Ackley and brass wear


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mwsenoj
July 5, 2013, 02:22 PM
Before I get to the main question, I am full aware of the reduced brass flow around the shoulder in the Ackley since it has the sharper angle. I am more concerned with overall brass life ie primer pockets/cracks/web.

Specifically, is Ackleyizing a case going to let you increase velocity by adding more powder while not increasing pressure/brass wear (at all or as much) compared to a hot unAckleyized load.

Case in point,
Standard 260 with 43.1gr of H4350
Compared to
Ack 260 with 43.1gr H4350

Will the two loads have similar velocity but lower pressure in the Ackley?


Or maybe a better way to ask,

Standard 260 @ 2850fps
Compared to
Ackley 260 @ 2850fps

Will the Ackley be easier on the brass?

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rcmodel
July 5, 2013, 02:33 PM
IMO: No, not if loaded to the same pressure & velocity.

And not if you set your sizing die correctly to prevent case stretch on the .260 Rem in your rifle.

The AO cartridges claim to fame is higher velocity due to slightly more powder capacity.

However, Ackley based his claims on pressure that would make a modern ballistician duck for cover.

rc

kendak
July 5, 2013, 03:52 PM
convert all my varmit rifles to Ackley ....just neck size only & in the 5.56 military brass I get 75 to 80 loads before neck splits ...think I could get more if I annealed the neck...P.O Ackley's theory was that with 45* shoulder less hot gasses would exit case therefore extending barrel leade life....I have [2] SS VS 700 Rem. in .223/5.56 that I built that have over 15K[#1] & 22K[#2] rounds through them [Shilen barrels] ...both will still put 5 rds. in 1" or less at 400yrds. with 29grs. of H335 behind a 50gr Ballistic Tip running 3850fps. ...also built 22-250, 6mm, 7/.284, 30/375 all with Ackley sh ...take care

Kachok
July 5, 2013, 06:03 PM
Sharp shoulder brass will stretch less then a 17 or 20 degree shoulder, the 40 degree shoulder does not allow the brass to flow outward as easily. That said converting a standard brass to AI weakens it some and some brass has to be discarded after fire forming. I would not make an AI to try and save on brass, there are several sharp shoulder production cartridges that I would re chamber to rather then fire forming brass. The 6.5 Creedmore offers a significantly sharper 30 degree shoulder and near identical ballistics to the 260, though the added case capacity of the 260 AI could push it a little faster then the Creedmore could hope to. The ideal shoulder angle is 30-40 degrees depending on who you believe, the WSMs are right in the middle at 35 degrees.

steve4102
July 5, 2013, 08:21 PM
Will the two loads have similar velocity but lower pressure in the Ackley?


Or maybe a better way to ask,

Standard 260 @ 2850fps
Compared to
Ackley 260 @ 2850fps

Will the Ackley be easier on the brass?

Yes, The Ackley is easier on brass if you stay within safe pressure limits. Some Ackley users run them hot where brass life can suffer.

The Ackley can achieve similar velocities as the parent case with less pressure, but with more powder. How much pressure depends on the parent case and the amount of increased case capacity.

The 260 is already a pretty straight case with minimal taper, converting it to Ackley will show little improvement compared to other cases with much more taper.

41 Mag
July 6, 2013, 05:45 AM
I can only comment on the difference I have seen shooting both a standard 25-06 and my AI version.

With the standard version I trim about every third load. No much but if I don't the 4th load will chamber tight due to the necks stretching.

With my AI version, I trimmed the cases after fire forming, more or less to simply square the mouths as once formed they are shorter. Once squared however I have noted no more than .005" growth in any of the cases I have shot the most. In 11 or so loads they have held up just fine and other than simply squaring the mouth up, they have not shown any significant increase in lenght. I have used Winchester, Remington, and Lapua cases, all showing identical results.

With the standard version I am loading the 115gr Partition to 3150fps out a 24" stock Remington barrel. With the AI version I am loading the 120gr Hornady and Rem CL to 3350"ish fps out of the 28" Broughton 5C barrel. Accuracy of either is around 1" at 300yds if conditions are good.

One note on AI conversions. If you read about them in depth, you will find that some cases will show a marked improvement, some won't. This is not to say you shouldn't build one if you want one, there is always the cool factor.:D

However, when working up loads, you have to pay particular attention to the fact that the cases will hold the walls of the chamber tighter, than the tapered version which can and will give way to showing any of the usual pressure signs.

So IF you go with the AI version, you have to bear this in mind. All of the loads I worked with on my AI version kept the barrel length in mind when testing. I accepted the fact that I wasn't going to gain much over the parent case, except what I could get with a slower powder and the added barrel length. Going from a 24 to a 28" lenght I calculated 75 fps per inch, and while probably not totally accurate it was what I used as a top end for my loads. With the top end of 3000fps from my standard version using the same powder, and 120gr bullets, I worked up to the noted above velocity in the AI version. I actually did work up higher, just to see where I would find the primers starting to flatten out, and while the velocity WAS higher and accuracy was still good, I settled on the lower load simply because I know it will shoot well in any temp I encounter, and I should still be easily within sane pressures.

There is no sense in pushing things just for the extra added velocity. Besides you are already getting the added performance from cases, and possibly bullets, and saving the barrels throat a bit in the process.

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