MYTH or FACT (velocity difference in rifling)

[Buffalobob]

Perhaps not what you asked but still relevant to the discussion. Different numbers of grooves will compress a bullet in different amounts. I have a four groove Lilja on my 7 AM and it will shoot the J4 jacketed 200 gr Wildcats just fine in moderate temperatures. The rifle was first proposed to be built with a three groove barrel but Kirby found that the compression distorted the bullet and caused them to blow up and went to the four groove. Others have reported that the 3 groove pac nors do not do well with ultra fast bullets.

Gain twist is a whole different subject and if I ever build another obermag screamer it will be with gain twist. I don't think it does much for rifles with moderate velocity shooting moderate weight bullets. However, my S&W 460 XVR has a gain twist barrel.

 

[elkaholic]

I blew up some 180 v-max bullets with a 3 groove Lilja in my 300 Rum. It had a 30" barrel and they would blow around 3400'. My 3 groove on my 6.5 Sherman does just fine with 140 Bergers up to at least 3200'. I've heard they don't work well on the hot .223's for the reason you mentioned. A little more forgiving, the larger the diameter...Rich

 

[AZShooter]

Good discussion. Hope more shooters add to this thread.

It was several years ago that my friend and I put together four 257 weatherbys with 3 groove SS Lilja 1 in 10 twist barrels. Used a Pacific Tool and Gauge reamer with shorter throat than Weatherby specs. All of these rifles shot very accurately with the 115 VLDs. Another friend made the fifth with same reamer and it shot just as well. One of my rifles got to round count 540 and began throwing the occasional flyer. Out as far as 10-12" at 100 yds! I did all sorts of rifle inspections including a bore scope and concluded the barrel was the cause. Moved to 110 accubonds and the rifle is back to shooting nice little groups. Based on a previously owned 3 groove I believe the worn throat of the three groove barrel is too much for the thinner jacket on those VLDs.

Previous 3 groove with same issue: My same friend and I were so happy with the 257 performance we bought two 3 groove 7mm barrels. Lilja only offered them in 1 in 7 twist. I specifically asked if the fast twist would cause any issues with 180 VLDs. Was told there will be no problems. My friend's was a 7 STW and mine was a 7 rem mag. His began to destroy the 180 VLDs at round count 175 or so. My rifle did the same thing at just over 200 rounds. Before that the 180s shot nice little clusters at 500M. Murphy's law had the 7 rem mag shooting beautifully during its first deer hunt. My friend shot his deer with this rifle at just over 400 yds. Three days later I shot at mine and it gutted it. I shot several more and my spotter was saying 5 ft high, 3 ft to the right etc for several shots. Talk about wrong time for that barrel to stop performing! I had to finish off the 400 yd deer with another rifle.

This is when I discovered that the barrel would still shoot bonded bullets and monos like the E-tip.

I hope this information can help prevent someone else from suffering the same fate.

 

[Bart B]

There may well be a difference in muzzle velocity with different rifling types for the same barrel length and groove diameter when the same rifle and chambering reamer is used. Unless the comparison is realistic and only one thing changes (rifling type and nothing else), any answer one gets is probably flawed. It takes more force to push a bullet into 6 grooves than any lesser number with the same bore and groove diameter as well as rifling shape with only the width of the lands being different. Which means there'll be more chamber pressure as the powder starts burning and that may well result in a slightly higher muzzle velocity

I've seen 3 groove barrels shoot just as accurate as those with 4, 5 or 6 grooves. I'm referring to those that will shoot bullets under 4 inches all day long at 600 yards. Therefore I don't believe that the number of grooves matters.

But there seems to be a difference in accuracy for a given bullet caliber and shape when fired through 4 or 6 groove barrels. Best example is Sierra's 155-gr. Palma bullet which seems to do best with 4 groove barrels. When it came out in 1991, folks with 6 groove barrels didn't shoot it as accurate as those with 4 groove barrels.

I find it hard to believe that anyone would claim that a 4 groove barrel would compress and/or reshape bullets such that they wouldn't shoot accurate. One would have to measure normally fired bullets (undamaged by impact in whatever they're caught in) to find out if they did change. 4 groove barrels have been in so many very accurate, match winning and record setting events so anyone knowing of this would believe there's nothing wrong with them. So in my opinion, anyone thinking 4 grooves ain't good for accuracy has been doing the wrong stuff to learn the difference.

Any difference between rifling types won't be enough to loose sleep over. However, folks wanting the fastes bullet speed possible as their top priority may be able to get one. If 50 fps more muzzle velocity is attainable with a 10% loss of accuracy, such is life.