I'm worried: 32 gr VMax

[TD-Max]

In order not to have to re-read the thread, do I take it you've found that the SBK's are working well?

[jo191145]

Wrangler

Just for ha ha's I ran my 6ppc 14twist with Barts 68gn Ultras through JBM's stability calculator one night.
Seems my ppc is'nt stable at any velocity the calculator can input. I've kept it a secret from my gun as its shootin darn fine as is
Needless to say I put little creedence in twist calculators.

I do agree the 12 twist is quite minimal in the 204. Just stepping up to an 11 does wonders.
I've been talking to Brian Hettrick at Savage Arms about this issue recently. I even campaigned for two factory twist rates in the 204 like they do for the 224 calibers. Thats not gonna happen, not enough demand. With any luck maybe they'll tighten it up to an 11 or 10.
I'm scheduled to take a tour of the Savage factory this month. I plan on barricading myself in the engineers offices until they listen to reason

Run the numbers on the 39bk. my current lot
.740.5
.746
.743
.741
.745.5

My quess is you'll find them unstable also. Just a quess, the results should be interesting.

[bow shot]

I seated the 32 gr SBKs another 0.015" deeper, close to Sierra's recommendation. They are flying well now, no key holes. One four shot group (the remaining 4 rounds of the hottest charge that were left after shooting a ladder) printed 1.7" @ 400 yards.

Sorry for the confusing use of the term "COAL" in the previous post. I meant to say something more like spec length. Someone once told me that COAL meant "correct overall length". My current understanding is that it means "cartridge overall length".

[kenbrofox]

Wrangler,
thanks for your reply to my question.Still to thick to understand it though.

[Wrangler John]

Wrangler

Just for ha ha's I ran my 6ppc 14twist with Barts 68gn Ultras through JBM's stability calculator one night.
Seems my ppc is'nt stable at any velocity the calculator can input. I've kept it a secret from my gun as its shootin darn fine as is
Needless to say I put little creedence in twist calculators.

I do agree the 12 twist is quite minimal in the 204. Just stepping up to an 11 does wonders.
I've been talking to Brian Hettrick at Savage Arms about this issue recently. I even campaigned for two factory twist rates in the 204 like they do for the 224 calibers. Thats not gonna happen, not enough demand. With any luck maybe they'll tighten it up to an 11 or 10.
I'm scheduled to take a tour of the Savage factory this month. I plan on barricading myself in the engineers offices until they listen to reason

Run the numbers on the 39bk. my current lot
.740.5
.746
.743
.741
.745.5

My quess is you'll find them unstable also. Just a quess, the results should be interesting.

I used Bart's 66 grain Flat Base bullets in my Sako L-461 6mm PPC (1:14") and they shot phenomenally. The Sierra 70 grain HPBT Match shot excellently even with a S.F. of 1.043 (yes they are marginally stable). In fact, all .243 lead core bullets from 58 to 70 grains shot very well. The problem came with the 62 grain Varmint Grenade, as I mentioned.

My 1:12" .204 Ruger barrel shoots very well with the 26 grain Varmint Grenade, .247" for 10 shots at 100 yards even with an unstable 0.937 S.F., although they are susceptible to occasional fliers. What I am trying to eliminate is the fliers and misses at ranges beyond 200 yards.

What I have discovered is that the problem is expressed in two scenarios. Small volume lead core bullets, with low S.D. and B.C., such as .204 - .224 and all powdered metal core lead free bullets. The addition of a polymer tip seems to add a factor of intrinsic instability maybe because the internal cavity reduces core mass further and offsets the rotational center of gravity? The problem may be related to core placement and tip construction. There are so many variables it is almost impossible to identify all the contributing factors.

I have not come across another cartridge where bullets become completely unstable by lengthening seating depth. This may have something to do with allowing gas bypass to establish a pressure bearing that centers the bullet and cushions rifling engraving?

What the faster twists seem to be doing is allowing a wider range of weight and type of bullets to perform over a greater range of conditions. This same effect is why most AR platforms in .223 tend toward faster twists that stabilize heavier bullets yet handle the lighter weights with aplomb.

Being an experimenter, this is of interest to me. It is not of great concern to the factory rifle purchaser, but may effect someone like me who builds rifles, and has way too much time on his hands.

