Gobears16
Well-Known Member
Great question. I'd like to know the downside of going 7 twist. If there is no downside then I'll go that route. Who knows what the future holds for heavy 6.5's
PRC twist rate 7,7.5,8?
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Great question. I'd like to know the downside of going 7 twist. If there is no downside then I'll go that route. Who knows what the future holds for heavy 6.5's
SwampDog13
Well-Known Member
I think it's still unproven just how many rpm these bullets can really handle. That's why many are calling for the safe bet of 7.5". You start throwing the 140s through a 7" twist gun at over 3200fps+ you'll be in uncharted territory. We've seen claims of the eld line blowing up mid flight. Nothing against hornady, just all I've seen so far. The reason I would chose the 7.5" is its the safer bet and I tend to fail conservative. I know the 8" can be adaquet with what we call heavy now and still be safe for the 140s so I'm only interpolating that another .5" would not kill them. And still allow for a little weight gain in the future.
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sable tireur
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Watch for the little white puff...
http://img.gg/m9TAt9y
As you can see, the bullet blows up, self-immolates in the blink of an eye. If you do not know what to look for, you will miss it. When everyone is focused on their scopes for the trace or the tablet to see the results, they miss the event.
This was a 6.5 Creedmoor, factory Hornady 147gr ammo in a factory rifle with a 1:8 twist.
http://forum.accurateshooter.com/th...p-was-the-things-one-sees-at-a-match.3984873/
http://img.gg/m9TAt9y
As you can see, the bullet blows up, self-immolates in the blink of an eye. If you do not know what to look for, you will miss it. When everyone is focused on their scopes for the trace or the tablet to see the results, they miss the event.
This was a 6.5 Creedmoor, factory Hornady 147gr ammo in a factory rifle with a 1:8 twist.
http://forum.accurateshooter.com/th...p-was-the-things-one-sees-at-a-match.3984873/
Stokesrjsr
Well-Known Member
I'm not a PRC competitor but from many years of NRA High Power Rifle Competition I've seen dozens or maybe even hundreds of mid flight bullet failure. Although usually it isn't a white puff but a blue one. This problem is what drove Berger to introduce a thicker jacket on what is now called the Target VLD and the hunting VLD is the original thinner jacket. The most common cause was not an excessively fast twist, although I herd it commonly blamed. The real culprit turned out to be excessive carbon build up at the throat. I learned this after purchasing a Hawkeye bore scope and then examining barrels that had suffered this match loosing trait. It usually happened only once in a 50 or 80 shot course of fire but in more severe cases it would produce multiple blue puffs of death. The problem was easily resolved by polishing the carbon away with JB bore compound.
DaleJ
Active Member
maximini14 223
Well-Known Member
Good eye....amazing video.
I really curious to find out what the diagnosis is!
I shoot 162gr eldx in my 7rem mag at 3100fps out of off the rack Abolt with no problems ....1/2" groups.
Is it due to thinner jackets on the eldm???
I would go 7.5 if you plan to go heavier than the 147. The 147 works fine in an 8 twist as I shoot them in that in my Creedmoor. Thousands of them in matches and never an issue also. Not sure what was happening above but there are other reasons than the bullet for those issues. I have shot many thousands of ELD-Ms in multiple rifles and never had a bullet not make it to target.
SCSCHNUR
Well-Known Member
I have heard this but never experienced on before. That was an amazing catch on video. Thanks for the post.
What about a transitional twist barrel?? IMO, an 8 twist at the breech transitioning to a 7 at the muzzle. Best of both worlds.
I have recently finished a 264 win that I did a 32" 8-7twist. I'm sending the 160g Matrix in my rig right at 3,100 with single digit SD and solidly repeatable 0.5 MOA accuracy. I was able to get to better than 3,300 FPS but found best SD by choosing to throttle back.
I have recently finished a 264 win that I did a 32" 8-7twist. I'm sending the 160g Matrix in my rig right at 3,100 with single digit SD and solidly repeatable 0.5 MOA accuracy. I was able to get to better than 3,300 FPS but found best SD by choosing to throttle back.
sable tireur
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And here is the response from the actual shooter:
My response a few days later:
-------------------------------------------------------------------------------------------
I apologize for not posting this before - I wrote it up, thought I had posted it, and saved the original. Just realized my oversight today.
