Question, guys. I have a 6.5 cm with a 27” criterion barrel. I know guys like Nathan Foster of Ballistic studies say different powders for longer and shorter throats. I have been using IMR 4350 and have Varget. I see almost everyone says H4350, something I don’t have. It doesn’t seem to matter. Any input would be appreciated. It seems like a must have for my .270 win and creedmoor.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
Different Powder for Longer Barrels?
- Thread starter WillyG
- Start date
powders
Willy -
Howdy !
The rifle's "expansion ratio " is basically what you are starting to talk about, here. To quote reknowned ballistician Homer Powley, from the Guns & Ammo 1974 Annual:
" Expansion Ratio determines how much of the chemical energy, is converted to kinetic energy ".
He also stated: " For best efficiency, a gun should use as much powder as it will hold ".
For a given calibre and case capacity, the way to change the rifle's expansion ratio is change the barrel length.
For a given calibre and barrel length, the way to change the rifle's expansion ratio is change the case capacity.
Classic expansion ratio math does not factor-in bullet wt ( FWIW ). Total
I'm a big fan of shooting "high load density". My varmint/target rifle is chambered in my " DEEP 6 " wildcat. Case capacity is 51.2gr H20.
Compare to .243Win @ 54gr H20, and 6mm Rem @ 55 gr H2O. For loading a 6mm cartridge of this case capacity, a lot of shooters would go w/ H4350. Temp stable, and high velocity would be pretty well assured.
My rifle has a 29" SS 1-8 Broughton. For max load density, and to exploit the capabilities of hte 29" barrel length; I went w/ Powley's recommendation.... fill the case w/ powder. To do this and still have safe pressure, I went slower than H4350 on my burn rate choice(s). I was able to completely fill the DEEP 6 case w/ IMR7828, under all 6mm bullet weights ( moslty VLDs ) from 88 - 107gr... and had great accuracy w/ safe pressures.
I was able to very-nearly fill the case completely.... using RL-22. In fact, I pretty much could shoot the same RL-22 charge wt under the same bullet weights mentioned;
and obtain good accuracy. I only had to slightly adjust the charge .1 or .2gr for each separate bullet wt; to tighten the groups to best obtainable. I shot my best every 100yd 5-shot group using RL-22 and Berger 105VLDs. After reading that RL-22 " burns " really hot ( compared to some other powder choices ), I decided to try out
other powder choices around this burn rate range.... that are temp stable and could pretty much fill the case and still have safe pressures. ( I am working w/ the
Sierra 95 T-Mk at the moment ).
I am doing a 3-way run-off between loads using RL-22, RL-25; and RL-26. For my shooting needs, I don't have to reach any certain velocity. I want useful vel along w/ great accuracy. And no, I have no chrono numbers to pass along. Once I find the accuracy I want, I'll chrono that load.
My point:
I do think that long(er) barrel lengths can really perform for you, when an informed powder choice is made.... one that exploits the powder combustion gas expansion opportunity these longer lengths can offer.
With regards,
357Mag
Going w/progressively longer barrel length options for a given chambering ( and yes... a given bullet ) allows one to shift to selection of slower " burning " powders.
Willy -
Howdy !
The rifle's "expansion ratio " is basically what you are starting to talk about, here. To quote reknowned ballistician Homer Powley, from the Guns & Ammo 1974 Annual:
" Expansion Ratio determines how much of the chemical energy, is converted to kinetic energy ".
He also stated: " For best efficiency, a gun should use as much powder as it will hold ".
For a given calibre and case capacity, the way to change the rifle's expansion ratio is change the barrel length.
For a given calibre and barrel length, the way to change the rifle's expansion ratio is change the case capacity.
Classic expansion ratio math does not factor-in bullet wt ( FWIW ). Total
I'm a big fan of shooting "high load density". My varmint/target rifle is chambered in my " DEEP 6 " wildcat. Case capacity is 51.2gr H20.
Compare to .243Win @ 54gr H20, and 6mm Rem @ 55 gr H2O. For loading a 6mm cartridge of this case capacity, a lot of shooters would go w/ H4350. Temp stable, and high velocity would be pretty well assured.
My rifle has a 29" SS 1-8 Broughton. For max load density, and to exploit the capabilities of hte 29" barrel length; I went w/ Powley's recommendation.... fill the case w/ powder. To do this and still have safe pressure, I went slower than H4350 on my burn rate choice(s). I was able to completely fill the DEEP 6 case w/ IMR7828, under all 6mm bullet weights ( moslty VLDs ) from 88 - 107gr... and had great accuracy w/ safe pressures.
I was able to very-nearly fill the case completely.... using RL-22. In fact, I pretty much could shoot the same RL-22 charge wt under the same bullet weights mentioned;
and obtain good accuracy. I only had to slightly adjust the charge .1 or .2gr for each separate bullet wt; to tighten the groups to best obtainable. I shot my best every 100yd 5-shot group using RL-22 and Berger 105VLDs. After reading that RL-22 " burns " really hot ( compared to some other powder choices ), I decided to try out
other powder choices around this burn rate range.... that are temp stable and could pretty much fill the case and still have safe pressures. ( I am working w/ the
Sierra 95 T-Mk at the moment ).
I am doing a 3-way run-off between loads using RL-22, RL-25; and RL-26. For my shooting needs, I don't have to reach any certain velocity. I want useful vel along w/ great accuracy. And no, I have no chrono numbers to pass along. Once I find the accuracy I want, I'll chrono that load.
My point:
I do think that long(er) barrel lengths can really perform for you, when an informed powder choice is made.... one that exploits the powder combustion gas expansion opportunity these longer lengths can offer.
With regards,
357Mag
Going w/progressively longer barrel length options for a given chambering ( and yes... a given bullet ) allows one to shift to selection of slower " burning " powders.