Would IMR 4320 do relatively well in the 6mm ARC

[SD guy]

Looking at cleaning up some IMR 4320 That has been sitting on the reloading shelf for a lot of years. Is IMR 4320 too bulky or too slow for the 6mm ARC?

 

[6MMsteve]

I ran it in 223 had a few lbs, it's not temp stable for sure, also ran it in 220 swift and 22250 with light bullets, if your running lighter bullets yes, but maybe some of the other guys with tons more knowledge will chime in

 

[6MMsteve]

I would say yes it's not temp sensative, I ran some in a dasher just playin, and forgot about winter summer loads and had a sticky situation

 

[SD guy]

Comparisons I am seeing Would suggest roughly same charge as IMR4895 to 10% less than Varget. This will be in a bolt gun. Looking at 85 GR to 105 grain with an Emphasis on 85 t0 100 grain projectiles. Happy to be corrected here.

 

[Evan]

My lots of 4320, one from 1991 and the other from 2007 are both very consistent and sit right on top of varget for burn rate. Same grain charge weights yield the same muzzle velocity in both my 22BR and a 6.5x47.

 

[Ned Ludd]

In my hands with .308 Win loads, IMR 4320 was very close to Varget in terms of burn rate and energy. IMR 4320 was more temperature-sensitive than Varget, and it seemed to cause a much more abrupt transition from high-end charge weights to suddenly over-MAX. As long as the [older] Lot# of IMR 4320 you have is still good (i.e. hasn't degraded during storage), it's probably worth a try. My biggest concern would be that it works really, really well, because IMR discontinued IMR 4320 some time ago, and getting more will become increasingly difficult over time, if it can still be found at all. If your immediate intent is simply to use up what you have remaining, try it and see how it works out. However, as a more long-term goal, it might be better to focus on a powder that will continue to be commercially available.

 

[bozo699]

In my hands with .308 Win loads, IMR 4320 was very close to Varget in terms of burn rate and energy. IMR 4320 was more temperature-sensitive than Varget, and it seemed to cause a much more abrupt transition from high-end charge weights to suddenly over-MAX. As long as the [older] Lot# of IMR 4320 you have is still good (i.e. hasn't degraded during storage), it's probably worth a try. My biggest concern would be that it works really, really well, because IMR discontinued IMR 4320 some time ago, and getting more will become increasingly difficult over time, if it can still be found at all. If your immediate intent is simply to use up what you have remaining, try it and see how it works out. However, as a more long-term goal, it might be better to focus on a powder that will continue to be commercially available.

What Ned said is spot on correct!…. I have used a lot of 4320 back in the day but it’s been outta production for quite a while now.
Wayne

 

[SD guy]

Thank you all. I have a couple of pounds of the 4320 that have been stored well. Im opting to use this powder just to use it up I suppose. Ill likely give up 10% velocity give or take. Opened up a can today & smelled strong in a good way. Have some 107 gr Sierras I am playing with at present.

Feeling a bit antsy today I suppose despite our high 20 to 30 mph winds & temps in the low 30's temp's I loaded up a few rounds at 27 grains in the 6 Arc under the 107's at magazine length. Did not bring along the magneto speed so a did not confirm velocity yet. Despite weather conditions MOA seems to be easy achievable from the light contour CZ527. Todays results prove further testing has merit.

 

[bozo699]

Thank you all. I have a couple of pounds of the 4320 that have been stored well. Im opting to use this powder just to use it up I suppose. Ill likely give up 10% velocity give or take. Opened up a can today & smelled strong in a good way. Have some 107 gr Sierras I am playing with at present.

Feeling a bit antsy today I suppose despite our high 20 to 30 mph winds & temps in the low 30's temp's I loaded up a few rounds at 27 grains in the 6 Arc under the 107's at magazine length. Did not bring along the magneto speed so a did not confirm velocity yet. Despite weather conditions MOA seems to be easy achievable from the light contour CZ527. Todays results prove further testing has merit.

It will work fine in it until you run out then grab some varget
Wayne

 

[SD guy]

We will see how obtainable Varget is, When this IMR 4320 runs out

 

[bozo699]

We will see how obtainable Varget is, When this IMR 4320 runs out

I bought -16 lbs last week
Wayne

 

[MrK.]

Anyone try 4320 in their 6ARC yet? I know burn rate charts are rough generalizations but it seems to fall somewhere between Varget and LVR. I know that there are better options out there but I am old and trying to find use for components I have on hand. I have both Varget and LVR as well. My CMMG 6mm ARC upper likes Varget at about 2700 fps, LVR not so much yet...using 95gn SSTs anyway (this rig is a <300 yd deer killer). My old Speer #11 lists 4320 with the 6PPC and 90 grain bullets. I am aware of the different pressure limits with both cartridges but it seems doable. I'm just looking for a starting load, I can figure out where to stop. A 6ARC case will hold about 29.5 grains of 4320 filled to the base of the neck FWIW.

 

[Frankm]

I doubt you ll be able to get enough in the case to get in trouble with bullets from 80-100 grs. I got 28.5 grs of H4895 loaded with an 80 gr Sierra and doing 2950 fps. This is a bolt gun so factor that in. As you know 4320 is slower than H4895. With a 108 gr bullet and 26.5 grs of H4895 I was a little on the warm side but it’s a pretty full case. You might get 27-27.5 grs of 4320 as it’s a small powder.

Just begin lower end of manuals and use Varget as a starting point and you s/b fine…. Just go slow as a half gr of powder increase is a much higher percent with this tiny case vs a 22-250, 243, etc.

Good Luck and pls share your results.

I m planning on playing with a little H380 in my ARC as like you and your 4320, I ve got a couple pounds of it. H380 is just on the slower side of LVR so it should work, just might not get to full pressure/velocity.

 

[MrK.]

I loaded up a ladder of 18 shots from 25.3 grains up to 28.7 grains with IMR 4320 and 85 gn Speer boat tails. I was planning on going to the range today but Wifey turned up feeling ill so I will put that off until one afternoon next week. I did however shoot the 25.3 and 25.5 grain loads into the dirt in my back yard yard. The primers in those two rounds looked as expected for starting loads. I'll post back after I shoot the full ladder.