at a time until I was happy. If you're not going to crimp you could do the same thing with hammers but they'll probably be totally fine the first place you seat them. Guys who shoot bean fields tend to seat way out for max FPS. Guys who walk around seat them for max case alignment stability I think. I've never read about anyone needing to tune with seating depth for any reason other than preference. Hope that helps. Edit: I got a long freebore in a short action on accident but it hasn't had any negative impact, even with the soft target pills. I literally think the ELDM are jumping almost .110.