.300BO, H110, and 125 gr. in AR platform

[Mike_in_FL]

I've recently got into the caliber to use as a short range hunting rifle. Hodgdon has a very conservative max of 18.0 grains with the 125 NBT, and I've exceeded that looking for something accurate. I am just curious if anybody has any info they would share.

While searching for information on the subject I happened across an article written on some testing done with a bolt gun. What I found the most interesting was that varying the charge by .3 of a grain was enough to go from < .5" to over 1.5" group size. That seems to be what I'm encountering.

 

[spife7980]

What I found the most interesting was that varying the charge by .3 of a grain was enough to go from < .5" to over 1.5" group size. That seems to be what I'm encountering.

.3 grains is 1.6% of 18 grains.
.3 grains is .6% of 50 grains.
A kernal has 3x the magnitude of change going into a small case based on percentage of the total.
The smaller the case the finer the increments will become.

My 300 BO shooting subsonics have a similar change on target going from 12.1 to 12.0 (I dont have any super sonic experience). You may luck out and have a very wide node on your barrel or you might get a finicky one like I have. Try another powder and you might find that your barrel likes that one better. Or a different bullet. Or primer. Only one way to know.

 

[padom]

I only shoot supers out of my 10.5" 300blk. When I set out to build my first 300blk SBR/Pistol last year my goal was to build something very accurate shots from 100yds and in. I never got on the 300blk wagon because I was told by my friends that had them that they were just fun guns, not accurate like my precision AR's and bolt guns. I finally set out to find out how true that was.

I have to say in my experience its all in the barrel. The first 2 barrels I purchased, a 9" and a 10.1" both shot like shit. I mean looked like straight 12gauge buckshot down to maybe 2-3" groups at 100yds. I performed extensive load testing with H110 and Lil Gun and 125smk's and 125TMK's with both these barrels and just could get the accuracy I set out to get and started believing what I was told was true. I sold off both those barrels and decided to try one more barrel then I was giving up. I bought a 10.5" Rainier Ultramatch (Shillen blank) and that was the golden ticket. I loaded up 125smk's with H110 to test the barrel in the 17.0 - 19.0g range and was amazed at what I saw. I then tested the 125 TMK with H110 in the same range. I found the center of my node at 18.6g with both bullets. Im using 1xLC converted brass with CCI 450 primers. Velocity is 2100fps and accuracy is sub 0.5moa all day long with many groups in the .3's and .4's. All 5 shot groups at 100yds.

Here is a target I shot after confirming my load and zeroing my rifle. I shot 7 groups, 5 shots each and the agg across these 7 groups was 0.521! I LOVE this gun and its my go to defense rifle loaded with 125 TMK's. The 125TMK is what Black Hill's uses in their personal defense load. My buddy and I tested a bunch of different 300blk loads through phone books with wet denim laid over the front and water jugs behind. Everything we tested didnt expand for shit except the 125TMK. Its my go to load for my gun.

 

[Yondering]

My buddy and I tested a bunch of different 300blk loads through phone books with wet denim laid over the front and water jugs behind. Everything we tested didnt expand for shit except the 125TMK. Its my go to load for my gun.

I'm curious what else you tested. If you tried the 125 NBT, 125 TNT, 110 Black Tip, or 110 V-Max and didn't get good expansion from those, the problem was your test medium, not the bullets. Those four have been the go-to supersonic 300 Blk bullets for a long time now and have been well proven on game animals.

 

[black5.3]

The barrel is indeed the heart of the ar platform rifle. When i built my 300blk sbr the barrel was the most expensive part. I bought a 8.2" noveske and it has proven to be accurate. I havent done any real load development, just a pressure ladder and measured velocities. I settled on 18.0-18.1 grains of h110 behind a 110gr vmax with a cci 450 primer. When i was sighting in my scope on the rifle it was not hard to get 3/4" groups.

 

[mark5pt56]

That is some awesome stuff Padom! So are you guys finding the magnum primer a better option?

 

[padom]

I'm curious what else you tested. If you tried the 125 NBT, 125 TNT, 110 Black Tip, or 110 V-Max and didn't get good expansion from those, the problem was your test medium, not the bullets. Those four have been the go-to supersonic 300 Blk bullets for a long time now and have been well proven on game animals.

