6BR-AI loads wanted

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Fire Dog
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Joined: Fri Apr 12, 2019 7:03 pm

6BR-AI loads wanted

#1 Postby Fire Dog » Thu Jul 18, 2019 1:55 pm

Is anyone shooting a 6mm BR-AI ?
I cannot find any load data for this round.

My PT&G reamers arrived today and my old worn out 6mm BR barrel is heading for the recycling bin.
I will have a 1:7 Hardy barrel and want to try out some Berger 115gr along with the Sierra 107's that are working a treat in the current barreled 6BR.
Just shot 1000 yd last weekend in a 20-28 kmph wind and the 107's were everywhere so hopefully the 115's will track better at that distance and buck the wind a bit better...
Still managed to keep up with the 6.5 Creedmoors, but barely.

brain3ze
Posts: 2
Joined: Wed May 10, 2017 10:51 am

Re: 6BR-AI loads wanted

#2 Postby brain3ze » Thu Jul 18, 2019 6:44 pm

I've been running the cartridge for the past couple of years through 2 barrels. The first was a 1:8 the second a 1:7.75.

Like most AI's you can generally start towards the top of the recommended load for the parent case and work your way up safely.

My go to powder is 2208 and my fire forming load is 30gn of 2208 with 105/108gn projectiles.

In a formed case I generally start my load development at 30.6gn of 2208 and work up from there. There is normally a wide node in the low 31gn range and I have 1 barrel running on 31.2gn 2208 with Berger 105VLD's and the other on 31.5gn 2208 with Berger 108BT's. I've never loaded above 32.2gn (on a day with temp in the high 20's I started to see the primer edges flattening and had no desire to push it when I'd already found a good node).

I've also never tried 115's in these barrels.

Good luck with it, I've always found it a very easy cartridge to tune.

willow
Posts: 242
Joined: Sat Aug 15, 2015 9:51 pm

Re: 6BR-AI loads wanted

#3 Postby willow » Thu Jul 18, 2019 7:06 pm

I stick to 105s in this cartridge after running out of 108s. Brave move running 115s, personally I think it's a little too much bullet for the case but see how it goes I guess. 2208 is flexible, I use it for fireforming, kicking off at 30gr with 95gr bullets - works a treat.

Frank Green
Posts: 259
Joined: Wed May 28, 2014 11:48 pm

Re: 6BR-AI loads wanted

#4 Postby Frank Green » Fri Jul 19, 2019 5:18 am

brain3ze wrote:I've been running the cartridge for the past couple of years through 2 barrels. The first was a 1:8 the second a 1:7.75.

Like most AI's you can generally start towards the top of the recommended load for the parent case and work your way up safely.

My go to powder is 2208 and my fire forming load is 30gn of 2208 with 105/108gn projectiles.

In a formed case I generally start my load development at 30.6gn of 2208 and work up from there. There is normally a wide node in the low 31gn range and I have 1 barrel running on 31.2gn 2208 with Berger 105VLD's and the other on 31.5gn 2208 with Berger 108BT's. I've never loaded above 32.2gn (on a day with temp in the high 20's I started to see the primer edges flattening and had no desire to push it when I'd already found a good node).

I've also never tried 115's in these barrels.

Good luck with it, I've always found it a very easy cartridge to tune.


Good place to start as he posted. My forming load is actually like 29.7gr. of H4895/2206 with a 105 Hornady and 107smk if I remember correctly. I have loaded the 2208/Varget as well for forming. Both have worked very nicely.

Now that I have some formed cases...I am going to load up some of the new 110gr. Hornady ATIPS and see how they work/shoot. Not a 115gr. bullet but it's getting there. My barrel is a 1-7 twist.

later, Frank
Bartlein Barrels

Gyro
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Location: New Zealand

Re: 6BR-AI loads wanted

#5 Postby Gyro » Fri Jul 19, 2019 7:11 am

I had a 6mm SLR using the 115 DTACS in a 7" twist barrel. A .236 Lilja 3 groove. I could NOT get it to work. The pressures were crazy high way before I got to the velocity I wanted. I tried all kinds of powders, then gave up.

