7-300 Win Mag: OAL for 180gr ELD-M

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Archibald

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I'm building a rifle in 7-300 win mag on a Winchester 70 and will be utilizing the Hornady ELD-M in 180gr. I am soliciting opinions on OAL as I have to decide if I need to do some more work to the magazine and bottom of receiver. I also posted this project at large in the gunsmithing forum but I thought this specific question would be better suited for this forum.

Below are photos of the resized 300 Win Mag brass using the 7mm Rem Mag full length die to make a standard 7-300 Win Mag wildcat cartridge, being careful to not bump the shoulder back any further than the 300wm full length die.

- I removed the spacer in the factory magazine box and now it's internal dimension is 3.630". A bullet seated to 3.600" OAL fits nicely inside.

- There is a Wyatt extended magazine box that has an internal dimension of 3.825", and if I further modified my action that would fit and I could seat bullets to 3.800" OAL.

-I assume any capable gunsmith could ream the freebore for whatever bullet I request and with the desired jump to the lands that I request. There would be a little more case capacity potential with a longer magazine, but I want to know if there would be a noticeable deficiency in seating the 180gr Hornady ELD-M at 3.60" vs 3.80".

In your opinions, would I gain anything by utilizing the extended magazine box? In contrast, is there any disadvantage of going that direction?

***I am not attempting to start a discussion or debate of the merits of the 7 PRC, 28 Nosler or 7 STW - or why would be a better optiom then 7-300 win mag.

Thank you.

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Have you taken a Hornady Lock n Load tool with a modified case yet and checked your bullet jam lenght ? 🤷🏼‍♂️
I would do this first and see what lenght you can go to . RJ

I do like that 3.800 lenght thou . I never like my bullet to be seated any further then the shoulder diameter .👍
 
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I feel the same way Jim, I'm inclined to go that way.

As you can see on my build thread, I am not at jam length because I don't even have a barrel yet. I'll get it chambered for whatever length I decide on.
 
I am not Jim - he may have his own reply - but I suspect that COAL sort of a rifle to rifle thing - has to do with the cutting of the chamber area or the amount of wear on the lands - can look up in Woodleigh manual or several other places how to determine where the lands are, in your rifle - without buying tools to do that. Then, Woodleigh suggests .020" to .040" less than "hard on the lands" - for your pressure test. Then might want to seat slightly deeper or shallower for "accuracy" - I tend to set for .030" (or what I think that is) and then can not demonstrate to self any difference by going shallower or deeper - store bought or mil-surp guns, old guy shooter. Perhaps others can and do see a difference. As per a CGN posting, old school target shooting (bench rest) guys used to ram their bullets hard into the lands - the bullet got seated as the bolt was closed - probably not a good plan for a hunting round.

About second rule for hunting ammo - the round HAS to fit into the box magazine, likely with a bit of end-play clearance, to function - regardless where the lands are. Not an issue, if you hunt or shoot "single shot". About first rule for most hunting - never want bullet jammed or engraved into the lands - "touching", at most, or some "jump", is probably desirable. Some mono-metal type bullets want a LOT of jump - like .070" or more for best "accuracy".
 
Potashminer, I appreciate the response but it seemed to be directed towards questions that I didn't ask. Perhaps you didnt read my initial post., I WAS NOT asking how to generally find the max OAL for a rifle, or what is the ideal amount of bullet jump. I'm trying to decide on if I need to have my yet-to-be barreled rifle throated long for a specific bullet with an associated longer box magazine - which I only ask because (of course) I'm aware that the OAL needs to fit within the box magazine of a repeating rifle. So "thank you" anyway, 😃, and I do like having engagement from then group.

To rephrase my question to Jim, I'm wondering what the OAL is on your 7-300 Weatherbee Magnum with a 180gr ELD bullet or similar long bullet. My followup question would be how far down it sits into the case, i.e. is it below the shoulder/body junction and does he see a steep velocity decrease due to bullet taking up powder volume? What rifle is it chambered in?

I'm pretty sure I'm going to order the Wyatt extended box (or make my own) and do the required work to the bottom of my receiver so that I can seat the 180 eldm out to 3.800, and I'll have the rifle chambered to reflect that (obviously).
 
seat the bullet in your chosen case to the depth you want then build according if you want the bullet seated to the base of the neck then build the rest around that spec
 
Unfortunately for Archibald, this thread is hilarious! Opinions aren't facts... so that may be an issue in the request.
Anyway... answers to actual questions:

I assume any capable gunsmith could ream the freebore for whatever bullet I request and with the desired jump to the lands that I request
Correct. Or you can do this yourself with a piloted throat reamer,

There would be a little more case capacity potential with a longer magazine, but I want to know if there would be a noticeable deficiency in seating the 180gr Hornady ELD-M at 3.60" vs 3.80".
A little more in this case is actually quite a bit, ranging anywhere from half to a grain and a half of powder. If you are planning on running at or near the pressure red line, then this could be 50 to 100 fps, maybe even 150, depending on powder choice. More is always more. The deficiency would be noticeable..

