Effects of 3 and 4 Groove Barrels on thin Jacketed Bullets

Broz

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OK, much of this is related to what I have seen first hand and how we were able to fix some problems. The rest is from some research I have done over the years.

It started years and years ago with reports of some jacketed bullets "blowing up" on impact with little to no penetration. Back then I did some research and found that many of the rifles exhibiting these results were smaller calibers, with the exception of a 7mm or two. What they all seemed to have in common was, lighter bullets for caliber, fast twist rates, high velocity, and 3 or 4 grove barrels.

Some were so severe that the bullets would come apart in mid air, usually before 200 yards. Just recently I was contacted by a shooter who had a rifle and in a 5 shot group a bullet or two was simply gone. He was blaming the jacketed bullet. This was a fast twist 7mm ( I think 28N). I asked him about the barrel groove count. He told me it was 3 or 4 (I honestly cant remember) I suggested with that twist, groove count and chambering, he should try some Cutting Edge solids. He contacted me again and thanked me for "fixing" his rifle and it was shooting awesome now.

I am doing more research to find the factual dimensions, But I have been told that 3 and 4 grove barrels use wider lands and typically taller too. So, this results in a wider and deeper inscription in the bullet jacket. Knowing some of the most popular jacketed bullets have fairly thin copper jackets, it is easy to see that we could be, in some cases setting the bullet up for failure before it ever leaves the barrel. For sure this could be the reason for different terminal performances from the same bullets in hunting situations.

The benefits to less grooves and lands is reported to be, 1: Easier cleaning due to less groves. 2: Longer throat life from the wider beefier lands, however this is an assumption / observation and I find no documented proof. 3: More velocity. However it seems to be accepted that #2 and #3 are small enough gains that you could have have a larger variance between two like barrels from the same manufacturer. So very hard to prove and small if any real gains.

Barrels with less land and groove initially , if my research is correct, were designed for small varmint calibers to increase throat life. Back years ago, many years ago, I had a custom barreled 220 swift and if I loaded a 55gr jacketed bullet over 3800 fps the bullet would turn into a gray puff about 150 to 175 yards and be gone. I don't recall the groove count on that barrel. But I have my assumptions. I had other 220 Swifts hitting very near 4K fps. that shot fine.

Not throwing stones at all here, we are a PROOF dealer and I am using their barrels too on my new 300 HCM build. But PROOF barrels of smaller caliber (I believe 270 and down) are all 4 groove. Above .270 they are all 5R grove. They are very popular barrels, they shoot very well, but are we headed for a storm with today's more popular faster twist rates and all the 6.5's being built? Krieger for years only made 4 groove, then the demand insisted they add 5R as an option to their barrel line. I remember that at least one of the "they blow up on hide" bullet reports was a fast twist 4 groove Krieger.

We have two match rifles being built as we speak by Snowy Mountain Rifles. These rifles are being chambered in 6mm Creedmoor and will be on Kreiger 4 groove 7.5 twist barrels. In between matches, I plan to do a little testing on all this. I will not use these for hunting. But I look forward to some tests of my own.

In summery, It is something to consider, especially for a hunting rig with fast twists and high velocity cartridges.

What you all say? Any first hand info on this?

Thanks
Jeff

 

El Matador

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I remember talking with the guys at Pac-Nor about this when I rebarreled my 270 WSM. They said the 3-groove barrels were not a good idea for shooting light bullets but I don't recall if they gave any specific reasons. It seemed to me that a short bearing surface and only 3 grooves would tend to concentrate the rotational force on those 3 points and tear the jackets up. I only intended to shoot 150 grain bullets with that gun so I ended up with a 3-groove barrel and it shoots nicely.
 

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.........Some were so severe that the bullets would come apart in mid air, usually before 200 yards. Just recently I was contacted by a shooter who had a rifle and in a 5 shot group a bullet or two was simply gone. He was blaming the jacketed bullet. This was a fast twist 7mm ( I think 28N). I asked him about the barrel groove count. He told me it was 3 or 4 (I honestly cant remember) I suggested with that twist, groove count and chambering, he should try some Cutting Edge solids. He contacted me again and thanked me for "fixing" his rifle and it was shooting awesome now........

