.308 168gr SMK and IMR 4064 different charge ranges???

[critrxdoc]

Hello all. Experienced pistol reloader but new to .308. Have 168gr SMKs and IMR 4064

IMR data set charge range for 168gr is 41.0 to 45.9

SMK HPBT 168gr data set charge range is 37.8 to 43.4

Why such a drastic difference in charge ranges and where do I start to work up a load for my 700?

 

[HodgdonExtreme]

Different bullet lots, powder lots, test barrel, chamber, pressure reading equipment and lawyers is why you see differences from one manual to the next.

45+ of 4064 sounds like a lot based on my experience with 4064, but maybe that'll be OK.

Start around 42 or 42.5, and work up in .3 to .5 increments. Stop as soon as you experience a stiff bolt lift or an ejector mark on th e case head.

I run mostly 175 sierras, and generally they shoot best around 43 or 43.2 in Lake City brass. A solid load but not "max". You oughtta end up ~.75-1gr hotter.

I might add: The sierra load manual is notoriously conservative on charges. Hodgdon/IMR is generally more "liberal" and closer to what I think is probably max safe. Always (ALWAYS) exceptions though.

 

[Twoboxer]

Since you have the exact components, you may be interested in this thread, particularly Post #11. 168gr FGMM (Federal brass, 168gr SMK, and 42.7(5)gr IMR4064) shoots very well out of many rifles . . . and certainly does out of mine. Interesting thread in any case.

 

[nso123]

Mine likes 42.8 grains of IMR 4064, and chronos dead on with FGMM and has same point of impact. Only difference is it doesn't cost me over $1.00 per round.

 

[StampCreek]

Yeah, with FGMM or any heavier brass (less capacity) start low. But 42.7-42.9gr is perfect.

 

[critrxdoc]

Thank you so much! Sounds like 42 as a start and will work up in 0.3 increments. Planning to load 5 rounds each and pattern to find the sweet spot!

 

[ptaylortx]

43.6 is the sweet spot for mine with 175 smk. I worked up to 44.5 with no pressure signs. So I would expect you would be safe with 168 around that range

 

[pawprint2]

Sierra lists max load at 43.4 grains, and 2700fps, 41.5 is a well known "accurate load" and is listed at 2600 COAL 2.800. FOR THE 168SMK, when you move up in weight to 175 Sierra lists 42.8 as the MAX load. IMHO, when ever one is working a load up to or beyond maximum published data(two or more sources, with different Max loads), always consider the lower maximum charge as a place to start LESS THAN!

 

[Prebanpaul]

I loaded mine with 43 grains and 2.805 over all length with spectacular results today.

 

[BCP]

Those two sets of data are with different brass, heavier brass for sierra (they used Fed brass) means lower charge weights at max pressures. Starting at 42 is a safe bet no matter your brass type with either a 168 or 175 grain bullet.