In your opinions, would I gain anything by utilizing the extended magazine box? In contrast, is there any disadvantage of going that direction?
The opinions again... This really depends on what you're trying to accomplish, and what the use is for the build. Since it is a Model 70, one would think this is more of a hunting rifle as opposed to a chassis'ed up long range rig. Whatever it is, the cartridge choice is leaning towards performance. The gain in performance in running a longer COAL may or may not be enough for you to want to do it. See the numbers above. The fact that you're asking is leaning towards the Yes.
Model 70's don't tend to lend themselves to modifications as easily as a Model 700, so you may or maybe not getting into Trick Move territory. If there are no issues as far as fit and finish, collector grade rifles, and all that jazz, then why not put the box in, and get the performance?

R.
 
SigWig said:
That short neck isn't ideal in theory.
300 wm has the same problem.

7-375 h&h?
Click to expand...
This is a bit of baloney... Proper reloading set ups and techniques make this "problem" pretend. If the neck is concentric, and the grab consistent, how much neck does a fella really need? More misunderstood hype about nothing.

R.
 
Archibald said:
To rephrase my question to Jim, I'm wondering what the OAL is on your 7-300 Weatherbee Magnum with a 180gr ELD bullet or similar long bullet. My followup question would be how far down it sits into the case, i.e. is it below the shoulder/body junction and does he see a steep velocity decrease due to bullet taking up powder volume? What rifle is it chambered in?

I'm pretty sure I'm going to order the Wyatt extended box (or make my own) and do the required work to the bottom of my receiver so that I can seat the 180 eldm out to 3.800, and I'll have the rifle chambered to reflect that (obviously).
Click to expand...
Also not Jim...
Jim's OAL set up doesn't really matter for you. Any capacity used up by the bullet decreases potentially available powder volume, which will reduce performance. The steep velocity decrease is an opinion thing, as 50 to 100 fps may not mean the same to someone else as it means to you.
The facts are as above. There are pressure and volume factors to consider, of course.
Generally speaking, more powder equals more speed.
Also, most want the top of boat tail at or as near as possible to the top of the shoulder neck junction. There is zero advantage to having any amount of bullet shank below that junction.

R.
 
I’m trying to understand something here. So I’m guessing you have a factory winchester in 300 win mag? And you’ve decided it’s not really an ideal cartridge for what you want to do so you’re planning on going down to 7mm in the same cartridge to gain some ballistic advantage? This is just a rebarrel scenario of an existing factory rifle? Not a full custom? If this is the scenario than I’d do what you’re saying and cut the box longer and notch the feed ramp as long as the cost wasn’t outrageous ($300–$400 tops) and I was certain it would feed propery after I was done. I’d probably also get my freebore cut to roughly 3.750” to the tip. This would give you a bit of wiggle room to get right up to the lands if you want and you’d be able to chase them a bit after some erosion if you chose to do so. In reality, I’d probably buy a few different bullets that are similar and see how each fits in your case just in case your gun doesn’t like that eldx for whatever reason.

If you’re looking at doing a full custom from the ground up than I’d start over and pick a different case.
 
One more thing. I can’t tell from your photos, but I try to line up the bearing surface/boat tail junction with the neck/shoulder junction on the case and maybe a tad deeper. I think jim mentioned above about having .284 or 7mm of bearing surface in the neck as a minimum, but I like a bit more like I mentioned.

If you’re gunsmith can’t cut the freebore you want from a dummy round that you supply than you need to find a different gunsmith.
 
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Rman,

I already had a MacMillan M40 fiberglass stock inletted for a Winchester 70 with a huge barrel channel for near straight taper. I'm writing you from the target and precision rifle forum, so this isn't an average hunting rig. I'm going to fit this with a 28" m24/40 contour barrel.

I've already done the work to make it a magnum action I.e. bolt stop, ejector, magnum extractor en route, top of action opened, magazine opened and new follower. I see your points about the deep seated bullet taking the place of grains of powder - yes I'm going for performance (which includes more velocity). I might as well go all the way and open the bottom of the receiver as well so that I get the max velocity I can and seat those long 7mm bullets further up in the case.
 
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