300 whisper super-sonic load range results

[kurtz]

Went to the range this weekend to test some super-sonic loads and came across something interesting and need some advice….may be a case of reloading basics but I had not picked up on it until recently….I have been working up super-sonic loads using 110 and 125 grain bullets with H110 powder….The brass that I have been using is commercial Winchester formed with Hornady 300 Whisper dies and trimmed to 1.355”…I had hit a max load at 2340fps with the 125 grain bullets and a little over 18 grains of H110, bolt was tight coming out of battery and primer was flat….during reloading I would full-length size the brass and tried different overall lengths to see how it affected accuracy and pressure indicators….over the last few weeks I purchased a neck-sizing die to see if that would help accuracy….not only did neck-sizing the fire-formed brass help the accuracy but I can now drive the 125’s over 2450fps and 110 VMAX over 2640fps with right at 19 grains of H110 and no signs of high pressure, bolt lifts easy and edges of primer are round with no extruding of metal around firing pin strike…..has anyone else seen or is it common for pressure indicators to drop so drastic with neck-sizing fire formed brass?

[320pf]

Kurtz,

I think is has to do with the headspace. When you first form the brass you set the headspace on the cartridge. If the headspace in you rifle is a bit longer than the die, every time you shoot the brass the cartridge gets fire-formed to the exact chamber dimensions. When you full-length resize the brass to reload it you push the shoulder back the the original position.

With a slightly long headspace, when you fire the round the cartridge gets slammed back into the boltface and this flattens and primer and deforms the brass (simplified description). I think this is also why some people say that they can load hotter loads on once fired brass.

Try this experiment. Start with a 223 case and trim it to approximate length, then run it part way into the sizing die... try the cartridge in you gun. Initially, the bolt will not close on the round. Take the same cartridge and resize it again after screwing the sizing die down a bit. Do this until you can just close the bolt on the cartridge with only a slight resistance. This should be the exact headspace for your chamber.

Set and lock the sizer die down and from some brass. Try working up some max loads with this brass and see if you get similiar results that you get with the once shot-neck-sized only brass.

Good luck with the experiment!

320pf

[kurtz]

320pf,

Thanks for the info, headspace sounds like the answer....makes sense now that I think about it....for about the last year I had been full-length sizing and had never tried moving the shoulder/die up more that the die maker recommended one half turn up from top of ram stroke....

On a side note, I found that by neck-sizing only about 75% of the neck and leaving the 25% at the shoulder fire formed to chamber size my groups got considerably better, I guess it helps center the neck in the chamber better or causes less tension on the bullet??

Thanks again....I'll try a few different full-length shoulder heights to see what fits....

[pug]

I would say he hit it on the head about the head space also. Like said back the die off until the bolt will just close with one finger for proper headspace or at least thats my gauge. You may possibly once again loose some accuracy by fl sizing even if you do back it off because it is still sizing the body a little. For a bolt gun neck sizing is usually the way to go for best accuracy because the shoulder doesn't get blown out during extraction like in a semi and the case body is a perfect fit to the chamber. Happy testing :).

[320pf]

Kurtz,

I have a question/request for you. Tell us about your barrel and gun. length, twist etc...

thanks
320pf

[kurtz]

320pf,

The rifle is a CZ527 laminate stock with a 24" 1:11 PacNor barrel and a Leupold 6.5x20 (pictures of rifle and range results are on the Quarterbore photo server 300 whisper section)....I had PacNor reduce the throat length to use 110 to 125 grain bullets....my finished loads with 125 TNT's will touch the riflings at 1.595 measured at the ogive...my SSK rifle loaded with 220SMK touch the riflings at 1.670 measured at the ogive...

thanks for all the feedback and questions,
kurtz