[jo191145]

John

Length of the bullet is the largest determining factor in stability vs twist rate. Hence the 62 VG will not stabilize in a 14 twist. Tried it myself in a 14 twist 6BR.
Might be why adding a polymer tip to the other non lead core bullets creates instability. Add the length of a tip to an already long bullet and the twist rate must be tightened to compensate.
Velocity comes next and weight is of little consequence beyond the fact it effects velocity. Weight of the projectile was used as an easy on the consumer determination of compatiable use. Worked fine in the old days when bullets were all constructed the same. Nowadays with VLD's and non lead bullets profiles (length) can alter considerably within a single weight range.

No offense to bowshot but COL will not cause tumbling. Not in its entirety anyway. Theres other forces at work here.
I've tumbled a couple hundred 39bk's and Yes, even a few 32Bk's in some of my barrels.
Its not a stability issue. The super soft jackets are being compromised/damaged.
Sierras are the softest contstruction in 204. If something is just not right they will let you know first.

I would think shooters buying a factory rifle would be very interested in its twist rate and suitability to shoot thier chosen projy's. JMO

[bow shot]

No offense taken at all, I sincerely value the advice. I'll be studying my data to see what I may have missed!

[bow shot]

... of testing 100 and 300 yard groups I've learned these things:

1) The keyhole-ing was fixed either by seating deeper, or by a thourough barrel cleaning. Not sure which it was. I saw that after 200 rounds, a dry bronze brush pushed out all kinds of carbon crap out the barrel. So for this gun, cleaning matters.

2) I was able to duplicate my best 32gr VMax groups with the 32 gr Sierra SBKs.

3) I believe that (poor) shooting skill had more to do with my group sizes than I thought. Mainly, once I was able to control recoil to a predictable pattern, the groups shrunk. Though I was originally quite steady on slicing the bull into quarters with the scope, my reaction to recoil was very unpredictable. I'm working hard on this.

4) Flash hole deburring diminished my groups by a size of about 20%.

5) Federal brass that I acquired from 1x fired factory ammo has very consistant neck wall thickness (less than 0.0015" variance per piece)

6) The brass case volume difference between the different mfgs is not the same. The Federal and Hornady brass were equal, but the Nosler brass was more (I'll post data when I get back home).

7) My 400y ladder tests were all over the map, indicating (to me, anyway) that my barrel oscillation is NOT in a nice, neat, little vertical swinging pattern. It is much more horizontal. I was able to confirm this with repeated tests.

I'm sick of shooting for groups, but glad I did it. Time to kill critters!

[bow shot]

For Savage 12 VLP
.204 Ruger

Bullet: 32 gr Hornady VMax or Sierra Blitz King
Powder: 26.8 gr Benchmark
Brass: Federal
Brass trim: 1.837" +/- .001"
Primer: Federal 205M
COAL: apx 2.334"
Size: Lee collet neck sized
Seated: Wilson seating die, stem adjusted @ 1.7000"
TIR: (@ case side of bullet olgive) <0.002"

Best 3 shot yields so far:
VMax: 0.24" @100y, 1.0"@300y.

Blitz Kings (with untrimmed Nosler brass): 0.3" @100y (26.8, 27.6 gr Benchmark), 1.7" @ 400y (27.6 gr Benchmark)

[FireBallGuy]

Still playing with that bowshot?

[bow shot]

I'm considering this one OVER, LOL!!

[bow shot]

Thanks kindly to all the wise ones that have been so generous with such good advice!! Its been a long hual, this one.

[bow shot]

In the mix of all this, I did buy a flash hole prep too (actualy a center drill, thanks for the recommendation Uncle Nick!) a sinclair pocket reamer, and a VLD chamfer tool. So all the brass now gets the total prep with these, as well as an outside deburr with an RCBS tool.

We are now working with brass that has under 0.0015" ncek wall thickness variation, and shooting only rounds with under .002" TIR and having equal case lengths (unless plinking or fouling).

The value in all this is confidence that that quality of the ammo can resonably be put out of the equasion. That's a big deal to me, to just get it out of my head when I'm working up a load, and not be "wondering".

A couple other notes:

1) Compared to the Fed and Nosler brass, the primer pockets on the Hornady brass were so tight that I couldn't get the pocket reamer in there. The hornady brass was the only brass that did NOT end up with flattened primers.

2) The Fed and hornady brass held about 3 grams less H20than the Nosler.

[dozernomore]

http://i844.photobucket.com/albums/ab6/ ... ger001.jpg[/img][/img]
my savage model 25 light weight varminter 204 ruger,and some handload development

[bow shot]

There should be a drool emoticon, LOL!!