220 gr. and A1680 in a 9" barrel & Suppressed

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SkunkWerX
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220 gr. and A1680 in a 9" barrel & Suppressed

Post by SkunkWerX »

Hello everyone, I have been reading here for a while, thanks to everyone here for all of their useful information.
I have reloaded for numerous calibers over the years, .223 .308 .30-06 .35 Rem etc.

I just tested my first run of subsonic suppressed loads.
They were:

RP 223 Brass converted (all same vintage)
CCI SR primers
220 gr. FMJBT's (Blems from Midway)
10.9 gr. of A1680
COAL 2.100
no crimp

9" AAC upper 1in8 twist, with SDN6 in place.

Chrono'd from 1051 to 1083 FPS with bore approx. 10-12 feet back from chrono.
Cycling fine, locked back like a champ.
Doesn't look too bad for the first test run. :)

Questions:
1. Should I be happy with this and move along, or do tweaking? (I can never seem to leave well enough alone)
2. Will slowing it down slightly (maybe 1025 to 1050) make it any quieter?
3. Would you drop the powder charge to 10.8 and check the results?
4. or Possibly increase COAL to 2.200?

At most, I'm looking for a tad bit quieter (if possible) but not dropping FPS too much.

All thoughts welcomed. Thanks again for all of the great info!
AAC 9" upper
Remington 700 SPS
SDN6
Klem
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Re: 220 gr. and A1680 in a 9" barrel & Suppressed

Post by Klem »

Some thoughts, and feel free to discount them.

As another poster pointed out, muzzle pressure is gunfire sound and this needs to be minimised. For the same velocity faster powders give lower muzzle pressure and are therefore quieter, but as the powder gets faster so too does the peak chamber pressure climb. Using SAAMI's 55,000psi limit, and what works supersonic I'm sticking to 45,000psi as a safe peak level. With this in mind I need the powder that will give the lowest muzzle pressure that will cycle the gun reliably, and not exceed 45,000psi.

Yes, slowing it down from 1080fps will lower sound. I figure with the chrono at 12ft it's about 10fps more than what it's showing. As I understand it, the sonic boom starts at 100fps below the speed of sound and increases to a peak 50fps above the sound barrier. So, whatever the speed of sound is at your altitude at this time of year, take 100fps off that and that would be my target velocity.

To my mind, shedding velocity even lower than 100fps below than the speed of sound could be quieter than sticking doggedly to the 100fps below. I am talking about lowering the muzzle pressure. Below the speed of sound a bullet retains momentum more efficiently than above the speed of sound so on your ballistics program you will notice velocity does not shed as much as supersonic over typically longer ranges, so by the time the subsonic gets to 100yards you probably won't notice a difference in impact potential from a bullet starting at say 1010fps to one starting at 940fps.

The shape of a subsonic bullet is also important depending on what you want it to do at the target. Retained momentum and shorter ranges mean it doesn't have to be as 'pointy'/low drag as a supersonic bullet. Lapua have designed their purpose built subsonic 200gn 30cal projectile to be still pointy but stubbier and with a centre of gravity further forward than supersonic. If your bullet, travelling slower than designed, doesn't open-up on hitting the target it will penetrate further, but with more chance of continuing on out the other side.

OAL...may as well use the full internal length of an AR magazine. The SAAMI spec for max OAL is 57.4mm with an AR mag about 57.1mm. By loading as far forward as your mags will take means you minimise the jump to lands (accuracy). A Sierra Pro Hunter seated at max 46.75mm still has 2.5mm jump to lands in my chamber. A 210 Berger VLD has 3.5mm. To find this I loaded a bullet proud in a case with no powder and hand fed it into the chamber. Then tapped the carrier with a nylon mallet until the bolt went into battery. Then pulled the bullet out (it sticks a little) and measured. Then loaded a fresh empty case to that and continued doing this until it just touched but no friction on extraction.

I can do a simulation on Quickload for you if you can give me more detail about the brand/type of bullet.
Whole Bunches
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Re: 220 gr. and A1680 in a 9" barrel & Suppressed

Post by Whole Bunches »

My experience has been that as I made the oal longer, I had to use more powder to get the same velocity. So, if you increase the oal with the same powder charge, don't be surprised if the velocity decreases. Keep that in mind as you read my chronograph results from today.

