Gunsmithing 6.5 barrel twist for 139 to142gr

[mike harper]

What twist rate should be used in a 24" to 27" barrel for 139gr to 142gr. 26o.Rem, I'm wanting to use 140gr VLD's.

Thank you

Mike Harper

 

[dvdt]

Re: 6.5 barrel twist for 139 to142gr

I have a 1:8.5 twist for both of my rifles. I've seen 1:8 recommended as well. My bolt gun (6.5CM) has a 1:8.5 twist.

 

[Sportin Wood]

Re: 6.5 barrel twist for 139 to142gr

1:8 will work great

 

[Tac284]

Re: 6.5 barrel twist for 139 to142gr

Most the guys I shoot with are running 1:8 with those bullet weights but a 1:8.5 will get the same job done I bet.

 

[ANGLICOMarine]

Re: 6.5 barrel twist for 139 to142gr

I have a 1:8 in my 6.5 CM and 6.5x284

 

[Bone318]

Re: 6.5 barrel twist for 139 to142gr

I've never ran the 142's, but have run the 139 scenars through an 8.5 twist since late 2008 with really great results.

 

[2clicks]

Re: 6.5 barrel twist for 139 to142gr

Word on the street is 1-8.5 will get more velocity than a 8 twist... So I got a 8.5 Bartlein 5R rifling works well 2800+ with a gap smithed 260. Just one guys experience... Hind sight being 20/20 I probably should have went with the 6.5 super long story why I didn't.

 

[Bone318]

Re: 6.5 barrel twist for 139 to142gr

I have also run the 5r up to this point. However, a bunch of guys I shoot with have found that 4 grooves seem to shoot a little better so that's what the barrel I have coming in will be.

Just my .02

 

[mm509]

Re: 6.5 barrel twist for 139 to142gr

If you go to Obermeyer's website, Boots goes in to depth as to why his standard twist for the 6.5mm is 8.75tw. I was extremely, and I can not emphasize "extremely", optimistic about going with that slow of a twist, but figured WTF.

I was even more scared when my first box of 140 AMAX's said "recommended twist 7.5 and faster". I have taken my rifle to 1780 yards, and still had splash on full size silhouette targets. We managed to retrieve a couple of bullets at the 1 mile mark that impacted dirt, and every single one was nosed in to the ground and starting to turn to the right.

We tried to push this same load out of a 9tw Nemesis barrel and they hit the same target sideways (tumbling).

My load throws the 140 AMAX at a fairly modest 2800fps from a 22" barrel. Hope this helps, or at least gives a little insight.

Matt

 

[2clicks]

Re: 6.5 barrel twist for 139 to142gr

Bones318 any speculation on the 4 groove success? I wonder if the longer bearing surface of the 140 class 6.5 would benefit from less drag of the 4 groove rifling. There is less drag in a 4 groove isn't there?

 

[Bone318]

Re: 6.5 barrel twist for 139 to142gr

2clicks, not sure. I'll ask the guys and get back to you. Have some real knowledgable people to pull from. As stated, I have had good success with 5r. It's just that 4 grooves seem to be a little better with same accuracy.

I'll get back after 1/8/12

 

[Frank Green]

Re: 6.5 barrel twist for 139 to142gr

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bone318</div><div class="ubbcode-body">I have also run the 5r up to this point. However, a bunch of guys I shoot with have found that 4 grooves seem to shoot a little better so that's what the barrel I have coming in will be.

Just my .02 </div></div>

Shoot better how? For the most part barrel life and accuracy the number of grooves has no bearing/impact on it.

Later, Frank
Bartlein Barrels

 

[Bugholes]

Re: 6.5 barrel twist for 139 to142gr

8.5 is a good safe twist for the 140s in a 260, Overstabilizing is a problem, and it's more than just bullets coming apart

 

[1snowcat]

Re: 6.5 barrel twist for 139 to142gr

Im curious as well... I am in the process of building a 6.5 x 284 and looking at 140-120 gr. bullet category... Really want to be able to put the hammer on deer/elk or sheep.... At distance as well as close up...

