cooper arms 6br twist rate ?

[22/250]

hi guys seen a cheap cooper in local gunshop and its in superb condition but its a 1 in 14 twist what bullet weight would this limit the rifle to. would it shoot 68 grain bergers or would that be pushing it abit for this twist ?

 

[ReedG]

I have a 6BR with 1:14 twist and it shoots up to 75-gr. HPs very well. Really hums with 57-gr. also. The normal 62-, 65-, 68-gr. bullets will work great in it ... enjoy if you decide to get it. If not, let me know how "cheap" it is ...

 

[22/250]

I have a 6BR with 1:14 twist and it shoots up to 75-gr. HPs very well. Really hums with 57-gr. also. The normal 62-, 65-, 68-gr. bullets will work great in it ... enjoy if you decide to get it. If not, let me know how "cheap" it is ...

thansk reed would prob shoot 65 grain vmax or 68 grain berger bullets in it. the rifle is up for £800 which is pretty cheap here as there around £1400 when imported here to england. i thin i could get it for less though. as its been sat on the gun shelf for abit in the shop.

ive had a good look over it and the guy that works in the shop i know well. he said the guy there selling it for. likes to buy different rifles have them for a bit then just sell them when he is bored. he said i bet it would have been lucky to see 100 rounds !

 

[DOGCAPPER]

58 grain v max worked great in mine...Gave club match grade accuracy..... sold it when I thought I wanted something better ........wish it was back in the safe....LT

 

[RonAKA]

You may want to try playing around with the calculator at the Border Barrels site. I put in the measured dimensions of a Berger 68 grain and got the following.

http://tinyurl.com/285cntk


This calculator is suggesting a required twist of 12.5 to get a 1.5 stability factor. The graph at the bottom is suggesting a 14 twist will give you a stability of 1.2.

Berger says you need a twist of 13. That gives you a stability of 1.4 which is good. I think 1.5 is a little overkill.

The question is what can you get away with. I found out that in a hunting gun I had less twist than I though and had a stability of about 1.1, but when the temperature drops it goes close to 1.0, and groups open up to 2-3 times the size.

My thoughts are that you are on the edge with a normal flat base 68, but probably can get away with it.

Berger makes a high BC 69 grain that is quite long. That one may not fly for you. It works in my 12 twist, but I suspect is getting close to the limit.

Not sure if you have the means to measure it but throat length is the other issue. With a 14 you will be stuck with the lighter bullets. Did they shorten the throat so you can still make the lands with the lighter bullets? It is a bit of an issue in my Savage. That 69 grain for example is seated so far out in the neck that I can easily pull it out of the neck of a loaded round with my fingers. It still shoots quite well, but certainly is on the limit of what I can do with this gun.

Hope that helps some.

 

[22/250]

You may want to try playing around with the calculator at the Border Barrels site. I put in the measured dimensions of a Berger 68 grain and got the following.

http://www.border-barrels.com/cgi-bin/barrel_twist.cgi?diameter=.2426&length=.840&nose=.487&meplat=.078&base_diameter=.2426&angle=&boat_tail=&twist=14&secant_radius=&unit_length=inches&temperature=59&humidity=0&local_pressure=29.92&pressure=29.92&altitude=0&density=11.4&custom_density=

This calculator is suggesting a required twist of 12.5 to get a 1.5 stability factor. The graph at the bottom is suggesting a 14 twist will give you a stability of 1.2.

Berger says you need a twist of 13. That gives you a stability of 1.4 which is good. I think 1.5 is a little overkill.

The question is what can you get away with. I found out that in a hunting gun I had less twist than I though and had a stability of about 1.1, but when the temperature drops it goes close to 1.0, and groups open up to 2-3 times the size.

My thoughts are that you are on the edge with a normal flat base 68, but probably can get away with it.

Berger makes a high BC 69 grain that is quite long. That one may not fly for you. It works in my 12 twist, but I suspect is getting close to the limit.

Not sure if you have the means to measure it but throat length is the other issue. With a 14 you will be stuck with the lighter bullets. Did they shorten the throat so you can still make the lands with the lighter bullets? It is a bit of an issue in my Savage. That 69 grain for example is seated so far out in the neck that I can easily pull it out of the neck of a loaded round with my fingers. It still shoots quite well, but certainly is on the limit of what I can do with this gun.

