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SHERMAN MEGA LINE

Has anyone done a 338 mega on a 3.100" box length yet? My rifle started as a 6.5 PRC with a box length of 2.990" and my smith has now installed a 3.100" Wyatt's box for chambering the 338 max. But I am thinking of going on up to the 338 MEGA if it's more worth it with a magazine box that short 3.100"? Planning on shooting either the 250 Berger EH's or the 230 ELD-X's?
 
I built mine on a Tikka action and using Mountain Tactical bottom metal and mags. The inside length of those is 3.418" - FYI
I've got a feeling that it would probably be a smarter decision going with the max sized case over the mega in a 3.100" maximum length. I just think the mega case dimensions are much more generous as far as powder capacity at least. I just don't know how much it would hinder the velocity of a 338 mega shooting a 250 Berger at a COAL of only 3.070" or thereabouts to fit in my shorter magazine versus a normal COAL of 3.200" plus?
 
I've got a feeling that it would probably be a smarter decision going with the max sized case over the mega in a 3.100" maximum length. I just think the mega case dimensions are much more generous as far as powder capacity at least. I just don't know how much it would hinder the velocity of a 338 mega shooting a 250 Berger at a COAL of only 3.070" or thereabouts to fit in my shorter magazine versus a normal COAL of 3.200" plus?
my buddy and I that both built 338 Megas are running 250 grain bullets at 2900ish
 
my buddy and I that both built 338 Megas are running 250 grain bullets at 2900ish
I'm also in Cache Valley, just got my 338 carbon blank in yesterday. It's 21". What powder are you running? Standard reamer or long throat? If its not too much to ask, I would appreciate any load data you have.
 
Hey guys, I'm gonna be loading up some fireforming rounds tomorrow for 338?Mega, long throat. I'll jam 285 ELD-M's .020, and probably use N160 to fire form. Anyone know a good safe place to start with this combo for forming my cases? I do have other combos available, but this would be my preference, as these bullets and powder I won't be using for load development.
 
I have some data for a new 300 Mega build I thought I'd share with the group; happy Father's Day to all my fellow dad's out there by the way! So after fire forming my brass I began load development right after lunch time this afternoon. It didn't take but about 4 different load tries and I landed on a great consistent load. I also weighed out H2O capacities for a piece of twice fired 300 WSM brass I had (Norma brand) vs a twice fired piece of 300 Mega brass. I will be posting a picture of my findings but basically the 300 Mega has 5.4 grains more case capacity than the 300 WSM Norma brand brass. My rifle is built on a Defiance XM length medium action of 3.200" with a 24" Bemchmark carbon wrapped barrel 1 in 9" twist. The load I settled on was 70.0 grains of RL-26 with a Berger 230 grain Hybrid Target bullet giving average muzzle velocity of 2,794 FPS with single digit ES. Will post pics of the Garmin chrony data as well as one of the groups I shot with it today (not cherry picked; just an average sized 3-shot group with this load). Shot a couple other groups also with one being right at .4" and one being right under a 1/4". So this is actually the worst group of the 3 measuring .44" at 100 yards. Scope on the rifle is a Nightforce NX-8 4-32 MOAR reticle FFP. I found no excessive pressure signs at all at 70 grains RL-26 and probably could go another grain higher comfortably but single digit ES and consistent .4" MOA accuracy all the way out to 725 yards (that's as far as I shot it today) is really good numbers from a shorter magnum like the 300 Mega. Anyways, happy Father's Day guys and here's some pictures of my 300 Sherman Mega.
 

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