I don't see anything about the accuracy you obtained with your subsonic load; was it accurate enough for your purposes? If NO, then you should try differing powder charges until you get the accuracy you need. For my subsonic shooting, I try differing powder charges (and sometimes differing oal) to get the best accuracy (as long as it is still subsonic). Accuracy first; specific subsonic velocity second for me.

With a suppressor mounted, you can get closer to the chronograph if you want (the suppressor will reduce the muzzle blast). Today I was shooting (suppressed) with the muzzle 3' from the center of the chronograph screens to get a truer picture of muzzle velocity.

I normally use surplus WC680 with 220gr subs in the AR. I've used up 4 of the 8 pounds I had. Since WC680 is no longer on the surplus market, today's testing was getting some subsonic loads with A1680 to try for accuracy tomorrow. 11.7gr WC680 (otherwise the same parameters as below) gives average of 1026fps and nice accuracy. My goal today was 1026fps, hoping for the same point of impact when I shoot for accuracy (I chronograph in my front yard and do accuracy testing at a range), but when I looked at the data, I discovered the low extreme spread of the 11.9gr A1680 load. I therefore loaded up 11.9-12.1gr for accuracy testing tomorrow.

10.3" Delta Co Arms bbl
Gemtech Quicksand suppressor
Formed LC brass
No anneal
No crimp
220gr SMK blems from Midway
A1680 powder
Wolf KVB 223M primers
2.2" oal

11.9gr gave average of 1007fps and extreme spread of 4fps
12.0gr gave average of 1014fps and extreme spread of 35fps
12.1gr gave average of 1026fps and extreme spread of 44fps
SkunkWerX
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Re: 220 gr. and A1680 in a 9" barrel & Suppressed

Post by SkunkWerX »

Klem, thanks.
I am approx. 500 ft. above sea level and it was about 74 degrees. I was actually going to address accuracy later.
Not using as a hunting round, so, as long as I can hit paper & steel in a consistent fashion, Ill be happy, given it's subsonic.

I was minding my COAL based on everything I've read about magazine and feeding issues with the BLK. When loading my .223 service rifle match loads, (69gr. SMKs) I do indeed load them long to keep my jump-to-lands as low as possible without violating SAAMI specs and the magazine internal length.

Maybe load incrementally longer and observe if feeding issues ever develop? thoughts?

WholeBunches, thx, also.
Mine are FMJBT's, yours are SMKs, so, assuming your bullet's total length is a bit shorter than mine.
I'll edit this, and post my projectile's OAL.

I do find your chrono results very interesting, since you are up in the 11 to 12 gr. range using A1680.
Obviously, your extra COL length is making a difference. With that, I may experiment and drop to 10.8gr of A1680 and/or increase COAL just a bit.

My plan at this point is some new test loads:
-The same 10.9 gr. load ,but projectile seated longer (2.2-ish?)
-Another test using 10.8gr. with the original 2.100" COAL

Proceed from there, depending on results of the 2 tests above.
AAC 9" upper
Remington 700 SPS
SDN6
rjacobs
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Re: 220 gr. and A1680 in a 9" barrel & Suppressed

Post by rjacobs »

I just ran my AAC 9" 1/7 upper with H buffered lower down to 10.7g of A1680(started at 11.2g) with the 220SMK's at 2.120 with full function. I was getting really nice groups as well(better than any of the other loads) I am going to go even lower and see when the gun stops running. I dont have a chrono at this time to know what velocity I am getting, but am going to use my buddies next week.
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Klem
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Re: 220 gr. and A1680 in a 9" barrel & Suppressed

Post by Klem »

Yes, that's another reason why I seat the subs as long as the magazine will allow, to maximise the powder needed to achieve 1010fps. More powder = more chamber pressure for reliable cycling, but unfortunately it also means more muzzle pressure, making it louder.

With a 16" carbine length gas system I need to squeeze as much cycling pressure as I can out of the load. The alternative is I load for as quiet as possible and hand operate the charge lever like a bolt gun...for that one ultra-quiet shot.

