Suppressors Subsonic Load Development (Keyhole Concerns)

jstrong

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Sep 22, 2013
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I just got my stamp for my 300 BLK sbr (8.2" barrel), and I've got a stamp for a Thunder Beast 30B coming in another month or two. In the meantime, I wanted to work up a good subsonic load. About a year ago when I first started the stamp process, I remembered reading something about "keyholes" being a problem and people ruining their suppressor because they were getting keyholes. I've poked around a little, but I couldn't find anything talking about keyholes or suppressor prep 101. Is this really something I should be concerned about? Also, is it only a problem for subs, or do I need to do something if I shoot supers through the suppressor too (mainly on a Remington 700).

Thanks.
 

wilsey

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Load a few rounds of each charge weight. Working down until you see signs of keyholing on paper at 25 yards or more. Start with the highest charge first! A chrono will help out with velocity too. Stay around 1050 fps. Don't sorry about the supers with the rifle. You will be fine as long as your threads on your barrel are concentric. Good luck and start saving for your next can.
 

Assault116

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What twist rate is the barrel that you're planning to run the subs with? And what bullet are you looking at using?
 

itieknots7

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Is this an AR?


If so, I wouldn't get too crazy with reloading a bunch of rounds using powder other then (1680). A lot of powders will not cycle the bolt fully, and you will need to experiment with your actual AR and suppressor setup. 1680 is what AAC/Remington recommends for reliable cycling/bolt lock back for subsonics.

The downside to 1680 is it's not the quietest powder available.
 

Assault116

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Is this an AR?


If so, I wouldn't get too crazy with reloading a bunch of rounds using powder other then (1680). A lot of powders will not cycle the bolt fully, and you will need to experiment with your actual AR and suppressor setup. 1680 is what AAC/Remington recommends for reliable cycling/bolt lock back for subsonics.

The downside to 1680 is it's not the quietest powder available.

Yes This ^^^ 1680 is what I've been using and it's the only one I've tried that reliably produces subs that will run the action without issues.
 

SharpsNitro

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Yes This ^^^ 1680 is what I've been using and it's the only one I've tried that reliably produces subs that will run the action without issues.

What size of gas port does your barrel have? I have a Wilson Combat barrel on the way, my powder stock is basically H110 and Lil'Gun.
 

Assault116

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Luckily I have it off the upper right now to take to a smith and have it shortened up a bit and re-threaded hahaha.

Gas port is .105 and it's kind of a wierd length between a pistol and carbine. It's a PRI barrel from a Bergarra Blank. Shoots and runs pretty good but want to take it down from 18" to 16".


I've used H110 and lil-gun both for supers and lil-gun produced some really accurate loads with Speer 125 gr TNT's. Never tried lil-gun for subs, but H110 just didn't get it done on the action end of things, neither did 5744. 1680 works like a champ though.
 
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SharpsNitro

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Luckily I have it off the upper right now to take to a smith and have it shortened up a bit and re-threaded hahaha.

Gas port is .105 and it's kind of a wierd length between a pistol and carbine. It's a PRI barrel from a Bergarra Blank. Shoots and runs pretty good but want to take it down from 18" to 16".


I've used H110 and lil-gun both for supers and lil-gun produced some really accurate loads with Speer 125 gr TNT's. Never tried lil-gun for subs, but H110 just didn't get it done on the action end of things, neither did 5744. 1680 works like a champ though.
Thanks. My understanding is that the Wilson barrels have gas ports that run on the small side. I guess I'll have to see how it works out, they use a carbine length gas system. My patience with the AR platform is running out, if I have trouble with this one I'll sell it off and wait for the DT MDR.
 

Joea132

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Jan 23, 2014
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Get your twist rate and bullet info and plug it into a stability calculator. Jbm has one for free online. That will give you tangible numbers to work with. To test it yourself, without the can, shoot at paper or cardboard 5ft from the muzzle and then out to 30-50ft. You will be able to see if the holes are off center. That's my personal preference for checking for keyholing.

If you use published loads, you can be relatively sure that they're stable. But it doesn't hurt to check yourself after waiting all that time and putting money into a can.

I use converted and annealed LC cases with AR match primers, 11.2gr of 1680 under a 208 amax seated to 2.245". Cycles reliably out of a 10" pistol and 16" rifle.
 
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mike in pa

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Yes test your reloads without a can. Make sure that they are good to go at different ranges before canning. My buddy had issues with keyholes using 4227 in the 300 blk.
 

jstrong

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Sep 22, 2013
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Thanks for the advice. I'd like to get my hands on some 1680, but I haven't been able to get any for about a year... Yes, my rifle is an AR, and the barrel's twist rate is 1:7.
 

verdugo60

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    IMR 4227 works fine suppressed with 220 gr smk subs. Cycles the bolt on my 8" home-built 300 BO upper no problem and on my brother's 8" AAC BO. Just check hodgdon load center for starting loads for both subs and supers with it.
     

    rmfield

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    Thanks. My understanding is that the Wilson barrels have gas ports that run on the small side. I guess I'll have to see how it works out, they use a carbine length gas system. My patience with the AR platform is running out, if I have trouble with this one I'll sell it off and wait for the DT MDR.

    Wilson 300BLK barrels have .106" gas ports and that is on the large side by design for subsonic use. I have a 1:7 Wilson 16" (carbine gas) and it runs +200 grain subs with A6180 and IMR4227 just fine suppressed or unsuppressed.