1:8 or 1:8.5???

 

[Bone318]

Re: 6.5 barrel twist for 139 to142gr

@ Frank - guys are getting better velocities. not huge, but noticeable. FYI, thanks for all of the group buys you all have done for the NCPPRC. I am running Bartleins on all my rigs and love them.

jerry

 

[Frank Green]

Re: 6.5 barrel twist for 139 to142gr

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bone318</div><div class="ubbcode-body">@ Frank - guys are getting better velocities. not huge, but noticeable. FYI, thanks for all of the group buys you all have done for the NCPPRC. I am running Bartleins on all my rigs and love them.

jerry </div></div>

Hey Jerry! Thanks for using the sticks and that you guys are liking them!!!

The number of grooves with the bore surface area being different etc....should have no bearing velocities. Very interesting.

Also a variation of up to a 100fps. is normal from barrel to barrel etc... I remember years ago we made two barrels back to back s/n's etc... for Warner Tool. One barrel went on Al's gun and another for a close customer of his. Both barrels where <span style="font-weight: bold">4 groove .30cal.</span> As identical you could make two barrels. One barrel was a <span style="font-weight: bold">flat 100fps faster</span> than the other.

It would be interesting to know what 4 groove barrel they are being compared to. I don't care about the maker but what I would like to know are the bore and groove sizes/dimensions, groove width etc....what I'm saying here is what does the actual bore size measure and groove size. A tighter or looser bore and or groove size can have a huge bearing on what a barrel produces for velocity.

Is the same chamber reamer being used in the barrels that are being compared? This is another variable.

Bugholes, I don't think there would be a big difference in between a 1-8 vs. a 1-8.5 twist. I would say it would depend on what it's chambered in and velocities you are getting that this will effect over stabilization and bullets coming apart etc.... another thing that effects bullets coming apart are the bore sizes. A tighter bore where the rifling is cutting into the bullet jacket more will have an impact as well. If you are shooting some bullets with a thinner jacket and the rifling is cutting deeper into it this will cause stress points on the jacket and if it's cutting thru the jacket to the core these are things that are going to cause the bullets to fail as well. I also feel that the 5R with the gentler angles and the odd number of grooves will help distort the bullet jacket less and this will help with bullet failure.

You start combining a tighter bore, faster twists, higher velocities the style of grooves, a thinner jacket bullet is all leaning towards producing bullet failures in my opinion. Again there are just a ton of variables.

Spinning the bullet faster if you are shooting a poorer grade/quality type bullet or if your ammo has a lot of run out I would agree with as a start as this can and will have an impact on accuracy.

Back in 2008 we made a 4 groove and a 5R barrel both 1-8.5 twist for Berger bullets and they also got some barrels from another barrel maker and they did testing on velocities, bullet failure and they beat the crap out of the bullets and loads on the ammo etc....and if memory serves me right velocities where not a big concern but bullet failure was.

Later, Frank
Bartlein Barrels

 

[jcsguns]

Re: 6.5 barrel twist for 139 to142gr

hello, my 14 year old son shoots a h s precision built 6.5 with a 26 inch barrel and a twist rate of 1/9. my load info is 140 smk 47.2 of n160 oal 2.995. good luck i hope this info help you out.

 

[LSandBinc]

Re: 6.5 barrel twist for 139 to142gr

Running a 6.5x47L with a 1/8 twist at 2830 fps shoots 5 shot groups into .120

 

[JC Steel]

Re: 6.5 barrel twist for 139 to142gr

1 and 8.5 should be perfect.

 

[2clicks]

Re: 6.5 barrel twist for 139 to142gr

Frank,
So would it be correct to say all factors being equal as far as bore/chamber dimensions a 4 groove compared to a 5 groove Should theoretically produce the same velocities. I realize nothing is ever exactly the same but if it was possible would this theory be true? Looking for a better understanding of rifling 101 here.. Thanks for all the insight!

