Hey, has anyone shot mk248 mod 0 ammo from their 300WM. I recently found some for a decent price and got a few hundred rounds to try out. It all failed spec due to it being 3.470 instead of 3.340 oal.
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MK248 Mod 0 Ammo?
- Thread starter pewpew300WM
- Start date
My understanding is that it exceeds SAAMI pressures too, .gov wasn't worried about reloading it so some flattened primers and swipe marks were ok.
I’ve cloned both mk248 mod 0 and 1 using 77.6 and 76.2 grains respectively h1000 in a Fed military case and 215 mag primer when I had my Mod5 as well as shot the real stuff and all were lasers but use caution if you don’t have a chamber cut to handle the pressures. Neither my loads nor the factory stuff exhibited any pressure signs. Pressures are said to be north of 78,000 psi peak in the chamber. Standard SAAMI is set up for 62,000 psi, I believe.
My mod 5 had the Mk248 mod 1 chamber. If you have a standard SAAMI 300wm chamber, I would advise using extreme caution.
My mod 5 had the Mk248 mod 1 chamber. If you have a standard SAAMI 300wm chamber, I would advise using extreme caution.
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I’m just going by what the seller told me that the oal was 3.470. I haven’t measured it myself.
I just have a Rem 700 action, planning to have it trued up and match chambered here in the next few weeks.
specify you want the mk248 mod 1 chamber if you want to shoot 220 SMKs at or close to 3000+ feet per second safely. If you want to drive something like a Berger 215/230 at similar velocities safely, work with the gunsmith to select an appropriate reamer.
With the 220 smk I was jumping .020 and had plenty of room in the mag but that reamer wasn’t as ideal for the 215 as the jump was around .150” for it to fit.
The right reamer/chamber really brings the win mag into the 21st century and makes it comparable to the other modern 30 cal magnums in terms of performance potential.
No reason to use an old school SAAMI reamer if you can avoid it, IMO.
I typically shoot 200grn eldx ammo but found the mk248 mod 0 for a dollar a round and figured it work for practice ammo and get me a decent amount of brass stashed up for when I start hand loading. I doubt I’ll ever shoot over 200s for now. That’s why the smith recommend the match reamer for now.
I may be wrong, but I think you’re misunderstanding what nn8734 is trying to tell you. Mk248 is a very hot load. Because you have a bunch of mk248 that you want to shoot, you need a mk248 chamber in order to be safe. If you get a tight chamber, and jam a mk248 load into the lands, it could cause damage to you and/or your rifle. It has nothing to do with “what you typically shoot”. It’s about being safe.
Hi,
I would suggest you look into finding a new smith that understands the interior ballistics of the Mk248 ammo.
Sincerely,
Theis
Practice Ammo? lol.
Agree with @THEIS in that if your smith knows you plan to shoot mk248 loads and is recommending some off the shelf match reamer, it’s time for a new smith.
Contact LRI or Raven Rifles. Both of these shops understand those loads and can chamber your rifle with the proper reamer.
I just talked to the guy with the ammo and this is what he sent me. 190gr SMK, FC brass, GM215M primer, Reloder 22, approx 2925 fps, 3.470" oal.
The packaging says "Out of OAL SAAMI spec"
That's because SAAMI max length is 3.340 and this ammo is 3.470 by design.
Mod 1 was their attempt to push the cartridge to limits beyond what was practical.
Basically, 220gr loaded longer and a high charge of H1000. Required longer freebore. Some shot in standard chambers and had high pressure. Also, the cartridge had excessive barrel wear.
The Mod 0 pressure spec is 68,000 max (ahead of the case mouth, not conformal). This lot of ammo was at under 64,000.
Hey I don’t want you to think I’m being arrogant or anything like that. I appreciate the advice 100%. I’m just going by what the guy told me. I posted word for word what he sent me below. I want to know before I shoot a round and end up trashing my action in the process.
Hey I don’t want you to think I’m being arrogant or anything like that. I appreciate the advice 100%. I’m just going by what the guy told me. I posted word for word what he sent me below. I want to know before I shoot a round and end up trashing my action in the process.
