Good morning everyone and welcome back to another edition of TFB’ Silencer Saturday brought to you by our friends at Yankee Hill Machine, manufacturers of the Turbo and Turbo K line of suppressors. Last week we discussed some buying tips for silencer newbies and many of you added advice from your own personal experiences in the comments section. Guidance like don’t wait for wait times to drop before buying, the market for used suppressors is almost non-existent and suppress the caliber, not just the gun, that you shoot the most, is all solid advice. As always, thank you for reading and sharing your knowledge. This week I wanted to touch on selecting ammunition for longer 9mm platforms. Specifically, H&K SP5 subsonic ammunition choices. Easy, right? Just pick a subsonic round and go to work. Hang on, we’ve got a bit of velocity estimation to do first.

Thanks to Jack for sending in his question about SP5 ammo choices.

SILENCER SATURDAY #127: H&K SP5 Subsonic Ammunition Choices

When discussing subsonic ammunition, our first stop as consumers is usually the information on a manufacturer’s website or printed right on the box itself. Unfortunately, this only tells us part of the story – temperature, elevation (air density), humidity (minimal) and other environmental factors can have an effect on bullet velocity. But more importantly, these variables will also play a factor in the speed of sound.

Remember, to avoid the supersonic crack, our projectile needs to stay under the speed of sound; hence the term subsonic. Since the speed of sound can vary, you need to take in to account the environment in your AOR.

The speed of sound at different elevations:

The speed of sound at different temperatures: 

While we do care about environmental factors when picking subsonic ammunition, when we are looking for  quiet ammunition specifically for the H&K SP5, our main concern is barrel length. Because 9mm Luger is primarily used as a handgun round, printed velocities in manufacturer’s product materials are based on one of the most common handgun barrel lengths: 4 inches. The H&K SP5 barrel length: 8.9 inches.

Heckler & Koch SP5

https://hk-usa.com/hk-models/sp5/

Let’s take a look at some industry standards and practices.

Sporting Arms And Ammunition Manufacturer’s Institue – SAAMI

http://www/saami.org/about-saami

The Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI) is an association of the nation’s leading manufacturers of firearms, ammunition and components. SAAMI was founded in 1926 at the request of the federal government and tasked with:

• Creating and publishing industry standards for safety, interchangeability, reliability and quality
• Coordinating technical data
• Promoting safe and responsible firearms use

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Subsonic 9mm is predominately loaded with 147gr (and heavier) bullets since it’s easier to hake heavier bullets fly slower with a “standard” powder charge than it is to reduce a powder charge with lighter bullets. As you can see above the recommended velocity of 124gr 9mm bullets from a 4 inch barrel is right around 1100fps. Already too fast even for pistols with short barrels

I know this may all be pretty basic to you, but the point is, the velocity printed on the box is meant to be relative to your GLOCK 19, not your H&K SP5. Those with less experience that see “subsonic” and want to head out for some quiet shooting, they may be disappointed with the performance in a longer barrels.

Let’s do some velocity estimations to see if we can find a magic number we can use to predict subsonic speeds with a 9 inch barrel.

Ballistics By The Inch

http://www.ballisticsbytheinch.com/9luger.html

Although dated and not as comprehensive as we would all like, Ballistics By The Inch has a a table of different 9mm loads in barrel lengths from 2″ to 18″. Unfortunately we only have one 147gr load to work with.

Using the Federal Hydra-Shok 147gr sample above, a 4″ barrel launches the bullet with a muzzle velocity of 951 f/s. The same bullet leave a 9″ barrel at 1055 f/s. A difference of about 100 f/ps or about 9%.

However, as we discussed in the first section both temperature and elevation can play a role in the speed at which sound travels. Depending on where you live and the weather on a particular day, these 147gr rounds may go transonic or supersonic in the H&K SP5 9″ barrel.

Let’s take a look at some currently available factory subsonic 9mm ammunition and their muzzle velocities.

The SP5 had two or three rounds that may have gone transonic (to my ear) and had an average muzzle velocity around 1,050 fps.

Conclusions:

Getting 147gr 9mm rounds to stay subsonic in longer pistol caliber carbine barrels is a bit of a guessing game. I’d suggest testing a small batch of quality ammunition marked as 975 fps or lower before making a an investment in hundreds or thousands of rounds that you hope to be subsonic in your H&K SP5. You’ll also want to make sure that your ammo will confidently cycle your roller-delayed action – some of the lower pressure rounds may be a bit anemic in anything but unsuppressed pistols.

Thanks for reading. Have fun, stay safe and we’ll see you back here next weekend for another edition of Silencer Saturday.

Silencer Saturday is Sponsored by Yankee Hill Machine:

Buy YHM silencers and accessories at:

Silencer Shop – Hansohn BrOthers – dead eye gun supply –

Mac tactical

All YHM Products At Brownells

DEALERS: If you want your link to buy YHM suppressors included in future Silencer Saturday posts, email: silencers@thefirearmblog.com

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special Thanks: Mac Tactical

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