Sierra Matchking Bullets 300 AAC Blackout (308 Diameter) 125

[Ohio300Blk]

I just went to the range Saturday and laddered loads in .2 increments from 17.2-18.2. Using a 3x magnified eotech, 16" barrel AR (CMMG), spikes bolt, and found that pushing on the 125gr. Sierra just spread out my groups. Shot at 100 yds. I used the OAL that matched the Remington OAL at 2.25" (avg. of a box of 20).
When I checked the OAL using my Hornaday bullet comparator #6-27 they all yielded a 2.677" measure (factory Remington). I set my seater to match the factory's. Found that any longer and the OTM would hit the mag front rib so... 17.2-17.5gr H110 gave me excellent 1-1.5" groups. 17.6gr started to blossom and anything higher grew to 2.0"+. 17.8gr showed primer flattening and 17.8-18.2 as well. The barrel is a 1 in 8 twist. I have loaded alot of 135gr. Sierra HPBT and found them more accurate than the 125gr. If the people reading this understand the mechanical and physical variables I would call this the middle of the road for good 125gr. work ups.. Hope this helps.

[flgunner]

Ohio300Blk
Thanks - gives me another good data point to watch as I build up my loads, also for a CMMG 16" barrel.

[FMJ]

Ohio300Blk

What is your load data for the Sierra 135?

My data for Sierra 125 matches yours almost exactly. I'm using H110 17.5, anything more and I'm seeing pressure signs in hot weather.

Thanks

[Ohio300Blk]

FMJ
I admit I have simply loaded and shot more 135gr. SMK's because they were available but none the less more accurate than the 125gr in my rifle
Case: turned on a lathe to 1.359" (made a slick shell holder so 1.359" repeatable over 1000 cases)
Formed: 1.366"
Primer: CCI #450 magnum small rifle
Powder: 17.5gr H110
OAL: 2.158" or 2.734" using Hornaday Bullet comparitor
Crimp: Lee factory medium (case crimps vary on brass wall thickness)
Never had a FTFeed or Fire (seems key to deburr the inside wall last to avoid neck swell when seating)
With the prior mentioned eotech and magnifier I have made 2" holes at 100yds with an entire magazine (felt like a girl at a Justin Bieber show, front row)

The 1/8 twist idea: that's what's stamped on the barrel I'll check it next time I put a cleaning rod through it but I have read that 300Blk was best served in 1/8.
Also got a precise recipe on 200gr. SMK BT Spitzers in sub-sonic (exact 12" drop @100yds 2.5" groups...)

[randyrucker]

Ok I just took my 125g MK loads to the range today. My primary purpose was to determine which powder was more accurate H110 or Lil Gun. I did 3 six shot groups. For Lil Gun I got an average group size of 0.74 in. and avg. vel. of 1994 fps. using 18.0 gr. For H110 it was 1.3 in. groups and avg. vel. of 2136 fps using 17.8gr. My conclusions thus far: 1. I like the bullet it seems to be very accurate. 2. Lil Gun gave me tighter groups. 3. Lil Gun avg velocity was less than I expected. I'm going to start bumping up Lil Gun to 18.5gr and see if I can get speeds in the mid 2100's and still keep the group size below 3/4 of an inch. I honestly don't see how Sierra is posting that they are getting velocities of 2200 fps with only 17.2gr of Lil Gun. I am at 18.0gr and only getting 1996 fps.

[20X11]

Lil gun has some bizarre power curves...try backing the loads down instead of up...You will be surprised.

[randyrucker]

Lil gun has some bizarre power curves...try backing the loads down instead of up...You will be surprised.

I thought you were loading this with Lil Gun at 18.5gr? You think I should go down from 18 ?

[tallburnedmidget]

Ok I just took my 125g MK loads to the range today. My primary purpose was to determine which powder was more accurate H110 or Lil Gun. I did 3 six shot groups. For Lil Gun I got an average group size of 0.74 in. and avg. vel. of 1994 fps. using 18.0 gr. For H110 it was 1.3 in. groups and avg. vel. of 2136 fps using 17.8gr. My conclusions thus far: 1. I like the bullet it seems to be very accurate. 2. Lil Gun gave me tighter groups. 3. Lil Gun avg velocity was less than I expected. I'm going to start bumping up Lil Gun to 18.5gr and see if I can get speeds in the mid 2100's and still keep the group size below 3/4 of an inch. I honestly don't see how Sierra is posting that they are getting velocities of 2200 fps with only 17.2gr of Lil Gun. I am at 18.0gr and only getting 1996 fps.

People have reported that the Sierra loads seem off. I load Lil'Gun and I have loaded as high 19.1gr of Lil'Gun in a couple of different loads w/out signs of pressure. I AM NOT SAYING to load 19.1gr, I am simply saying you can likely work up a bit from 17.8 to get higher velocities. Always work up sensibly

[20X11]

Lil gun has some bizarre power curves...try backing the loads down instead of up...You will be surprised.

I thought you were loading this with Lil Gun at 18.5gr? You think I should go down from 18 ?

I get mid 2100s out of 17.5 grs lil gun...mid 2200s from 18.5.grs...sorry, I thought you were targeting a specific velocity...the 18.5 gr load is my favorite and most accurate.

[randyrucker]

Lil gun has some bizarre power curves...try backing the loads down instead of up...You will be surprised.

I thought you were loading this with Lil Gun at 18.5gr? You think I should go down from 18 ?

I get mid 2100s out of 17.5 grs lil gun...mid 2200s from 18.5.grs...sorry, I thought you were targeting a specific velocity...the 18.5 gr load is my favorite and most accurate.

I'll try it and let you know how it does for me.