Friday, June 22, 2007

It's not the rifle.

Readers will recall that in this post I discussed what happens when one changes handloaded components. In that post I noticed that a 168gr Sierra HPBT bullet, atop 42.5 grs of 4064 powder, in a BHA case would group with deadly accurate consistencies, whereas an identical load but built with FC match cases wouldn't group at all. Since the latter produced velocities about 5% faster than the former, I was left to speculate whether the discrepancy was due to

  1. the brass design of BHA brass (more consistent neck tension? more consistent bullet release?), or
  2. the rifle had a sweet spot for 168gr HPBT bullets at around the 2550fps mark.
So, I worked up a set of loads using only FC match cases, while varying the powder weight from 39.6grs to 42.5grs with a 0.5gr delta. Here are the velocity curves, as compared to previous measurements with BHA brass.

As one will recall, the load built with BHA brass produced an accuracy (and velocity) sweet spot at around 42.5grs of 4064, which also corresponds to the inflection point on the powder weight vs. velocity curve -- YEEHAW, theory matches empirical measurements.

Sure enough, an inflection point was observed with FC brass also, at 41.0 grs and a velocity of 2529+-15.3fps. But the accuracy at this point wasn't stellar; sub-MOA, for sure, but not 0.3MOA as was observed with BHA brass.

Now, in the 2550fps region, there was a velocity consistency sweet spot at 41.5grs of 4064, for a velocity of 2575+-10.8fps, but accuracy here was even worse. Sure, there's 3 shots through the same hole, but two seriously bad fliers.

The best accuracy was achieved with 40.0grs of 4064 for a velocity of 2444+-21.5fps, but even here there's one bad flier.

Ironically, the best velocity consistency was achieved at 42.5grs of 4064 for a velocity of 2658+- 5.1, but accuracy here was very poor.

So what does this all mean? Theory still predicts practice, in that an inflection point in the powder vs. velocity curve does imply a sweet spot from a consistent accuracy standpoint. But, at least in this case, trying to achieve sub-0.5-MOA accuracy with FC match brass is an exercise in turd-polishing. It ain't gonna happen. Though my rifle does like 168gr bullets to be travelling in the 2550fps region, there's something about BHA brass that really works in my Remington 700PSS. Good thing I recently bought 200 more rounds of BHA brass.

It just occurred to me that FC brass might have thicker necks than BHA brass, and since I'm using the same neck-only sizing dies, the resultant loads built with FC brass may have greater neck tension than the BHA brass. Hmmmm ..... perhaps there's hope yet for FC brass, if I spring for Redding competition dies with changeable neck inserts. More experimentation is required, perhaps with Winchester brass also.

And the verdict is ....

Measured a couple of case necks, going around, 90degrees at a time, and measuring.

BHA -- 0.010"-0.011"
FC -- 0.012"-0.014"

  1. BHA cases have thinner necks than FC match cases. Since I use the same neck-only sizing dies, this will result in greater neck tension in the case of FC and hence greater release inconsistency and potentially more damage to bullet jackets.
  2. BHA cases have more consistent neck thickness, resulting in better bullet concentricity with the bore.

There ya have it .......

Sunday, June 17, 2007

A great 9mm Luger defensive load, or “Remington Golden Sabre rules”

I’ve been skeptical about 9mm Luger loads with 147gr bullets, because given the limited OAL as required by a typical 9mm magazine, one must seat the rather long 147gr bullet so deeply into the case, that the volume left for powder is limited. This skepticism however changed when I recently picked up a 9mm Luger barrel for my CZ 52.

As any gunnut astute reader will know, a CZ 52 pistol is traditionally chambered for the Russian 7.62x25 Tokarev round, which is typically 1.380” long. A typical magazine limited 9mm Luger round is only 1.150” long, so allowing 9mm Luger rounds into a CZ 52 magazine opens up vistas of interesting 9mm Luger loads with heavy bullets.

I tried two bullet types,

  1. a Winchester 147gr JHP bullet and
  2. a Remington 147gr JHP Golden Sabre bullet.

To my disappointment, I couldn’t seat the Winchester bullet out as far as I had hoped because, though the CZ 52 magazine can accomodate longer rounds, the barrel is cut for traditional 9mm Luger loads and hence the furthest I could seat the bullet before it contacted the lands of the barrel was for an OAL of 1.130”.

