Thread: Loading for .300BLK

Interesting read. I got back today from a hunting trip a mate and I both run 300BLK we got six stags between us I gave him some 194gr Lehigh ME to try for the first time as he’s been using the 208gr A-max for the last 4-5 years in his Rem 700 mostly for head neck shots. It was the first time he’s shot over 180m with his blackout, and I dailed out to 260m on a 26 degree up hill shot in the lungs. We both lined up the stags and fired 2 shots each in 5 seconds after they dropped and slid off the hill the hill erupted in other stags bolting up the hill. The first for the trip we shot two Hummel spikers fighting in the fog at 60m.

Back to reloading I’m running ADI 2205 for everything supers and subs, home made 300BLK brass from LC 223 cut down, sized, trimed to spec then I weight each case into 3 weight groups to get the lowest ES for best long range. My 12” barrel shoots the 194gr ME 9.1gr of ADI2205 @ 1018fps, with the same batch my mates rem 700 16” barrel is doing 1070fps. Going super I’ve only used nosler 125gr BT @ 2005 fps, I do know of a guy down south using hornady 110gr v-max and has shot 100 deer with his AR 300BLK.

So as you see the new 125gr TMK is about the same length as the nosler 125gr BT but the flat base meant more case room and less compressed loads.
I loaded the TMK to a little over half way down the neck which gives me about 30 thou to the lands. While some may think that is quite a big jump, keep in mind this projectile was designed for the .300blk in the AR15 platform. These Sierra bullets apparently cope with big jump just fine. Either way I loaded them toward the long side as I have a non restricting AI mag so just set them up the same as my 240gr Subsonic base to ogive measurement.







Next I loaded up some test loads with H110 in 0.5gr increments from 18.5gr to 20.5gr.
Yes I know that's a big increment but I know this cal well and knew what I was looking for.



Out of interest I looked up Sierras load data for this 125gr TMK and they state a max charge of 18.7gr of H110 in a 16" 1-8" twist with an COAL of 2.260 giving somewhere in the 2200fps range.
However I have mine loaded at 2.322" which will drop the pressure and velocity compared to their loads and considering my nosler 125gr load is running 20.5gr of H110 I knew I wasnt pushing any new limits with my loads. The pic below is a case from each of the loads showing pressure clearly increasing from left to right. Even the load of 20.5gr wasnt showing any high pressure signs other than a slight primer crater typical of the Rem 700s but the group and velocity spread was the tightest at 19.5gr giving me an average speed of 2390fps.








Out to 100 yards I put them on paper along side my Nosler 125gr ballistic tip loads. The Noslers have always been my best shooters in all my .300 Whisper/BLK rifles but they have never done better than a inch in this one. Today was no different.. they shoot at 2420fps in the 1-9" 16" barrel but the same load used to give me 2500fps in the 1-8" 17 inch whisper barrels with tiny ragged holes at 100 yards.
Here's the Noslers cherry picked group..





I was very happy to see the new TMK halved that inch group on a very moderate load. I may still push it a bit faster and try some ADI 2205 behind them as one of my BLK AR15's seemed to favour that powder over the H110 with the 125gr loads.

Hi Wingman have you tried lil'gun in your supersonic loads, I've had good results with both 110gn vmaxs and nosler 125gn
Thinking of trying the 135gn fmx heard they work well

Originally Posted by 300MAG

Hi Wingman have you tried lil'gun in your supersonic loads, I've had good results with both 110gn vmaxs and nosler 125gn
Thinking of trying the 135gn fmx heard they work well

Lil'gun really sparks things up

Originally Posted by 300MAG

Hi Wingman have you tried lil'gun in your supersonic loads, I've had good results with both 110gn vmaxs and nosler 125gn
Thinking of trying the 135gn fmx heard they work well

Nah Ive never tried the Lil Gun, Ive always had great results with H110 for both subs and supers so never really strayed from it. I used 2205 on one of my AR15 BLKs bit that was more of a gas flow issue I was chasing.

Interestingly Sierra doesnt have data for LilGun with their 125gr TMK but do have it for the 110gr and 168gr.

What is its case fill like behind a 125gr and what is the approximate velocity with a max load in a 16" tube?

I see hodgdon have it on their load data website, I did my development back in 2012.

Lilgun for me was better than H110 - 110gn vmaxs at 2500fpc max and 125gn 2450fps max I settled just below these maxs in a 16" barrel AR. Case life seemed ok being AR lost quite a few

Looking at ordering some 135gn FTX and ADI 300brass for a bit more development