Hornady Headspace Comparator Kit: What You Get, How to Use It, and a Lower-Cost Alternative (2026)

Last updated: November 2026 | By AltitudeCraft Team

The Hornady headspace comparator kit (item HK66) is a B-2000 comparator body plus five bushings that clamp to your calipers. It measures from the case head to the shoulder. You zero on a fired case, resize, and read how far the shoulder moved.

It does not measure bullet seating depth. That takes Hornady's separate B14 insert set.

Disclosure: AltitudeCraft makes the AC272 alternative discussed below. Hornady facts come from Hornady's own documentation.

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AltitudeCraft Bullet and Headspace Gauge Comparator Kit with 14 Inserts and 6 Bushings

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What comes in the Hornady headspace comparator kit?

The Hornady Lock-N-Load headspace comparator kit is sold as item HK66: one B-2000 body and five bushings. According to Hornady's headspace bushing page, the five bushings are A (.330"), B (.350"), C (.375"), D (.400") and E (.420").

Hornady also sells HK55 (bushings only) and the AB1 Anvil Base. Other sizes, including the G-.240" (17 Hornet) bushing, are "sold separately." Its HK55 instruction sheet says the bushings fit "the same B-2000 body as found on our Bullet Comparator." Own a Hornady bullet comparator? Then HK55 is enough.

On November 6, 2026, KYGUNCO listed HK66 at $39.77 and Sportsman's Warehouse listed it at $59.99, which also lists it as made in the USA. Hornady's B14 bullet insert set was $65.99 at Sportsman's. AltitudeCraft's AC272 (headspace plus bullet inserts) lists at $49.99, and the headspace-only AC270 at $30.99.

Which bushing does the Hornady kit use for your cartridge?

Pick the bushing whose hole lands roughly halfway down the case shoulder. Three common examples from Hornady's chart: 223 Remington uses A.330, 6.5 Creedmoor uses C.375, and 308 Winchester uses D.400.

For an unlisted cartridge, Hornady's rule is to add the neck diameter and the shoulder diameter, divide by two, and use the closest bushing. Every other cartridge is in our headspace comparator bushing size chart. The 6.5 Creedmoor setup has its own guide: which Hornady comparator for 6.5 Creedmoor.

How to use a Hornady headspace comparator: the 6-step method

To use a Hornady headspace comparator, zero your calipers on a fired case, resize it, and read the difference. That difference is your shoulder bump. These steps follow Hornady's instruction sheet.

1. Mount the body square. Thread the thumb screw into the B-2000 body and slide it onto the fixed jaw. Close the jaws snugly to align it, then tighten the set screw and thumb screw.
2. Insert the right bushing. Use the chart or the formula above.
3. Seat a fired case. Center the shoulder in the bushing and bring the moving jaw onto the case head. Hornady says to rotate the case while you take out the slack and to "be consistent."
4. Zero on the longest fired case. Measure several cases from one firing and zero on the longest.
5. Resize one case and re-measure. The negative reading is how far the shoulder moved back.
6. Adjust the die in small steps. Hornady recommends .001" to .002" of set-back from the fire-formed dimension. That is bolt-gun guidance. Semi-autos and repeaters typically need .004" to .005"; see the Whidden note below.

The right bump depends on the action. In American Rifleman, Keith Wood cites John Whidden, a six-time national long-range champion and die maker. Whidden "recommends 0.001" to 0.002" of headspace on bolt-action rifles and 0.004" to 0.005" for repeaters."

To turn that number into a die setting, see how to set up a full-length sizing die. Ultimate Reloader compares three headspace methods in this video.

Why do Hornady headspace comparator readings change from case to case?

Comparator readings drift because brass, lube and technique change the measurement, not because the tool is broken. Hornady's sheet says brass from different lots "may measure differently due to alloy and temper variations." It also warns that "a variation in your lube technique can and will be detected by the gauge."