The Remington Golden Sabre bullet however is a horse of a different color. You’ll note that Golden Sabres don’t have a uniform diameter but instead have a 0.18” wide “drive band” near the base, which is 0.356” in diameter, and then the bullet diameter abruptly steps down to 0.348”. This allows the bullet to be longer than would be the case if the diameter was uniform. But more importantly, in my case, it allows one to seat the bullet further out of the case before it makes contact with the barrel lands. I could build a cartridge with a length of 1.190”, longer than what I could do with the Winchester bullets.

I wanted a load that would achieve at least 1050fps with a less than +-10fps velocity deviation. I chose Power Pistol (because that’s what I have) and varied the powder weight from 4.2grs to 5.3grs, with a 0.2gr delta. This was done with care, as my Speer manual recommends not going beyond 5.0 grs for this loading.

Fortunately, no signs of overpressure (flattened primers, shiny case bases) were observed. The following shows the curves of powder weight vs. velocity of the two loads with y-axis error bars showing SD in velocity.

As expected, the curve of the Winchester loading, with it’s smaller powder volume, starts to reach a plateau at around 5.0 grs of powder, whereas the curve of the Remington loading, with it’s larger powder volume, is still linear up to the limit of this experiment. 5.1grs of powder seems to be a sweet spot, from a velocity deviation standpoint, for both loadings, with a velocity of 1041+-7.8fps and 1004+-8.9fps respectively.

Accuracy-wise, all rounds landed in 2-3” circle, firing offhanded, unsupported, through a Chrony from 15yds.

Since the Remington loading is still linear at 5.2grs of Power Pistol, naturally we must find the point of inflection there too. Stay tuned next week ..... [Did I already say that I love Remington Golden Sabre bullets?]

A great 45 ACP defensive load, or “I finally figured out how to handload with Remington Golden Sabre bullets”

I’ve wanted to see how fast I can push a 185gr JHP bullet out of a 1911. I’ve had tons of Remington 185gr Golden Sabre bullets lying around, but have had poor accuracy with them. Recently, I realized that my loading technique may be the problem. You’ll note that Golden Sabres don’t have a uniform diameter but instead have a 0.2” wide “drive band” near the base, which is 0.451” in diameter, and then the bullet diameter abruptly steps down to 0.441”. This allows the bullet to be longer than would be the case if the diameter was uniform.

I’d been loading to an OAL of 1.220” such that the case mouth ended up just past the end of the drive band and with a fairly tight crimp. Remembering that a 45ACP round headspaces on the case mouth, thinking about this more, I realized that with the case mouth crimped down past the end of the drive band, the diameter of the case mouth was now smaller than it should be for proper headspacing and thus accuracy/consistency would suffer.

I tried an experiment where I loaded to an OAL of 1.230” such that the case mouth ended up just before the end of the drive band, and applied a very light crimp so as not to push the case mouth into the drive band. WHAT A DIFFERENCE!!!! But more on accuracy later.

So, now that I could achieve good accuracy, I experimented with velocity. I wanted a load that would achieve at least 1100fps with a less than +-10fps velocity deviation. I chose Power Pistol (because that’s what I have) and varied the powder weight from 8.2grs to 9.9grs, with a 0.3gr delta. Two velocity sweet spots appear:

  1. at 9.0gr, velocity was 1102.2+-6.6 fps
  2. at 9.9gr, velocity was 1187.2+-9.2 fps

No signs of overpressure (flattened primers, shiny case bases) were observed but past 1150fps, cases were being flung a good 20 feet away, even though I had a 18.5lb recoil spring in my Rock Island Armory 1911.

So, 9.0grs it is. Winchester cases, CCI 300 primers, OAL=1.230”, or seated so that the case mouth is just shy of the end of the drive band, and a very light crimp.

The following is the powder weight vs. velocity curve, with y-axis error bars showing SD in velocity.

As for accuracy, all 40 rounds I fired during the measurements landed within a nice 3” circle. The target was 15 yds away and I was firing offhanded, unsupported, through a Chrony. Naturally, accuracy was not the primary concern here, but even so, a 3” circle is reasonable considering the Rock Island Armory is my “beater” 1911.

Monday, June 11, 2007

A pointless post, or Pictures of a beautiful shootin' iron

There's no point to this post, other than that I had my camera and tripod out, and realized I'd never taken a picture of my "cowboy rig". So here you have it.

That's a hand-built US Firearms SAA (Single Action Army) done in their Dome-Blue finish, riding in a handtooled leather rig, finished in "ox-blood". The thing is so beautiful, it almost hurts to shoot it.

Yup. No need to thank me. The gun porn is on me.

