OCW interpretation

[Twitch2120]

i have been trying to force a load with CFE for a while first using 178 AMAX and now 175 SMKs. i see nothing here but perhaps a more trained eye can spot something. all were fired round robin style with 10 min cool downs inbetween shots except the 3rd shots (and 4th in some cases) which had to be fired in a string. pop up thunderstorm. a bit concerned the best group of the bunch is .3 past book max. the 48 gr load POA was the diamond tip.

 

[Pinecone]

I would try some more in the 47.5 to 48.0 range. Group center POIs are similar.

Then work the seating depth.

 

[HobbyShooter]

You'd want all your groups to have the same number of shots. Pick either three shots or four, but I wouldn't do both. Also, the 48.0 charge should have been 48.1 so all the test charges are evenly spaced.

The results are a little odd. Normally you'd see accuracy and scatter nodes about 1.5% apart, but it seems to alternate starting at 46.9. As long as you weren't seeing any pressure signs (I usually see ejector pin marks first), I wouldn't worry too much about what book max is. If you're rifle, brass, primer, or seating depth is different from what they used to come up with their max, then your own max charge may be higher or lower.

I've found that my tests are easier to interpret when my seating depth is set to where the ogive of the bullet is just touching, or just barely off of the lands. I tried .020" jump at first and was pretty confused by what I saw. I'd redo the test with only 3 or 4 shot groups, neutral seating depth, and hope conditions allow you to finish round robbin.

 

[Dan Newberry]

CFE223 is what I call a "hold my beer and watch this powder"... I know folks are getting super-fast MV's... and such. But I continue to wonder how well these powders will behave long term, and in various environmental conditions.

I've seen very (very) few examples of this new generation of powders working well for folks. Sometimes people get good results temporarily, then next time to the range or field, things get squirrely. I'm not speaking of pressure problems (but pressure swings, when you're driving something like you stole it are always going to be on the verge)... I'm talking about accuracy going to hades, one trip to the next. Long range vertical spreads may also be an issue--if not on this range trip, perhaps the next, or the one after that...

I think I'd look for a kinder, friendlier powder for your .308. You will find great accuracy nodes using the 178 AMAX using Varget at 43 to 43.3 grains in Winchester brass... with 4064, the same charge should work. 42.0 grains of IMR 4895 is a solider performer with this bullet. And even W748 at the charge areas you'd use with 4064 or Varget will serve you well.

Dan

 

[Twitch2120]

i already have a great load with the 178 amax and imr 4064. unfortunately 4064 and 178s are hard to come by right now so i figured i would try working with something i had a surplus of, being 175 smks and cfe223. the reason for some shots having groups of 4 was for the final group if something seemed to show itself. i didnt see anything so figured an extra round wouldnt hurt, particularly if i pulled one without it being really obvious.

 

[Dan Newberry]

try working with 47.8 then, and see if it'll repeat. Change the seating depth in and out by .005" and compare those group sizes to another 5 shot group with the original test length.

There ought to be another node at 46.5 grains, if there's indeed an OCW at 47.8, so you may try shooting that area if 47.8 seems too hot.

Good luck.

Dan

 

[Twitch2120]

Excellent, thanks for the info.