.308 Subsonic Issues?

[Brandon05_88]

I’ve been an experienced reloader for a few years after learning on here, but I’ve recently voyaged into subs.

Rifle: Rem 700 .308 16.5” 10” twist
Load: 175 RDF X.X gr Trailboss Lapua CCI BR-2 2.850”

I tested 12.5 down to 10.0 gr Trailboss weighed on a beam scale with a MagnetoSpeed Sporter for the following velocities unsuppressed:
12.5 1305
12.0 1260
11.8 1247
11.5 1234
11.2 1177
11.0 1176
10.8 1165
10.5 1135
10.2 1124
10.0 1095
All bullets were well stabilized on foam poster board at 100 yards.

I loaded some more rounds for a velocity test at 9.6, 9.5, and 9.4 gr Trailboss to check velocity, stability, and accuracy unsuppressed.
9.6 1062
9.5 1076
9.4 1042

I checked the foam poster board, and each shot a nice round hole at 100, so I installed the can (TBAC 30P-1). I shot a 3 shot group of each at 9.6, 9.5, and 9.4 suppressed. Accuracy was actually pretty well for the first 2 shots (of 3 shot groups) of each averaging 0.4”. The 9.5 load was actually 0.82 MOA at 100 yards. However, I recorded (with iPhone) the 3 shots of 9.4 gr Trailboss suppressed, and I think I could hear a sonic crack. I could hear the bullet slap the target and the dirt backstop. Temp was 55*, so speed of sound was approximately 1112 fps. The 9.4 load chrono’d 1042 unsuppressed. Side note, unsuppressed subsonics are 4.0 mil low from normal zero, and suppressed subonsics are 3.0 mil low from normal zero.

Is the can adding 70 fps from a subsonic load?

 

[culater]

You could be getting some add velocity I would put you magnetospeed on you can and find out. i wouldn't worry to much about POI. I would go down to 9.3 gr of Trailboss and call it good.

 

[Brandon05_88]

It's my buddies MagnetoSpeed Sporter, but I'm not sure they work being that far from the muzzle mounted on a can.
I plan on checking 9.5 down to 9.0 by 0.1 the next time out.
I think I'm overanalyzing it since supersonic sounds don't generate 70 fps at that muzzle pressure, so why would a subsonic generate near that much?

 

[spife7980]

I havent diligently tested it myself but I never took note of any jump in velocity near that much (70 fps) when going from brake to can after doing my stability tests etc to ensure I didnt get a baffle strike.
I did notice that some of my extreme spreads were a bit wide and so in the same powder weight class a few went supersonic while a few stayed under. That could be what you are noticing?
9.6=1062, 9.4=1042 One would expect 9.5 to be 1052 based on interpolation but you recorded 1076. Thats just one thing I noticed.

My goal is to stay around 1050 fps so that I never really have to worry about them going above. At 10 degrees the speed of sound is 1062, Its rarely colder than 40 here in S Texas which is around 1095. Setting my bar at 1050 was an easy compromise. 40 fps isnt going to do a whole lot for my elevations in comparison with how shitty the trajectory is period at these low speeds so trying to toe the line wasnt worth it IMO.

I wold shoot groups of 9.6-9.3 in .1 increments and see which groups best and be done with it.

 

[fdkay]

It's my buddies MagnetoSpeed Sporter, but I'm not sure they work being that far from the muzzle mounted on a can.
I plan on checking 9.5 down to 9.0 by 0.1 the next time out.
I think I'm overanalyzing it since supersonic sounds don't generate 70 fps at that muzzle pressure, so why would a subsonic generate near that much?

The muzzle has nothing to do with the operation of the magneto speed, it is the bullet passing over the device.
You are concerned with the speed once it exits the suppressor.
They work just fine on the end of a can.

 

[Brandon05_88]

I havent diligently tested it myself but I never took note of any jump in velocity near that much (70 fps) when going from brake to can after doing my stability tests etc to ensure I didnt get a baffle strike.
I did notice that some of my extreme spreads were a bit wide and so in the same powder weight class a few went supersonic while a few stayed under. That could be what you are noticing?
9.6=1062, 9.4=1042 One would expect 9.5 to be 1052 based on interpolation but you recorded 1076. Thats just one thing I noticed.

My goal is to stay around 1050 fps so that I never really have to worry about them going above. At 10 degrees the speed of sound is 1062, Its rarely colder than 40 here in S Texas which is around 1095. Setting my bar at 1050 was an easy compromise. 40 fps isnt going to do a whole lot for my elevations in comparison with how shitty the trajectory is period at these low speeds so trying to toe the line wasnt worth it IMO.

I wold shoot groups of 9.6-9.3 in .1 increments and see which groups best and be done with it.

Admittedly, I haven't ran more than a single charge over the chrono. It was one each. I was too fast for the 1050 target velocity, so I graphed it and the trendline revealed exactly what you caught with the 9.5 being fast. 9.6 and 9.4 fell exactly into line tho. I will need to run more rounds of the same charge weight, but I was just trying to get in the area and a general idea for accuracy. But watching the video, all three rounds sound the same. Maybe I need to try and embed the video?

I'm in WV, and we can see 20s and 10s while hunting in late December. At 10*F, it's at 1062 fps. That's a big reason why I want to test 9.5 to 9.0. Trendline reveals 1054 (9.5) to 1012 (9.0).

 

[spife7980]

I'm in WV, and we can see 20s and 10s while hunting in late December. At 10*F, it's at 1062 fps. That's a big reason why I want to test 9.5 to 9.0. Trendline reveals 1054 (9.5) to 1012 (9.0).

It is tough to tell volume over video. I would test the range you said and go with whichever patterns best.

I developed my subsonic 220 rn loads for pig hunting. It doesnt matter that they are subsonic, its still relatively loud and the pigs still all scramble after the first shot anyways so I now only load up enough to fart around with and show people that have never heard it a silenced subsonic. I hunt supersonic with 150grs now since the one benefit I was hoping for (pigs standing around oblivious) didnt work out like I thought it would.

What prompted you to go 175 over something heavier/lighter?

 

[Brandon05_88]

The muzzle has nothing to do with the operation of the magneto speed, it is the bullet passing over the device.
You are concerned with the speed once it exits the suppressor.
They work just fine on the end of a can.

Shoot, the bore is what I meant. The can doesn't get hot at all, so I may try to talk my buddy into strapping it to the can.
Any idea on sensitivity settings?

 

[fdkay]

Shoot, the bore is what I meant. The can doesn't get hot at all, so I may try to talk my buddy into strapping it to the can.
Any idea on sensitivity settings?

Sorry, can't help you there. I am only familiar with it, as I know someone who has used one on a can.

 

[Brandon05_88]

It is tough to tell volume over video. I would test the range you said and go with whichever patterns best.

I developed my subsonic 220 rn loads for pig hunting. It doesnt matter that they are subsonic, its still relatively loud and the pigs still all scramble after the first shot anyways so I now only load up enough to fart around with and show people that have never heard it a silenced subsonic. I hunt supersonic with 150grs now since the one benefit I was hoping for (pigs standing around oblivious) didnt work out like I thought it would.

What prompted you to go 175 over something heavier/lighter?

Honestly, because I had them on hand. I've ran quick ballistics on a handful of bullets from the 175 RDF to 180 & 220 round nose, 200 Gameking and a few SMKs in that range. It impressed me that all bullets were within 10" of each other for drop at 300 yards from a 100 yard zero. Later on, I may test a heavier bullet.