B
Badmouser
Guest
Just fired my first few 6mm ppc at a target 50 yds. The holes in the paper indicate bullet tumbling. Where have I gone wrong?
Thanks
Thanks
So, generally, the three variables are:
1. What is the twist of the barrel?
2. how long is the bullet?
3. How fast are you shooting it?
As for #1, don't take the manufacturer's word. Measure it with a cleaning rod and a tight patch. For #2, if you don't have calipers, what is the brand & weight of the bullet? #3 is hard to estimate without a chronograph, but given an *average* barrel and load data, we could make a guess.
This for dynamic stability issues. And just BTW, usually before bullets tumble, they group into about 8 inches at 200 yards. You getting big groups?
Another possibility (but unlikely in a 6PPC) is the bullets are coming apart, and what you're seeing is the print of the jacket. Again, they won't group. As the usual culprit with bullets coming apart is heat, this is unusual in a PPC -- it's hard to get enough powder in the case, and the bullets have a shorter bearing surface, to build up that much heat.
As always, there is a faint possibility it's neither of these, and you have a head-scratcher that will require a gunsmith going over the rifle.
Good luck with it
1. What is the twist of the barrel?
2. how long is the bullet?
3. How fast are you shooting it?
As for #1, don't take the manufacturer's word. Measure it with a cleaning rod and a tight patch. For #2, if you don't have calipers, what is the brand & weight of the bullet? #3 is hard to estimate without a chronograph, but given an *average* barrel and load data, we could make a guess.
This for dynamic stability issues. And just BTW, usually before bullets tumble, they group into about 8 inches at 200 yards. You getting big groups?
Another possibility (but unlikely in a 6PPC) is the bullets are coming apart, and what you're seeing is the print of the jacket. Again, they won't group. As the usual culprit with bullets coming apart is heat, this is unusual in a PPC -- it's hard to get enough powder in the case, and the bullets have a shorter bearing surface, to build up that much heat.
As always, there is a faint possibility it's neither of these, and you have a head-scratcher that will require a gunsmith going over the rifle.
Good luck with it
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A
abintx
Guest
Here's a quick and dirty from right off the internet:
Bullets fired from a rifled firearm should NOT tumble in flight. If they do so, it is a sign of problems. This may be caused by different matters that all relate to the rifling in the firearm, and the bullet.
First is rifling is badly worn, if the bore is oversized for the bullet, or if rifling is badly fouled with lead/ jacketing metal/powder deposits, the bullet will not be gripped by the rifling and spun, and may not be stable in flight (tumbling) Try cleaning the bore properly, and check for excessive wear at the muzzle.
The second condition is the wrong weight/length of bullet for the rate of twist of the rifling. A fast rate of twist, combined with a very fast bullet, MAY result in the bullet "stripping", and not being spun by the rifling. Or a very heavy, slow bullet may not be spun fast enough to stabilize the bullet.
SGJennings
New member
What bullet?
What powder at what charge?
What powder at what charge?
I'm not sure that the cause of bullets coming apart is heat. Or to put it another way, IF it's heat then there's enough heat generated in even a short pistol bore to melt the lead.... witness this video http://uverseonline.att.net/tv/show/top-shot#play=ae___AE_253613_ASSET
IME bullets pop from over-rotation
al
IME bullets pop from over-rotation
al
Al, it is almost always a combination of factors, with the biggest culprits being heat and rate of twist. Tooley has done a fair bit of work on why bullets come apart, as has R.G. Robinett. Both got involved because of some long-range flat base bullets -- a 121-grain 6mm for Randy, a 140-grain 6.5 for Dave.
In the case of the 140-grain 6.5's, we're pretty sure it was a problem with the jackets, though all that means is these long-shanked bullets (more heat from friction) in fast-twist barrels were stressed beyond what those particular jackets could take.
And not always, of course, Using a 9-twist 6.5/06 AI barrel, I got smallest group of the year at Hawks Ridge (1,000 yards) with those bullets in 2005. Beyond that one group, Dave, Steve Shelp and I got any number of match wins. And too many losses, where there were only 4 on. Or one on.. Dave set up a sheet of paper 15 feet in front of the muzzle, and you'd see where, periodically, molten lead hit, as well as the jacket -- or occasionally a couple pieces of the jacket. Switching to plywood, Dave even figured out where the bullets were coming apart -- just above the point where the shank merges into the ogive. And of course, that fits with Henry's calculations.
