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Wildcatting Subtle Improvements

Wildcatting Subtle Improvements

To Ackley Improve (AI) a cartridge, essentially, the shoulder angle is flattened to 40º and you get an increase in powder capacity, and there are many calibres that have benefited. The neck remains the same, so allowing you to fire-form or even use standard brass/ ammunition in the new chamber dimensions. Subtleties on angle and even body taper can also be addressed too.

Perfect number

There is something about the 6.5mm or 0.264” bore size that lends itself towards excellent performance. Bullet weights coupled to their length offer very good ballistic coefficients (BC) making it a near perfect number in all associated calibres. So, how would an old timer like the 6.5x55mm Swedish fair, certainly in the face of the more modern 6.5s, like the Creedmoor?

Dependent on manufacturer’s case, the internal capacity will change, due to differing metallurgy of the brass used and thus case wall thickness. A typical 6.5x55mm Lapua case holds 57 ml of water, compared to the 62 ml of the AI version. That’s a 5-grain gain in powder capacity, which is well worth having, as it translates into an extra velocity. This, combined with the beneficial effects of the AK case design and why would you not want it? The only real hassle is case preparation/alteration.

However, and like the Creedmoor, a 6.5x55mm AI can have a chamber specifically cut to suit a bullet of your choice and rifling twist rate. This not only maximises the accuracy and consistency of the round but, by throating the chamber long, you gain the benefits of extra case capacity for even more powder, which is where the design really comes to the fore.

Sore throat

I tend to use an RPA Quadlite action for testing, as I have a Ken Farrell switch barrel vice, so it is easy to exchange and test differing calibres off the bench. It also means that it is cheaper than a full-blown custom and is faster to make. I had a Walther match grade, stainless steel, 26”, with a profile of 1.25” at the chamber end and 0.840” at the muzzle, threaded for 5/8th x 18.

The internals are the important part of any wildcat build and the 5-groove barrel had a 1 in 8” rifling twist rate, to stabilise up to 160-grain bullet. Also, on the lead in, I wanted a shallower rifling edge and so the normal 3º profile was reduced to 1.5º and the throat was specified for 140-grain bullets with the Pacific Tool and Gauge reamer. At 26”, you get the best out of this cartridge, as I wanted to explore the longer-range potential, but it would equally good in a 24” sporter set up.

Normally with my small calibre cartridges, I have a shorter throat, as the higher velocities tend to erode the it badly. However, as it wears, you can chase the rifling up the bore by seating the bullet out further, thus extend its life. This 6.5 AI was different, because it’s milder and I wanted maximum case capacity and so a longer throat.

Single shot

The RPA is a single shot action, so no problems with a longer COL, as there is no magazine to feed through, like in a hunting rifle. I fitted the barrelled action to a Mc Millan A3 stock and attached my favourite scope, a Kahles K6-24x56mm illuminated scope and an MAE T12 sound moderator.

As with all new barrels, a good break-in procedure is needed to condition the bore, which also allows you to see the extent of how it’s going to copper up or not. I also use this period to sight in and in this case, fire form brass, with a ¾ load. Plus, the bullet in the lands helps to centralise and form the AI shoulder perfectly, otherwise you can get stretching in the wrong places.

Load up

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Reloading kit is easy to come by and firms like Redding, Sinclair, Wilson and CH4d offer the standard 6.5x55mm Swede but the AI version is a bit more difficult. I use re-chambered or cut Redding Comp dies to alter the shoulder and also some custom Wilson blank dies cut to match the chamber for a bush seating die. I still like a neck sizing die, so I can vary the neck tension and match each bullet to the case and alter the height of the portion of neck sized.

You can, and this is a good idea, anneal any wildcat case that needs a degree of neck and shoulder manipulation. This 6.5 x55mm AI case is not that severe but annealing the neck helps stop the brass becoming brittle when re-formed. As you have gone to all the trouble and expense of a wildcat, it is important to pay attention to the cases primer pocket. I always uniform it and cut it square with a K&M cutter. So, the base is flat, and it seats perfectly level. Also, I uniform (de-burr) the flash hole, in truth Lapua cases need very little work, but it can’t hurt.

The neck can be turned if necessary, to remove any high spots but try to get the end totally square and uniform with a good chamfer and de burr to the rim to release the bullet perfectly.

Down range

There is no shortage of bullets for the 6.5mm calibre, allowing the use for vermin, fox, deer and even Moose or African game. The choice of construction is important too, as it must be matched to the task or game species you are targeting, as light and fast is not the recipe for success in all situations!

If you are going to use the 6.5x55mm AI for foxes, then a light, more frangible bullet is preferable over a more predictably expanding bullet designed for deer. Sierra’s 85-grain hollow point is a varminter designed to expand rapidly and shoot fast.

I had some 95-grain V-MAX and lighter 100-grain bullets but ran out, so went to the 120-grain.

Here, you have a good choice and you can go Hornady A-Max, Lapua Scenar 123-grain for longer range use or Sierra and Speer Spitzers, which exhibit controlled expansion and would make a good flatshooting deer round with an aerodynamic performer.

The 129-grain weight is a little quirky, but Hornady offer their good SST bullet and it’s a great all-rounder for deer, with a high BC, polymer tip and good internal construction with the Interlock gripping lead core to copper jacket. It expands faster than a conventional Interlock, but less than other polymer tipped designs. The Accu Bond 130-grain is very accurate and penetrates deeper.

The best all-rounder would be the 140-grain range, with 139 and 143-grainers from Berger, Lapua and Hornady in the shape of the Hunting VLD Scenar and newer ELD-X, as well as SST and Interlock loads. The 160-grain Hornady stands out as capable, but its round nose design and large sectional density lends itself to greater penetration on deer than say a Ballistic Tip.


Compared to the original 6.5x55mm, the AI version gives a good 250 fps more velocity with a longer barrel. Compared to the 6.5 Creedmoor, the AI is bigger with its 55mm case length over the 48mm of the former, but the Creedmoor is not far behind. Due to the nature of the custom dies etc. for the AI Swede, many may just say, sod it and buy a 6.5-284; it’s bigger and works extremely well. But, in real terms, the choice is yours and with so many good factory rifles and ammunition now for the Creedmoor, the Wildcat route is really for diehard reloaders who like the pain. Like me, as I’m necking down a 7.5x55mm Swiss case to weird calibres next!


JMS Arms Quickload and MAE mods 07771 962121
RUAG Kahles and Norma 01579 362319
Norman Clark Reloading supplies 01788 579651
Edgar Brothers Hornady, Hodgdon 01625 613177
RPA Range masters 0845 880 3222
Hannam’s Reloading Lapua, Vihtavuori 01977 681639
L to R: 6.5 Creedmoor, 6.5x55mm AI, 6.5-284 Win, Henry Krank Sierra 0113 2569163


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