Powder position sensitive for aa1680 in 300blk

[BK7saum]

I shot a few rounds yesterday. 300 blk with 247 whisper gas checked and tumble lubed. First 3 shots 978,844,791. Rifle was kept level on bags as action was cycled. Last 3 shots, 1024,1016, 1029. Rifle muzzle was elevated, then lowered before each shot.

Just an fyi for folks chasing wide extreme spreads. Aa1680 fills the case about 3/4 full or more. I wouldn't have thought there would be positional sensitivity with the powder.

Brad

[Nobade]

It's not position sensitivity. It is pressure. That powder needs a lot of pressure to burn right and you're not pushing it hard enough to do so. I find the same thing in my 7.62x39, if I am trying to load it light. I can't just reduce the powder charges to drop velocity or accuracy goes to pot. But if I drop the charges and fill the case with granular filler I can get it to shoot slower and still be accurate with tight velocity spreads. If it will cycle your rifle, AA#9 would be a better choice for powder than 1680.

[BK7saum]

Where is aa#9 in burn rate compared to 1680? I cant get unique or faster powders to shoot with this alloy. Too much nose slump I guess. There is a little slump with 1680 but it shoots pretty accurately.

If it is strictly a pressure issue, can you tell me why did the last three shots have only a 13 fps extreme spread while the first three had a 187 fps extreme spread. The only difference was the position of the powder in the case. First three were forward against the boolit and the last three the powder was back against the web.

Does having the powder against the web increase the pressure by providing a more uniform ignition? If so, it is/can be a pressure issue relating to the position of the powder in the case.

Brad

[Larry Gibson]

I shot a few rounds yesterday. 300 blk with 247 whisper gas checked and tumble lubed. First 3 shots 978,844,791. Rifle was kept level on bags as action was cycled. Last 3 shots, 1024,1016, 1029. Rifle muzzle was elevated, then lowered before each shot.

Just an fyi for folks chasing wide extreme spreads. Aa1680 fills the case about 3/4 full or more. I wouldn't have thought there would be positional sensitivity with the powder.

Brad

The others are correct; by raising and lowering the barrel you consistently positioned the powder for better and more consistent ignition. Yes that powder is indeed position sensitive with that charge and bullet weight in that cartridge. Drop 1/2 gr and add a 1/3 - 1/2 gr dacron filler and possibly work back up. That will take care of the powder positioning problem and probably will i,prove the internal ballistics for you also.

Larry Gibson

[runfiverun]

another thing that happens also is that the lube you use takes a bit of time to fully work the barell.
it takes a bit of heat/friction for everything to even out in a barell.
the old lube dries up a bit and needs to be fixed.
sometimes this is one shot sometimes it's a couple of shots.
in our testing we have see the first shot show higher velocities/lower velocities.
and not be part of the group,sometimes we can reduce the powder by 4-5% and get the first shot to group.
on a clean barell i have seen it take up to 11 shots to have a barell conditioned with an even layer of lube all the way to the muzzle.

[uscra112]

I want to explore Nobade's idea that 1680 is not working up to its' best pressure in that load. Using Quickload.

Do I understand that you are shooting a 247 grain boolit? What is your seating depth?

#9 is significantly faster than 1680. I use it in .25-21 Schuetzen loads at a calculated 11,000 psi. for 1400 fps. It gives me very good S.D., and does not seem position sensitive even in that long, skinny case. Have not had any 1680 to try, but it being significantly slower it probably will want more pressure than that to be consistent. What I do not have a handle on is what pressure your load would calculate out to. Hence my questions above.

Even without doing the calculations, I'd be trying #9 or 300MP in that situation. Maybe even something much faster, like Red Dot. Subsonic loads meant to be quiet should use small charges of faster powders, so that the burn time is short and the muzzle pressure is low. That won't cycle a semi auto, but for that kind of load you don't want it to, IMHO.

[BK7saum]

Yes, I'm shooting the NOE 247 Whisper boolit. It is seated to the crimp groove. I've never measured the OAL on this load.

[BK7saum]

Just looked up the powder burn rate table. While #9 is faster than 1680, it is also slower than unique. It might work. Of course #9 is also listed as approximately the same rate as alliant Steel and close to 2400. I have one bottle of steel on hand that I might try. Like I said, Unique builds pressure a little too fast, causing poor accuracy even with my boolits checked.

[uscra112]

Yes, I'm shooting the NOE 247 Whisper boolit. It is seated to the crimp groove. I've never measured the OAL on this load.

Don't have that boolit in the database - would need dims and OAL length, or at least seating depth to run the computer model. Is it a flat base? Gas checked? Boat-tail?

Don't want to pressure you, but I'm very interested in this kind of loading.

You must have a ferociously fast twist in that barrel, nicht war? 8 inch?

[BK7saum]

No problem. This is a gas checked boolit. The twist is indeed 1 in 8. Let me look back to the group buy schematic to see what numbers I can come up with. Otherwise someone here might chime in with an OAL when seated to the crimp groove.

[BK7saum]

Looks like the OAL of the loaded cartridge would be about 2.25 based on the cartridge/boolit drawings
http://castboolits.gunloads.com/showthread.php?133407-NOE-311-247Gr-FN-Whisper-Re-run&highlight=NOE+247+group+buy

What other dimensions do you need to help with the calculations?