 

[BruxBarrels]

Re: 6.5 barrel twist for 139 to142gr

2clicks, from what we have seen here at Brux Barrels with various testing is that it doesn't really matter how many lands/grooves there are, but its more dependent on the groove to lands ratio. There seems to be a happy medium in there.

 

[Frank Green]

Re: 6.5 barrel twist for 139 to142gr

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 2clicks</div><div class="ubbcode-body">Frank,
So would it be correct to say all factors being equal as far as bore/chamber dimensions a 4 groove compared to a 5 groove Should theoretically produce the same velocities. I realize nothing is ever exactly the same but if it was possible would this theory be true? Looking for a better understanding of rifling 101 here.. Thanks for all the insight! </div></div>

Correct. The number of grooves should have no real bearing on accuracy or velocity as long as the surface area of the bore is the same like I stated before. You start changing bore size and groove size will have a bigger impact.

I've got a conventional 5 groove barrel on my 6PPC gun and the velocities are not really any different than other 6PPC guns is another example as most guys are shooting standard 4 groove.

That's why I say when someone says I get 200 more fps. out of my barrel than my buddies barrel. They are not necessarily comparing apples and apples. I've got this going on with a manufacturer right now. They are not happy with they're current supplier and are purchasing barrels from several different makers. I told them to make sure they spec. all the barrels the same so when they do testing they are comparing apples and apples when looking at velocities and accuracy etc...

Later, Frank
Bartlein Barrels

 

[mdesign]

Re: 6.5 barrel twist for 139 to142gr

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Brux Barrels</div><div class="ubbcode-body">.....groove to lands ratio. There seems to be a happy medium in there. </div></div>

If I am understanding this correctly, the G/L ratio has to do with what percentage of the area of the bore is grooves and what percentage is lands? And if the width of the groove was the same as the lands the ration would be 1 to 1 (or 50% to 50%)providing there was an equal number of G/L? So if the number of grooves changes the width of the groove has to change as well to maintain the same ratio.

I have an older 30 cal 3-groove barrel that shoots very well but I have noticed that the grooves are much wider than in my 5R or 5C barrels. Always wondered why they made them that way as they seem pretty wide when just looking at them.

 

[Frank Green]

Re: 6.5 barrel twist for 139 to142gr

mdesign, Looks like you got it right. To maintain the same bore surface area yes the groove widths etc...have to change with the different number of grooves.

Your 3 groove barrel. I don't know who made it but you are probably seeing it correctly. The lands/grooves are wider. Some barrel makers just took the dimensions for a standard 6 groove .30cal. barrel and divided the numbers in half and that's how they made the 3 grooves. A little speculation on my end as I cannot see the barrel and exactly what that barrel maker did only he would know off hand.

Back when we we're at Krieger we made some 3 groove tight bore palma barrels for one of the top palma shooters in the country. The bore and groove came out to be basically a 50/50 land to groove ratio. He told me accuracy was just as good as the 4 grooves we made. Absolutely no difference. But velocity of the 3 grooves where a flat 100-150fps. slower. We made like two or three of the barrels not just one. My only speculation here is maybe the bore and groove sizes where a little different than his 4 grooves or that the wider land of the 3 grooves was putting a little more drag/resistance on bullets etc....no sure about those anymore as that was around 10 years ago.

With that being said we have made some 3 groove 6mm barrels for the short range bench guys shooting the 6PPC and the comments back was there was no difference between those and the 4 grooves we make so for the most part we don't make the 3 grooves as no one really wants to pay the extra cost to make the 3 grooves.

Later, Frank
Bartlein Barrels

 

[mdesign]

Re: 6.5 barrel twist for 139 to142gr

Thanks Frank...After I got a bore scope, I really started paying attention to what the inside of barrels looked like. The different styles of rifling do look different and you see some interesting things when looking at the length of the bore.

My 3-groove is a Lilja and I've probably had it for 10 years. Shoots real well with minimal fouling.

Really would like to try one of your gain twist barrels in 7mm one of these days.