Subsonic 308 without trail boss

[mic2377]

Ok but 60% of a full charge of h4895 will not be subsonic. I haven't been to the range in 6 months due to multiple pretty lame reasons, but next time I shoot subsonic it will be with red dot. Also H4895 is pretty much unobtainable too. I heard it's no longer being imported. Would imr 4895 work?

I do believe IMR 4895 is a reasonable substitute for H4895. They are both easy to ignite stick powders of a similar burn rate. As it is available compared to H4895, I recently loaded bunch of 308 reduced loads using the 125 SST and will report back on its consistency and accuracy with similar "60% reduced" loads.

If it works for these loads with a stable burn rate and no crazy velocity fluctuations, I may also try it under heavy bullets (IE 210-220 gr class) in the 308 as well, to see how close these end up to subsonic.

 

[mattri]

Very interested in hearing about IMR4895 subsonic loads for the 308. Can't get much around here but see IMR4895 fairly often.

 

[Dimner]

Unique is what you guys want to use. Some also do it with red dot, but I have found unique to always give better results. Don't use fillers. Fillers and pistol powders will destroy your rifle or at best ring your chamber, which means you have to set back and rechamber the barrel.

Loads will probably be position sensitive at the extremes (IE if you shoot while the cartridge is pointing almost straight down)

I didn't have a 308 long enough to get far with sub sonic loads and unique. However I have done hundreds of cast bullet loads with the 3006 and unique (and trail boss, but for some reason unique did better)

A couple things to be aware of:

1) you MUST develop a fool proof method to avoid double charging your case. I use the case mouth down without powder, and flip, fill and seat a bullet all at once. Single stage press. No chance of a double load. I also tend to use powder charges that should be ok pressure wise (although at the max) IF somehow I double charge.

2) for an idea of load dara, use cast bullet data, but stay far away from the max loads. Those max loads are designed for all lead bullets. Lead has a lower shot start pressure than jacketed bullets.

The other way to do this is with rifle powders in the h4198 to h4895 range with Dacron fillers. But I won't go into that because it's still a risk to ring a chamber when done incorrectly. Research fillers on cast bullet sites. However, you won't get sub sonic speeds.

 

[mattri]

Lol Unique?? Our choices are IMR3031 or IMR4895 and you better decide quick or it will be gone.

 

[mic2377]

So I promised to report back regarding results from reduced load testing with IMR 4895. I don't foresee this being able to be downloaded enough to work for subsonic rounds with consistent velocity. Given the 60% rule and a max load of ~52 gr per Hodgdon, I started with 33 gr under a Hornady 125 SST, and worked up to 41 gr. 33 gr gave a velocity of 2250 fps, up to 2650 fps with 41 gr. ES and SD numbers were not as bad as one would think given the moderate pressures, and accuracy was quite good with no charge grouping worse than 1.5" for 5 shots. Recoil was very mild out of my heavy varmint barreled Rem 700. While not subsonic these will make a fantastic reduced recoil hunting load.

I am planning to do some experimenting with N340 as well as Red Dot my next range trip for 308 subsonics.

 

[mattri]

Thanks for the update.

With a 190gr bullet and H4895 Hodgdon lists a max load of 42gr, and a subsonic load of 13.3.
60% of 42 is 25.2, way above their sub load.

 

[mattri]

 

[ScottMcc]

I have never seen published subsonic data with real rifle powders. What source is that? Do they show loads for 168's?

 

[mattri]

The Lyman manual for the AR rifle #2.

 

[ScottMcc]

Bumping this up. Mattri, does it show a load for 3031 and 4895 with a 168?

 

[mattri]

That's all the info I have so far.

Was hoping to be further along with this project by now but my barrel is in cerakote purgatory.

 

[philip brousseau]

Tag

 

[mattri]

Hopefully rifle will be together soon and testing can start.

 

[3Ackleys]

Hodgdon has subsonic loads for a lot of rifle cartridges, including 308 w/168-220 gr bullets. On the main load data page near the top, click on "subsonic".

Reloading Data Center – Hodgdon Reloading Data Center

hodgdonreloading.com

 

[mattri]

Finally got the rifle together and to the range today!

Was focused on initial barrel break in/sight in but did try two sub loads.

First load was 190 sub-x over 8.7gr of TiteGroup as listed on Hodgdon's site. Vel was right at 1060-1080 and accuracy at 50 was about 3/4". Only shot 5 rounds but looks promising.

Second was also 190 sub-x over an extrapolated amount of IMR4895. Vel was lower but consistent. Accuracy suffered from vertical stringing but could be tied to the lower vel, will adjust and report back.

Both loads were in virgin Starline brass with CCI200s Tilted the rifle in various ways to disturb/distribute powder, made no perceivable difference.

 

[Eagle1899]

I did some testing the other day. 20" 308 with a can. 215 Powder coated lead RNFB with 7.0 of Titegroup got me 1,010fps. The recommended load for a 220 of 8.9 was 1,285. Did not test for accuracy beyond 35 yards on a steel plate.

 

[Bill K]

My thought also. Always thought Sub-Sonic was 1000 FPS or slower. Right or wrong ?

 

[Oso]

1,100fps is the max, but more like 1,050fps so there is some cushion to cover any minor variations in your load. Also, I would recommend testing your rounds at 50 yards, you'll be just fine at shorter distances.

Have you considered buying a new rifle chambered in 300BO or perhaps a nice large caliber revolver?! It always feels so sketchy seeing people try to load subsonic for .308 with 8-9 grains of powder... that little amount of powder gets so very lonely in that big empty case...

 

[Dimner]

Finally got the rifle together and to the range today!

Was focused on initial barrel break in/sight in but did try two sub loads.

First load was 190 sub-x over 8.7gr of TiteGroup as listed on Hodgdon's site. Vel was right at 1060-1080 and accuracy at 50 was about 3/4". Only shot 5 rounds but looks promising.

Second was also 190 sub-x over an extrapolated amount of IMR4895. Vel was lower but consistent. Accuracy suffered from vertical stringing but could be tied to the lower vel, will adjust and report back.

Both loads were in virgin Starline brass with CCI200s Tilted the rifle in various ways to disturb/distribute powder, made no perceivable difference.

I have found unique to be very good as well if you have some of that to try. No experience, but I have heard countless reports that red dot is another one that works well.

 

[Oso]

Shotgun powders are bulkier than modern rifle powders, which might be an additional advantage (more case fill). The downside is that shotgun powders are notoriously dirty. This shouldn't be an issue in a bolt gun, but would be rough in a AR10. If running AR10 suppressed then I would want to pay attention to amount of debris deposited in the upper/lower. You'll want to clean frequently.