Why Ackley Improved?? Vs std choices

[MagnumManiac]

I went with a 7 twist

Having difficulty sourcing a blank in 7" twist here. Importing barrels privately now is cost prohibitive due to import/export duties.

Cheers.
P.S. Nobody is willing to mark the postal box as "Tomato Stakes Only"

 

[Koda_]

Having difficulty sourcing a blank in 7" twist here. Importing barrels privately now is cost prohibitive due to import/export duties.

Cheers.
P.S. Nobody is willing to mark the postal box as "Tomato Stakes Only"

yikes, I see now your in Australia.

FWIW I waited a very long time for my 7 twist to get made. 7.5 twists are slightly more "popular"... quoted because only within the custom build crowd. I dont know why even faster twist rates than 8 are not more popular there isnt a downside to them anymore, that Im reading anyways...

 

[MagnumManiac]

My list of improved cases, mostly to reduce case taper, are:
22-250AI, 7" twist 30" 4 groove barrel.
257AI, 10" twist 24" 6 groove barrel.
260AI, 8" twist 30" 4 groove barrel.

Also run other improved cases, either my own design or dropped factory options like throat length, all of my Weatherby cases on full length brass, have traditional .500" freebore parallel sided at .0005" over bullet OD. My 257's and 270 have .376" (3/8") freebore the same as above as designed by Roy Weatherby. SAAMI messed with these dimensions…
Looking at AI'ing my 7-08 7.5" twist 32" 4 groove barrel. Have plenty of barrel knox form (1.5" no taper) to cut back, re-thread and re-chamber. Don't have dies, but easy to get.

Cheers.

 

[Tiny Tim]

FWIW I waited a very long time for my 7 twist to get made. 7.5 twists are slightly more "popular"... quoted because only within the custom build crowd. I dont know why even faster twist rates than 8 are not more popular there isnt a downside to them anymore, that Im reading anyways...

I think it has to do with the fact that there are issues with such extremely fast twist barrels. Manufacturers want satisfied customers. Had a discussion with a premium barrel maker over a 7 tw 6mm. He wanted more details about what I was doing before proceeding. His concerns were bullet failure as the throat eroded. Not saying he would refuse to sell me what I asked for, but would do so with the full knowledge of what to expect and what he may warranty if said problems arose. FWIW, this was for a 6 Sherman Max build. Should push 112-115 gr to around 3400 fps.

 

[MagnumManiac]

@Tiny Tim
I had 2 3 groove 7" twist .224" blanks, one was earmarked for .223AI for a customer, the other was for another customer and he pulled out of the deal at the last minute. So, I chambered it in 22-250AI and proceeded to go through 69g SMK load work-up. The last 3 loads, some bullets were not reaching the target…
I had no idea that these barrels had issues when pushing extra velocity in long barrels of 32".
I even had issue with Berger bullets striking sideways, which I believe were just the jacket.
So, I had to use extra heavy bullets to curb the situation of 77-80g and 88-95g bullets. Not exactly what I built it for, but there you go.

Cheers.

 

[AZShooter]

Interesting comments everyone. There are some cartridges that are almost AI cases like the 284 Win with its 35 degree shoulder and the Creedmoor line up with a 30 degree shoulders. These would not require fireforming the shoulder.

Didn't read anyone mentioning steep shoulder angle prevents the throat from wearing as quickly. Thinking of the 243 vs the 243AI.

Regarding a 1 in 7 twist 3 groove barrel. It was years ago when a friend and I ordered two 7mm barrels with the aforementioned combination. We wanted to shoot new higher BC 180 Berger hunting bullets. I had a 7 Rem mag and friend had a 7 STW. When this was brought up here a few posters said it would be a bad combination having a 3 groove with that fast a twist. They were right.

Just like MagnumMania we had issues. First the hunting bullets began to unravel with the 7 STW with around 100 rounds. He went to target versions which lasted a bit longer and they also had integrity issues. My 7 Rem mag made it to a bit over 200 rounds and with same issues. Switched to Accubonds or monos which solved the issue. Unfortunately, the BCs were lower and I lost interest in the barrel.

 

[FEENIX]

I think it has to do with the fact that there are issues with such extremely fast twist barrels. Manufacturers want satisfied customers. Had a discussion with a premium barrel maker over a 7 tw 6mm. He wanted more details about what I was doing before proceeding. His concerns were bullet failure as the throat eroded. Not saying he would refuse to sell me what I asked for, but would do so with the full knowledge of what to expect and what he may warranty if said problems arose. FWIW, this was for a 6 Sherman Max build. Should push 112-115 gr to around 3400 fps.

My .257 WBY and .264 WM has 1:7" and .338 Thor has 1:8" without any issues thus far.

