9mm 147gr subsonic handloads vs. factory ammuniton

[MCMXI]

I recently returned an MPX to SIG to have them figure out why it would throw bullets all over the place at 50 yards. It runs very well but the accuracy/precision has been frustrating to say the least. I tried suppressed and unsuppressed, two different optics, iron sights and at least four factory loads ranging from 115gr to 147gr. No combination would reliably hold a group so back it went. I got it back in a little over a week with a new barrel installed.

A couple of years back I started to work up a 147gr handload for suppressed shooting but the results were bad to very bad so I put the MPX on the back burner. It had me thinking that the Vortex optic was defective. Over the Christmas break I wanted to see what it would do with factory subsonic ammunition. I bought a few boxes of SIG 147gr FMJ with an advertised MV of 985 ft/sec and the results were so bad i.e. 12" or greater groups at 50 yards with bizarre "fliers" that I decided to contact SIG.

To be honest, I don't have much experience with subsonic 9mm so what is a reasonable expectation using factory ammunition at 50 yards? If you've handloaded subsonic ammunition, what have you achieved at 50 yards? SIG did ship the MPX back to me with a new barrel that shoots a lot better than the original barrel but still not much better than 6" to 8" (10 shots) at 50 yards using the SIG 147gr FMJ load. The included test target shows a 5-shot, approximately 3/4" group at 25 yards using 115gr ammunition. Are 9mm firearms and heavy for caliber subsonic loads a finicky proposition at 50 yards?

Thanks.

 

[fxvr5]

Are 9mm firearms and heavy for caliber subsonic loads a finicky proposition at 50 yards?

No. Different guns have different preferences. You have to try different ammo to see what yours likes. Several 9mm Bullseye shooter use 147 grain bullets at 50 yards, as indicated on the Bullseye website, so they can't be that bad.

Also, see the article below for testing at 25 yards. three guns don't all like the same ammo.

https://www.shootingillustrated.com...mo-accuracy-15-loads-in-three-different-guns/

 

[ATLDave]

Have you chronoed the 147s?

An issue with 147's in 9mm carbines can be that they are decelerating as they leave the barrel. That can cause various issues.

 

[MCMXI]

@fxvr5 and @ATLDave, thanks for the responses and the link. I'm back at the beginning with this stuff. I've never done 50 yard testing with pistol ammunition other than shooting .45 Colt and .357 Mag from a couple of Marlin 1894s so this is all new to me.

Have you chronoed the 147s?

An issue with 147's in 9mm carbines can be that they are decelerating as they leave the barrel. That can cause various issues.

No, not yet but that will be the next step. I've never heard of the 147s decelerating that so thanks for the heads up.

 

[jmorris]

Subs don’t have to be inaccurate, there are lot of examples of very accurate subsonic projectiles.

Using a decent bullet is a good start.

If a firearm doesn’t shoot anything good, it likely won’t do great with anything, including subs.

 

[ATLDave]

Things to be aware of:

• Bullets in barrels are encountering force from behind (the expanding gasses from the gunpowder plus the primer), but also forces pushing in the opposite direction (primarily barrel friction).
• Longer barrels give more time for the expanding gas to work on the base of the bullet and apply more accelerative force... but as the sealed borespace behind the bullet increases, the amount of pressure the gas is exerting on the bullet diminishes.
• At some barrel length, the gas pressure's force diminishes below the forces working to slow the bullet, and additional barrel length begins to reduce speed.
• The more gas the cartridge generates, the longer the length of barrel before you hit this deceleration point. The more friction the bullet has in the bore, the shorter the barrel length at which you hit the deceleration point.
• 9mm cartridges don't make much gas. Heavy-bullet 9mm cartridges make even less gas than lighter bullet cartridges (lighter powder charges required because of greater initial pressure because of greater bullet inertia).
• Heavy 9mm bullets have more bearing surface and, thus, generally have higher bullet/bore friction decelerative forces than lighter 9mm bullets.

This stuff makes heavy 9mm an iffy combination with carbine-length barrels. At least one of my reloading manuals cautions against using the 147 grain data in carbines because of the risk of sticking a bullet in the bore - i.e., the bullet may decelerate to ZERO fps before reaching the muzzle!

 

[MCMXI]

@ATLDave, it sounds like I really need to set up the LabRadar next time to see what's going on. I've shot 250 of the SIG 147gr FMJ factory load and every bullet has made it to the target. The barrel on mine is 8" long, it's the factory SBR version, so are you talking about longer barrels than 8"? A coworker is going to lend me his CZ Scorpion so that I can get another data point or two. He has a similar set up to me so it'll be interesting to see how well his carbine shoots the SIG load.

 

[ATLDave]

Ah, wouldn’t expect too much difficulty with an 8” barrel. Still, chrono might give a clue.

 

[jmorris]

I have a number of 16” 9mm carbines and never stuck a bullet. Most of the rounds I shoot are 147’s that happen to be subsonic (“minor” loads), using some of the fastest powders available in small charges.

 

[LiveLife]

SIG MPX ... 6" to 8" (10 shots) at 50 yards using the SIG 147gr FMJ load

... test target shows a 5-shot, approximately 3/4" group at 25 yards using 115gr ammunition.

Is the 6" to 8" scatter round or verticallyh elongated?


BTW, these are 25/50/100 yard 10 shot groups using different powder loads.

Vectan Ba 9.5 is close to Red Dot in burn rate

IMR Target powder work up

And for 50/100 yard testing, I elected to go with lighter 100 gr bullet to reduce bullet drop as I was seeing 6"-8" vertical spread at 100 yards with 115/124 gr loads.

You can see the vertical stringing from bullet drop

 

[jmorris]

A example of what I was talking about bullets making a huge difference.

This is a 10 shot group from one of my 9mm carbines at 100 yards using a plated bullet load that’s just fine for steel at 25 yards.



This is the same everything but with 10 rounds loaded with a good JHP.

 

[MCMXI]

@jmorris and @LiveLife, thanks for the information. I'm particularly interested in 147gr performance since I plan to shoot that bullet weight exclusively with the MPX which will be suppressed 100% of the time.

@jmorris, that's a huge difference for sure! I'm just trying to get a better sense of reasonable expectations for accuracy and precision.

 

[jmorris]

The two groups above were fired from my backyard coyote gun. The barrel is 8” with the rest, out to 16.125” (with end cap removed) being the suppressor.





Mixed range pick up brass and Win SPP, using bags off a bench.