Plausible Explanation for the Blowing Up Bullets
(If you do not want to read all the details, here is the conclusion.)
• The bullets got too hot, the lead melted, which caused the jackets to crack and the bullets to disintegrate or blow up
• The most common cause for the bullets to get too hot is a barrel that is too hot. (*)
Please note that I had shot 300 rounds prior to this day with that barrel, using the same loads, and did not have any problems. After a close examination of the barrel, it was concluded that there was nothing wrong with it. Not long after that, I shot 200-15X and 200-10X at 600 yards with bullets from the same lot, and same loads.
A few days after the occurrence, I talked with reps from Sierra, Berger, Krieger, and Lapua, and with my gunsmith. Most would not say they were 100% sure, but they doubted that the barrel would be the culprit. The rep from Berger and my gunsmith concurred without doubt on the source of the problem: (*) the bullets got too hot; the lead melted, expanded, and cracked the jackets as the result of the barrel being too hot.
This phenomena was analyzed in an experimented conducted by MIT, in conjunction with Berger, many years ago using thermal imagery and high-speed cameras. After that, Berger started using thicker jackets for the match bullets – not the hunting bullets.
The bullets get hot due to friction in the barrel and on its way to the target, and in some cases a barrel that is too hot can exacerbate the condition, which can cause the failure.
Was my barrel too hot that day?
Oh, yes! And here is why –
That match consisted of 60 rounds (3 x 20) shot on Saturday, plus 40 rounds (2 x 40) shot on Sunday.
We had wind and flying popup canopies during the first two 20-round matches on Saturday, which slowed things down a bit. That first day there we had at least four shooters on most targets, and we also had a brief rest between the first two matches. After the second match, the rains came, and we had a one-hour delay. By the time we shot the third 20-round match, the barrels had cooled down.
Sunday started without any problems, but several of the shooters had left, and some targets, such as mine, had only three shooters. Things got underway rather well, and we started shooting.
Not long after I shot the first match of the day, my turn came up to shoot again rather quickly – my final match of the event. My friends Brian and his wife Amanda helped me move some of my stuff to the firing line. As I went to pick up my rifle, I inadvertently brushed my hand against the barrel, and immediately uttered and expletive. Amanda said, "Still hot, isn't it?" Yes, it was sizzling hot.
If I recall correctly, after converting my second sighter, I tried to shoot fast, but after a couple of rounds, I shot two or three 9's, so I decided to go back to my normal pace. I had the wind figured out, and resumed shooting 10's and X's. But with just a few rounds to go, I scored a 7, and then a 6! Whoa! Something must be wrong with the SM Target, I said out loud. One of the other shooters then said, "Alex, your bullets are blowing up". Inexperienced as I am, I had never heard of such thing, and was in disbelief.
Then he showed me a video he had just taken with his phone, which showed the bullet blowing up. Wow! At this point Brian asked me if I had any rounds from the previous day, which I did. I shot two more rounds from Saturday, the bullets did the same thing, and Brian videoed one of the shots.
...and that's the rest of the story...
Alex
Danehunter
Well-Known Member
My 6.5 PRC Browning X-Bolt Pro with a 24" barrel has a 1:7 twist but I think a 1:7.5 would also be good. 1:8 is good for 6.5 CM but too slow for for properly stabilizing faster moving heavier 6.5 PRC bullets from 147 grains on up.
This has been my experience with my 1:8 twist, 26" barreled Ruger Precision Rifle and 147 gr. bullets. They just don't group as well as 140 gr. ELD-M ammo.
And, when I get to finally shooting it in two weeks, I expect my 6.5 PRC X-Bolt Pro will do much better with the 147 gr. Hornady ELD-M ammo and some 150 gr. hand loads.
Then on to 153 gr. A-Tip hand loads.
Eric B.
This has been my experience with my 1:8 twist, 26" barreled Ruger Precision Rifle and 147 gr. bullets. They just don't group as well as 140 gr. ELD-M ammo.
And, when I get to finally shooting it in two weeks, I expect my 6.5 PRC X-Bolt Pro will do much better with the 147 gr. Hornady ELD-M ammo and some 150 gr. hand loads.
Then on to 153 gr. A-Tip hand loads.
Eric B.