Sunday, June 3, 2007

Trigger job for your Mosin-Nagant 91/30

I picked up a 1943 Soviet Mosin-Nagant 91/30 recently for $89 at Big 5. The 91/30 (if you don't recognize it) is the second from the right in the following picture.

Nothing spectacular. It's a fine shooter that can group to 4" at 100yds. But the trigger was heavy and chunky. Naturally, this had to be remedied.

There are lots of websites discussing disassembly of the 91/30, so I won't repeat the recipes here -- consider it an exercise for the student. Here, we'll discuss only
  1. how to lighten the trigger, and
  2. smooth out the trigger pull.
After disassembling the rifle, and placing the action upside down on a table, you'll see the trigger and a leaf spring, screwed to the action, holding the trigger in place. This leaf spring serves two purposes. It provides trigger tension and is also the sear, which engages the bolt striker.

Unscrewing the screw holding the leaf spring in to the action, and pushing the trigger pivot pin,

frees the trigger and leaf spring from the action.

The tension in the leaf spring is what gives the trigger its weight. One can reduce tension to reduce the weight of the trigger. Simply put it in a vice between two pieces of hardwood

and bend, in the direction you want, to increase or decrease weight. Note, the nub sticking out is the sear, so be very careful not to damage it. Using very light HAND PRESSURE ONLY, bend the leaf spring in small increments, testing repeatedly. My trigger was too heavy. I wrapped a towel around the sear and pulled on the towel away from the sear to reduce tension in the spring.

You know you've achieved the right amount of tension when the spring lies flat when placed in the action and doesn't acquire any more tension when the screw holding it to the action is screwed tight.

The crunchiness/chunkiness in the trigger can be eliminated by gently stoning the surface of the sear and removing any burrs from the edges.

If you're feeling adventurous, and wish to reduce the length of pull (distance trigger has to move before the gun fires) of your trigger you can remove some material off the top face of the sear. This can be done with a file or with bench grinder. Be sure to take off small amounts of material at a time and retest often. After grinding/filing, apply the stone to the face of the sear and edges to give a nice smooth finish.

The most powerful handgun in the world

Since seeing the movie Sudden Impact, where Clint Eastwood's "Dirty Harry" character dispatches a bad guy with an Automag, I've wanted one. Recently all versions of the model 180 Automag were placed on the C&R (Curio and Relic) list by the ATF, so I could get one in CA. And get one I did -- I actually got two, but that's a story for another day.

I got a TDE branded Automag made in 1973 at the North Hollywood plant. When I bought it, it appear unfired, a condition I quickly remedied. There are many pages detailing the history of Harry Sanford and the Automag corporation, so I won't repeat it here.

Contrary to popular belief (if you take the Wikipedia site as the source of all truth -- UPDATE: The Wikipedia site has been fixed) the Automag action is not gas operated, but is a short recoil action. The breech is locked by a multi-lugged, rotating bolt much like what one finds on AR-type rifles, only bigger.

In recoil, the slide is decelerated by a pair of beefy springs on two steel rods on either side of the frame.

The slide can be pulled back by grasping the two serrated cocking pieces, one on either side of the rear of the slide, with the thumb and index finger of the non-shooting hand. Unfortunately, for those familiar with the "whole hand" cocking method deployed with 1911s (placing non-shooting hand on slide with web over rear sight) this will be the only disappointment with the Automag; cocking is a bitch.

The other peculiarity about the Automag is the thumb safety; it can only be activated with the hammer down. Now, the Automag is a single action pistol so it would make sense to carry it in condition 1 (one up the pipe, hammer cocked, safety on) but the safety cannot be activated with the hammer cocked back; what's the point of the safety exactly?

Yeah, yeah, but is it accurate? I worked up a load using Hornady 240gr XTP/HP bullets, seated to 1.600" in new Starline cases primed with CCI 350 (magnum) primers, over Alliant 2400 powder. I worked up the powder weight from 18.6gr to 21.6gr with a delta of 0.3gr. The sweet spot appeared at 20.7gr for a velocity of 1329+-10.4fps. This load grouped to under 1" from 15yds, shooting offhand while standing up. (The flier in the lower left of the group is a "pull")

And how's the recoil? Not as bad as full-house 44 magnum loads out of a 6" S&W 29, meaning I feel comfortable it shooting one-handed .... and the cases land neatly at my feet.

The most powerful handgun in the world? Nah .... been eclipsed by various revolver chamberings and the Desert Beagle in a 50AE chambering. But it's a finely crafted handgun. Now if only someone would build me a M1 carbine in 44 AMP ... I'll be happy.