Re-chamber a .300 AAC Blackout to .300 Ham'r?

[BluRidgDav]

All Wilson .300 Ham'r barrels are rifled with a 1-in-15" twist,
which makes them less suitable for loading heavy bullets at subsonic velocities.
But, there are many .300 AAC Blackout barrels with 1-in-7" or 1-in-8" twists.
Could a .300 AAC barrel be re-chambered to .300 Ham'r with a reamer?
(using a stainless steel barrel to avoid any chrome-lining or nitrate-coating issues)

Thanx, Dave.

[Unclenick]

It looks like it to me. The 300 HAM'R is longer everywhere. The drawing on Wilson's site doesn't give diameters, but since the round was designed to maximize powder space, it's unlikely that it is narrower at corresponding distances from the head. You could probably call Wilson and ask if there is any reason you couldn't do that.

[Scorch]

The 300 Hamr uses 223 brass, so no bolt change is needed. It is loaded with light bullets at higher pressure than 300 BO in order to get higher velocities. You could use a 300 BO barrel but you would need an adjustable gas block to get the gun to run right. Also, 300BO barrels use pistol length gas systems, which will cause problems at higher pressures. I don't see a huge problem with the project, but the twist rate of the 300 BO is optimized for heavy bullets at subsonic velocities. If you want to shoot higher velocities, OK, but realize that the fast twist will upset bullets faster and the gas system will cause issues. If you are looking to shoot subsonic just go with the 300BO.

[BluRidgDav]

Thanx Guys!

Good point about the AAC's pistol length gas system and higher pressures.
Perhaps the better way to go would be to re-chamber a Wilson 7.62x40 WT barrel.
with it's carbine length gas system and a slightly faster 1-in-12" twist.

[Jim Watson]

Since the BO will drive a 240 gr bullet to 1000 fps, what would be the advantage of a larger chamber for subsonic loading?

[BluRidgDav]

Jim, The difference would be with supersonic loads.

As currently designed with 1-in-7 or 8" twists, the .300 AAC is great at launching heavy bullets at subsonic velocity, but kinda weak at launching lighter bullets at supersonic velocities, due to smaller case capacity.

The .300 Ham'r is great at launching lighter bullets at higher supersonic velocities because of it's greater case capacity, but due to it's 1-in-15" twist, it is all but useless at firing heavy bullets at subsonic velocity.

I'm trying to get the best of both capabilities.

[reynolds357]

Originally Posted by Scorch

The 300 Hamr uses 223 brass, so no bolt change is needed. It is loaded with light bullets at higher pressure than 300 BO in order to get higher velocities. You could use a 300 BO barrel but you would need an adjustable gas block to get the gun to run right. Also, 300BO barrels use pistol length gas systems, which will cause problems at higher pressures. I don't see a huge problem with the project, but the twist rate of the 300 BO is optimized for heavy bullets at subsonic velocities. If you want to shoot higher velocities, OK, but realize that the fast twist will upset bullets faster and the gas system will cause issues. If you are looking to shoot subsonic just go with the 300BO.

I have seen carbine gas systems on blackouts.

[eastbank]

I have a Remington model 7 in .300 bk with a 16" barrel, what increase in speed would I get with 125 gr bullets if I rechambered it for the 300 ham,r?

[taylorce1]

I don't think you could use very many bullets much over 150 grains and stay within magazine restrictions of an AR15.

Originally Posted by reynolds357

I have seen carbine gas systems on blackouts.

Yes you have, but most new production uses pistol length gas tubes to get rifles to cycle with subsonic bullets. There are many well documented issues with cycling with longer gas tubes.

Originally Posted by eastbank

I have a Remington model 7 in .300 bk with a 16" barrel, what increase in speed would I get with 125 gr bullets

About 300 FPS.

Wilson Combat

WILSON COMBAT LOAD DATA

Sierra 110gr HP-V #2110, 2.160” OAL
WC 300 HAM’R case
Start load: 25.5gr A1680 or 26.0gr H CFEBLK
Max load: 27.5gr A1680 or 28.0gr H CFEBLK
CCI450
Velocity range 2500 – 2600FPS

Lehigh 110gr CC #05-308-110-CUSP, 2.245” OAL
WC 300 HAM’R case
Start load: 25.5gr A1680 or 26.0gr H CFEBLK
Max load: 27.5gr A1680 or 28gr H CFEBLK
CCI450
Velocity range 2500 – 2600FPS

Sierra 125gr SBT PH #2120, 2.245” OAL
WC 300 HAM’R case
Start load: 25.0gr A1680 or 26.0gr H CFEBLK
Max load: 26.5gr A1680 or 27.8gr H CFEBLK
CCI450
Velocity range 2450 – 2500FPS

Speer 125gr TNT #1986/#3725, 2.245” OAL
WC 300 HAM’R case
Start load: 25.0gr A1680 or 26.0gr H CFEBLK
Max load: 26.0gr A1680 or 27.2gr H CFEBLK
CCI450
Velocity range 2450 – 2500FPS

Speer 130gr FPHC #2007, 2.175” OAL
WC 300 HAM’R case
Start load: 25.0gr A1680 or 26.0gr H CFEBLK
Max load: 26.5gr A1680 or 27.8gr H CFEBLK
CCI450
Velocity range 2450 – 2500FPS

Hornady 150gr SST #30303, 2.245” OAL
WC 300 HAM’R case
Start load: 23.8gr H CFEBLK
Max load: 24.8gr H CFEBLK
CCI450
Velocity range 2190 – 2250FPS

Speer 150gr FNHC #2011, 2.145” OAL
WC 300 HAM’R case
Start load: 23.6gr H CFEBLK
Max load: 24.8gr H CFEBLK
CCI450
Velocity range 2180 – 2240FPS

All loads were produced with WC 300 HAM’R cases, reduce the above charge weights by 5% if using cases made from .223/5.56 brass.

WARNING: Due to barrel bore dimension variations and powder lot differences WILSON COMBAT strongly recommends the use of a chronograph to work up loads in excess of the starting loads. Do not exceed the highest velocity listed for any load and do not substitute any other component for those listed.

Velocities were recorded using a Wilson Combat 18” barrel with Labradar in 90-100 degree temperature. Reduce or add 12FPS per inch for shorter or longer barrels.

NOTE: The 300 HAM’R is designed to use 110-150gr bullets at supersonic velocity and is NOT suitable for heavy bullet sub-sonic use.