308 subsonic

[Artful]

Originally Posted by thehouseproduct

I am also curious about this. I have a LR308B with an 18" barrel with a carbine gas length system. I think I could probably get subsonic easier with the shorter gas system.

Well the gas will bleed off the bore starting sooner but I don't think it will impact the speed that much - it will give more pressure to try and cycle the action but I never found a load that cycled by FAL repeatedly in all conditions. I found that with parially filled regular cases I had trouble unless you loaded in the same manner and shot at the same attitutude (angle) which is why I pestered David at Liberty to make the batch of reduced capacity cases - they work find for shooting level, uphill or downhill as the load density is almost 100% with trailboss.

[michael30.06]

Since we are reducing the powder charge and therefore the pressure inside the case. Do we have to use something quite as problematic as hot lead or as easy to shatter as epoxy? What about something with a bit of flexibility, I have seen projectiles made from hot glue, what about using hot melt glue to fill a case then drill out new case dimentions from that?
I'm going to try both the molten lead and the hot glue to make a reduced capacity case. If it works I will pass on all the details if not, I'll go back to the drawing board.

[michael30.06]

Got my own reply. TOO SOFT. Too flexible, oh well never mind.
So many jobs are best done with a lathe make what you need complete from scratch, maybe that is the way to go new case turned from solid brass, then cut any chamber size I need. But that is why we do this for enjoyment rather than get paid for it.

[Artful]

did you try the lead? did you use pure lead or an alloy?

[michael30.06]

I have tried the lead, it was wheel weight lead that I had on hand. A Pain to drill very prone to grab and change the angle of the drill bit. 6 out of 10 cases survived. Then I ran into a cash flow problem a 6.5mm swedish mauser that I had to have, along with the Leed loader, no drill scope mount Long eye relief scope and a thumbhole stock for a small ring mauser that took a few days of inletting to fit. I will be back on track and on schedule by christmas 2010, maybe. Had an idea about mini power heads on a compound bow.

[Artful]

those 6.5 swedes are slick - and my friends seem to be almost like electric shock on deer, you should like it.

[atrdriver1]

I have my LR-308 functioning very reliably with sub-sonic ammo fed from a mag after making some serious modifications.

***CAUTION***

These mods can be dangerous with full power ammo.

First I started by drilling out my gas port on the barrel. After stepping it up all the way to the same diameter as the ID of the gas tube (no point in going any larger than that), it was still short stroking.

I then started cliping coils off of the recoil spring. After clipping NINE coils off it ran fine with the following sub sonic load.

11.1 gr. Trail Boss
Winchester brass with standard flash hole
Fed 210 large rifle primer
190 gr SMK projectile at 1025fps

This load also shoots sub MOA in my rifle.

I am using a 3 position adjustable gas block so I can switch back to a VERY small gas port and still shoot full power ammo if I need to in a pinch. I have tested a couple of mags of full power ammo and it functions, but the BCG hits the end of the extension tube MIGHTY HARD. I have an extra full length recoil spring I can put in for running standard ammo.

I am pretty sure that if I accidentally left the gas block on the large port and fired standard ammo it would send the BCG through my shoulder.

I have 4 LR-308's, so I am able to leave this one as a dedicated sub-sonic / night vision platform.

If you want to switch back and forth between subs and standards I consider the two things below mandatory.

--Adjustable gas block.
--extra recoil spring.

Am I kinda crazy? Probably.
Am I very pleased with how this project has worked out? ABSOLUTELY!

I am using the Paladin Machine adjustable gas block, but I do not recommend it. It carbons up and then you can't move it. If you use pliers to rotate it, it still doesn't help because the ports get so packed with carbon that they are plugged completely and you have to drill them out to clear them. I would recommend the JP gas block instead.

[Alleycat]

[Artful]

Originally Posted by atrdriver1

I then started cliping coils off of the recoil spring. After clipping NINE coils off it ran fine with the following sub sonic load.

Have you considered an smaller spring wound opposite of the factory spring with a short length with a higher rate to sit inside you shortened spring and only help with the last inch or two of arresting BCG?


If you want to switch back and forth between subs and standards I consider the two things below mandatory.

--Adjustable gas block.
--extra recoil spring.

Have you seen the AR whisper with two gas ports -one pistol the other regular? - tube adjustable gas selection.

Sounds like your well on your way to having a dual purpose set up.

[LouBoyd]

Originally Posted by Artful

Sounds like your well on your way to having a dual purpose set up.

I own both LR-308s and 300 Whispers. None of them has or needs adjustable gas blocks or needs special buffer springs. I don't attempt to use supersonic loads in the 300 Whisper or subsonic loads in the LR-308.

There are a lot of reasons not to have a "does it all" subsonic/supersonic ARs. The main ones are:

different optimum barrel twist rates
different barrel length for desired performance
large difference in gas system Over 5 times difference in
available propellant gas.
Difficultly in achieving low velocity dispersion using excess capacity cases.
Wimpy performance from supersonic 300 Whisper compared to a 308 with no benefit.
Different throat requirements for light supersonic versus heavy subsonic bullets.
Different scope choice and different sight adjustments for super and sub sonic shooting.
Different suppressor requirements (if used)

By having separate dedicated rifles both can remain set up and and immediately ready for use.