Pistol Brand Accuracy Demystified

[flyfishmatt]

Did you ever notice that when you go on the web to do some research about a new pistol you always run across a thread where one person is hailing the virtues of their new purchase while another is telling the person about their terrible experience with the same model or manufacturer? It often leaves the reader with a sense of bewilderment as they try to separate fact from fiction.

Well folks there is a reason why this occurs so let me explain.

The success of every assembly that is manufactured depends upon the stack up of tolerances of the underlying parts. The process used in manufacturing to determine the success rate is know as statistical process control. When the manufacturer goes into production acceptable tolerance ranges are established for each part. Since hand selecting and fitting is expensive, generally a pistol with a low price point is assembled from parts with "looser" tolerances than say a pistol which will be hand fitted (where the parts are often oversized and hand fitted/assembled). In the budget market, the manufacturer is looking for 100% success in assembly with little or no hand fitting or waste.

In the pistol world when it comes to accuracy, generally the better the fit the better the accuracy. In terms of pistol fit there are three categories of pistol fit. There is the "perfect" fit, "optimal" fit and everything else. The "perfect" fit 1911 (a pistol where each dimension, surface and angle are exactly fit to each other and the design) will not function if even the smallest piece of debris enters into the working surfaces of the pistol. The slide will seize up and stop working. I once spent the better part of 120 hours with lamp black, file, and emery cloth to get a pistol to fit perfectly. I soon learned the pistol was not practical so I was forced to loosen the tolerances ever so slightly to get the pistol to the "optimal" fit.

In the world of manufacturing pistols, it is statistically possible that any single pistol can come together from parts which when assembled will result in a pistol that comes very close to an "optimal" fit. The closer the tolerances are for each part the more likely it is that the pistol will come together close to an optimal fit. Maintaining very close tolerances is very expensive. It requires new machines, sharp tooling and the steel must be consistently sourced. Some manufacturing techniques such a MIM have reduce cost and help tighten up tolerances at what many believe is too great a cost in overall quality (I am staying out of that fight). Generally, the closer the "tolerances" the higher the production cost. The only exception to this rule is triggers, which require some attention to surface quality. Generally, you cannot manufacture a great trigger it must be hand fit.

I often hear people degrade Kimber pistols. One of the best pistols I have ever owned was a Kimber Team Match which out shot my Les Baer (one with the 1 1/2" guarantee). You may ask how is that possible? It is simple, the pistol I had came together from parts that when brought together they were very close to the optimal fit (I understand Kimber does some hand fitting in their production). Now does that mean every Kimber will do that? Of course not. But it can happen and it does with some regularity. The likelihood again comes down to how tightly the tolerances are managed (or hand fitting is used to size the parts). The same holds true for any pistol that is manufactured whether it be a Colt, S&W, Glock, H&K or Sig.

One it comes to hand fitted pistols some of the same rules apply. An outfit like Les Baer owns new state of the art machines. I image because he controls the machining, he can change out the tooling more often to ensure closer tolerances and better surface quality. Outfits that buy their frames and slides from others are dependent upon either total hand fitting or their source maintaining tolerances to their liking. Generally, the likelihood of getting a pistol that is optimally fit is far greater from a hand fit company then elsewhere.

Thus, while price point is often a good measure of likely performance, it is not always the case. So as you read the post of someone buying a budget pistol and getting great results it may not be just a case of extreme "newgunitis." It may just be that the person just happened to get a pistol where the tolerances of the underlying parts came together closer to the optimal fit than others of the same model and from the same manufacturer. Similarly, when you read a post from a person with a bad experience it could be that his/her pistol came from parts that when assembled came in at the other end of the fit spectrum.

Buying a pistol from a reputable manufacturer that is known for producing solid pistols with good accuracy will get you a good pistol. A great pistol comes from either paying for hand fitting or the luck of the draw (pun intended).

 

[Tirod]

I used to work in an assembly plant fabricating automotive parts on a 100 ton press brake.

