7 saum 3.1 mag length

[jtr1997]

I have a seekins ph3 6.5 prc with a magazine length of 3.14. Im looking at getting a 7 saum barrel setup for 180 eldm or 180 hybrid. Curious if anyone can tell me a optimized coal with either bullet?

 

[wapitispokes]

There is a fair amount of info regarding that question on RS and other forums like longrange... I know, because I also plan to add a 7 SAUM barrel on a short action, so I've spent too much time researching that question and related elements.

I'm pretty sure that the answers you will get from folks that are shooting that combination will be:

1) if you want to keep the heel of the 180 eldm out of the neck shoulder jxn, you probably won't quite get there with a COAL of 3.10" or a magazine length of 3.15. But you will be close. Accordingly, WRT to the 180 ELDM the answer is - the optimal COAL in you magazine is probably the longest you can make it in your magazine, and with your bottom metal and action while still getting good cycling.

2) The 175 ELDX is a little bit shorter.

3) "Optimization is good" but dance with what brung ya. Meaning, you'll be fine with what you have. Just let the bullet jam a little bit into the powder below the neck shoulder junction if need be.

You might look up some posts by "Mark at EXO". He has been shooting 7 SAUM in both SA and XM length and SA length, and I believe he prefers the SA for HIS style of hunting. He also has some write-ups on the EXO website and has discussed his rifles on the EXO podcasts - I think #370 and perhaps others. Not to take away from many others on RS that also have great info. and experience...

If donuts are your concern, I would suggest that the risk of donuts becoming an issue that requires resolution is probably lower if you are using 7 SAUM brass and not neck turning. But the way I look at it is, if I shoot the brass enough for donuts I'll pat myself on the back for my perseverance and either ignore it (because it probably won't cause a pressure or accuracy problem), address it, or get new brass. The third option isn't the end of the world.

I had one gunsmith tell me that many people are having great success with 7 SAUM and 180 ELDM in a traditional short action with a COAL of 2.9 or shorter...with the base of the bullet well below the neck shoulder jxn. His advice to me was not to worry about donuts because they probably won't form - at least if loading with actual "7 SAUM" brass.

Based on reports by Mark at EXO and a number of other people, I think you can expect between 2,700 and 2,800 fps out of a 7 SAUM on a SA with a 20" barrel and a COAL around 2.90. I think Mark eventually moved to an 18" barrel and was probably still above 2,700 fps, but I don't mean to speak for Mark on those details - I'm not sure if he ever mentioned his 175 ELDX velocities in the same discussion with CBTO or COAL. This is based only on my research not direct shooting experience with the 7 SAUM.

If you calculate the down range velocity numbers on the 7 mm 180 ELDM using Hornady's 4DOF calculators and assume (for instance) 5,000' elevation and a muzzle velocity of between 2,700 and 2,800 fps, then the bullet stays above 2,000 fps out to.... working from memory here, but around 700 yards, and IIRC, it stays above 1,800 fps to just over 800 yards. The 5,000' elevation assumption helps with the velocity retention. The 175 ELDX numbers are not far behind the 180 ELDM. Wind drift figures are great too, of course.

Everyone has their own view on what they are looking for but from my perspective, 700 to 800 yards is a LOT further than I ever plan to shoot at a large animal like an elk while using a moderate weight short action rifle, so I'd rather focus on managing recoil and practical accuracy vs looking for more velocity. Meaning, I (me - maybe not you) prefer to live at a muzzle velocity of 2,700 - 2,800 fps and I don't need to stretch the COAL to the 3.2 ish length that might be desired to keep the heel of the bullet above the neck shoulder junction and perhaps also gain a little more velocity. Sure, I'd love to get the bullet out further but I've resigned myself to living with the base of the bullet close to or below the junction.

 

[Bater]

3.140” should be sufficient