An unsized fired neck can also rub the bushing edge, so the case doesn't seat the same way twice. Gavin Gear at Ultimate Reloader notes that the "sharp edge around insert (mouth/hole) is susceptible to slight inconsistency and is fragile."

Check your own repeatability: the 5-reading test

Before you chase a .001" change, find out how much your own setup moves. Take one sized case and measure it five times. Rotate it 90 degrees and re-close the jaws between readings.

Subtract the lowest reading from the highest. That range is your noise band. Write it down for each cartridge and brass lot.

1. Record the cartridge, brass lot and bushing on a notecard.
2. Write down reading 1 at 0 degrees.
3. Rotate the case 90 degrees, re-close the jaws, and write down reading 2.
4. Repeat at 180 and 270 degrees for readings 3 and 4.
5. Return to 0 degrees for reading 5.
6. Subtract the lowest reading from the highest. Log that range as your noise band.

Reading rule: if a die adjustment changes the reading by less than your range, treat it as no change and measure more cases. If the range is as large as the bump you are aiming for, fix technique first. Check that the neck is sized, the bushing edge is clean, and closing pressure is the same each time.

Hornady Lock-N-Load headspace comparator alternative: Hornady vs AC272

The main difference is scope: Hornady sells headspace and bullet-seating measurement as two kits, while AC272 puts both in one box. Both use the same five standard bushing sizes, A.330 through E.420. Neither replaces a GO gauge.

Hornady's B14 covers the same 14 bullet diameters as AC272, per Sportsman's Warehouse's B14 listing. Both Hornady kits share the B-2000 body, so HK55 plus B14 saves you a second body.

When is the Hornady kit the better buy, and when is AC272 enough?

Buy Hornady if you already own a B-2000 body, load 17 Hornet, or want US-made parts. Buy AC272 if you want shoulder bump and CBTO from one kit. For headspace only, technique matters more than brand.

What mistakes throw off headspace comparator readings?

Most problems with headspace comparators come from how they're used. In 100 Amazon returns of AC272 that we reviewed in August 2026, 21 traced back to how the tool was used or which part was used, not to a defect.

• Common mistake 1: Checking it against a GO gauge. A comparator isn't a headspace gauge, so its number won't match the gauge's stamped value. See headspace gauge vs comparator vs case gauge.
• Common mistake 2: Putting a bullet insert on the shoulder. Bushings go over the shoulder and inserts go over the ogive.
• Common mistake 3: Expecting it to work on pistol brass. Straight-wall cases like 9mm have no shoulder to measure.
• Common mistake 4: Zeroing on new brass. Unfired brass hasn't taken your chamber's shape yet.

Frequently Asked Questions

How much shoulder bump for an AR-15 or AR-10?

Whidden's figure is for repeaters; AR-15/AR-10s fall in that group. John Whidden, quoted in American Rifleman, recommends .004" to .005" for repeaters and .001" to .002" for bolt actions. Hornady adds that rotating fired cases in the comparator reveals bent rims.

Do I need the anvil base?

No, but it helps. Hornady says the AB1 Anvil Base gives case heads and bullets a larger surface to rest on, which makes measurements easier. Our anvil base kit serves the same purpose.

Do Hornady bushings fit the AltitudeCraft comparator body?

We haven't tested cross-fit, so we won't claim it. AC272 already includes the five standard sizes plus an F.450 bushing.

Can a headspace comparator measure chamber headspace?

Not by itself. It measures the case your chamber fire-formed. For true headspace, use GO and NO-GO gauges in the rifle.

So which kit should you buy?

The Hornady kit is a proven, US-made tool. It ships with five bushings and no 17 Hornet bushing or bullet inserts.

If you only need shoulder bump, it's a solid buy. If you also want CBTO, the AltitudeCraft AC272 Bullet and Headspace Gauge Comparator Kit covers both jobs in one tin. For headspace only, there's the AC270 headspace comparator kit.

Shop the AC272 Comparator Kit