# Subsonic .308 load development



## Griffin (Aug 2, 2006)

Started working on a subsonic .308 load today for my savage model 10. I started with some Horneday 220 grain round nose bullets (heavy rounds stabilize well in a 1/10 barrel) with 10.50 grains of trailboss powder and federal large magnum rifle primers. I loaded 5 rounds this way then set up my chronograph with a piece of cardboard behind it at 15 feet. Fired all 5 rounds without the suppressor (just in case for now). Average velocity was 1150fps and they all appeared to be stable.
Back to the loading table. 10.30gr into 5 more rounds. Back outside to test, 950fps average still stable.
Back to the loading table. 10.40gr into 3 more rounds. This test was with the suppressor on... Average speed: 1021 fps.

Final Load:
10.40 grains of trailboss powder
220 grain Hornaday bullets
Used brass
OAL: 2.604 inches

Sound level: the brass hitting the hood was about the same volume
Video coming as soon as its finished uploading
ADDICTED!!!


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## Griffin (Aug 2, 2006)

Here is a video to give an idea of the results. The camera is 15 feet in front of the gun.


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## Bird (May 10, 2005)

Very cool. I'm going to work up a few loads this week hopefully. I'll add your recipe to a list of loads to work up. Current recipe I'm going to start with uses Sierra 180gr round nose, 9.3 grains Trailboss, CCI-BR2 primers.

A local gunstore I shop at sells 308 subs but they're 150gr FMJ's and while stable downrange, don't have a lot of punch. Fun to plink but not much for hunting.

I love a 308 that sounds like a pellet gun.


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## Griffin (Aug 2, 2006)

We'll let me know what you come up with. I think I'm going to load some 180's next time. I've got about 80 more of the 220's to load first though. Man this is addictive!


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## Griffin (Aug 2, 2006)

Anyone else have a good recipe?


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## Bird (May 10, 2005)

I've got a couple more using lighter bullets, 150gr and 170gr. Unless you are just plinking, I'm not sure how useful they really are. Since sub rounds are limited by velocity, they suffer stability and accuracy downrange. If you look at the ballistics of a 150gr sub versus a 220gr sub, the 220gr round will have better ballistics, especially regarding drift. 

The difference between 180gr and 220gr in bullet flight path is only .1" at 125 yds (100yd zero) but the energy delta is almost 100 ft/lbs at 100yds in favor of the 220gr round.

Let me know if you'd like the 150/170gr recipes and I'll send'em


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## horned frog (Nov 9, 2008)

These won't cycle in a semi-auto (but that's what 300 Blackout is for). They work great in my bolt action .308, ballistics are similar to .38 special.


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## horned frog (Nov 9, 2008)

I picked up the Hodgdon's 2013 Annual Reloading Manual (magazine) at Hastings Bookstore today. There is a lengthy article about working up subsonic loads with Trail Boss powder. It's a pretty good read. 

The technique was to basically start with nearly a case full of Trail Boss and slowly work down 0.5 to 1 grain increments until velocity was no less than 1050 fps.

They also recommend a maximum bullet weight of 180 grains for .308 subsonic loads from a 10 inch twist barrel.


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## Bird (May 10, 2005)

I will look for this article. I'm waiting for my 180gr and 220 gr bullets to come in. As soon as they do, I'll load up both of them. I've got a couple different recipes for both rounds. Major difference is going to be bullet weight and drilled out flash hole or just reamed smooth. I'll work up the loads a grain or so every 5 loads to stay just under sonic crack. The big thing to remember is that all of my loads will be shot suppressed, 1:10 twist, 22" barrel. I'll post up results when I can finally put rounds on target...


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## Griffin (Aug 2, 2006)

I'll have to check out that write up! Did they say why they were calling for a max of 180? Mine stabilizes the 220's great and for hunting hogs (like I'm sitting here doing right now) it seems like they would have more energy down range, although I haven't done the math.


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## Bird (May 10, 2005)

Griffin said:


> I'll have to check out that write up! Did they say why they were calling for a max of 180? Mine stabilizes the 220's great and for hunting hogs (like I'm sitting here doing right now) it seems like they would have more energy down range, although *I haven't done the math.[*/QUOTE]
> 
> I ran some quick numbers through my ballistics app for 180's vs 220's and the energy difference downrange is significant. Assuming 1000fps muzzle, both round nose bullets:
> 
> ...


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## Griffin (Aug 2, 2006)

That is a considerable difference! What app do you use?


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## Bird (May 10, 2005)

I use Bullet Drop+. I paid the $1 to upgrade from the free version so I could save my load data. The free one will do all the same calculation, just not save the data. Info needed for calculation:
bullet weight in grains, muzzle velocity, ballistic coefficient, sight height above centerline of barrel, drag function (most bc's are G1), zero range, wind speed mph, wind angle

I'm still waiting on my 180's and 220's to show up in the mail. Backordered...grr


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## horned frog (Nov 9, 2008)

I ordered 220 gr Match Kings directly from Sierra this week. A bit more expensive, but theta have 100 rd boxes in stock.


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