Are my subsonic loads too low in MV?

[projo198]

I loaded my first subsonics this weekend and shot them through my chrono yesterday.

I did 4 laod increments starting with what Allian Powder prescribes for subsonics, and then what AAC recommends. These were fired through a 9" 1:7 twist barrel with a 1:7 twist with a pistol length gas system with a YHM Phantom supressor and using 220g Nosler Partitions and A1680 powder. All rounds fully cycled.

LOT 1: 10.9g powder = avg. Mv. 885.45

LOT 2: 11.0g powder = avg. Mv. 854.9

LOT 3: 11.1g powder = avg. Mv. unknown (all 5 shots were error through chronograph).

LOT 4: 11.2g powder = avg. Mv. 893.3


My question is this; from this site and others I have noticed most people reporting much higher fps with similar rifles and loads, well over 1,000 fps. Is this normal?

[gds]

I would add some powder.

Best to get it as close to 1000fps as possible.

A lot of that will depend on your OAL.

It has been a while since I used the 220smk, but as I recall I was using less powder then you but had a short OAL, and had 980fps as I recall out of a 16 inch barrel

[farm use]

That is low. I use 10.6 gn of A1680 with 208gn Amax and get Avg of 1035fps. With 220gn you need to start with 11.4 gn of A1680 and adjust accordingly.

[projo198]

Sorry I should have listed my OAL, mine were 2.120 (AAC recommendation). Plenty of room to shorten them if needed, even with those monster 220s I was well short of making compressed loads.

More powder? I thought the goal was to load as light as possible and still cycle?

[gds]

Sorry I should have listed my OAL, mine were 2.120 (AAC recommendation). Plenty of room to shorten them if needed, even with those monster 220s I was well short of making compressed loads.

More powder? I thought the goal was to load as light as possible and still cycle?

yes but if you are only getting under 900fps, out of a 9 inch barrel, you want to add more powder to get more velocity. I would not touch your OAL based on my knowledge. the only other option is add more powder to get closer to 1000fps

That same load in a 16 inch would be 80 to 100fps faster so take that into consideration also.

[projo198]

Sorry I should have listed my OAL, mine were 2.120 (AAC recommendation). Plenty of room to shorten them if needed, even with those monster 220s I was well short of making compressed loads.

More powder? I thought the goal was to load as light as possible and still cycle?

yes but if you are only getting under 900fps, out of a 9 inch barrel, you want to add more powder to get more velocity. I would not touch your OAL based on my knowledge. the only other option is add more powder to get closer to 1000fps

That same load in a 16 inch would be 80 to 100fps faster so take that into consideration also.

Ok, I will check into this. Though I wasn't measuring noise these round were a little louder than I want them to be, To be honest I didn't notice much of a difference between these and the supersonics I load when fired through the suppressor.

[300Blk]

I would try to get 1000 fps but I try to avoid more than 1000 fps.

Maybe it is super cold where you are?

[projo198]

I would try to get 1000 fps but I try to avoid more than 1000 fps.

Maybe it is super cold where you are?

It was in the teens yesterday, might be a factor.

One question though; I thought the goal for quiet subs through a suppressor was to get as low a MV as you could and still cycle? If this is true shouldn't I be trying lighter loads instead of trying to get up to 1,000 fps?

[Sharkbite]

I would try to get 1000 fps but I try to avoid more than 1000 fps.

Maybe it is super cold where you are?

It was in the teens yesterday, might be a factor.

One question though; I thought the goal for quiet subs through a suppressor was to get as low a MV as you could and still cycle? If this is true shouldn't I be trying lighter loads instead of trying to get up to 1,000 fps?

The goal is to have the bullet remain below the speed of sound and still function the gun. Anything LOWER then that just reduces the effectiveness of the bullet. Both from a terminal ballistics AND a trajectory standpoint.

I go for loads that run about 1000 in the summer here. That gives me a little wiggle room for those COLD Colorado winters

[projo198]

I would try to get 1000 fps but I try to avoid more than 1000 fps.

Maybe it is super cold where you are?

It was in the teens yesterday, might be a factor.

One question though; I thought the goal for quiet subs through a suppressor was to get as low a MV as you could and still cycle? If this is true shouldn't I be trying lighter loads instead of trying to get up to 1,000 fps?

The goal is to have the bullet remain below the speed of sound and still function the gun. Anything LOWER then that just reduces the effectiveness of the bullet. Both from a terminal ballistics AND a trajectory standpoint.

I go for loads that run about 1000 in the summer here. That gives me a little wiggle room for those COLD Colorado winters

Oh ok, gotcha. Sorry I am new to reloading subsonic.

So basically with the speed of sound being approx. 1100fps (temperature and altitude dependent) I have successfully created subsonic ammo, correct? So now I am being told that to decrease my powder loads won't do much to quiet them down, to do so would just be affecting accuracy?

I suppose I was just expecting them to be more quiet, but next time I will either find a way to measure DcB or shoot supersonics as well for comparison.

EDIT: Also failed to correctly list the powder loads in my first post. The 4 loads go up by .1g powder increments. It's fixed now.