308 subsonic

[JF]

I'll jump right in here and share my success with .308 subsonics:

I begin with a starting load of Accurate 5744 powder. I then work backwards until I reach the subsonic speed I desire. I will chronograph each load for a particular gun and write it down in my log book. In my 308 Encore barrel (23 inch, 1:8 twist) I hit a good subsonic velocity at about 12gr of powder using a 220gr Sierra HPBT match bullet. I have been using magnum primers and a good crimp on the bullet but this is not always necessary or desired. My accuracy in this barrel with 220gr subsonics has easily been MOA at 100 yards. The velocity spread also has been low.

I find that each barrel will be a little different in resistance so one load recipe will not always work in a different barrel. My bolt gun (18 inch, 1:10 twist) was way off of a good subsonic speed with the same load that worked great in my Encore. I believe that this critical subsonic window is why there are not very many over the counter 308 subsonic loads. What may work great in one gun may be too slow in another etc....

I don't like to guess a subsonic load because that is where you may end up with a stuck bullet in your bore. I always work backwards from the published starting load a little at a time until I reach a good subsonic speed.

Don't use just any powder for loading subsonics in rifle size cases. There is dangers associated with using low volumes of slow powders. Accurate 5744 is one powder that I keep coming back to because it just works. It is not effected by low charges in a case. In fact, the person I talked to over at Accurate powder tells me that it was designed to not be position sensitive with low charges in relatively big cases. It also has a higher nitroglycerin content for easy ignition.

Another powder to try is IMR SR4759. They sell it in the metal IMR cans but you only get a 1/2 pound since it is so bulkey. It is in the same class as Accurate 5744 but is a more bulkey powder.

Fast pistol powders will work, but there is a danger of a double charge of powder causing more pressure than is safe. I stay away from them for this reason. With 5744 and 4759, you can visually inspect the charged cases before seating a bullet and easily see if there is a possible double charge. A double charge of these (when measuring for subsonic loads) will not be over the maximum load listed in the manuals.

If all you have is a 1:10 twist barrel, you will have problems with accuracy if you go heavier than a 180-200gr bullet. I would suggest that 180gr bullets be max for the slower 1:10 twist barrels. If you use a bullet that is too heavy for your twist, you may have a hard time hitting the target at all. They will flop around in the air like a poorly thrown football and you can actually hear them wobbling through the air down range.

[Cornholio]

JF,

I know you mentioned only using 180-200gr bullets in a 1 in 10" twist, but what about the Hornady RN 220gr flat base bullets? The OAL of the 220gr bullet is about the same as a 175gr Sierra Match King, and I've used those subsonically without keyholes nor baffle strikes. The fact that they have a flat base rather than a boat tail should help in their stability in a 1 in 10" twist. I haven't tried them yet, but just thinking out loud because I was looking and comparing the two bullets at the reloading shop last week.

I've always used bulky fast pistol powders like Unique and Red Dot. Red Dot works fine in the winter, but is VERY temp sensitive, and oftentimes goes supersonic on me in the summer. How much case volume does the two powders you mentioned take up (grain for grain) compared to flake powders like Unique and Red Dot? I was thinking of trying VVN310 or Titegroup next (supposedly case position insensitive).

What do you think?

Thanks!

[JF]

I haven't been able to get good subsonic accuracy with the Hornady 220 round nose in my Whisper or my 308. Both of them are 1:8 twist barrels. I wouldn't think that a 1:10 twist would make their accuracy any better. Yes they are shorter but the driving area or something does not seem to like the slow speed or lower pressures. This Saturday I decided to give up on them after repeated testing in my Whisper (I was only getting 3 to 4 inch 100 yard groups). Sierra makes a heavy round nose bullet also but I haven't tried it yet.

I don't know the exact volume percent that 5744 and 4759 gives me in a 308 size case. I would guess that it is about 1/3 to 2/5 of the case or so. It is substantially more than the fast pistol powders.

Some powders are more position sensitive in the case than others when lower volume charges are used. Tipping the barrel down or up before chronographing your loads will tell you this. The fast pistol powders, in my experience, seem to suffer from this more than 5744 and 4759 do.

[Cornholio]

JF,

Thanks for your thoughts.

What suppressor are you using? I'm using a Thundertrap on a 16" Savage barrel.

You seem to be interested in getting maximum precision and consistency. I like those attributes too, but I must admit I'm seeking ultimate sound suppression.

I would have to think that the larger charge weight of your 5744 load (~12 grains as opposed to ~8.5 grains of Unique or Red Dot) would make it slightly louder because the suppressor has more gas work. Did you find this to be the case? Also, since I'm only using a 16" barrel, I figured the fast pistol powders would be fully burned and easier to suppress than the slower 5744. What do you think? Am I barking up the wrong tree?

I'm trying to disagree with you. I'm trying to learn something and hopefully find a more effective load than the one I've been using. If your load is safer, more precise, and JUST AS QUIET as the ones I've been using, then I owe you a huge debt of gratitude for sharing your success with us.