It was similar with the 121-grain 6mms, but Randy took a different path. He got them to stabilize in a 10-twist barrel, (Dasher) using that coating they now favor up there (something other than moly, but same general idea). Believe they were even able to get them to work in with a bigger case than the Dasher, same approach.
OK. I'm assuming with his 6PPC the OP isn't using a long-jacketed bullet, and it probably isn't, what, a 5-twist barrel? That's about what it would take with PPC case.
It *could* be defective jackets, but even here, they're usually good enough that problems don't show unless you're stressing them with both unusual heat & twist.
Can't really even begin to diagnose the OP's problem without more information. And best would be to be there, at the range, with a borescope...
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B
Badmouser
Guest
All good advice
I will start with rate of twist - and a clean barrel.
Thanks All
I will start with rate of twist - and a clean barrel.
Thanks All
SGJennings
New member
Could you post a picture of the holes that make you believe the bullets are tumbling?
B
Badmouser
Guest
Picture of hole
Do not have a picture, but the hole was about 1/2 to3/4" long an angled up to the left. This was at 50 yards
Do not have a picture, but the hole was about 1/2 to3/4" long an angled up to the left. This was at 50 yards
DeltaBravo
Member
Badmouser,
I had the same problem in my then-new Shilen DGV 8-twist, 4-groove 6BR. I started out with 87 grain V-maxes and THEY WOULD NOT SHOOT! I had key-holing and absolutely no accuracy. My best "group" at 100 yards was over an inch and a half! I finally got wise and switched to Berger 80 grain flat base match varmints and I now get better than 1/4 MOA consistently, and better if I really do my part. With the Bergers, my 6BR is pretty happy with loading into or out of the lands, and 27 +/- 1.2 grains of 8208-XBR.
So sum it up - try some different bullets to start and good luck!
Dennis
I had the same problem in my then-new Shilen DGV 8-twist, 4-groove 6BR. I started out with 87 grain V-maxes and THEY WOULD NOT SHOOT! I had key-holing and absolutely no accuracy. My best "group" at 100 yards was over an inch and a half! I finally got wise and switched to Berger 80 grain flat base match varmints and I now get better than 1/4 MOA consistently, and better if I really do my part. With the Bergers, my 6BR is pretty happy with loading into or out of the lands, and 27 +/- 1.2 grains of 8208-XBR.
So sum it up - try some different bullets to start and good luck!
Dennis
DeltaBravo
Member
al,
I'm not sure what a "fat neck" chamber is. Mine is .270 for the Lapua blue box brass and a loaded round is right at .268, giving about 1 thou all around. Is that too "fat" and if so, why do the flat base Bergers shoot so well (for me anyway)?
Dennis
I'm not sure what a "fat neck" chamber is. Mine is .270 for the Lapua blue box brass and a loaded round is right at .268, giving about 1 thou all around. Is that too "fat" and if so, why do the flat base Bergers shoot so well (for me anyway)?
Dennis
This is odd. A fair number of us shoot 6mm 105-grain bullets, some of which are VLDs, out of an 8-twist barrel. At least one guy, Jason Baney (Pennsylvania 1-KB) with a plain 6BR.
When I say "poor grouping" I'm talking about 8-inches at 200 yards. Pie-plate size groups. 1.5 nches don't qualify ;-)
You're right that if a bullet won't group, move on. And there is no reason to shoot the 100+ grain bullets if you're not going to shoot 600+ yards. But the bulk of them should not only work, but work well. See R.G. Robinett's page for 6mms & twist:
http://bibullets.com/products-2/
To quote on the heavier 6mms:
I bring Randy up becase he's always made great bullets, but some of his just set the new all-time small group record of .0077, so he's esp. hot just now.
al,
I'm not sure what a "fat neck" chamber is. Mine is .270 for the Lapua blue box brass and a loaded round is right at .268, giving about 1 thou all around. Is that too "fat" and if so, why do the flat base Bergers shoot so well (for me anyway)?
Dennis
I was wrong.
The problem isn't your neck clearance
The reason (IMO) that you need the tight neck is to guide the bullet straight into the lands as VLD style bullets have long lever arms front and rear (boattail and 9"-12" ogive) coupled with short bearing surface so they tend to go down the pipe crooked which results in cant, 'inbore yaw' and all sorts of nefarious eccentricities and wobbliegooks...