After doing some online research about it I discovered it was stated by some who had struck the same problem that a 7 twist barrel was just too fast. The analogy given was the fast twist was like having the bullet "hit a wall" ?

Maybe the 115 Berger will be different ? Maybe the 6BR-AI is a totally different situation ? Good luck anyways.

AlanF
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Re: 6BR-AI loads wanted

#6 Postby AlanF » Fri Jul 19, 2019 8:15 am

Gyro wrote:...After doing some online research about it I discovered it was stated by some who had struck the same problem that a 7 twist barrel was just too fast. The analogy given was the fast twist was like having the bullet "hit a wall" ?...

Interesting. Perhaps that phenomenon is what puts the upper limit on very long bullets in other calibres e.g. you don't hear of much success with .223 above about 90gn, 7mm above about 185gn, 30 cal above about 220gn.

ben_g
Posts: 174
Joined: Sun Apr 24, 2016 7:37 pm

Re: 6BR-AI loads wanted

#7 Postby ben_g » Fri Jul 19, 2019 9:22 am

I’m not sure a 115gr Berger can be pushed fast enough to have an advantage over the 105gr Hybrid.

My Dasher comfortably runs the 105at 3030fps, never felt any need to go heavier.

I would stick to the 107 Sierra or try some 105/108 Berger’s.

Frank Green
Posts: 259
Joined: Wed May 28, 2014 11:48 pm

Re: 6BR-AI loads wanted

#8 Postby Frank Green » Fri Jul 19, 2019 10:39 am

Gyro wrote:I had a 6mm SLR using the 115 DTACS in a 7" twist barrel. A .236 Lilja 3 groove. I could NOT get it to work. The pressures were crazy high way before I got to the velocity I wanted. I tried all kinds of powders, then gave up.

After doing some online research about it I discovered it was stated by some who had struck the same problem that a 7 twist barrel was just too fast. The analogy given was the fast twist was like having the bullet "hit a wall" ?

Maybe the 115 Berger will be different ? Maybe the 6BR-AI is a totally different situation ? Good luck anyways.


Not necessarily and you probably had a combination of things going on that caused you problems.

Twist first....for the most part twist doesn’t effect pressure. I’ve seen data on a .308 and other caliber barrels but sticking with the .308win. And doing pressure testing that a 12 twist vs a 10 and even 8 twist there wasn’t any real gain in pressures at all.

Your barrel being a .236” bore. That is tighter than standard spec. Standard spec. Is .237”. Any time you start changing the bore size you start effecting pressures and just because the pressure went up doesn’t necessarily mean your velocity is going to go up. Also do you know what a the actual groove size your barrel was? If that was tight also that actually has more of an effect on the pressure than the bore size but again anytime you start changing the total surface area of the bore you effect the pressure curve. So if you ran that load in a previous barrel and didn’t have any issues you have to ask your self was the previous barrel the same bore and groove size as the next one you put on.

Recent example I seen about a year and a half ago was in a 6.5 caliber test barrels. I’m not going to name the cartridge as I don’t want it taking out of text or say it was the problem and it wasn’t. The maker of the test barrels made a mistake and didn’t check the bore and groove size before they shipped. Yes I know how the maker was. The bore and groove where both .0005” undersize. This drove up the pressures of the reference ammunition up 8k/10k psi higher than what it was suppose to be running at.

Frank Green
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Re: 6BR-AI loads wanted

#9 Postby Frank Green » Fri Jul 19, 2019 10:43 am

I’ve got a 6.75 twist 6.5mm on my rifle right now in 6.5CM.

I’ve run box ammo and handloads with 135gr, 140, 147, 150 and 153gr bullets with no problems in the 6.75 twist. Same loads I ran thru a 8 twist barrel with some of those loads and box ammo with no issues or big velocity swings at all. Barrels where standard min. Spec. .256”x.264” + the .0005” tolerance for each but not undersize.

wsftr
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Re: 6BR-AI loads wanted

#10 Postby wsftr » Fri Jul 19, 2019 10:57 am

I understood that specific testing had been done RE: the effect of twist rates on FPS and the impact was minimal. Stress on Jackets was another matter.
In FTR for heavies its proven that more pressure via tighter bore groove dimensions doesn't translate to more FPS - in fact the opposite. i.e. if you are running < .300x.308 you are guaranteed to run into early pressure and lower FPS.
Long/er bearing surface bullets with tighter bore groove dimensions is a guaranteed mix to cause early pressure.

