Saturday, November 20, 2010

Aguila 60 grain subsonic .22lr ammunition

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At last count I had nineteen different types of .22 rim fire ammunition. This morning, I have to make that an even twenty. Once again I have fallen to the curiosity of an offering previously unknown to me.

This time it is, perhaps, the most unusual .22 rim fire round I have seen. Aguila, a company not afraid to offer something different, brings us it's 'Sniper Subsonic' round with a 60 grain solid lead bullet. Yes.... 60 grains.

The heaviest .22 rim fire normally encountered is 40 grains. Higher velocity rounds usually drop that to 36 grains, or even 30 grains.

Aguila managed to squeeze that huge slug into a long rifle sized package by taking a unique route. They used a .22 short case, with a reduced powder charge, and loaded a very long lead bullet into it, bringing the whole cartridge out to .22 long rifle length. The SSS round looks the part too, with half the cartridge length being lead bullet. That's more than unusual, it's down right strange looking.

The idea is fascinating, with the heavy bullet retaining substantial energy while the low velocity and charge give greatly reduced noise. The problem with this approach is one of bullet stability.

Heavier low velocity bullets require a rapid twist rate to stabilize the bullet in flight. Lighter high velocity bullets can use a slower twist rate to accomplish the same stability. Bullet design also comes into play in the equation. Even the type of rifling can have an effect.

Typical .22 rim fire firearms shooting a 35 to 40 grain bullet at 1000 fps work well with a 1 in 16" twist rate, and this is standard for these weapons. A .223 center fire shooting a 60 grain bullet at 3200 fps usually works well with a 1 in 9" twist.

A .22 rim fire shooting a 60 grain bullet at subsonic velocities? A rapid twist would be in order, and its doubtful that 1 in 16" will do it. The test is simple. Load an accurate .22 rifle with the new ammunition, sight on a reasonable target, and note the results. That is exactly what I did, and the results are shown here.

The rifle chosen was a CZ452 Trainer, and is exceptionally accurate. It has shown a tolerance for various cartridges, without being overly picky about what it will shoot well. The long barrel and deep rifling may have something to do with that, as well as the tight bore. This rifle, even with open sights, constantly surprises shooters with it's consistent ability to group tightly.

Setting simple 4"x6" card stock targets at 50 feet, several rounds were fired. Only a few were needed to answer the basic question. The very first round was a classic keyhole, as was every round after. The Aguila 60 grain bullets simply would not stabilize in the 1 in 16" twist CZ barrel.

Fired at both a paper target and a block of pine, the imprints are clear sideways impacts of a bullet tumbling in flight.

Perhaps this ammunition would be better suited to a .22 wearing a custom rapid twist barrel, as many folks have fitted to Ruger 10/22s. Also, it might be a perfect round for an AR equipped with a rim fire conversion, especially if it has a suppressor can installed. For my .22's, all of which have 1 in 16" twist barrels, I'm afraid this Aguila offering is useless.







Thursday, November 11, 2010

Firing protrusion adjustment on a classic Mauser action


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I have two 1938 Turkish Mausers. Having typical 1898 Mauser actions, these are robust and simple. The same techniques used by generations of shooters on Mausers work just fine on these old Turks.

One Turk is set up as my ‘military rifle shoot’ competition piece (known and feared on rifle ranges everywhere as ‘The Grand Old Turk’). I also have about 2500 rounds of 1950’s 8x57mm ammunition. The idea being to use the surplus for practice, and my quality hand loads for competition.

Sounds like a plan, doesn’t it?

There is a fly in the ice cream with this plan…. my Turks won’t shoot the Yugo ammunition reliably. I get what appear to be good firing pin strikes, but every other round fails to fire. The same ammo, even the FTF rounds, will all shoot with 100% reliability in my Yugoslavian M48B (another version of the 98 Mauser).

Clearly the ammo is good, and there’s an issue with the Turk’s that I needed to find.

My first thought, and a good one, was firing pin spring strength. The M48 is about fifty years old, while the Turks are much, much older. Springs weaken with age and the Turks are noted for it. New 24 pound springs were ordered, received, and installed. Immediate range tests revealed no change at all in function. The Yugo ammo still had about a 50/50 failure rate in the Turks.

Careful side-by-side inspection of the M48B bolt vs. the Turk bolt showed the problem to be one of firing pin protrusion. The M48B was 0.058” while the Turks were 0.030”. Since the spec for firing pin protrusion on a model 98 is .055" to .065", No matter how hard the pin struck on that Turk it simply wasn’t hitting deep enough to set off the stubborn and hard Yugoslavian primers.

Mauser 98 actions do not offer ready firing pin protrusion adjustment like a Mosin does. It’s built into the engineering, and pretty much soldier proof. That left me with a problem and no easy solution. New firing pins cost roughly what I paid for the rifles to start with, and were not guaranteed to solve the issue. I needed a tinker fix.

I determined the limiting factor on firing pin protrusion to be the striker stopping against the bolt shroud. Modifying that requires disassembling the bolt and some careful dressing with small files. This work is touchy and must be taken slowly. Too much metal removed means a trashed part and a trip to the Internet for new components.

It might also mean pierced primers and a dangerous rifle. If you chose to follow in my footsteps, be careful. If minor gunsmith work is something you fear, leave this job to the pros.

The following photos illustrate the process. Taken slowly, step by step, it's an hours work..... but well worth it.

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Follow up adventures in Mauser bolt workings:

Using the procedure detailed above, I continued a step at a time till I arrived at 0.055” protrusion on the firing pin. This should be acceptable with a Model 98 Mauser action, which calls for 0.055” to 0.065”.

The results are thus: From a 50% fail to fire with 1950’s Yugoslavian surplus, the rifle now has a 10% fail to fire. While not perfect, it’s far better than it was. Since the firing pin protrusion now stands at only 0.003” different between the M48 and the Turk, any more fail to fire with the Yugo surplus ammunition is probably caused by another factor. (I suspect the shape of the firing pin tip….)

More to the point, the old Mauser shoots it’s favorite hand load considerably better. Fliers are a thing of the past. I have since shot a military rifle match that entailed a fifty-eight round course of fire. Eight sighter rounds, with fifty for score. In that entire match I did not have a single flier. On top of that, my score came up substantially from previous matches with little else changed but what is detailed above.

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