Saturday, January 29, 2011

In Search Of Accuracy

In a firearm, specifically. This is an interinting topic to search, as many people have opinions on it, but few have any hard data.

I have a varmint rifle that will shoot <1MOA all day long, and I guess I've gotten spoiled by it. I also have a Hi-Point carbine that shoots about 3 MOA. For this gun, that's probably not unreasonable, but why be reasonable if it presents a chance to tinker.

I found a thread in the Hi Point discussion group that mentioned that the barrels of H-Ps were not crowned. The moderator pointed that crowning cost money, and H-Ps were built to a price point, not an accuracy standard. This seems reasonable, as the easiest way to get a sum-MOA gun is to put about $3000 on the table, and wait for it to get built. Still, I know that some massaging will improve accuracy, and it doesn't have to be prohibitively expensive, so I looked into crowning.

For you non-gunnies, the crown is the recess cut into the business end of the barrel of the gun. The form varies, depending on how fancy you want to make it. Most guns use a double radius, so the end looks like a donut, radiused into the hole, and out to the outside diameter. This is easy to cut, and not expensive. There was a discussion at Snipers Hide on the relative merits of crowning that was reminiscent of .45 vs 9mm arguments. There was one post there that cited some actual data, suggesting that the difference between a nice square crown, and a 30 degree hacksawed barrel was mostly to move the shot group, although it was noted that if you cut off your barrel with a chainsaw, you can expect your groups to increase from 1 MOA to 1.5 MOA. One could conclude that the primary function of the crown is to prevent damage to the inside of the barrel while the gun is banging around behind the seat of your pickup truck.

Bill Johnson has a more exhaustive piece on accuratizing that has the advantage of having reasonable extensive documentation, and the inclusion of a control rifle. His test rifle started out at 4.5MOA which is worse than mine, so I felt this was a relevant study.

Polishing the barrel using Dave Tubb bullets with abrasive embedded into the jackets took him down to 2.67 MOA which is an impressive drop for an easy job, plus the price is reasonable, and you get to go shooting in the process. Shooting abrasive bullets down your barrel sounds scary to me, but this seems to work.

A trigger job made more difference than I would have expected, but hey, whatever works. I suspect that most trigger jobs involve simply polishing the parts to get rid of the scratchyness and reduce the friction. To that end in might be fun to see what throwing a disassembled trigger group into a tumbler with metal polishing media would accomplish.

Bedding the action helped, but only on the looser of the two rifles. Once you get to a certain point, the return on your investment falls off rapidly. It helped for Mr. Johnson, whose 4.4 MOA gun now shoots <1MOA. I'm not sure what bedding the action might entail on a gun that the furniture comes in a left half and a right half held together by screws that pinch the halves together over the metallic innards, but I guess I could have a look while I'm looking into the trigger group.

Keeps me occupied during the winter, I guess.


Brad K. said... out of Wichita, KS, sells Xado products.

Xado oil treatment is a small tube of stuff you squirt into the oil. It is carried by the oil to places where the metal rubs and gets hot - like piston rings and cylinder walls. Then the guck combines with suspended metal in the oil (metal is rubbing, remember?) to form a tough, low-friction ceramic-metal compound that rebuilds the metal parts.

Use one tube to lengthen the life of your engine, three tubes to 'rebuild' the engine over the course of a couple of hundred miles of driving.

I told you that story so I can tell you this one.

They also sell variations for small engines, grease for any moving gears, and a version that you smear on bullets to rebuild your barrel.

The barrel-rebuild takes three related but different tubes of guck, and each is smeared on 100 of your bullets. Then you start shooting.

The Xado (pronounced "hah-dough") oil treatment promises longer engine life and better fuel efficiency at idle speeds (lower friction). I don't know that the barrel treatment should increase muzzle velocity or accuracy. But it might.

I used the oil treatment, and it worked as advertised. My Ford Escort Wagon ran like a top, until that Chevy 1/2 ton pickup turned into me. But I don't consider that a lubrication system failure.

Billll said...

Lubricating the bullet should have the same effect as polishing the barrel. It makes me wish I had a half-million dollars worth of test equipment so I could quantify the amount of vibration a rough barrel imparts to the gun as the bullet travels down it and measure the effect of this on accuracy.

At the end of the day, the problem seems to devolve down to vibration. The less you impart, the more accurately your bullets fly.

You can buy molly-coated bullets right now which makers of claim more speed and smaller groups. Probably the same effect.

Brad K. said...


The Xado approach isn't to lubricate. It comes from a Russian research effort, and actually rebuilds eroded metal with a stronger, lower-friction ceramic-metallic compound.

The barrel treatment goal would be to rebuild the highest temp, highest friction micro-local locations. Reducing vibration would be a side effect, not the intent.

jed said...

Ya know, there's folks selling anti-vibration doughnuts that you slip onto your barrel. Some of 'em work, IIRC.

You might consult teh Ghougle re. fire lapping. Lead bullets and valve grinding compound, or the moral equivalent, might be cheaper than a specialty kit.

I don't recommend putting your trigger group into a tumbler. You don't want to round off the edges of your sear and disconnector engagement surfaces. (Disclaimer, I'm not a gunsmith, just read a bunch of descriptions of DIY trigger jobs, and none of them mention tumbling. They do mention deburring, polishing, and flattening those engagement surfaces, but doing so while removing as little metal as possible, and making sure to not change the angles of engagement, or the overlap.) One friend of mine uses a small hard Arkansas stone to polish trigger surfaces. I think tumbling is too indiscriminate.

Billll said...

Good point about the edges and corners. The trigger group does not come out readily, but what you can see looks fairly rough. Maybe just a bit of polishing.