I only tested the 125smk and 125 tmk since those are the 2 bullets I shoot and both are very accurate. The 125smk just bend like a banana. The 125 TMK expanded beautifully. My buddy tested some of his subs which is what he mostly shoots and they didn't perform anything like the 125tmk.

I have some 110vmax and 110 black tip but have yet to load or test them since the 125tmk does so well.

 

[Mike_in_FL]

I bought a 10.5" Rainier Ultramatch (Shillen blank) and that was the golden ticket...

Thank you for posting this info again. I thought I had copied it from the Scout site. However, I didn't remember you were using small magnum primers. I'm using WSR which are supposedly hot for a small primer and new Win brass which I think has a larger volume.

I was going to buy one of the RA 16" barrels but since I started wanting a .300, I have yet to see them in stock. I might just go to Seekins since I think they're Rock Creek.

I have another set loaded up for a 100 yard round robin. I only had 6 rounds loaded at 18.2, my max last time. The 1st 3 shot group was under .5 with 2 touching. The second set opened up a LOT. If it continues to suck, I'll cut my losses and get a new barrel.

 

[eicas]

110gr Barnes Blacktip
Hornady cases
20.2gr H110
CCI #400
CBTO 1.508"
COAL 2.250"
2141fps@600DA

The above load is out of a 8" AR upper. Less than 1"@100yds. I definately noticed shrinking groups (dramatically) from 19.8gr of H110. From what I know from .357 magnum pistol loading, this appears typical of H110. You get best performance at the upper end of the spectrum.

*Your milaeage may vary.*
*Professional driver on closed trst track.*
*Objects in mirror closer than they appear.*
*Void where prohibited by law.*

yada, yada, yada

 

[Yondering]

110gr Barnes Blacktip
Hornady cases
20.2gr H110
CCI #400
CBTO 1.508"
COAL 2.250"
2141fps@600DA

The above load is out of a 8" AR upper. Less than 1"@100yds. I definately noticed shrinking groups (dramatically) from 19.8gr of H110. From what I know from .357 magnum pistol loading, this appears typical of H110. You get best performance at the upper end of the spectrum.

*Your milaeage may vary.*
*Professional driver on closed trst track.*
*Objects in mirror closer than they appear.*
*Void where prohibited by law.*

yada, yada, yada

You forgot *don't try this at home*

I use almost the exact same load with similar results from a 9" AR pistol. That's a really good round. I've noticed the same with top end loads of H110/296.

A couple other things I've noticed about H110 and Lil'Gun in the Blackout:
- H110 performs best at top pressures, while Lil'Gun is better when backed off a little. Similar velocity is attainable either way, but I've found some weird velocity changes with Lil'Gun when approaching max.
- Lil'Gun gives significantly less blast and flash than H110 in short AR barrels. If you're going to shoot indoors or at night, Lil'Gun is much more shooter friendly.

 

[eicas]

Thanks for adding the observations. Havent tried Lil'Gun but heard good stuff like you mentioned. Practice plinker loads are bulk 165gr soft points with 1680 to push them. The 110gr Barnes load is a specific use critter load when I want something more than a traditional pistol on the back 40. The expansion on those TSX's is scarey!

 

[Wayne McNeely]

My 300BO loves 1680 in the supper sonic loads and with good bullets, thinks it's a benchrest rifle. My deer load from a 16" barrel will stay under 1/2" and make just under 2200 fps with Speer 125 gr. TNTs. Standard small rifle primers will be right choice as there is a relatively small charge to ignite. And for the record, my barrel is a no-name nitrided, 8 twist that I bought for $109.00 shipped, guess I just got lucky. I shot a 30BR for a couple of years in Benchrest competition, and had some 110 gr. match bullets left, those would shoot one ragged hole at 100 yards from this barrel. It has a pistol length gas system, and a Sig muzzle device to attach a Sig suppressor to round it out. It will cycle sub-sonic with out the suppressor attached. As an aside, my barrel did not like H-110 or Littlegun as well as 1680.

Wayne