Help reloading 300 win mag

[Plinker 73]

I’m not new to reloading , been doing it for over 50 years, just mot for long range. I haven’t begun to find the proper oal for this gun. What I cant understand is the load developed by CRANE as the Mk 248 mod 1 round calls for an oal of
3.500 “ . If I measure a Federal Mk248 Mod 1 round it measures 3.340 “. My question is why would the round be shorter than spec. And possibly sacrifice accuracy by being that far off the lands. Any help to understand this will be appreciated.
I am new to reloading the 300 wm round.
Thanks
Rad

 

[99106]

Stop worrying about noise. Go watch Erik Cortina's videos. Find what your gun likes, what you can run based on mag length or single load, and just shoot. Start at jam and work back or book oal for your bullet and work up to 5 thou short of jam. The answer to your question is here. https://www.americanrifleman.org/articles/2017/5/24/unsung-hero-the-mk-248-mod-1/

 

[TheOfficeT-Rex]

The SMK bullet that they use is jump tolerant, so it probably does not sacrifice much accuracy with increased distance from the lands.

IIRC, none of the contract ammo is sold to the public - so unless it fell off a truck, you may have a SAAMI spec commercial round.

 

[nn8734]

I’m not new to reloading , been doing it for over 50 years, just mot for long range. I haven’t begun to find the proper oal for this gun. What I cant understand is the load developed by CRANE as the Mk 248 mod 1 round calls for an oal of
3.500 “ . If I measure a Federal Mk248 Mod 1 round it measures 3.340 “. My question is why would the round be shorter than spec. And possibly sacrifice accuracy by being that far off the lands. Any help to understand this will be appreciated.
I am new to reloading the 300 wm round.
Thanks
Rad

I copied the Mk248 mod 1 using a FC case, 215 mag primer, 76.2g h1000 and a 220 smk. I was jumping .020” and launching it at 3000 fps with no pressure signs. The overall length was just under 3.550”

This was in my mk13 mod 5 reamed with the mk248 mod 1 reamer. I would use extreme caution trying to duplicate this unless your chamber is designed/cut to handle it. Otherwise work up. If you want more specific info, PM me and I’ll see if I can help out...

 

[TxWelder35]

Johnnys Reloading Bench on YouTube did a clone of this round. Easy to figure out. Contract docs are public

 

[Plinker 73]

Thanks for all the info. FYI: I an shooting this in an actual MK 13 MOD 7 clone rifle . I was just curious about the differences in the CRANE spec and what I am seeing in a box of issued ammo and what I am reading about OAL on this board. I am using h1000 powder and smk bullets in once fired FC military brass to developer my loads. I didn’t ask the gentleman who provided the ammo with my rifle where it came from. I was very grateful to have it.

 

[TheOfficeT-Rex]

I'm not saying you got commercial rounds in a military box, but I am saying those are commercial length and not contract length.

Does it matter? Nope. Especially if you are going to reload after you fire them. Like @TxWelder35 said, JRB did a pretty decent teardown for his video if you want to straight up clone the contract rounds.