What causes a bullet to tumble?

[Swede 45]

I used to shoot a soft 148gr commercial swaged HBWC and had problem with tumbling.. got the advice to go to a faster powder with less gas volume to keep the gas from "flipping the bullet" as it exits the barrel.. especially on shorter barrels! Theory was that the high peak of gas preasure would push to hard on the HB of the bullet and make it flip..?

I shoot a 4" Ruger GP100 and a 2½" S&W 686.. and the snubby was terrible with this load! Not so much with the 4" but with clear tendencies to tumble at 25 meters. Changing from Vithavouri N-340 to N-320 solved the problem in the 4" and shot great! My luck, the bullet is no longer available!

Now, my recent problem!
I have the same problem with my new load!

Ruger GP100 4"
Lee .358-148gr WC with a alloy that gives about 12BHN according to the calculator.
Sized .358 and lubed with TAC-1
2.8gr of Norma R1 (Same result with Vitha N-310 load at same vel. and accuracy)
Standard primers.
.357 cases, bullet seated flush to case, just the small "button" sticking up.
No rollcrimp, just a taper to keep the bullet in place and the cases to feed. (crimping/or longer c.o.l messes upp the accuracy on this load)
Velocity runs at about 220m/s at 3meters ( 722f/s at 9 feet)
Accuracy is great, sub 1 inch at 25meters, but about 2-3 bullets out of 10 shows slight tendency to tumble. Not completely sideways, just a slight oval strike and a smear on one side at the paper.

I get no leading in the barrel, but some in the cylinder throats..

So, any ideas from you guys what causes this and things I can do to fix it?
My own thoughts are towards too slow velocity, and that the bullet doesn´t get the "spin" enough to stabilize.. but I like the accuracy and the soft recoil.. I´ve tried stiffer loads with the R1 and Vitha N-310, but get accuracy problems then!
Softer/harder alloy?
Slower powder?


(I shoot mainly competitions, and a hit larger than 11mm (.433) from a 38spl are judged as null due to ammo malfuction.)

Swede

[FLHTC]

Step it up to around 850 to 900 fps. Your bullet isn't stabilizing at 722fps. That is a bit slow.

[NSB]

Speed, diameter (too small), and twist rate all contribute to tumbling.

[Larry Gibson]

As mentioned you need to step it up a bit if you are going to shoot past 25 yards. Suggest 3 - 3.2 gr of the R-1 in 357 cases under that bullet.

Larry Gibson

[runfiverun]

if the faster speed is still causing you problems I would investigate that leading in the cylinder throats.
they may be making the boolits smaller than the barrel causing your boolit to lose grip on the rifling.
the slower speed may be allowing them to barely grab the rifling and stay stabilized, whereas the higher velocity ones aren't able to do that.

[williamwaco]

Lee .358-148gr WC with a alloy that gives about 12BHN according to the calculator.
Sized .358 and lubed with TAC-1

I use that exact bullet, same hardness and sizing but lubed very lightly with LLA.

I use 3.2 to 3.5 grains Bulls Eye. That should produce around 825 and 900 fps.
There is no difference in accuracy - 1.25 " average for several dozen 6 shot groups at 25 yards.

2.5 to 3" groups at 50 yards. ( I don't shoot much at 50 yards with the wad cutters. )

Neither shows any tendency to tumble at either range. the 3.5 grain load cuts slightly cleaner holes at 50 yards.

These results include 2 S&W .357 revolvers 6" bbls. One Ruger GP 100 6" bbl, one TC Contender with 12 inch bbl.

The "Time honored" standard load of 2.7 grains of Bulls Eye, ( About 625 fps. ) does not work at all for me. tumbles slightly at 25 yards and badly at 50.

NEXT -

Speer swaged 148 grain wadcutter.
Exactly the same load and the same results.

Hornady swaged 148 grain wad cutter.
Exactly the same load and the same results.


Bad tumbling from the snubbie:
Your load is probably not producing 650 fps from that short bbl.

I am going to tell you something I don't think I have ever told anyone, ever, before.
You need more powder. Check your manuals and be sure you loads are above 800 fps.

Now it is your turn:

Explain to me what this means.


(I shoot mainly competitions, and a hit larger than 11mm (.433) from a 38spl are judged as null due to ammo malfuction.)

[Schnizel_fritz]

It means that if a bullet keyholes the target and the hole is longer than 11 mm it doesent count. The result of that hit iss null.

[Swede 45]

Yeah.. more powder !! :-P
Thats my usual attitude,, (on a swedish forum I go by the nick "Max Charge" :lol:
But since I usually get a evil eye from the powderpuff guys at competitions, I started do download a bit..

I´ll start by bumping up the charge.. the 2.8 is the min for my Norma manual.. I guess that the manuals tests are done with longer barrels and therefore gets higher vel and better stabilizations..
I tweak the charge to a higher vel and work on the load from there on crimp and seatingdepth to see where the accuracy goes..

If the keyholing tendency remains or other problems shows up.. I look into that if, and when, it identify itself..

The quest proceeds!

Tack Fritz.. kul att se en svensk till här !
Yes, if a bullethole is larger than 11mm (from a 9mm/.38 cal) and not easily identified as a double hit, it doesn´t count..

I´m happy with the TAC lube.. I started of with LLA on this bullet, but got vertical stringing and variations in velocity..
The TAC gives uniform vel and nice groups..

[w30wcf]

if the faster speed is still causing you problems I would investigate that leading in the cylinder throats. they may be making the boolits smaller than the barrel causing your boolit to lose grip on the rifling.
.....

+1 Also letting disruptive gas getting by.....

w30wcf