Hope that helps some.

hi there going over the gunshop in a moment i no the old owner shoots 55 grain blizkings. but i need it to shoot heavier bullets other wise im not getting anything over the 22/250 i have.

i have seen a custom barnards action 6br with 1 in 12 twist walther barrel in a mcmillan stock. for 400 pound more so that would be a better bet

 

[dlong]

My cooper 6BR can shoot one ragged hole 5 shots at 100 yards with 70 gr matchkings with N135. I have shot up to 80 grains, but the the 70 gr Mk's and 68 gr Bergers do real well.

 

[250AI]

Have a Cooper Varmiter 6BR,1-14, 24 inch barrel.Shoots 68gr. Bergers and 70gr BT's better than I can with N135 and Varget. The throat is long and I can't reach the lands. Shoots better when the bullets are seated where the base of the bullet is about half way down the neck. I've tried some of the shorter 80gr. (Speer)but beyond 100yds. they won't stabilze. Hope this helps.

 

[jo191145]

Don't believe those twist rate calculators too much.
Normal twist in a PPC is 14. We know they shoot right
My PPC does just fine with 68gn fare. Thats exactly what its designed for.
JBM twist calculator says it can't shoot. My targets disagree.

I have a 6BR 14 twist Pac-Nor barrel on a Savage action. It also shoots the 68's just fine. Just as accurate as my PPC, maybe even better.
It does like those 58 V-Max too. Ugly, short, squat bullets shoot better than they look ;D

 

[RonAKA]

Don't believe those twist rate calculators too much.
Normal twist in a PPC is 14. We know they shoot right
My PPC does just fine with 68gn fare. Thats exactly what its designed for.
JBM twist calculator says it can't shoot. My targets disagree.

I have a 6BR 14 twist Pac-Nor barrel on a Savage action. It also shoots the 68's just fine. Just as accurate as my PPC, maybe even better.
It does like those 58 V-Max too. Ugly, short, squat bullets shoot better than they look ;D

The issue is that they are fairly conservative by including a factor of safety to cover things that just are not fully understood. The main variable is the bullet density and center of gravity compared to the center of the air resistance force. Actual tests are the best way to determine what works and what does not. There is the speed of the bullet, and those like Berger do not specify velocity, so they have to cover that off too with some safety factor.

The other issue is temperature. I'm sure there is not much benchrest shot in cold weather. I was at the range the other day, and discovered the temperature had dropped enough to make two bullets I was shooting obviously unstable. I figured out the stability factor after the fact, and one was 0.95, and the other 1.02. So it does happen, and I think those numbers are surprisingly close to the theoretical of 1.0.

Out of curiosity I ran the Border calculator again to see at what temperature stability in a 14 twist got down to 1.0 at 3000 fps. It turned out to be -35F. So if you stay away from benchrest in Canada in the middle of winter, you should be fine!

 

[jo191145]

;D Dunhams Bay NY. Some of the craziest guys on the planet. Group shooting midwinter. I only made it there twice and my trigger finger is still numb ;D

 

[wooger]

I have a cooper in 14 tw and so far it has shot well with 68 berger fb and 70 grn mk although it will not group below .390 and the average size is probably in the .550's. It also has a long throat and there is no chance of reaching the lands. I have some 60 grn bergers to try next, I did tie for the win in a local varmint class steel match with the 68's!

 

[DCRYDER]

You fellas having trouble reaching the lands need to give the 75gr Sierra varminters a try. I used to load for a friends Cooper 6br and they shot lights out. They are flat base with a long bearing surface, prrobably go halfway down neck.

If it were my gun i would set it back and rechamber with less freebore. I have a reamer with just .030" freebore and it works fine even with the 58gr vmax.

 

[RonAKA]

You fellas having trouble reaching the lands need to give the 75gr Sierra varminters a try. I used to load for a friends Cooper 6br and they shot lights out. They are flat base with a long bearing surface, prrobably go halfway down neck.

If it were my gun i would set it back and rechamber with less freebore. I have a reamer with just .030" freebore and it works fine even with the 58gr vmax.

If I can get my hands on a box, I will give them a try in the Spring. The BC seems quite poor compared to Berger FB 68 and 80's. So yes, they must have a stubby nose, and longer bearing length.