I believe the future of smaller bore, heavy for caliber, high velocity shooting will increasingly belong to the mono's.
 

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I seem to remember when the Allen Mags first came out that many of them were built with Lilja 3-grooves...maybe that's why they couldn't get accuracy above about 3400fps with Bergers!?
 

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I’ve been told 3 groove Lija’s can be hard on jackets when paired with fast twist rates and high velocities. How much of that was actually the barrel’s groove count and how much of that was just straight over spinning it to begin with is my question.
 

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I’ve been told 3 groove Lija’s can be hard on jackets when paired with fast twist rates and high velocities. How much of that was actually the barrel’s groove count and how much of that was just straight over spinning it to begin with is my question.
But, when the same criteria is met, only difference being the groove count, and the 3 comes apart and the 5 does not, we know there is a negative effect is some instances.

Jeff
 

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What I also noticed from my experience and studying others problems with this is that with the heavy high BC bullets and fast twist barrels is that the 5R rifling fix the problems when the 3 groove,4 grove and 6 grove were causing bullets to fail and come apart. I have heard people say its because there are no lands directly opposing each other, but I wonder if it has more to do with the radias on the lands are easier on the jackets at the faster twist , especially when trying to push them at the high speeds we tend too push them at. I personally feel it does. I know the guys at Bartlein found this out resonantly with the 6.5 barrels and the 150gr 6.5 SMK's, the 5R barrels seemed to solve the problem of bullet failure.
 

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I have two 3 groove 6mm, 8 twist, barrels on target rifles. A Pac-Nor and a Lilja. The Pac nor has very wide lands. I have had no problems with either. Bullets from 75 but mainly use 105 or 108 Bergers at about 2950.
Both are great barrels and clean up easily.
Some speculation a 3 groove may last a bit longer FWIW
 

Broz

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I have two 3 groove 6mm, 8 twist, barrels on target rifles. A Pac-Nor and a Lilja. The Pac nor has very wide lands. I have had no problems with either. Bullets from 75 but mainly use 105 or 108 Bergers at about 2950.
Both are great barrels and clean up easily.
Some speculation a 3 groove may last a bit longer FWIW
Yes, the barrel life thing was the driving force behind the 3 groove. Although I agree with your speculation as I have not found 100% solid data to support. What velocity are you pushing and do you hunt with these rifles?

Jeff
 

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These are prone rifles for LR sling comp. All my loads are around 2950. So not high velocity, but when the wind is down we crank 25 rounds in 10 minutes or so. They do get warm. I expect to get around 3000 rounds of accurate life on them
Both clean up very easily
 

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I am no expert on this but I do have a theory, based on different posts by shooters. Putting the different pieces together, the one thing that seems to stand out in the cases where a bullet comes apart is the 3-4 groove barrels and the sharp forming the grooves have on the bullet.

Essentially, the sharp or deeper grooves weaken the already thin jacket thinning the jacket even further along the groove lines as they form the bullet. The G-forces of the bullet spinning at high speed puts extra strain on the weakened jacket and the bullet comes apart from the inertia.

I think this is seen in the smaller calibers as they tend to have thinner casings than larger and heavier bullets as there is just not enough volume to create the weight if they made them thicker. Additionally, they are generally spun at a higher rate and pushed faster than heavier rounds thereby creating the perfect storm.

To validate this, we would need to see a barrel that has had bullets come apart to check the imprint of the grooves on the bullet. I would also like to see a similar barrel that has not had any come apart to compare the imprint of the grooves on the jacket.

I think if we ran these two samples through a CT 3D Scan or X-Ray 2D Scan that the bullet from the barrel that has had failure will show the ridge created by the groove has thinned the jacket to the point it cannot support the forces. Likewise, I think that the bullet from the barrel of the other barrel will show that the ridges are less obtuse and therefore tend to not thin the jacket as they form the grooves.
 

Broz

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I am no expert on this but I do have a theory, based on different posts by shooters. Putting the different pieces together, the one thing that seems to stand out in the cases where a bullet comes apart is the 3-4 groove barrels and the sharp forming the grooves have on the bullet.

