How slow can you go?

[andym79]

Hi guys, I don't like to ask questions like these, but as I have no empirical data and the twist calculators all seems to vary a lot from each other.

I was hoping someone here could give me some first hand experience on how slow you can go with a .308 180 grain 1" long bullet in a 1:14" twist before stability is lost?

Say for example a 311041?

Or pushing it larger a 311291?

I only have a 1:10" twist barrel on one of my rifles.

Calculators are giving me number from 1000-1700fps!!!

[1johnlb]

The miller calculator has a 1.5 stability factor at 700 fps on the 180gr bullet. I wouldn't want to shoot that slow.

http://www.bergerbullets.com/twist-rate-calculator/

[andym79]

I agree, I should have been more specific, I was think more 1000 fps!

[1johnlb]

I'm shooting 2400 fps with the 311299, up to 2800 fps with the xcb in my 1in14 308win. Sorry I'm really not going to be much help at lower velocity. Although, 1.5 is sufficient stability according to the calculator. Real life may vary.

[44man]

Only shooting long range will show if stability is gone. You need to shoot faster with 1 in 14".

[Larry Gibson]

Andym79

"I was hoping someone here could give me some first hand experience on how slow you can go with a .308 180 grain 1" long bullet in a 1:14" twist before stability is lost?

Say for example a 311041?"

Or pushing it larger a 311291?

At 1" length; 550 - 600 fps with both bullets. However, both my Lyman 311041 and 311299 are less than 1" in length and thus could be taken down to 450 +/- fps theoretically according to the Miller Stability program in a 14" twist.

Larry Gibson

[44man]

I never found any formula to work. Only actual shooting. Same as to what a boolit does to deer, have to shoot deer.
I watched thousands of bullets/boolits through spotting scopes. I seen over spun and under spun. Over spun was accurate but POI would change at ranges since the bullet would rotate around the flight path. Under spun would go way off target at range. Gremlins threw out the sail on those.
Over spin is not good at close ranges, had rifles that would not shoot at 100 but at 350 yards I shot 5 into 1/4". Boolits will "go to sleep."
Even a S&W 29 would have boolits rotate if 240 gr but 250 eliminated it. You have to see it.

[andym79]

So no one has tried subsonic with a 1:14" twist 30 cal barrel?

[Larry Gibson]

Yes, but not with those cast bullets.

Larry Gibson

[Outpost75]

I have a 16" twist .30-30 which stabilizes Accurate 31-155D subsonic with 4 grains of Bullseye. Bullet is 0.84" long.

The same bullet is also stable at 700 fps from my 4" Colt Police Positive revolver in .32 Colt NP with 5.5 grs. of Alliant #2400

187464

[andym79]

Thanks Outpost.

So which bullets have you taken to subsonic with success Larry and in what set up?

[Larry Gibson]

I cast the following very soft, lube with a light coat of LLA and push through size at .310 - .311seating a GC If a GC'd bullet. I usually use my own GCs made of .012 brass or .014 aluminum. I have used the Lee TL314-90-SWC, the NOE 311465 and the RCBS 30-150-FN.

In my 14" twist .308W Palma rifle with 27.6" barrel I push them usually to 900 - 1050 fps but have taken the 30-150-FN as low as 289 fps. I use well fire formed cases with drilled out flash holes (#28 drill) and standard LR primers (usually WLRs but I use up odds and ends I have left over from tests or those I pick up here and there for a good price with these type loads). The cases are NS'd and a 31 M-die is used. With the 90 gr SWCs resizing the neck between firing usually isn't needed.

I use Bullseye (Alliant) powder exclusively for theses loads. Red Dot is a good 2nd choice though. I have not found any other powders to work as well with these "cat's sneeze" type loads. Depending on bullet and velocity I use between 1.2 gr and 8 gr. No wad or filler is needed or used.

Always have a good cleaning rod handy when loading really low as you will eventually stick a bullet in the barrel. With such loads always make sure the bullet has exited the barrel (hole in target, tin can knocked over, dirt clod hit, etc.) before loading and firing another round. These stuck soft cast bullets are easy to push out. However, with loads in the 900 - 1050 fps range the psi is high enough I have never had a stuck bullet, even in faster twist .308Ws.

Larry Gibson

[andym79]

I should rephrase how I ask the question, I want to be able to shot cast bullets from a 308 1:14" barrel at around 1000fps what bullets would you recommend?

[Outpost75]

Accurate 31-155D was intended for this specific purpose. We use it primarily for Junior Program and Appleseed classes firing the 03A3 Springfield, mostly at 100 yards, but it also groups well at 200 if it is not too windy.

4 grains of Bullseye in the .30-'06 is as low as we've gone. 6 grains gives excellent accuracy, as does 7 grains, but then you are approaching transonic velocity range, depending upon barrel length, etc.