180 grain subsonic load in a ar platform

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180 grain subsonic load in a ar platform

Post by tumbleweed » Thu Jan 07, 2021 6:39 pm

Probably beat to death but I could not find any info on search, I just got my form1 and a can so now I am looking for load data but because components are hard to find I would like to use some I already have on hand mainly 180 grain 308 and lil' gun any thoughts?

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Re: 180 grain subsonic load in a ar platform

Post by noname » Fri Jan 08, 2021 9:28 am

Do you have someway of determining bullet speed? My goal is somewhere around 950 fps. With the supersonic crack, it is more of a range than a specific fps point to stay under the supersonic crack. With a 180 gr bullet and LG, sub-sonic in an AR you most likely will need an adjustable gas block and/or fiddle with your buffer weight to get reliable cycling. It is really hard to take someone else load data without fine tuning it to your rifle without some means of testing the load/bullet combination. Most everything less than 220 gr bullets I use my bolt gun instead of my AR.

Something else. If you have the ability to stop bolt cycling with an adjustable gas block, you eliminate about 115 db of noise caused by the bolt cycling. Makes it more or less a bolt gun.
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Re: 180 grain subsonic load in a ar platform

Post by HK91 » Mon Feb 01, 2021 12:25 am

I have loaded 180gr moly coated BTHPs in my 300 BLK. Here is the info for 3 different barrel combinations. The 16" barrel gun with a rifle buffer/spring was when I first got into the 300BLK and it has a carbine length gas system, the 10.5" Ice Arms and 8.5" KAK barrels both have pistol length gas systems and regular carbine buffer/springs.

All loads were 10.2 gr Alliant Power Pro 300 MP, it is similar to H110, but not the same. CCI 400 primers, LC 07 home converted brass, OAL 2.15", 180gr very light moly coated Hornady BTHP blems, I did the moly coating several years ago.

8.5" Vel 1030, sd 30, note: functioned fine, but bolt did not hold back with suppressor attached.
10.5" Vel 1020, sd 27, note: functioned fine, bolt held back, suppressor attached.
16.5" Vel 1138, sd 11, note: functioned fine, bolt held back, suppressor attached.

Typical accuracy was 1.5-2" out of the 16" rifle at 100 yards for a 5-shot group and 1-1.5" out of the 8.5" and 10.5" barrels for a 5 shot group at 50 yards.

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