recently loaded up some .223 69gr smks with h4895. used the coal i used for a couple years to mag length of the rifle with cfe223. used hodgdons load data saying 24-26gr for the h4895 and 69gr bullet in .223. loaded up a ladder test between these charge weights in 0.2gr increments and got pressure signs around 24.4 or 24.6. my lee book also shows 24-26. just wondering what other manuals say or what experience anyone else had with this powder and bullet weight.
also did the same with 50gr, not sure the exact charge amounts now but i loaded in the same way. min to max in 0.2gr increments. about the same result 2 or 3 loads and stopped due to pressure signs.
What has magazine length got to do with where the lands are?
Measure the CBTO for your rifle with each bullet type and bullet weight you want to reload for; they can be a LOT different from one another.
I use H4895 exclusively in my .223 bolt rifle. Looking at my notes, with 69gr SMK, I started to get flattened primer and slight cratering pressure signs when I got to 25.0 gr to 25.1gr with definite over-pressure signs at 25.3gr. I stopped and pulled everything above this, dropped back to 23.0 and went to 25.0 at 0.2gr increments to find my best charge weight. I then seated bullets with the best charge weight I found for my rifle starting at 3-5 thou off the lands and going all the way to 30thou off the lands at 5 thou steps. Best accuracy
FOR MY RIFLE, using PPU brass, S&B primer and 69gr SMK is at 20 thou off the lands with 24.3gr H-4895. I have tried all sorts of bullets and worked up quite literally hundreds of different loads and seating depth combinations but the absolute best is with the 69gr SMK. Second best is with Barnes 69gr Match Burners. Incredibly good - at least for me in the .223.
As an aside, I haven't managed to find a good accurate load for my 6.5CM with the 140gr Barnes MB. I was hoping based upon my results with the .223. Again, the 140 and particularly the 142 SMK are my go-to for it with H4350 although the HRN ELDM 147gr are pretty decent as well.
I have found a pretty decent load and seating depth for the Barnes 175gr MB and Varget in my .308 which I am currently working on refining.
And now to maybe get some comments, changing my seating depth by up to 25thou from almost jammed, to needing binoculars to see the lands, on each of these rifles while holding the charge steady results in a maximum of about 10fps average change. That is pretty much the exact same change in velocity I see from a 0.1gr change in charge weight on the .223 to a 0.2gr change on the 6.5 or .308. Repeated over hundreds of tests (around a thousand rounds now) since I chrony everything going downrange with my orange plastic box (LabRadar). Finding the proper seating depth after finding the proper charge has paid off immensely in my accuracy, making groups go from around MOA to sub 0.5 MOA. Groups are consistently in the 0.3 or less to under 0.5 MOA range with the .223 at 300 to 500m under good weather conditions and in the 0.4 at best to 0.6 MOA range with the 6.5CM and .308. Maybe I am flinching a bit. I'll keep working on it.
I guess that if you are going to be feeding from a mag then it is important to keep your rounds at a length they will fit. This will become your maximum seating length as long as it is less than the maximum length resulting from the CBTO measurements. I put single shot followers in my rifles so I don't worry about the magazine length.