Essentially, the sharp or deeper grooves weaken the already thin jacket thinning the jacket even further along the groove lines as they form the bullet. The G-forces of the bullet spinning at high speed puts extra strain on the weakened jacket and the bullet comes apart from the inertia.

I think this is seen in the smaller calibers as they tend to have thinner casings than larger and heavier bullets as there is just not enough volume to create the weight if they made them thicker. Additionally, they are generally spun at a higher rate and pushed faster than heavier rounds thereby creating the perfect storm.

To validate this, we would need to see a barrel that has had bullets come apart to check the imprint of the grooves on the bullet. I would also like to see a similar barrel that has not had any come apart to compare the imprint of the grooves on the jacket.

I think if we ran these two samples through a CT 3D Scan or X-Ray 2D Scan that the bullet from the barrel that has had failure will show the ridge created by the groove has thinned the jacket to the point it cannot support the forces. Likewise, I think that the bullet from the barrel of the other barrel will show that the ridges are less obtuse and therefore tend to not thin the jacket as they form the grooves.
^^^^ I agree with this^^^^ I have sent emails to a well known 4 groove small caliber barrel maker and asked for the measurement of increase in land height and width compared to their 5 groove barrels. This email went unanswered. I need to try other manufacturers for this info.

Jeff
 

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Don't under estimate the condition and finish of the bore. I have seen quite a few bullets come apart and they are typically very new (sharp lands) or old barrels with eroded throats. And rarely do they fail on the first shot, much more likely when the barrels heats up and is fouled a bit

Lots of variables to be considered but my 3 groove barrels have the same set of bore/groove dimensions as my 5R barrels. My thinking has always been a barrel with an even number of lands (opposed) and conventional rifling is harder on jackets. A 5R Bartlein would on the other end of the spectrum.
 

Broz

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my 3 groove barrels have the same set of bore/groove dimensions as my 5R barrels. .
This goes against what barrel makers have stated so I must be misunderstanding your post. Are you saying the lands in your 3 groove barrels are the same width and height as a 5R barrel ? Meaning both would inscript the jackets the same depth and width? If this is true I would love to see documentation because something has changed over the years then.

Please let me know and Thanks!

Jeff
 

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My post went away. Broz No I am saying they are both 237/243 barrels so the height of the lands is about the same, The 3 grooves have wider lands, but the ratio of land to groove area is about the same. As I mentioned, the PAC NOR does seems to have wider lands than the Lilja
 

Broz

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My post went away. Broz No I am saying they are both 237/243 barrels so the height of the lands is about the same, The 3 grooves have wider lands, but the ratio of land to groove area is about the same. As I mentioned, the PAC NOR does seems to have wider lands than the Lilja
Thank you for the clarification. My understanding is the lands in the 3 and 4's are wider and taller. I need to take some time and get some hard numbers on this.
 

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I have one of the earlier Kirby Allen .270 Allen Magnum's with a 3-groove Lilja, 1-8 twist. I have only used about 10 of the 140gn Nosler Ballistic Tip (@ 3650fps), the now gone Wildcat 169.5gn ULD RBBT's (approx 100 @ 3450) and 170gn Elite Hunters (25 @ 3450 & 25 @ 3000fps). As you can see I haven't shot it much and I dropped my current load from 3450 to 3000fps thinking it would "preserve" the barrel somewhat. Now that I'm thinking about it, I'm not sure that 450fps is gonna make that much of a difference in terms of barrel erosion/wear.
Kirby sent me the following via email, August 2016:
"We found that over time, the 3 groove barrels started to rip apart conventional lead core bullets. The reason we found was total baring surface compression percentages. Basically, there was alot of the baring surface of the bullet touching the bore and this weakened the core/jacket bond and bullets would often come apart in flight.


This was often the reason for these rifles being sold as owners t hought the barrels were shot out. That is not entirely true. In my testing of these barrels when they were having issues with soft bullets, we tested hard bullets such as those from Barnes and the nosler accubonds and had great results for many hundred more rounds down the bore.



Now however, on these rifles, we use specific barrels that have less then 20% baring surface compression on the bullets and have no issues. Using mainly bartlein 5 R barrels now.



Just something to keep an eye on.



K

APS"

Hope this helps. JohnnyK.
 

