6.5 PRC 156gr Berger EOL twist dilemma

[Darryle]

Was getting ready to order a #3 or #3b Bartlein, decided to use the twist stability calculator and it flip flops both sides of marginally stable/stable in our atmosphere/altitude depending on temperature with the 8 twist, 7.5 twist is fine. No plans to use monolithic bullets and I am limited to 3.010" magazine, so the 2.950" will be fine. Intended load data is 2850/2880ish depending on who you are asking, this is also with a 26" which I have no desire for on this rifle.

The #3 7.5 twist is available ready to ship, the #3b is special order or do I call them up and get a 7 twist on order. I could probably do flutes, but would rather not.

Plan to finish at 24", so the #3 will be slightly easier on the shoulder, roughly 4oz difference in blanks. McMillan Game Scout stock is 29ish oz and inlet for the #3 contour.

Order the #3 7.5
Order the #3b 8
Special order the #3 or #3b in a 7 or 8 twist?

*Edit to correct grammatical and spelling errors*

 

[RockyMtnMT]

I would recommend the faster twist for best performance.

 

[wasskeet]

I never had any issues running the 156 EOL at approx. that speed out of a 1:8" Bergara. It was good to 1000yds. at 1800ft. down to probably 40 degrees. That said - if I had a choice, probably would go with 1:7.5". Good luck with your new project!

 

[Dragoon300]

Was getting ready to order a #3 or #3b Bartlein, decided to use the twist stability calculator and it flip flops both sides of marginally stable/stable in our atmosphere/altitude depending on temperature with the 8 twist, 7.5 twist is fine. No plans to use monolithic bullets and I am limited to 3.010" magazine, so the 2.950" will be fine. Intended load data is 2850/2880ish depending on who you are asking, this is also with a 26" which I have no desire for on this rifle.

The #3 7.5 twist is available ready to ship, the #3b is special order or do I call them up and get a 7 twist on order. I could probably do flutes, but would rather not.

Plan to finish at 24", so the #3 will be slightly easier on the shoulder, roughly 4oz difference in blanks. McMillan Game Scout stock is 29ish oz and inlet for the #3 contour.

Order the #3 7.5
Order the #3b 8
Special or the #3 or #3b in a 7 or 8 twist?

Order the 7.5 it should work for your description.
I have their gain twist in 1:8.35 to 1:7.35 5R Lefthand rotation that really works for my 6.5 PRC with 153.5/ 156 Bergers. I am sold on Bartlien and gain twist Lefthand rotation for the Northern hemisphere and the 5R rifling. I have not anything bad to report, great accuracy!

 

[highdrum]

7.5 all day with my last 4 65mm pipes. No complaints shooting 140-156gr bullets. The newest is a 20" Saum and I want to run 130 grain stuff to keep velocity up. Will see how those do. Will try the heavies too.

 

[Darryle]

We don't have really cold weather often, sub 30º. Elevation is 1630ish ft. I had pretty much talked myself into the 8 twist 3b because I will mostly use the 140gr EH and VLD-H and the 153.5gr LRHT. I just happen to have a good supply of the 156gr EOL for the 6.5-280 Ackley build and thought it may come in handy to have the extra twist if I need it. I knew it certainly wouldn't hurt.

Stability calculations

8 twist

50º

30º

7.5 twist

50º

30º

20º

 

[Lee7588]

I have a 1- 7.5 twist on my 6.5 PRC and when this burn burns out I'll order a 1-7 twist.

 

[FEENIX]

Was getting ready to order a #3 or #3b Bartlein, decided to use the twist stability calculator and it flip flops both sides of marginally stable/stable in our atmosphere/altitude depending on temperature with the 8 twist, 7.5 twist is fine. No plans to use monolithic bullets and I am limited to 3.010" magazine, so the 2.950" will be fine. Intended load data is 2850/2880ish depending on who you are asking, this is also with a 26" which I have no desire for on this rifle.

The #3 7.5 twist is available ready to ship, the #3b is special order or do I call them up and get a 7 twist on order. I could probably do flutes, but would rather not.

