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300 WSM with 225 gr ELDM

02 Aug 2023
@ 10:02 am (GMT)

Skylar Acock

This concept is pretty simple:

Rem 700 LA custom clone action (for ample magazine length)

Magnum bolt face

24" Varmint contour match grade custom barrel 5 groove/ 1:9 twist

chambered to .040" off the lands with a throating reamer from a dummy round seated where boat-tail/ shank intersection is at the neck/ shoulder junction (COAL = 3.193/ CBTO = 2.430 +/- .001")

Opinions? Potential snake bites? Will the chamber geometry still work optimally with the lengthened free bore?

I would rather use the more efficient case of the WSM than the Win Mag, but if the Win Mag just makes better sense, then so be it. If I am a crazy mad scientist, then I will own it; just don't want to waste time and money chasing a bad idea.

I appreciate any input or criticisms.



03 Aug 2023
@ 08:58 am (GMT)

Nathan Foster

Re: 300 WSM with 225 gr ELDM
Hi Skylar, it pays nto set the throat so that following throat wear, you can seat out a bit - rather than starting right at the junction. Also, it pays to set the dummy on the lands and then experiment back from there. In other words, it might be helpful to go about .080" shorter than what you were initially considering.

A SAAMi spec chamber results in a typical OAL of about 2.953" with the 208gr and around 2.993" with the 225gr. The 225gr ends up quite a way down in the powder column. If you are going to tweak it, try doing so in a way that retains versatility with other bullet designs, leaving you free to experiment. In other words, try to avoid extremes.

The exact case base to .307" ogive measurement can be difficult to obtain in a DIY setting. The cosine math thereafter is also critical in order to complete an accurate chamber drawing. Best performed with a jig / comparator specifically designed for this task. Without such items, opt for caution as suggested in the first paragraph (or use a no-throat reamer with separate throat reamer).

9 twist will likely go OK for this project. If you run the numbers, you may find that its not completely necessary (versus the potential projectile stress). Run the numbers for yourself and have a think about it. Consider the pros and cons and again try to avoid extremes.

Is it a good idea? Well thats up to you really, I don't see anything majorly wrong with the idea. If you are running a long mag box, the Win Mag may be the better option - or the 300 PRC if you want something specifically designed around the 225gr and have an extra long mag to work with. But if the mag is not so long (regardless of it being a long action) then the WSM may be a better fit, provided it feeds OK (feeding will need to be checked before going ahead). It would certainly have more poke than the standard item.
04 Aug 2023
@ 08:35 am (GMT)

Skylar Acock

Re: 300 WSM with 225 gr ELDM
Thank you Nathan. You have addressed, precisely, my internal doubts in this concept.

Going back to front, I am absolutely attempting to mimic the concept of the 300 PRC with the 225 gr ELDM but in the WSM platform (sacrificing some speed, but I don't really need it to get out to 700 yds, which is further than my threshold anyway), without the punishing recoil. Short & fat case with a heavy projectile, using the magnum case capacity to get to a little over 2600 fps at the muzzle with the 225 gr ELDM I recently shot a fancy underweighted custom rig with a brake in 300 PRC. I am not super sensitive to recoil, but that was just ridiculous... The rifle I am building, would be 11 lbs +/-, so maybe tolerable. Certainly worth exploration.

I flip-flopped a lot on 9 twist versus 10 twist. I certainly don't want to lock myself into only one projectile, so I agree with you that I should study on what twist would give me better options with a few different projectiles.

The barrel maker offers chambering services (Pac-Nor). They did my 280AI and were very thorough on reamer dimensions vs. actual throat dimensions vs. my dummy round. I intend on requesting a regular SAAMI chamber, then adjust the throat with a throating reamer based on the dummy round. But, before I opened the can of worms, I wanted to make sure I wasn't asking for something that made no sense.

I had done some simple math to try to find the middle ground on depth to lands that would work with a conventional 200 gr soft point as well as the 225 for a dual loading, but your advice here is where I really needed some input. I ended up getting some HotCor 200gr projectiles (actually want the 200 gr Partition but they are not available currently), made a dummy round to its max OAL and compared the two dummy rounds. With your advice here, I can see that I need to tweak my variables just a bit, but it looks like I was heading down the right path. I was shocked to find such a difference in the base to ogive dim's. I felt I was about to pigeon hole myself with only one projectile option if I went with the 225 ELDM. I am coming to the conclusion that maybe I would be better off designing around the 208 gr ELDM and experimenting with the 225 just to see what's what.

I appreciate your response very much. I also greatly appreciate all of your work in the Long Range and Practical Guides series of books. I use them as reference almost daily.

Best regards and many thanks,

09 Aug 2023
@ 10:32 am (GMT)

Rob Bird

Re: 300 WSM with 225 gr ELDM
Nathan will correct me if I'm wrong, but you should be able to beat 2600 fps in a 30-06AI with the 225 gr pill. I get 2800 fps with a 208gr in a 26" barrel. Perhaps with a 24" you will not quite get there.

I have some 200gr Partitions that I'll let you have for what I paid for them if you like. I'm in the eastern US.


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