6.5 PRC 156gr Berger EOL twist dilemma

[Krowen]

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

No problem easier for old eyes to read

 

[CoachChris]

I recently rebarreled my 6.5 PRC.
I went with a 1:7 Shilen Varmint contour.
I live at 6300'

 

[JAYgs8163]

I built mine with a 7.5 twist after speaking with with Berger and Krieger about it. Works great with the 156 and 144 Bergers. Never an issue. I reside at about 2200' elevation and hunt in areas up to 7500 but mostly hunt at 3000-4000 el.

 

[tacomHQ]

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

Not necessarily applicable in this situation but very real.
Given the same twist rates:
We have found that Barrel MfrA can shoot Bullet MfrA but cannot shoot Bullet MfrB- as in won't stabilize.
But Barrel Mfr B can shoot Bullet MfrB but cannot shoot Bullet Mfr A. In some cases keyholes and or missed targets at 100yds.
This has been seen on multiple Barrel Mfg's and multiple Bullet Mfg's.
Solids are more susceptible - to date- to this phenomena.
We have seen this, repeating, phenomena even when twist rates are well within mfg's specs and meet stability specs.
While this is seen with solids predominately- barrels that could not shoot a specific solid bullet could all shoot copper/lead bullets. As in stabilized and not key holes.
NOTE: this will have to be further proven over "time" and standard tool changes at the Barrel Mfg to determine root cause.

Gain twist - in our experience - do reduce initial pressure values, bolt set back and initial felt recoil. We run single digit gains such as Bartlein to large 4+Twist gains using K.S. Arms Ltd . We have done this on 6mm to 460 cals.. We actually tested consecutive 460 barrels one with a 1GT and the other with a 4GT. Coincidentally in this test the 4GT had higher velocity per powder charge, could run a higher powder charge and had less felt recoil.
All of our shop guns now run the large gain twist... Another significant attribute does exist, potentially the most important attribute, but we are continuing testing to see what the downsides are.

 

[OG-danimal]

I run a 7.5 and have no issues shooting the 156 out to 1000 yards

 

[Phil Rizzo]

Tacom: Have you seen a pattern concerning accuracy with gain twist vs standard?

 

[Allen Kitts]

If the 7-1/2 is available I would take it. the 1 in 8 on my prc works just fine with the 156's but i was able to get the 140 Accubonds to shoot better, one hole, so that is what I am using and it has performed wonderfully on the game I have taken.
The faster twist will just allow you to go to the mono's if the bug ever hits ya. JMO and good luck.

 

[ARlife4me]

In my 6.5creeds and 260rems all are 8's including the 6.5prc (limiting myself @ 135ish grains). A purpose built 264wm 7.5t for 150smk's. The shorter barrel can keep the rpm's down to not blow up the bullets if going faster twist?

 

[Dragoon300]

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

In my gun (Desert Tech SRS-A1) the barrel is clamped in a 5" long section of receiver so Lefthand / righthand torque is not a problem. The barrel extension is righthand but does not see torque. I tend to load to the higher pressure end of the spectrum most of the time. I do see less pressure indication with the gain twist of 1 turn, and the 5R rifling is said to be easier on the jackets reducing friction too. The bullet continually sees engraving to the muzzle and lessens gas blow by. I have not seen any negatives in my barrels, accuracy is superb. I will continue to use this formula in future builds, and highly recommend it.

 

[7Rum Slayer]

I would grab the Bartlein #3 with the 7.5 twist. I have both contours, a #3 at 24 inch and it balances perfect on a mid weight hunting rifle. I have a #3b at 26 inches on a target/hunting rifle and the 3b is kinda heavy out front, both have muzzle breaks. I found that the Bartlein #3 was quite a bit heavier and beefier than I expected, should be perfect for 6.5 Prc and 156's. Cheers, Jason

 

[Darryle]

Just finalized the order, #3 7.5 twist is on the way. I will leave it finished at 26" and unthreaded to test, if it's too unweildy, I will have it chopped and then threaded.

Thanks guys, the little extra twist should suit everything I plan to shoot from the 140gr up to the 153.5gr. The rifle may never see a 156gr, but knowing that it's capable is peace of mind.

 

[tacomHQ]

In my 6.5creeds and 260rems all are 8's including the 6.5prc (limiting myself @ 135ish grains). A purpose built 264wm 7.5t for 150smk's. The shorter barrel can keep the rpm's down to not blow up the bullets if going faster twist?

Shorter barrels do not reduce rpm. A 8T is one turn in 8". Two turns in 16".
However- velocity becomes a unit of time. If I move a greater distance in a standard time (lets say 1sec) more revolutions will have occurred in that unit of time.

 

[ARlife4me]

Shorter barrels do not reduce rpm. A 8T is one turn in 8". Two turns in 16".
However- velocity becomes a unit of time. If I move a greater distance in a standard time (lets say 1sec) more revolutions will have occurred in that unit of time.

Sure shorter barrels will have less ram with the same twist due to less velocity. That's how it works. Are you trying to say a bullet going 2k fps and another going 3k fps with the same twist will have the same rpm. I guess there's no reason have rev limiters controlling your coil then.

 

[dug]

Revolutions per minute = rpm. Minutes are a unit of time
that is the way i understand it
i do think i understand ur thought ,
a curtain twist is needed to stabilize a bullet per yard of travel regardless of velocity ? Not sure how to explain right , not sure im in tune to that thought either , but a smart nerd type in ballistics like bryan litz or others may be able to dissect it into terms we can understand . No offense implied

i recently built a 223 with a 28" barrel for the 73-77 ish class of bullets
i choose a 1in9 due to added velocity from barrel length .
i have no issue with stabilizing bullets out to 1000 yrds and they are right on the edge of transonic which is where u want over stabilized bullet.