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Lands/Grooves choice

 
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  #1  
Old 07-20-2006, 06:25 PM
 
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Lands/Grooves choice

I was wondering what everyone prefers in the way of lands and grooves? Im looking to build a fast twist 280AI and so far Ive talked myself into a 5 groove, but I wonder if I would be better off with a 3 or 6? How do you decided what number of lands/grooves to get? Thanks.
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Old 07-20-2006, 07:11 PM
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Re: Lands/Grooves choice

Well from what I've delt with it seems that the more lands and grooves the more bullet friendly they are (ie) 40gr bullets at 4500fps.
And from what I have heard from guys that have shoot out both 6 groove and 3 groove in the same caliber the 3 groove will last longer.

In a case like the 280Ai , I don't think that you will see any problems blowing up bullets with the 3 groove to try to get a little longer life out of it.
But after owning both a 5r Rock creek barrel and a
5R Obermeyer they are both awsome tubes to.
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Old 07-21-2006, 06:51 AM
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Re: Lands/Grooves choice

MSUMarksman,

JDJones is right on with his comments as far as I am concerned.

Only time I do not use a 3 groove rifling design(Lilja) is when I will be driving a very heavy(long) J-4 jacketed bullet fast in a fast twist barrel.

The upper end range for a 3 groove barrel with a J-4 jacketed bullet seems to be 1-8 twist and around 3200 to 3250 fps. The SMKs allow significantly more velocity before being effected by the 3 groove as far as bullet failure.

In your case of the 280 AI. If your going with a fast twist barrel I assume you will be using heavy for caliber bullets as in the case of that chambering you will not have the velocity potential to do any damage to any bullet out there in the VLD or ULD design on any jacket that is currently being used.

The 280 AI is very bullet friendly, even with the heavy thin jacketed bullets so your selection of rifling design is not all that critical.

I have heard reports that the 5C and 5R barrels will get to significantly more velocity and less pressure then a conventional 3 groove barrel such as that from Lilja, I have not seen this with actual tests.

I actually tested a Broughton 5C barrel in 6.5mm and a Lilja 3 groove barrel of the same caliber, both chambered in 6.5mm WSM. The Broughton was advertised to make it impossible to loosen a primer pocket using appropriate powders for the selected round being used.

Well, I loaded up the Lilja barrel to top end loads and then did the same with the Broughton and in once fired cases, the Broughton barrel was loosening primer pockets with one grain less powder then the Lilja was.

This was not just a one shot test, this was an average of five cases at each load level. Same brass, same powder, same bullets, same exact chamber and throat.

Simply put, they were so damn close to identical it was not even worth comparing but the claims you can not loosen a primer pocket with the 5C barrel was not legit which I never beleived for a minute.

As far as accuracy was concerned, both barrels were 15" barrels on XP-100 handguns. They both were averaging in the 1 to 1 1/4" range at 300 yards so there was no sign that one was more accurate then the other, both shot amazingly well.

Simply put, with the chambering you are going to use, take your pick, it will not be critical in the 280 AI. Get a Lilja, Broughton, Rock, Krieger or Hall and you will be happy with the results if it is machined correctly on a square receiver.

Good Shooting!!

Kirby Allen(50)
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Old 07-21-2006, 04:53 PM
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Re: Lands/Grooves choice

Amongst top competitive rifle shooters, lighter/shorter bullets for a given caliber tend to shoot more accurate with fewer grooves than with more grooves. I don't know the details as to why, but the facts and results of accuracy tests seem to prove this out when the only thing different across them is bullet weight/length and powder charge weight and number of grooves.

I don't know about barrel life as I don't know of anyone who's made proper tests to get valid results. There are varying opinions about barrel life versus groove count. And "accurate" barrel life depends as much on how the accuracy tests are conducted plus how well the ammo's made and shot as the barrel quality and type, so one can get all sorts of numbers.
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Old 07-21-2006, 08:27 PM
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Re: Lands/Grooves choice

[ QUOTE ]
And from what I have heard from guys that have shoot out both 6 groove and 3 groove in the same caliber the 3 groove will last longer.


[/ QUOTE ]

This is not my experience at all. I have had several 3 groove barrels and while it is true the lands stayed put longer, the firecracking associated with a well worn barrel still affected the group size. I simple bore scope session with a 3 groove barrel on a hot rod will show just as much firecracking as an 8 groove barrel but the shooter may still be able to touch his riflings with the bullet. However, that will probably still not save it from shooting worse.
I do agree that 5's, 6's, and 8 groove barrels are more gentle on fragile bullets though.

Just my 2.
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