Tolerances are an easily misunderstood subject. What one company documents under their guidelines and guarantees with ISO certification as "tolerances" would be another company's junk rejects.

The AR15 has a blueprint specification of +/-.015" as a tolerance on a lot of it's parts - you can download them and see yourself online. What that doesn't tell you is how the company who assembles them manipulates the fit - with no hand finishing. They measure and batch items by size whenever possible, to work with parts also batched that have a working clearance that is optimum for that assembly. As pointed out, it's the dynamic clearance that counts - and you can get things too tight.

Tightly fitting parts are worse than loose ones. It's not what we think it is.

As you fire a gun, it gets warm, heats up, and the dimensions change. Same when carried outdoors. It's 17 degrees right now outside, a gun with closer fitting parts may shrink just enough to fall out of the operational window of optimum fit, too. That's why guns used in the Artic are better off with no heavy lubrication, it takes up too much space.

Back to the AR15, the bolt carrier and inside the upper both measure about 1" but the makers match the batches so that a carrier that is .998 isn't assembled in an upper that is just .001" bigger. It's not good. So, the carriers are run a bit small, the upper a tad large, and the assembly has the clearance - the space in between - that helps it to work at the temperature extremes.

There's a lot more to it that "loose" or "tight" tolerances, and it very much has to do with the overall stack - the added sum of all the parts when assembled.

When someone gets an upper that is large enough the barrel extension just falls in, complaints are heard about poor quality control. In reality, both parts may have been made to specification - they are just at the opposite ends, and the tolerance stack is less than optimum. Nonetheless, tighten down the barrel nut, and the assembly could still shoot 1 MOA. How the nut holds the barrel extension against the nose of the upper and it's rifling have their affect, too.

This is why in the "good old days" that there were 1 in 1000 rifles. Since the makers were conscientious about turning a dollar, they test fired guns for accuracy, and the ones that fell into the top tier were sold for a premium. It was all quite by accident, tho. There may have been ten in a row that did it, and another 3,000 that couldn't. They were just labeled "1 in 1000" as a marketing gimmick. It certainly was not exactly the 1,000th gun every time.

Auto makers do it, too. There are factory bearings and piston rings in the next .0001" increment for use in assembly to get the fit right - rather that trash a part that has no other fault than having an assembled fit up just a tad out of spec. It's a balancing act, that hand labor to redo something that robotics couldn't quite get right costs money. You can only do so many like that.

But - you can control the dimensions and batch the output to work cooperatively with other parts. Instead of hand fitting and filing, you simply pick the ones that are known to work together better and use them. It's a production control technique and needed because scrapping them isn't needed or profitable.

That's why it's said that every part on a 1911 requires gunsmith fitting. The tolerance stack is important in how the gun operates. Does the AR require gunsmithing to assemble? Not so much - it was designed to minimize finessing the parts, and exactly why it's a significantly different firearm. It was specifically designed to work in a harsh environment with a lot contamination.

A gun or car with tight tolerances is considered to be higher quality than one with some play, but it's the public's perception, and it's not necessarily correct. All mechanical parts have an assembled optimum clearance, and that is more important than say, not being able to slip a playing card between the upper and lower receiver. There is every possibility that a rattling older beat up gun can and will shoot more accurately than the "finely crafted" tight one. It's dynamic operation determines that, not the aesthetic look.

 

[tuj]

Joe Chambers (who builds great 1911's BTW) was claiming tolerances that were, well, pretty insane on his bushing fits and such. He's backed off that now, but it still stands that the tighter the tolerances, *in general* the better the gun will shoot.

That said I have seen rattle-trap 1911's that could hold 3" at 50 yards with a good load for 10 shots. So besides fit, accuracy is a lot about the barrel and its condition.

I have a Les Baer 1.5" PII that I bought used from a guy who shot it for years. Honestly, the barrel is shot out; it won't hold 3" with match loads at 50 yards. Heck it won't even hold 5". I talked to the man himself, Les, about it. He said the barrel is shot out, send it back.