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

[320pf]

Kurtz,

After I sent my post I flashed that I had seen load similar data on:

http://reloadersnest.com/frontpage.asp?CaliberID=135

to what you gave in your original post above. Then I remembered that those loads are yours.

I did some interesting experiments this weekend as well. I have a 20-inch 1:10 twist AR15 barrel on loan so I re-shot all on my 155 grs Palma loads from a 16-inch barrel posted on:

http://reloadersnest.com/frontpage.asp?CaliberID=135

By the way the "loaner" barrel shoots VERY VERY WELL!
One more set of experiments this weekend and I will get it back to the owner.
(Thanks RR.)

Adding 4-inches of barrels adds anywhere from 60 to 80 fps. Also seating the bullets about 0.05-inch deeper into the case adds about 50 fps but also seems to rise the pressures as well. It seems that there is a "sweet spot" as far as bullet seating depth and pressures/velocities go... too far out touching the rifling and the pressures will go up and too far into the case and the pressures will go up. The actual position of this "sweet spot" is dependent on the throat/freebore of the chamber. This is how Roy Wheatherby got the high velocities our of his rifles.

It is always fun to learn new things

320pf

[kurtz]

I am in the process of building a 20" AR also....It's going to be kinda of an odd ball.....something like a 300 whisper XL for super-sonic 110 to 125's.....Pug had listed a post a while back concerning a longer cartridge similar to the 300 whisper.....most of my 300 whisper brass comes out to around 34.4mm....HK developed a 7.62 subsonic load a while back based on a .223 case that works out to 7.62x37mm.....the load that I'm working on for my AR is based on a .223 case and works out to 7.62x39mm....I have formed up dummy loads and am having a reamer cut and getting all of the parts together to cut the barrel and assemble the upper....hope to have it running in two to three weeks...am trying to decide on a twist for the barrel, your last post on the 1:10 has me leaning in that direction....I have also seen the additional length adding several fps....the difference between my 16" and 24" bolt guns is about 200 fps average on super-sonic loads for a given charge....you wanna hear something funny, the 16" bolt gun shoots sub-sonic loads about 100 fps faster than the 24" gun with a given charge...

kurtz

[320pf]

Kurtz,

If you want to put together the fastest barrel that you can use a 3 or 4 groove barrel or better yet a Polygonal barrel with a 1:10 to 1:12 twist. You do not want to put too much of the powder energy into twisting the bullet like a standard 1:8 300 whisper barrel.

I have been doing a bit or research on Polygonal barrels. David Tubbs one of the top high power shooters uses a polygonal barrel. They are suppose to be very accurate and produce the highest velocities. They also do not foul as easily. Pac-Nor offers polygonal barrels if you are interested. Another source for a polygonal barrel is Schneider Rifle Barrels. This is who Tubbs uses.

I am pretty convinced that a 20-inch polygonal barrel is the way to go to get max. velocities out of an AR.

I am very interested in how the whisper xl turns out that you and Pug are experimenting with. Let me know how it works out.


"you wanna hear something funny, the 16" bolt gun shoots sub-sonic loads about 100 fps faster than the 24" gun with a given charge..."

I can believe that. In subsonic loads the gas pressure drops off to the point that the extra 8-inches add enough friction that it actually slows the bullet down. I bet that there is a lot less report with the 24-inch barrel than the 16-inch barrel (sans suppressor for the comparison)

thanks

320pf

[kurtz]

I had thought about trying a polygonal barrel but was a little chicken until I learned more about them....I knew that HK built production pistols and rifles with polygonal barrels but had not really thought about it until PacNor cut my last barrel and I saw polygonal listed as a barrel option......Hey, if Tubbs is using one it's kinda hard to argue with that, that guy is so talented I have a feeling if he was using a drinking straw and a hand full of peas he would be tough to beat....

The 220 SMK sub-sonics in the 24" 1:11 barrel kinda make a loud POP not so much a BOOM like in the 16" and yaw really hard at 100 yards....I was shooting on a rainey day a put one through the 100 yard 1/2" plywood target frame and could hear the bullet flipping/cutting through the knee deep grass all the way out to impact the 200 yard dirt berm....I walked out and recovered the bullet from against the berm....not a dent ding or deformation on it, besides the rifiling marks it looks like you could reload it again....If any interest in seeing it I can post a pic...

kurtz