DeltaBravo
Member
Charles,
After almost 200 rounds where the 87s were all over the paper - 3 or 4 inch "groups" - I ended up at 1.5 inches after trying EVERYTHING. Finally gave up and the 80s worked!
My 8-twist is a ratchet rifled 4 groove. It's a different animal and you should take a look at Shilen's site to see just how different. I'm just guessing - and it was suggested to me by another shooter - that the 87s didn't have enuf bearing surface.
al,
I agree about the lever arm, especially in the ratchet rifled 4-groove. The 80 grain FB bullet has its butt in the lands right from the git-go, so no pushing out of alinement like the BT.
Dennis
After almost 200 rounds where the 87s were all over the paper - 3 or 4 inch "groups" - I ended up at 1.5 inches after trying EVERYTHING. Finally gave up and the 80s worked!
My 8-twist is a ratchet rifled 4 groove. It's a different animal and you should take a look at Shilen's site to see just how different. I'm just guessing - and it was suggested to me by another shooter - that the 87s didn't have enuf bearing surface.
al,
I agree about the lever arm, especially in the ratchet rifled 4-groove. The 80 grain FB bullet has its butt in the lands right from the git-go, so no pushing out of alinement like the BT.
Dennis
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I have a Shilen ratchet rilfled barrel in my 6.5/06 AI. I & many others have also used the Broughton (now North) 5-R profiled barrels, about halfway down the road to a RR. I don't find either to behave that much different.
The notion that 87s don't have "enough bearing surface" is curious. Does he think the bullet is stripping? I kind of doubt that. If so, a 62-grain bullet on the .750 jacket should really strip, or even the 65-grainer on a .790 jacket. But a lot of people have used them, no trouble. And the longer 105-grainers should do real well, with their "longer bearing surface."
Now I don't doubt the 87 A-Max don't perform in your rifle. I simply think your reason is wrong. There have been 105 A-Maxes for a long time, and Bob Crone use to beat me & a lot of others, all too regularly, shooting them in his (what is now called) 6BRX.
Go down to 42 lifetime points & you'll find Bob Crone (He was also on the U.S. F-class team at the World Championships in South Africa, I believe):
http://internationalbenchrest.com/results/shooter_rankings/PrecRifLD.php
And his wife Leslie, a bit below at 36.5 points. Not all their points were with the 6mm & Hornady A-Maxes, but far too many, from my perspective!
http://internationalbenchrest.com/results/long_range/2013/Piedmont/511/Piedmont511.php
Here's another link to a 600 Yard match (which is neat because it shows a record target as the site comes up). Spool way down to the equipment list at the bottom of the page, and you'll see any number of 6mm BRs, or the BR configured as a BRX or Dasher. They don't give rate of twist of the barrels of course, but I'll bet almost all are 8-twist. And some of those Berger 105s will be of the VLD design, which also doesn't have much bearing surface -- I imagine less than the Hornady.
Right after the initial lot of 105 A-Max's, which were hand-built, Hornady started turning out a lot of ho-hum bullets. esp. in 6mm. But for the past few years -- at least 5 years -- & in part working with Dave Tooley, they have dramatically improved the routine production of the A-Maxes. It could be you have some old bullets, or it could be that your rifle just doesn't perform with them. These things happen. I've gone on overlong because the reason you give for your results just doesn't fit with my experience, which is is 17 years of 1,000 yard competition. Certainly not the best, but enough experience to think you're leading the original poster in the wrong direction.
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DeltaBravo
Member
Sorry, Charles,
Didn't mean to offer anything that disagrees with your experience. Mine was different and whether it's bearing surface or PFM, I don't know and really don't care at this point. The 87s didn't shoot and the 80s did/do. YMMV, obviously. Not trying to mislead the OP, and just wanted to offer some of my limited experience, but my apologies to him/her as well.
Dennis
Didn't mean to offer anything that disagrees with your experience. Mine was different and whether it's bearing surface or PFM, I don't know and really don't care at this point. The 87s didn't shoot and the 80s did/do. YMMV, obviously. Not trying to mislead the OP, and just wanted to offer some of my limited experience, but my apologies to him/her as well.
Dennis
SGJennings
New member
Keyholing and bullets all over the paper at 50 yards with a twist faster than is needed to stabilize that bullet... are you're sure you're not trying to shoot them out of a 6.5mm barrel?
Something is really off here. Crown is badly damaged or something.
Something is really off here. Crown is badly damaged or something.