[BK7saum]

uscra112,

BTW, this rifle is a Remington 700 with a 16" shilen barrel chambered in 300 whisper (or BLK or Whatever).

I was originally very concerned that this boolit wouldn't stabilize. I was trying to work up loads with the 220 grain RN j-words and they would not fully stabilize. I was getting oval tears on the target. When I finally got around to casting the 247s (actual weight is about 244 or 245 with a 50/50 COWW and SOWW), I was getting oval tears as well. But I was using American Select and Unique powders (just to see if I could get them to work). When I loaded the 1680, things started coming together. But my velocities were all over the place. I hadn't heard of anyone else having issues with position sensitivity of 1680 in the case, so I was a little baffled as to the cause. I know 1680 is recommended for subsonic use in ARs (with heavy J-words or boolits) to provide enough gas volume to cycle the action.

Just recently I started settling the powder to the back of the case. It's a lot more consistent. The velocity is right where I want it and the ES really decreased.

[mongoosesnipe]

I use h110 in my whisper ar what twist is your barrel if its a 1in8 you shouldn't be having trouble stabilizing 220s unless your velocity is way down if I remember correctly my load for subsonic a is 9.6 grains of h110 behind the 208 amax I would try around 9 for your cast boolits

[BK7saum]

mongoosesnipe,

I thought that the 220s would stabilize just fine, but even with velocities slightly supersonic, they were still unstable. I spoke with a friend (smith) and he had trouble with 220 RN and knew of others with issues getting 220 RN to stabilize. Don't know why, but I shot abou 45 of the 220s and kept getting slightly oval impacts. It would still shoot about 2-3 moa at 100 yards, but the target showed slightly keyholed impacts.

[mongoosesnipe]

I have never shot 220 round nose from mine I know when I tried some 110 rn as a pinker it couldn't hit the broad side of a barn but if your not finding a bullet that will stabilize it could be your crown rather than non stabilizing bullets causing your problems is the gun from AAC or a custom build

[crawfobj]

Interesting. This is the first I've heard about 1680 being position sensitive. Surprising given the small case, but your results sure point that way. Wonder if a SR magnum primer would help?

I have not noticed this in my 1680 tests, but I'm still early in the game. (1 in 8" AR, carbine gas with the NOE 311-247, WSR primer)

[BK7saum]

The 247 cast stabilize fine with the aa1680 powder. The long boolit combined with a 50/50 alloy and fast pistol powders (Am Select and Unique) were giving me grief early on. I have some Sierra 110 grain HP varminters that are awesome withe Am Select. Acccurate and WOW, are they quite. The hornady 110 RN were not so accurate. I think 4 moa or so, but the 110 Sierra's are right around 1 moa, maybe a little less.

[BK7saum]

crawfobj, I wondered if a hotter SR magnum primer might make a difference. But with the small case, I don't know if that might bring up different problems. I have a few and might have to try some when I load up my next batch of ammo.

[mongoosesnipe]

You could try smr mar primers but you may also consider going down a primer to a small pistol magnum considering the low pressure it shouldnt be a strengthissue and it would disrupt the bullet less before burning the powder which could be giving you some grief if your not getting a clean ignition in the case that the logic being the small primer in the benchrest cases

[uscra112]

Found a drawing. I used .460 seating depth. Now, your target velocity was just subsonic?

Backing into it I get your load of 1680 as being about 10 grains? If so then Quickload thinks your pressure is around 18k psi, and that does seem low for 1680. If you try AA#9, about 7.0 grains would calculate to 22k psi for 1010 fps., which is in the range that #9 likes to work at in my experience, both in the .25-21 and the .357 Magnum. Alliant 2400 is almost exactly the same speed, but isn't as consistent. I quit using it when I found AA#9. This new Alliant 300MP is also the same, and some of the Schuetzen guys I listen to are switching to it from AA#9. Hard to find it - I finally got hold of some by paying the HazMat from Wideners. :-( Haven't even broken the seal on a can yet. Another trick in my bag would be Lil'Gun - about 8 grains.

All of this is VERY approximate - there's a raft of other factors that I'm making assumptions for. Safety first. The obligatory warning about double charges applies!

If you try any of this, lemme know how you do. Always looking for field data to back up (or refute) the computer model.

[BK7saum]

My load is right around 10.5 grains for a muzzle velocity of 1040. I'll look into some of the other powders. And let you know the results.

Thank you for the info on powders and quickload information.

[felix]

The pressure curve shape is most paramount to this round's intended performance. The meager amount of powder space is expanded beyond that necessary to fully support bolt operations. The desired shape makes powder choice critical and suggests strongly the requirement of a variable gas takeoff mechanism. Wilson's Combat offers one. ... felix

[uscra112]

Maybe for a semi-auto Felix, but this poster is working with a Rem 700 bolt gun.

[runfiverun]

just a simple primer brand change could make a difference here.
if you are using win's,i'd try federals.
they have different priming compounds which will ignite the powder differently.
if that didn't do it i'd just use a step faster powder.
4227,h-110 area.