Brass Can Bite You in the...

by Bob Londrigan, published in Front Sight Magazine, May  2008

Brass can reach out and bite you in the middle of a match if you are not mindful of what differing critical dimensions can do to your extraction/ejection pattern. I recently had a customer who developed erratic ejection in his gun and came to me to fix it. During my conversation with him trying to diagnose the problem I asked if he had changed anything recently.  He mentioned he had “changed from 38 Supercomp to 38 TJ brass.” It turns out this is what was causing his problems.  His gun was set up with an Aftec extractor with the hook making contact with the extractor groove in the brass.  Measurements of his brass showed the rims being the identical diameter (0.384).  However, the extractor groove in his Supercomp brass measured 0.330 while the extractor groove in the 38 TJ brass measured 0.314.  This was enough variation to cause ejection problems.  A quick adjustment to his extractor and he was on his way – problem solved.  This scenario brings up an interesting point that will be the subject of this article.

For the best performance, I always recommend using new brass with the same headstamp at matches. A close second would be once-fired brass through your gun, and third would be used brass with the same headstamp.  There are several reasons for this such as more consistent chrono readings, better accuracy, consistent crimp, tight primer pockets, etc.  Add to this list consistent extractor tension which results in improved ejection/extraction and reliability.

Lined Up Brass Bacl-to-Back Brass

 

Before we get into measurements, we need to discuss exactly how your extractor is set up.  In 38 super and 40 cal extractors, the contact point on the case (spot that provides tension and holds the case) can be set up two ways – so that the hook contacts the extractor groove or so that the belly of the extractor contacts the outside of the rim on the case. In 38/9mm/Supercomp, I like to set it up so that the hook contacts the extractor groove (that is how an Aftec is set up).  In 40 S&W, the Aftec is set up belly on the rim.  Other extractors may be set up in either manner.  All 45 ACP extractors I have seen use the rim of the case. You will need to know how your particular extractor is set up in order to take measurements on your brass and properly set the extractor tension.  You will then  set/check your extractor tension based on the type of brass you will be using in the match.

Extractor hook on brass rim

In the following charts show the rim and extractor groove measurements from quite a few brass manufacturers that I had on hand.  These measurements were made mostly on used brass.  The fact that the brass was used accounts for some of the variation, but this data still gives you an idea of just how much variation there can be. 

38 Super

Headstamp

Rim

Extractor Groove

RP

0.401

0.340

Win

0.401

0.343

Starline 38 super

0.397

0.338

AP 04

0.400

0.339

PMC

0.400

0.340

WW nickel

0.402

0.343

Midway

0.401

0.342

CBC

0.400

0.341

AP 38 super*

0.385

0.320

Lapua 38 super*

0.382

0.334

Range of measurements*

0.397-0.402

0.339-0.343

*Please note that these are headstamped 38 super but are really rimless. 

38 Super rimless variants

Headstamp

Rim

Extractor Groove

38 Supercomp

0.385

0.329

Hornady 38 TJ

0.388

0.314

Starline 38 TJ

0.384

0.314

Range of measurements

0.384-0.388

0.314-0.329

 

9mm

Headstamp

Rim

Extractor Groove

WCC 1988

0.386

0.341

WCC 97

0.388

0.341

WCC 98

0.387

0.341

WCC 01

0.386

0.343

WIN

0.387

0.341

RP

0.388

0.336

CBC

0.386

0.338

S&B

0.386

0.344

LE

0.387

0.336

WW

0.386

0.341

FC NT

0.390

0.341

A-MERC

0.387

0.338

PMC

0.386

0.335

FC

0.388

0.338

Starline

0.388

0.340

Speer

0.390

0.334

Cor-Bon

0.387

0.335

Range of measurements

0.386-0.390

0.334-0.344

 

40 S&W

Headstamp

Rim

Extractor Groove

Starline

0.418

0.334

A-Merc

0.416

0.343

RP

0.419

0.334

Winchester

0.416

0.339

*I*

0.418

0.336

Speer

0.419

0.336

Cor-Bon

0.417

0.336

Federal NT

0.419

0.337

Federal

0.418

0.334

FC

0.419

0.335

BHA

0.415

0.340

CBC

0.418

0.340

PMC

0.425

0.342

GFL

0.417

0.333

S&B

0.420

0.340

Range of measurements

0.415-0.425

0.333-0.343

So, what do all these numbers mean?  The first thing that comes to light is that whether you index off the case rim or off the extractor groove there will be some significant variations in these dimensions from manufacturer to manufacturer.  I have found that even variations of as little as 0.005 diameter can cause problems depending on how the gun is set up. The exact position of the spot that the extractor contacts the case will vary by ½ of the variation of the diameter, but will also be affected by variations in the diameter of the rim.  You may have situations where one will cancel the other out or where they become additive.

Use this information to make a decision on how much extractor tension you need and how to measure it. If you are going to use only one headstamp, take a random sample and measure the applicable engagement point.  In quality brass you will see very little variation.  I measured a sample of new RP 38 super brass and found a variation of less than 0.001 in the rim dimension and the same for the extractor groove dimension. Used brass will vary a little more especially in the rim dimension as the cases take somewhat of a beating. If you are going to use a mixture of range brass, you need to select a headstamp to use for matches that is towards the middle of the range of dimensions of your brass.  Then set your extractor up so that it has the proper tension with the case that you have selected.  Save this case and when you are checking tension on your extractor later on always use this same case.

The procedure for setting up your extractor is as follows: 

If you set your gun up this manner, it will go a long way towards making it more reliable in a match.  Also, if you have any type of malfunction you will be able to measure your brass and, if it is way out of spec, you can be pretty sure that is what caused the malfunction.

 1911 parts at Brazos Custom