Gyro
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Location: New Zealand

Re: 6BR-AI loads wanted

#11 Postby Gyro » Fri Jul 19, 2019 1:05 pm

http://forum.accurateshooter.com/thread ... 7.3751124/

See the second post on that forum page by rcw3 ?

wsftr
Posts: 108
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Re: 6BR-AI loads wanted

#12 Postby wsftr » Fri Jul 19, 2019 3:14 pm

Maybe something about the 6s thats a problem. Pity RWC didn't mention dimensions.
I know some on this site have an issue with BL but his books and this reference shed reasonable light - for a rule of thumb if nothing else.

http://bulletin.accurateshooter.com/201 ... litz-test/

Frank Green
Posts: 259
Joined: Wed May 28, 2014 11:48 pm

Re: 6BR-AI loads wanted

#13 Postby Frank Green » Fri Jul 19, 2019 5:36 pm

Gyro wrote:http://forum.accurateshooter.com/threads/243-twist-1in8-or-1in7.3751124/

See the second post on that forum page by rcw3 ?


I’ll get a hold of Robert and ask him what he based that on and what the bore size of the barrels he was using etc...Robert is good people.

Makes you think if this is true....why just 6mm?

In other calibers like .224 we’ve made 1-6 twist barrels for a bullet maker (being shot and tested right now) and no weird pressure concerns have been noted as of yet.

In .308 we’ve made barrels in 1-7, 1-6, 1-5, 1-3, 1-2.5, 1-2, 1-1.5 and yes we even made 1-1 twist. You talk about looking down a bore of a barrel and all you say is nothing other than your mouth hanging open. Looks like a internally threaded bolt.

I haven’t heard of any data on pressures back from testing but I do know when they got to either the 1-5 twist or 1-3 twist the standard .30cal match bullets that bullet failure rate became a problem. This was testing being performed for a subsonic bullet/ammo and trying to get the ammo to be moa or better for accuracy out to 300 yards for military purposes. Besides the standard .30 cal.match bullets they where also testing custom solids.

bruce moulds
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Re: 6BR-AI loads wanted

#14 Postby bruce moulds » Fri Jul 19, 2019 6:39 pm

which raises the question re gaintwist.
startem spinning slow and finishem spinning fast.
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880
http://youtu.be/YRaRCCZjdTM

Frank Green
Posts: 259
Joined: Wed May 28, 2014 11:48 pm

Re: 6BR-AI loads wanted

#15 Postby Frank Green » Sat Jul 20, 2019 7:52 am

bruce moulds wrote:which raises the question re gaintwist.
startem spinning slow and finishem spinning fast.
bruce.


Bruce, I hate to start saying with “because” so here it goes LOL!

Because to my knowledge no modern day testing has been done to some extent in regards to gain twist barrels and the effects on pressure etc...that I can find. We did already do one round of testing. It’s going to be two rounds at least because we we’re not thinking far enough ahead due to all the different things you can run up against.

We made two ammunition pressure test barrels with the standard pressure port location which is just behind the shoulder of the case. One barrel was in .308win and the other barrel was in 6.5CM. We made/donated the barrels at n/c and Hornady did the testing at n/c.

Both barrels started out at 12 twist and by the time they got to the muzzle they ended at 8 twist.

In that round of testing there was no difference observed in pressure vs a standard 12 twist .308win barrel and a standard 8 twist for the 6.5CM. The barrels where so consistent to a standard SAAMI spec test barrel for pressures that after the testing was done I let them keep them for normal day in and day out testing.

Next round of testing we are making two more barrels. Same caliber and same twist but this time we are going to do the standard location pressure port so they can monitor that the pressures are what they suppose to be but we are going to add a 2nd pressure port approx. 6” in front of the chamber to see if the pressure is dropping faster than a standard spec straight twist barrel. Might put a 3rd pressure port closer to the muzzle as well.


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