I seat my subs to 56.75mm which is 2.23" in your speak.

The stubby round nose 220 Sierra Pro Hunters I use do interfere with the magazine ribs when loading however I have yet to have a feeding problem. After loading the first two they encounter the ribs and the tips pigeon-toe inwards. On feeding I assume they reverse back out to being parallel. By all means creep forward in your loading and see if it jams, however I'm thinking that might be a bit conservative. I think you'll find they feed fine up the ramps, probably better the longer you seat them!

The speed of sound in air at 74 degrees F is 1,132fps. The sonic boom starts building at 1,040 (92fps below the speed of sound), so anything below that is a good target velocity.
Legionaire
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Re: 220 gr. and A1680 in a 9" barrel & Suppressed

Post by Legionaire »

I see people stating they are having reliable cycle issues with sub loads is this with cans installed? I have tested subsonic loads from several 16" guns with carbine gas systems and yet to have cycle issues down to 940 fps with SMK and down to 850 fps with FBRN bullets. I have also fired different charges and another powder side by side with other people standing in different positions to help determine sound levels. The conclusion I came up with is 950 fps with a low charge of powder like 1680 is noticeably quieter. My personal subsonic load is with AA5744 at 927 fps and they are very quiet. These loads all cycle and lock back with a can installed and my 5744 load cycles but just misses bolt lock back without a can.
SkunkWerX
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Joined: Sat Sep 29, 2012 4:29 pm

Re: 220 gr. and A1680 in a 9" barrel & Suppressed

Post by SkunkWerX »

Thanks again everyone, I am going to start stepping them down in charge, then increase COL until I get down to an average of 1,025FPS or there about.

Klem, thanks for the details on length. That helped.
AAC 9" upper
Remington 700 SPS
SDN6
Klem
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Re: 220 gr. and A1680 in a 9" barrel & Suppressed

Post by Klem »

Legionaire,

My understanding of the process is that a can on the front contains gas that would otherwise dissipate into the air. That means you get more cycling pressure by fitting a can on the end. For those guys with loads and gas systems that are right on the edge of not cycling, a can will help tip them the other way and it works.

With certain cans you can also get a bit more velocity than you would otherwise in what's called 'freebore boost'. Those with an expansion chamber first and then baffles. The pressure expands into the expansion chamber but is still high and still contained forcing the bullet a little faster through the baffles. I read this can be up to 40fps more than if there was no can. That would be enough to change your zero, and make it louder than if you had done testing without the can.

I'm thinking the sound at the muzzle which a can is designed to tame is from muzzle pressure/temperature, not bullet velocity. Bullets give two types of sound; the supersonic crack that builds from about 1020fps upward, and the sound they make from air being displaced (at any speed). The shape of the bullet will likely influence the sound of air being displaced in the same way submarine design tries to minimise this through water. That said, I doubt whether shooters care as much as submariners if someone else can 'hear' our subsonic bullets cavitating through the air...but certainly the sonic boom is an issue.
Legionaire
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Re: 220 gr. and A1680 in a 9" barrel & Suppressed

Post by Legionaire »

True a suppressor does act on muzzle pressure and do you not agree that the higher the muzzle pressure the higher the bullets velocity would be? Therefore the slowest you can get you're velocity the quieter the sub round will sound. I asked if people are having trouble with cycling issues with a can because any proper made barrel with carbine or pistol gas should cycle perfect with any standard subsonic ammo with the suppressor installed.
Klem wrote:Yes, that's another reason why I seat the subs as long as the magazine will allow, to maximise the powder needed to achieve 1010fps. More powder = more chamber pressure for reliable cycling, but unfortunately it also means more muzzle pressure, making it louder.

With a 16" carbine length gas system I need to squeeze as much cycling pressure as I can out of the load. The alternative is I load for as quiet as possible and hand operate the charge lever like a bolt gun...for that one ultra-quiet shot.
I have not needed to maximize the powder charge to achieve proper cycling with a can thats why i asked if people had a problem with the can installed and cycling. Using 1680 with less than 10.5 grains of powder im getting 970 fps and perfect cycling and it is a very quiet load.
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