 

[Phil Rizzo]

I think it has to do with the fact that there are issues with such extremely fast twist barrels. Manufacturers want satisfied customers. Had a discussion with a premium barrel maker over a 7 tw 6mm. He wanted more details about what I was doing before proceeding. His concerns were bullet failure as the throat eroded. Not saying he would refuse to sell me what I asked for, but would do so with the full knowledge of what to expect and what he may warranty if said problems arose. FWIW, this was for a 6 Sherman Max build. Should push 112-115 gr to around 3400 fps.

Tim that looks like a VERY conservative velocity.?
Is that where you intend to run them, or a top speed?

 

[lancetkenyon]

If you like the 25s, and want more HP....

Again, 22" barrel, 135 Berger LRHT, shot # 115 from the barrel. This was max. First slight signs of pressure. I have backed it down to 3230fps.

 

[Phil Rizzo]

Lance that's 7.75tw, correct?

 

[lancetkenyon]

Lance that's 7.75tw, correct?

25PRC/SI is a 1:7.75"
25MBK is 1:7.5"
25SST is 1:7.5" (not shown)

 

[nksmfamjp]

I have a .270 AI (175 Matrix at 2996 FPS) and .30 Gibbs (180 Berger VLD at 2806 FPS with room to spare), and I am happy with them. Both dies are reasonably priced from Redding.

What is reasonable? I don't see 270AI in their charts. So, how much is their custom in your experience? ….thinking type S FL and Micro seater…

If you are looking for maximum powder case capacity in .473, the 6.5 WBY RPM is hard to beat.

Actually, that is a good option. When I kick this off finally, I suspect there will be more rpm dies. Peterson is making brass. Are the dimensions good on the SAAMI reamers?

 

[AussieWriter]

Having difficulty sourcing a blank in 7" twist here. Importing barrels privately now is cost prohibitive due to import/export duties.

Cheers.
P.S. Nobody is willing to mark the postal box as "Tomato Stakes Only"

Give Robert Tobler a call at Tobler barrels in NSW. They always made great barrels and I still have a .25/06 from them that is terrific.

 

[Hugnot]

I have a 10 twist 6mm AI and shoot the 87 Vmax at just under 3,500 fps using 50.5 grains of VN165. Accuracy is more than acceptable with 90% hits on pop can size rodents at ranges up to 400.

Going to to Ackey design fixed the slopey body 6mm Rem. I fire form cases using dried up coffey grounds & pistol powder. Despite its modest G1 BC of .4 the 87 Vmax does well up to 600 yards. An old 8 twist 6mm AI did well with the 95 grain Berger VLD at 3250 plus. The 6mm 95 Berger VLD has a low form factor (SD/G7BC) compared to other 6mm bullets and can be driven faster than 105's.

The latest & greatest 6mm bullet for rodents & such might be the Hornady 6mm 80 grain ELDVT. Running the Miller Sg calcs indicate marginal stability with a 10 twist but the bullet holes in paper indicate inadequate stability. The twist rate printed on the 80 grain ELDVT bullet box is 8 twist. The 80 ELDVT has a real low form factor compared to other & VLD type 6mm bullets.

Planned is a side by side ballistics contest between the 10 twist 6mm AL, 87 Vmax @ just under 3,500 fps & an 8 twist 6mm CM, 80 ELDVT at some 50-75 fps less velocity. Ranges will be up to 1,000.

The 6mm & 6.5 CM cases are similar to Ackley improved in regard to body taper & shoulder angle with very minor differences. A real big advantage with the 6 & 6.5 CM brass is availability & use of small rifle primers. Presently, I am buying once fired Federal 6.5 CM, small rifle primer brass for both 6 & 6.5 CM chambers with neck down for the 6mm & neck turning for both. Cheap $18 OTC Lee F/L dies, no expander/decap, are used for both 6 & 6.5 CM's, final neck sizing is done with Lee collet dies. Necks are turned to .268 OD for the 6mm & .289 for the 6.5mm.

Finding brass for the 6mm AI is a challenge. I have used PPU 7X57 brass with good results but with considerable effort including fire forming.

I might give up on the 6mm AI and re-barrel to a 6.5-06. I once had a 6.5-06 AI that shot 140's close to 3,000 & got hits on 1/2 gallon size rodents across an entire half section (880 yards). I used H1000 & the old 140 Sierra 6.5 GK bullet, 9 twist. The 6.5-06 AI might be a wasted effort as I now have a 8 twist 6.5 PRC but 6.5 PRC brass is pricy and velocity gains over the 6.5-06 are marginal.

Some 6mm AI pics



Shown is a 300 yard hit on mild steel (2.5 inch diameter) with the 6mm AI, 87 Vmax & finished round with anneal. It feeds perfectly thru a long action Ruger M77 MKII.

The competing 6mm CM is an accurate shooter and might be just as effective with less work & expense (5 shot group with easy & cheap components). I need to see this with the 80 ELDVT.