Plan to finish at 24", so the #3 will be slightly easier on the shoulder, roughly 4oz difference in blanks. McMillan Game Scout stock is 29ish oz and inlet for the #3 contour.

Order the #3 7.5
Order the #3b 8
Special order the #3 or #3b in a 7 or 8 twist?

*Edit to correct grammatical and spelling errors*

I went with 1:7" 5R on my .264 WM, specifically built for the 156 Berger. While I have a few different mono bullets in .26 cal. I, too, have no plans on using monos on this rifle. Good luck!

 

[Tucker65]

I've built quite a few of the 6.5 prc's and used 7.5 twist on all of them with the 156gr Berger's. All of the rifles had carbon wrapped barrels and were either 24" or 26" in length. The rifles were built on medium length actions also the OAL cartridge length was a little longer than yours. Speeds were 2950-3000 fps. burning Rl-26 or N565.

 

[dug]

1-7.5 would be my choice for the 140 class bullet you say would be used most of the time ,and the option for the 156 gr
especially if your not going to be shooting through transonic with the 156 ers at mile targets
in my opinion the 1-7 tw with 140's can turn pressure up before reaching max fps
again not a game changer depending where the barrel likes the accuracy note , but having to take the next note down because of pressure signs ,sucks.
its a balancing act on intended max range shooting (transonic)
and how important max fps is to hunting , which this rifle seems to be for ? ( #3 at 24" ) no one should be hunting at transonic .
time of flight can out run a higher BC for a while , but BC always wins if shot far enough. Run some velocity numbers with both bullets and see where the time of flight beats the higher BC in wind drift and impact fps which directly effects bullet performance On game.

case in point i run a 130 gr vld in my 260 rem gas gun , magazine length limits case capacity with 140's ,so the 130 at faster fps runs passed the 140 in max range i need for impact velocity for hunting . Shooting targets out to 1K yrds the slower 140's are king
but i dont hunt at those impact velocities .

a gain tw barrel, in theory ,can get your target tw rate and help keep pressure curve flatter .
i have no experience with them so i cant offer an opinion on them.
i have often wanted to try one , maybe the next blank i order

As to the left hand tw barrel it is a great idea to use. But how do you keep the barrel from loosening up with right hand threaded action and barrel tendon? Do you use a pin or set screws to secure it ? Years ago i asked many smiths about making a left hand tw barrel work on righthand threaded actions , no one was interested in helping me
hope this helps and doesnt cause more questions on the decision

 

[dug]

Sorry for the bold text , not sure how i did that. I didnt notice when i was typing it , old eyes are fun !

 

[SteveBurton]

I had issues using a 24" with 1:8 twist @1200' in the desert so 90 degree plus days are the norm. I was pushing 156s @2900 fps and they just wouldn't group well. I went with a 24" CarbonSix with 1:7.5 twist and haven't had any issues in AZ or in PA with 30 degree temps @1600'.

 

[lancetkenyon]

Most of my 6.5mm rifles run a 1:7.5" except two.

6.5CM (my older daughter's factory rifle) 1:8" shooting a 130 OTM
6.5SLR (my younger daughter's custom) 1:8" shooting a 130 OTM

All the rest run a 1:7.5"
.260AI w. 130 OTM, 130 TMK & 140 Hyb
6.5PRC w. 129 NABLR, 130 TMK, 130 OTM, 140 Hyb, 150 SMK, 156 Elite
6.5PRC/SI w. 140 Elite & 156 Elite
6.5SS (20") w. 130 OTM, 140 Hyb, 150 SMK
6.5SS (26") w. 156 Elite

I just purchased another 20" 1:7.5" to build a short/light .260AI that will run a 140 Hyb

The 156 states "for 1:8" minimum" on the box. But I feel the 1:7.5" is jist a bit better suited for them. Even the super long 150 SMK shoots excellent in a 1:7.5". I personally do not feel a 1:7" is NEEDED. But it doesn't hurt either.

I would go #3 1:7.5" myself.

 

[JuddL]

The current trend is to over twist but an 8 will work fine.

Between your choices, the twist wouldn't drive my decision the barrel profile would.