Broz

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Well as I suspected some of the rath of 3 and 4 groove barrels are showing up.
Be careful hunting with 3 and 4 groove barrels with cup core jacketed bullets.

These are NOT my results and NOT my photo's, but rather from a well known fb group demonstrating what I was fearing would happen.


Quote from a page member "When I talked to Hornady they said the four grove Proof barrels where eating there Bullets alive. None of the other manufacturers where having an issue unless they had a four grove by specific order."

As shown jackets are falling off in flight from the deep jacket inscription of a 4 groove.



 

Broz

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Christensen Arms makes 5 groove carbon wrapped barrels, and this is the main reason I am using them for a sheep rifle build that Dan's Custom Gun Service is assembling right now for a friend of mine.

Jeff
 

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Great thread! I have a new barrel on my 6.5 RSAUM running a 28inch Krieger 5R. Outstanding accuracy with Berger 140 and also 147 Hornaday ELDM.
Hornadays vaporize.. you can clearly see them pop around 100m. Shot them initially at 3100fps and then reduced velocity to 3000fps. At least 3 out of 10 dont make it to the target. I have shot groups where 4 Hornadays are super tight.. you see the bullet blow up.. but still get an impact on the paper, 3inches left an slightly high of grouping with no 5. Could not find what it was that made the sideways impact.. but i suspect it was the bulk of the core. The puff i think is the jacket we see rupture. I suspect the plastic tip is coming off first. My rifle is a single shot by the way, so the noses are not damaged in a magazine.
The Hornadays loaded super easy. Used my 140 Berger load.. same seater die setting, literally just stuck them in properly prepped and annealed cases for the initial tests. I read here that they were problematic.. but some speculated that it was due to eroded throats and shot-out barrels. Thought i'd check them through my new barrel which was barely settled velocity wise with my normal Berger load.
I immediately got very tight groups, without any developent.. when indeed they made it to the paper at 100m. It is the randomness which gets me. My ES's are under 10fps... so i am not sure that it is due to velocity increases in my instance?
The Hornadays would be a real good option for me if they can sort out the thin jacket. The accuracy is there for sure.. and despite a few not making it to the paper and even intermediate range steel.. they grouped real good beyond 1k. This is a sample of 1... but perhaps the indication here is that the condition of the throat or age of the bore is not the reason for the failures we see.
 

Broz

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We had Carson Lilja weigh in on our fb post. Since Lilja was among the first to get involved with 3 Groove barrels, I think this is valuable data.

I have asked if he knows of any barrel mfg. that increases the land height and will relay that answer here too when I get it. But he states that the lands defiantly widen, but Lilja's are not taller.

Below is the statement he gave us.

"Carson Lilja, Interesting read. Land to groove ration stays the same regardless of the # of grooves. 25%. So if you are comparing a 3-groove to a 6-groove, the lands are twice as wide. For example in 6mm, a 3-groove will have land width's of .063", and a 6-groove will be .031".

One of the big misconceptions is that 3-grooves are also taller lands. The only thing that changes is the width, everything else stays the same.

Typically the only time I've seen a bullet jacket coming apart is on fast twist 22 cals, with very long and thin jackets bullets. For example if someone is shooting a 80 grain or heavier bullet out of a fast cartridge like a 22-6mm, I'd recommend a 6-groove.

I've never had any issue's with bullets blowing up on any other calibers."
 

Broz

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Since we released a media post this am about this thread, we have had several shooter say they are experiencing issues with bullets coming apart. Mostly fast 6mm's and 6.5's, both 7 and 8 twist.

Jeff
 

Broz

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This was another interesting post from one of our followers.

Brad Bennett "When I ordered my last Benchmark I was asked what it was going to be chambered in and what I planned on shooting. She spent 30 minutes talking me out of a 3 grove barrel and into doing the 6 groove for this very reason."
 

Broz

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Reply from Carson Lilja when I asked if he knew is any other mfj. increased land height.

"Carson Lilja LongRangeOnly.Com Absolutely! That is a fair point however, I can only speak for the height of my lands. I spec all of that when I order a button, I can see no reason to spec taller lands. Is it possible other manufacture's spec it out differently? Of course.

