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180 ELDM (.284) notes and pressure questions

11 Oct 2021
@ 02:28 pm (GMT)

Jake Carey

I got back to the range today after a few months off and tested my final hunting loads my short elk hunt coming up this week. I really expected to be farther along and more confident by this point but I didn't foresee falling down the rabbit hole of bowhunting for the first time. That consumed all of my shooting focus for a few months. It was rewarding but derailed my longer range hunting plans for this year. I mainly wanted to share my findings so far on the 180 ELDM and then to ask a question about pressure buildup to see if I'm losing my mind or just doing it wrong. I'm shooting a 7mm SAUM out of a short action Savage model 10. I've got about 110 rounds down the barrel, which is a button rifled stainless 5R, 24" long. I'm using a FL bushing sizer that's giving me a strong 2 thou of tension, basically .0025. Today I was shooting "overhand" off a bipod due to the space constraints and tiny concrete tables at the range nearest me.

First I decided to test exactly how much pain I can inflict on the allegedly dainty 180 ELDM from Hornady in the form of crimping (Lee FCD), general abuse, and windowsill annealing. I know my velocities are not those of a magnum where bullet failure is reported. But I tried light crimp, heavy crimp, crimping just behind the ogive to severely dent the bullet, crimping pills that had been on the windowsill for months, and shooting bullets with the heat shield tip clipped off haphazardly after they were damaged in the bullet puller. Essentially my foulers were six or seven that had varying combinations of these treatments. Not only did none fail, they all shot in the same 1MOA group. This is on top of a .09 jump to the lands. My form and the busy, uncomfortable range didn't have me shooting well enough to know if the crimp improved accuracy, but it definitely didn't hurt it. I shot a half dozen moderately crimped with no other treatment at 200 and they again shot well, no better or worse. I still don't have a chrono so I can't report anything from velocities. I have one available to borrow but its owner was recently gifted the Delta variant by one of our many neighbors who view transmitting the disease as a way to flip the bird to the system. Anyway after the hunt I hope to confirm velocity. I'm sitting down to try to calculate it by my drops when I'm done this but I'm using 54 grains of 4831sc. I'm certainly not screaming but I don't think it's plodding either. Again, as discussed in another thread a while back I have a barrel and cartridge that put little stress on the 180, but I was still very pleased to learn a crimp is viable. Maybe it's not really a stressor, I don't actually recall reading that in the book series but assumed it.

The other load I tested today was the 168g accubond long range. Half of these I gave a moderate crimp and they did fine. No surprise, not a delicate bullet. No discernible difference in group sizes at 100 or 200. About half my groups overall were outstanding and half were just alright, but both of these bullets are proving to be superbly accurate then I do my part. Both are jumping almost a tenth of an inch but both seem to be very, very tolerant of that. I've shot under a quarter minute with both several times each. I find that worth saying since I'd read early on about the ABLR being inconsistent and/or fussy, especially about jump. The accuracy nodes are equally wide on both, the ABLR has been very unfussy (AFTER I laid sufficient copper in the barrel, it was bad before that.) I know its use on game isn't as advertised but it's been very friendly to work with. I'm looking at one group right now that's under a tenth of an inch, and all of the ABLR groups today showed almost no vertical spread, which tells me it's accurate enough that it's the best indicator I have about my own input.

I sidetracked myself a little there, I started that paragraph to ask about a problem I DID have with the 168 ABLR, but I think it's my method not the projectile. When I was shooting the crimped shells I happened to be shooting rather rapidly to test that skill and this happened twice: 1st shot fine, second shot fine, 3rd shot hard bolt lift. Not hammer-worthy by any means but VERY firm with a string ejector mark, as in any more and I'd have been missing a primer. This is almost 2 grains below where I got the beginnings of an ejector mark in similar ambient conditions. Now there are several things contributing: more copper in the barrel than when pressure testing, close successive shots, a barrel I hadn't let cool beforehand that was getting too hot, and a decent crimp. Are these things combined enough to cause that spike in pressure or am I missing something major? I know it's right in the middle of the pressure Venn diagram but it was a surprise to have such a strong result. Another surprise is that under those conditions the gun was very, very accurate. My experience with getting to that danger threshold is that the groups will open up erratically and do crazy new things. The same thing happened once to a much lesser degree with one 180 ELDM group as well. Is a hot barrel or a crimp just that much more of an influence than I thought?

Anyway I hope everyone is well. I hope to share some terminal ballistics in a week. My permit is for an immature bull or adult cow, truly a medium of the medium in terms of game weight. Since I didn't practice I'll be shooting within normal ranges at moderately built animals, but I'm curious to see any results. The recoveries I've been involved with were all whitetail deer shot at close range with 30-06 with heavy-ish but violent bullets. The old aluminum-tipped winchesters, core-lokt, and such.


13 Oct 2021
@ 12:53 pm (GMT)

Nathan Foster

Re: 180 ELDM (.284) notes and pressure questions
Hi Jake, thanks for sharing your results.

Its hard to say what was causing those pressures. A crimp can go either way depending on various factors. If its a regular load with a bit of a jump and stout brass, the crimp can rob a bit of energy from the load, seen as lower velocities over the chrony. In other instances, it can raise pressures.

Note that the Lee die does deform the body of the projectile quite a bit. It does of course sort itself out within the bore but is something to be aware of.

Inconsistent ignition is another factor as a result a weak mainspring. Primer seating depth and tension go along with this.

A slow and heavy build up of copper may lift pressure, but normally this comes on slowly and you'll see the groups change accordingly.

A chrony would be most handy for this, just as an additional tool.

So many factors. There are for example a number of smiths polishing the daylights out of both bores and chambers. If the chamber is polished high, the case will sometimes grip and sometimes slip. When it slips, thrust increases to the rear. But all of this is just theory with regards to your rifle and without a detailed investigation.

In any case, you are probably already away by now. All the best for the hunt Jake.
13 Oct 2021
@ 03:16 pm (GMT)

Jake Carey

Re: 180 ELDM (.284) notes and pressure questions
Thanks for your reply Nathan. I had no idea the crimp could actually sap energy, especially in thick brass, that's interesting. And a good reminder about copper buildup, I should know that by now, I had that happen once before. I think right now I can call them safe accurate loads and chalk it up to a hot barrel being a main, proximate factor. And I'm reminded I meant to all hell to poly pad that chamber before I put the barrel on, I can't remember if I did.

Anyway, I'm off tomorrow after a delay, thanks for the good wishes.


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