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> Precision long range hunting and shooting
> 7mm 180 Eld-m
7mm 180 Eld-m
@ 03:07 am (GMT) |
Brent WatkinsBuilding a 7mm Practical. I've got the reamer from Dave Manson and a Kraiger 1:9 HV contour barrel. My question is will the 9 twist do the job for stability? Or won't it stabilize it enough to beat the 162 Eldm. I have a lot of experience w the 162 amax out to 1300 yards. But no experience w this new super bullet. I'm not new to 7/300 Win Mags only this version is new to me. |
Replies
@ 07:58 am (GMT) |
Nathan FosterRe: 7mm 180 Eld-mHi Brent, the 1-8 Kreiger is a very finicky bore at magnum speeds. The reason why such things can and do happen was covered in the Accurizing and maintenance book.The 180gr ELD-M stabilizes just fine in the 9 twist Practical. My comments regarding twist rate in the 7mm Practical article still stand. Accuracy is outstanding in our 9 twist True-Flite bores, all other factors (epoxy bedding etc) being equal. The 9 twist is the most versatile in the Practical, allowing hunters to use a wide range of projectiles. I covered the ELD-M BC's in my latest blog post (you can download this as a PDF from the blog page. Expect sweet spots at 3000fps. If using the Hornady 4DOF calculator, use 1.04 as the axial form factor (thanks Chris Murphy for doing the initial field check on the form factor- you were quite right Chris). This form factor also puts it in basic agreement with Sierra software. As for beating the 162gr, the basic increase in weight and SD show increased wounding and penetration at both close and long ranges which goes beyond basic long range BC performance. BC is only a part of the equation as I have reiterated in the Cartridges book. Steph (in her Rem Mag 9 twist) and I have been testing this bullet inside and out. Of late, I have been shooting it pretty much every day. Hope that helps put you at ease. |
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@ 09:44 am (GMT) |
Nathan FosterRe: 7mm 180 Eld-mSorry, I want to go into this a bit further for 7mm Practical users. These notes do not apply to the Rem Mag.At 3000fps and with a 9 twist, you can start by inputting 1.02 into Hornady's Axial form factor tab (halfway between Hornady's recommendation and Chris's findings which work well in a variety of sevens. In a manual program, try inputting .798 to 2500fps and .777 below this (average .788) for the same 1.02 4DOF outcome. If you intend to shoot past 1350 yards, you can play further with other numbers such as dropping to .748. My blog PDF is an average and not specific to the Practical, best suiting the more common Rem Mag. Any minor discrepancies in turret calibration will obviously effect final outcomes. The difference between blog numbers and specific Practical BC's (including variations with Hornady's axial form) are around a half minute or 6" at 1200 yards. I have a feeling that the total potential variation from rifle to rifle versus MV's and twist rates is around 10" dispersion at 1200 yards. But as suggested, turret calibration can muddy these waters. One could easily confuse the two and by fluke, correct turret errors via axial form tweaks. It has taken me a heck of a lot of shooting to get to know this bullet in detail. The 285gr A-MAX was much the same and I felt very much exposed when I published the BC (Cartridges book) as .820 when most other shooters were stating .720. For a while I was sure that I must have done something wrong but I had to stick with and eventually publish my results regardless of what others were saying. Then finally Hornady revised the published BC to .820 following its rebranding. Another factor I found is that in the Practical, the 180gr ELD-M seems very sensitive to angles, more so than other combos as far as actual field work goes. If you do not get your angles just right, it may shoot clean over your target. |
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