Hornady Shell Holder #37 for Trimmer – 390577T
Brand: Hornady
Model: Shell Holder #37 for Trimmer
Part Number: 390577T
UPC: 090255701449 GrabAGun+2OpticsPlanet+2
The Hornady Shell Holder #37 for Trimmer (390577T) is a precision-machined, steel shell holder designed specifically for use with the Hornady Cam-Lock Case Trimmer. Built to securely hold 5.7x28mm FN and .25 ACP brass during trimming, this dedicated trimmer shell holder gives reloaders a solid, repeatable interface for consistent case length and safe, controlled case prep. OpticsPlanet+3Mid South Shooters Supply+3Graf & Sons+3
If you run a Hornady Cam-Lock trimmer and load 5.7x28mm or .25 ACP, Shell Holder #37 is the correct, purpose-built accessory to keep cases aligned and supported every time you trim.
Key Features – Hornady Shell Holder #37 for Trimmer
Purpose-Built for the Hornady Cam-Lock Case Trimmer
Hornady’s Cam-Lock Case Trimmer is designed to handle a wide range of cartridges—up to .50 caliber—with fast, repeatable case length adjustment. To work correctly, it must use Hornady trimmer shell holders instead of standard press shell holders. GrabAGun+2Red River Reloading+2
Shell Holder #37 is specifically machined to engage the Cam-Lock trimmer:
It positions the 5.7x28mm FN / .25 ACP case at the correct depth and angle.
It provides a solid, secure grip so the case doesn’t slip while the cutter contacts the mouth.
It maintains repeatable alignment from case to case, which is critical for consistent case length and neck tension. GrabAGun+2Mid South Shooters Supply+2
If you’re trimming 5.7x28mm FN or .25 ACP and want to get the full benefit of the Cam-Lock system, #37 is the shell holder Hornady built for the job.
Precision-Machined, Heat-Treated Steel
Retailers and Hornady spec descriptions highlight that this trimmer shell holder is milled from high-quality, heat-treated steel. Mid South Shooters Supply+2Reloading USA+2
That gives reloaders several advantages:
Strength under clamping force: It won’t deform under the compression of the Cam-Lock, even after many thousands of cases.
Long-term durability: Heat treatment and quality steel help ensure the holder performs for the “life of the press” and trimmer when properly used. Mid South Shooters Supply+2Reloading USA+2
Consistent machining: A precise, repeatable fit minimizes wobble and supports uniform case trimming.
For high-volume 5.7x28mm shooters or meticulous handloaders, this consistency translates directly into more uniform ammunition.
Wide, Rounded Opening for Easy Case Handling
The Hornady #37 Shell Holder for Trimmer is described as having a wide mouth and rounded opening, specifically shaped to make inserting and removing small, bottleneck cases like 5.7x28mm FN easier. Mid South Shooters Supply+1
Practical benefits include:
Faster case changes: You spend less time fiddling to line up thin cases in a tight opening.
Reduced risk of damaged rims: A smoother, rounded lead-in helps guide case heads into place without gouging or deforming the rim.
Better workflow during large trimming sessions: Especially useful when processing big batches for competition, training, or varmint hunting.
If you’ve ever fought a too-tight shell holder during case prep, this detail alone can be a real time saver.
Caliber Focus: 5.7x28mm FN & .25 ACP
Several retailers list Shell Holder #37 for Trimmer as designed for 5.7x28mm FN, with additional fit for .25 ACP. Graf & Sons+2Mid South Shooters Supply+2
That makes it an excellent match for:
5.7x28mm FN reloaders using Hornady’s Cam-Lock trimmer to manage case growth after multiple firings.
Shooters running .25 ACP in niche or collector pistols who want precise case prep for their small-caliber handloads.
Because 5.7x28mm FN is a relatively small, high-pressure rifle-pistol hybrid cartridge, trimming to consistent length becomes especially important for safe and accurate loads. Using the correct dedicated trimmer shell holder helps maintain that consistency.
Designed for Trimming – Not a Universal Press Shell Holder
It’s important to note that 390577T is a special trimmer shell holder, built around the geometry of the Hornady Cam-Lock Case Trimmer, not a universal shell holder for standard presses. GunStop+2Graf & Sons+2
For press operations (sizing, seating, etc.), Hornady offers separate press shell holders (like the standard #37 press shell holder). GunStop+1
For case trimming, you’ll want this “For Trimmer” version to ensure proper fit and engagement with the case trimmer’s spindle and cam-lock mechanism.
Matching the right shell holder to the right tool is key to safe, efficient reloading.
Ideal Use Cases for Hornady Shell Holder #37 for Trimmer
When used with a Hornady Cam-Lock Case Trimmer and appropriate safety practices, Shell Holder #37 is ideal for:
5.7x28mm FN bulk prep for competition or training ammo.
Precision 5.7 hunting loads, where consistent neck tension and case length matter for accuracy.
.25 ACP handloads where careful case prep is critical due to small case volume and tight tolerances.
Because this is a dedicated trimming accessory, it’s often purchased alongside the Cam-Lock trimmer, 5.7x28mm FN dies, and other case prep tools. OpticsPlanet+3GrabAGun+3Mid South Shooters Supply+3
Technical Specifications – Hornady Shell Holder #37 for Trimmer (390577T)
Compiled from manufacturer and dealer listings: Red River Reloading+4GrabAGun+4OpticsPlanet+4
Manufacturer: Hornady Manufacturing
Product Name: Shell Holder #37 for Trimmer
Part Number (MPN): 390577T
UPC: 090255701449
Series: Shell Holders – Trimmer-specific
Tool Compatibility: Hornady Cam-Lock Case Trimmer
Caliber Fit: 5.7x28mm FN, .25 ACP
Material: Precision-machined, heat-treated steel
Design: Special shell holder for trimming; wide, rounded opening for easy case insertion/removal
Safety, Use & Care Tips
Always confirm your trimmer is properly assembled and securely mounted before use.
Verify that each case is clean and free of obstructions before clamping it in the shell holder.
Wear eye protection when trimming to guard against brass shavings.
Follow Hornady’s instructions for the Cam-Lock Case Trimmer and consult reputable reloading manuals for your 5.7x28mm or .25 ACP load data.
Used correctly, the Hornady Shell Holder #37 for Trimmer 390577T is a small but crucial piece of gear that helps you get cleaner cuts, more consistent case lengths, and safer reloads for your small-caliber cartridges.
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