Your comment about being OK at 2930 FPS but bullets come apart at anything over 3,000 is similar to what I've seen with those fast 22's I mentioned earlier. Granted, it tended to happen above about 3300-3400. Like Brad mentioned below, I make it a point to discuss what the cartridge will be and what bullets they'll be shooting. The last thing I want is for someone to have issue's like this."
 

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I will chime in. My 6.5 PRC 8 twist 4 groove Proof is fine with 147s at 2930 but after the barrel sped up (same load over 3000) the bullets started going poof before 100 yards. I seemed to be around 15 rounds after cleaning it started and was about 50%. I have a sheep hunt coming up and have no time(nor do I really desire to waste my barrel life) to diagnose. It is not currently happening with 156 Bergers at 3040 fps.
 

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I still have half a box of the Hornaday 147's left. I will drop the velocity to 2950 fps and have a looksee if the jackets hold together there. Running an 8 twist on the 5R Krieger.
 

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I really wish this thread would have been out there about 7 months ago. My dad and I just built 2 6.5 PRC's with proof 7.5 4 groove barrels with the idea to shoot the 147's. Damn...
 

Broz

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I really wish this thread would have been out there about 7 months ago. My dad and I just built 2 6.5 PRC's with proof 7.5 4 groove barrels with the idea to shoot the 147's. Damn...
Its been a concern of mine for years and I have often suggested if you are building a hunting rifle with the intention of shooting jacketed cup core bullets, stay with 5 and 6 groove barrels. I saw the trend swinging back to what we saw years ago and started this thread back in March.

No solid testing done yet, but if you shoot the 156 Bergers you may very well be ok especially if you keep them under 3K. This is just an assumption at this point, terminal performance testing will hold the real answer.

Jeff
 

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Good info. I talked to the builder of our rifles today as i remembered him mentioning something about this before I started our builds and maybe he had a possible fix. Its what hr was running personally and having good luck. He's using a Muller modified land profile which our rifles have as well. I've been shooting the 147's and 143's and havent had problems yet but the more talk of issues I'm just a little nervous as these are hunting rifles and I can't have failures. Hes been seeing a descent amount of failures lately in 5r's as well. Maybe these are cheaply made/poorly designed bullets? Not trying to bad mouth and am definitely not an expert. Maybe just need to shoot something else? One of the berger 140's or 156?
 

Broz

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Good info. I talked to the builder of our rifles today as i remembered him mentioning something about this before I started our builds and maybe he had a possible fix. Its what hr was running personally and having good luck. He's using a Muller modified land profile which our rifles have as well. I've been shooting the 147's and 143's and havent had problems yet but the more talk of issues I'm just a little nervous as these are hunting rifles and I can't have failures. Hes been seeing a descent amount of failures lately in 5r's as well. Maybe these are cheaply made/poorly designed bullets? Not trying to bad mouth and am definitely not an expert. Maybe just need to shoot something else? One of the berger 140's or 156?
Can you offer us the specs on "Muller Modified land profile" please. I am not familiar with it.

I have never seen this issue with 5R but 8 twists are as tight as I have ran them. That is in a 30 cal with 230 Bergers to 3300 fps.

I really think your best bet is to run the 156 Berger. It should come in about 3k and I feel it should be ok. But as we stated, terminal performance tests should be conducted. Ryan Furman is running them from an 8 twist at 3K and they are shooting lights out to 1000

Jeff
 

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Can you offer us the specs on "Muller Modified land profile" please. I am not familiar with it.

I have never seen this issue with 5R but 8 twists are as tight as I have ran them. That is in a 30 cal with 230 Bergers to 3300 fps.

I really think your best bet is to run the 156 Berger. It should come in about 3k and I feel it should be ok. But as we stated, terminal performance tests should be conducted. Ryan Furman is running them from an 8 twist at 3K and they are shooting lights out to 1000

Jeff
Sorry just getting back to ya broz. Been away from internet service. Anyways, I will see what I can come up with. These rifles were built by Alamo Precision. Ive been talking to robert there the most. I don't know much or really anything about these details. Just what I wrote earlier and I havent had any issues. Yet...
 

