subsonic loads for 10.5 AR

[ezed]

I have spent hours searching here, going to the links at the top of the Whisper reloading forum, Google searches, etc. for subsonic loads for a 10.5" AR barrel, pistol gas port, tp555 gas block and have not found very much information for this specific set up. What I have found, is a ton of information for "16" ARs", "14" Contenders" and other configurations than what I am looking for. I do not have enough experience with the Whisper cartridge yet, but, from many years of reloading, and common sense, a load for a 16" barrel will not give the same velocities when used in a 10.5 barrel. Is it close enough? or is the difference enough that we should be concerned? Has anyone compiled a list of loads for this set up, similiar to "BUFFETDESTROYER" s post as below? A compiled list with this information would be fantastic. So, does this exist and I have not found it yet?Or, do I have make up a spreadsheet to list online here for people to fill out? Or? I am open for suggestions and comments.


[I]07-14-2010, 12:35 PM
buffetdestroyer
Member Join Date: Jun 2010
Location: Reno, Nevada

Spook's 10.5" AR barrel (great barrel if you are on the market for one) with 1 in 8 Twist and pistol length gas system Subsonic loads:

Hoser's Lake City Brass
220 Grain Sierra Matchking
CCI Small Rifle Primer
8.5 grains of 2400
Seated to 2.13" (if memory serves) - just go to where they feed in standard AR mags which is a little less than a quarter inch from the front of the mag for mine.

I also get great results from the same above with 175 Grain Sierra Matchking or M80 military bullets (147 grain)
and 7.5 grains of 2400All of these loads are subsonic and cycle my action with M16 type Bolt Carrier Group and standard carbine buffer and spring.

[Retooferab]

Good luck. I have been looking for the same thing for quiet a while with no luck.

[Expatriot]

There is lots of data on this website. You will just need to extrapolate a bit and then do some experimentation. Subsonics are fairly forgiving so you don't need an exact load to start with. You will need a chronograph though.

[AlcoholicusMaximus]

Originally Posted by ezed

I have spent hours searching here, going to the links at the top of the Whisper reloading forum, Google searches, etc. for subsonic loads for a 10.5" AR barrel, pistol gas port, tp555 gas block and have not found very much information for this specific set up. What I have found, is a ton of information for "16" ARs", "14" Contenders" and other configurations than what I am looking for. I do not have enough experience with the Whisper cartridge yet, but, from many years of reloading, and common sense, a load for a 16" barrel will not give the same velocities when used in a 10.5 barrel. Is it close enough? or is the difference enough that we should be concerned? Has anyone compiled a list of loads for this set up, similiar to "BUFFETDESTROYER" s post as below? A compiled list with this information would be fantastic. So, does this exist and I have not found it yet?Or, do I have make up a spreadsheet to list online here for people to fill out? Or? I am open for suggestions and comments.


[I]07-14-2010, 12:35 PM
buffetdestroyer
Member Join Date: Jun 2010
Location: Reno, Nevada

Spook's 10.5" AR barrel (great barrel if you are on the market for one) with 1 in 8 Twist and pistol length gas system Subsonic loads:

Hoser's Lake City Brass
220 Grain Sierra Matchking
CCI Small Rifle Primer
8.5 grains of 2400
Seated to 2.13" (if memory serves) - just go to where they feed in standard AR mags which is a little less than a quarter inch from the front of the mag for mine.

I also get great results from the same above with 175 Grain Sierra Matchking or M80 military bullets (147 grain)
and 7.5 grains of 2400All of these loads are subsonic and cycle my action with M16 type Bolt Carrier Group and standard carbine buffer and spring.

I have this setup, and when I want to drive tacks, I use 8.6gr AA#9 with a 220gr SMK. When I don't require sub moa precision, I use a Sierra 220gr pro hunter with the same charge. Bear in mind that gas port size will directly affect whether or not this load will cycle the action in your rifle. My gas port diameter is .086". Oal depends on whose barrel you are running.

[buffetdestroyer]

I have experimented and settled on two others loads for my 10.5" AR barrel since the post quoted above:

8.1 Grains of VV N110 powder

10.0 Grains or AA1680 powder

Both of these are subsonic in my barrel with 220 Grain Matchkings and I have since shortened the OAL to 2.09+/- due to feeding issues with certain magazines.

Accuracy is better out of mine with the Vihtavuori N110 powder so with $.40 bullets, I will load with the more expensive powder.

My next project will be to get a consistent subsonic load with 175 Grain Matchkings (the 2400 varied with the external temperature and some would crack on me). I picked up 500 of them from polygunbag cheap... Will try out 1680 to see what I get.

Maybe this weekend I will chrony some loads to figure out what is working best in my barrel.

My recommendation is to use the Sierra manual and work down to subsonic from the loads they list. My barrel tends to be much faster than the TC barrel they used and I have had to adjust my loads way down to where they may squib in other people's barrels. So, load five and test them out and then drop the charge if they are cracking. If in doubt, check to see if the barrel is clear rather than just firing another round. 30 seconds to check can save you the cost of a new barrel!

[buffetdestroyer]

One other thing about AR's that I have noticed recently is the factory gas rings are often too large to reliably feed at subsonic pressures. Even on a new LR308 with full power Gold Medal Match, I had the same problem.

The issue that you see is that the round doesn't feed all the way and the Bolt Carrier Group has about a half inch gap before it is seated properly. This is where you have to hit the forward assist to push the BCG into full battery.

It is an easy fix! Take the rings off and individually compress them to where the gap is about half of what it was (keep a gap or else you may run into other issues). Then put them on again. You have compressed them too far if the weight of the BCG is enough to lock the bolt if you stand it up on a table, bolt face down.

I am putting this here in case some other noobs to .300/.221 run into this while seeking loads.