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  1. #1
    LRO Owner ~ Review Editor ~ Long Range Hunting Specialist Broz's Avatar
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    Effects of 3 and 4 Groove Barrels on thin Jacketed Bullets

    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

  2. #2
    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.

  3. #3
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    Quote Originally Posted by Broz View Post
    .........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.

  4. #4
    Senior Member adam32's Avatar
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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!?

  5. #5
    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.

  6. #6
    LRO Owner ~ Review Editor ~ Long Range Hunting Specialist Broz's Avatar
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    Quote Originally Posted by TXSlayer View Post
    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

  7. #7
    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.

  8. #8
    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

  9. #9
    LRO Owner ~ Review Editor ~ Long Range Hunting Specialist Broz's Avatar
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    Quote Originally Posted by 10at6 View Post
    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

  10. #10

    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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