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I read this thread last night and got a terrible feeling, as I just purchased a 6.5 prc with a 20'' 1:7.5 proof barrel. I called berger tech support today and asked them about this issue. The man I talked to said it was the first he's heard of it. I asked if he thought I'd have any issue with the new 156's in my rifle and his reply was absolutely not and that if there was to update them so they were aware of this issue. Well I guess there's only one way to find out now. He did provide me with their reloading data for the prc with N565, N570 and H1000. If anyone is interested in I can post it.

Happy shooting to all!
 
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Broz

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I read this thread last night and got a terrible feeling, as I just purchased a 6.5 prc with a 20'' 1:7 proof barrel. I called berger tech support today and asked them about this issue. The man I talked to said it was the first he's heard of it. I asked if he thought I'd have any issue with the new 156's in my rifle and his reply was absolutely not and that if there was to update them so they were aware of this issue. Well I guess there's only one way to find out now. He did provide me with their reloading data for the prc with N565, N570 and H1000. If anyone is interested in I can post it.

Happy shooting to all!
So far we have not seen an issue with the 156 Bergers. But we have with 147 ELD's. Do I think it is a perfect scenario to use a 4 groove with a thin jacketed bullet, no. I choose not to. But this does not mean it will not work, only something to be aware of if you have one blow on impact.

Jeff
 

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I have not seen the issue with my 156s in my Proof but after the barrel sped up the 147s started blowing up. I would say 1 out of 10 are not reaching the target even at 100 yards.
 

Broz

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This is my concern. The 1 in 10 is not the issue, the other 9 on the verge of coming apart are why I wanted to bring this up for discussion. If we all keep an open mind and report solid data, we can help others.
 

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I have not seen the issue with my 156s in my Proof but after the barrel sped up the 147s started blowing up. I would say 1 out of 10 are not reaching the target even at 100 yards.
Have you had this issue with berger 140's? or just the hornadys?
 

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It has been years and many rifles ago since I have shot a 140 and don't see any in my future.
 

Fuzzi1

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My last post was #30. As promised, I dropped the velocity further still on my 6.5GAP (Krieger 5R barrel - 28inch) with the Hornaday 147 ELDM. Even at that low a velocity I am still popping the Hornadays. About 1 in 10 now as opposed to 4 out of 10 at 3050fps. I cannot detect a clear pattern, like more blow-ups when the barrel is hot versus cold bore. It is simply too random for me to make any sense of it. Anyway, moved on from the Hornadays. Real pity though as they were accurate. Managed a hit on a IPSIC size gong at 1750m after walking the last few shots in. The misses in the dirt were real predictable and I could easily compensate by aiming off in my reticle. Got lucky and rang steel on the 2nd last shot of the box..lol Waiting for the 156Bergers to show up. Hope they stabilize in my 8 twist as I am virtually on the high level mark at the coast.
 

Broz

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Here is a little data I stole from a fb page where it seems there are a lot of fast twist 3 and 4 groove barrels having issues with 147's and a few other bullets. I think I called this storm pretty close back in March when I started this thread.


1-8 3 groove pacnor... about 2950 FPS.


 

Broz

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Broz, that looks more like tumbling/not stable to me? Doesn't it?
He stated they were blowing up as indicated by the banana shaped one. And if you look close you can also see lead splatter on the paper.

EDIT to add: I would think the 8 twist should stabilize the 140 fine. But the thin jackets of the ELD M I don't believe like the 3 groove.
 
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6.5sandoz

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I guide in wyoming and i just had a bullet blow up on and antelope at 310 yards. I wasnt able to find out the number of grooves but was instantly suspicious it was a 3 or 4. Do to the distance of the shot and the weight of the bullet(195) and the small body size of antelope i didnt feel like there was a good excuse for complete blow up. Also will state that the rifle had a proof barrel and was a 7mm stw.
 

XTREMHTR16

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So what I can gather is this:
I have 2 proof sendero light 6.5mm barrels, both 4 groove 8 twist, 1 @ 20” and 1 @ 22”. I am planning on using the 22” to build a 6.5 PRC and run suppressed with my Ultra 7. I should be fine with the build as long as I stick with the 139 Scenar (my favorite) or the 140 or 156 Berger.
correct?
 

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