[JF]

I use an HTG suppressor. It is little known and relatively new on the market but compares better than some of the more popular models for its noise reduction quality.

Funny you should mention maximum quiet and precision. Those are my two primary objectives too! Yes, the less powder volume you burn the quieter things can be. But there are some limitations. My 308 is a 23 inch, 1:8 twist, Virgin Valley Encore barrel. And yes the faster light charges do produce less muzzleblast and noise. But I have not seen a huge deal of difference in noise between 5477 and the faster pistol powders out of the 23 inch barrel. Your shorter barrel might make more of a difference.

In my 16 inch 300 Whisper Contender barrel, there is a very noticeable difference in noise when comparing H110 with Winchester 231 in subsonic loads. Even with no suppressor installed, I can still hear quiet a difference between the two. I have access to some expensive precision sound testing equipment and am trying to test this out this weekend if I can meet up with the guy that has it. If I do, I'll post the results here.

The last time I tested my 300 Whisper with sound testing equipment, I brought along my RWS pellet gun. The pellet gun registered in the 113 to 115 decible range. My suppressed Whisper (using H110 powder) was very close to that. With these new 231 loads I have been trying, I fully expect the noise to actually register below the sound signature of my spring piston pellet gun. Like I said, I'll post these and the sound results of the 308 sub loads as soon as I can get this tested.

[Cornholio]

Originally Posted by JF

I use an HTG suppressor. It is little known and relatively new on the market but compares better than some of the more popular models for its noise reduction quality.

The last time I tested my 300 Whisper with sound testing equipment, I brought along my RWS pellet gun. The pellet gun registered in the 113 to 115 decible range. My suppressed Whisper (using H110 powder) was very close to that. With these new 231 loads I have been trying, I fully expect the noise to actually register below the sound signature of my spring piston pellet gun. Like I said, I'll post these and the sound results of the 308 sub loads as soon as I can get this tested.

JF,

That sounds fascinating and I'll eagerly be awaiting any results you have! When you were testing before, were you using the Larson Davis 800B sound meter with a 1/4" mic, with the muzzle 1 meter to the right of the mic? I ask because 113-115dB actually sounds a little low for an adult air rifle.

BTW, would you tell me more about this HTG suppressor? I've been looking for an upgrade.

[Cornholio]

OK, I did some research and see that HTG stands for High Tech Gunworks in Boise. Is that Jim Ryan's company? There seems to be alot of good suppressor mfgs in that area! I'd still like to hear more about the suppressor!

Thanks

[JF]

HTG - Boise, Idaho-208-323-7674. His suppressors are killer from a design standpoint. The HTG suppressors get about 33+ decible reduction from his 22/223 and 30 caliber models. He has some 9mm and 40SW models that will let the pistol cycle. Pretty cool! I'd love to get one of them.

I have one of the HTG 22/223 sups and it is real quiet when I put it on my bolt 22 rifle and feed it subsonic 22s. It is a hoot to use it for rodent hunting or animal control applications. About all you hear is the bullet impact. I can also stick it on my 223 AR and shoot without all that noise discomfort at my shooting range.

Yes to the Larson & Davis equipment and testing methods but I don't know the model number. I seem to recall from my past readings on some pellet gun website that the RWS spring piston pellets rifles are a little quieter than some of the others out there. I've never compared different pellet guns side by side though. I was simply trying to see if my suppressed 300 Whisper was near the sound reading of a pellet rifle. It was.

[Cornholio]

JF,

A few more questions for you (where were you 4 yrs ago when I started messing with suppressors?)

1) What's your suppressor guy's name?

2) Is there any sound difference between your subsonic 308s and your 300 Whisper (both suppressed)?

3) Would you mind sharing some of the dB numbers of different gun/suppressors you tested, including the .22s and .223s?

4) What's different about the design of HTG suppressors? Baffle design? Materials?

I'm thinking of another .30 cal can (was considering SWR, SRT, and Jet), and now the HTG has caught my attention.

[JF]

I said I would post some sound testing results so here it is. But let me say from the start that I do not claim to be a sound testing expert. Take this info for what it is and please don't bash my results. If you can use this info - great.

I started by testing 220 subsonic loads in my 300Whisper. If I switch from H110 powder to the much faster Winchester 231 powder, I was able to drop the sound by about 3 decibels. When you consider that to double a sound on the decibel scale you need to increase it by 3 dB, I think this is significant.

I was asked if my subsonic 308 loads were the same noise level as my whisper loads. No, the 308 was louder by about 3 to 4 decibels. But it is comparing apples to oranges I believe. If I had the same gun and the same type of barrel, powder etc, the results might be differrent.

unsuppressed 308 subsonic (5744 load) = about 154dB
unsuppressed 308 supersonic (4064 load) = about 166dB
unsuppressed 300 Whisper subsonic (H110 load) =about 151dB
unsuppressed 300Whisper subsonic (W231 load)= about 148dB
unsuppressed 300Whisper supersonic (H110 load) = about 157dB

Please note: I did not shoot tons of each load in an effort to get the most accurate averages possible. I only shot a few of each to get a general idea of the readings.