300 Blk 190 Grain SubX seating problem


Well-Known Member
Feb 9, 2021
Hello I'm new to reloading and I'm having problems getting my OAL to stay at specs. I'm using Hornady dies in a LNL AP. I'm seating the bullet to OAL and backing off to set my crimp. Then run seater down to touch and lock down. Then start my run and my OAL is all over the place over or under by maybe .002-.015. I'm going by the setup instructions with the die. It's not helping my confidence much! Lol. I know it's probably something simple. Any suggestions would be appreciated.
I have measured the brass and they all are consistent within a few thousandths. Using Top Brass. All I could find at the time. I'm also measuring from the tip to head of case. I do have a comparator set but I didn't use it. My memory is slipping a little!! So much to keep track of being a newbie. Bullet does have the plastic tip also. Is the ogive where I need to measure from? The rounds are just going to be used in my first pistol length AR.
then start my run and my OAL is all over the place over or under by maybe .002-.015.
I'm also measuring from the tip to head of case....Bullet does have the plastic tip also.
Measuring COAL from the red rubber tip? If so not a good measurement because of variations in the polymer. Measure CBTO using the Hornady comparator tool to judge the true seating depth/ if the die is holding it's adjustment. The Sub-X has a cannelure, if the case mouth is sitting in there on each round IMO you're more than in-spec for COAL of a subsonic 300 BLK load even if there is some variation in COAL or CBTO.

The rounds are just going to be used in my first pistol length AR.
What powder are you using? I had very good success with A1680, and it's been available lately. It's my go-to for anything that has cycling problems, it's never let me down.

My opinion time: PV has new Starline brass in stock at basically the same price per hundred as fired from Top Brass. IMO not worth the hassle of swaging or cutting used brass for 300 BLK when there are so many cheap factory options available. I got a 250-count bag from Starline directly recently, makes loading much easier than introducing random pickup brass.
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Thank you for the information. I'm using 12.4 grains of CFE BLK. I will definitely get some Starline brass. I do have the comparator tool but I just didn't think about using it. (Newbie!!!). I have only fired half a dozen and and they cycled good. I'm looking for a good red dot scope. So I didn't put anything on paper yet. I will pick up some A1680 and give that a try also.
I'm thankful for this forum. Someday maybe I can help someone. Thanks again!
I use an EO Tech XPS on my SBR, no problems hitting a foot tall mini-B27 silhouette at 100 yards with it, freestanding and moving. I consider ~6 MOA from subs out of an AR while moving more than adequate for my intended usage.

I've shot the Sub-X from my 300 BLK bolt action and can get decently tiny holes from a Hollywood-quiet rifle. I prefer the 200gn and 220gn Makers bullets as hunting rounds, they feed really well in my SBR.
I haven't been crimping my 300 BO subs that I run in a 7 inch AR pistol and have not had any problems. Skipping the crimp might help with your issues and help with SD/ES. While I agree that measuring COAL probably isn't as accurate as using CBTO, I have not had any issues staying consistent enough with COAL to maintain good 50 yd accuracy with the pistol.
I have found that for 300 BO subs, the seating depth seems to make a significant difference to my ES/SDs. When I use CFE BLK, it is particularly noticeable and the powder seems to much prefer a compact load. I had a hard time achieving a compact subsonic load with CFE BLK and 190 Sub-X. The problem was that if I seated the bullet deep enough to be compact, the rounds were too short to feed consistently in the AR pistol. I switched to A1680 which seemed less sensitive to being compact and seated the bullets further out at COAL 2.085, which is right at the bottom of the cannular.
I agree with the previous comments that Starline brass is a decent choice for 300 BO. You'll need to get it from Powder Valley though as almost everyone seems out of stock or is charging higher. Starline's web site isn't even taking back order which they normally allow so you might not to wait too long if you want some.

If you are looking for a good subsonic round for targets, I have had good luck with Hornady 225 match bullets that make for a nice compact load with CFE BLK at 2.200 COAL.
Thanks for the information. Sounds like I will definitely be ordering the A1680 and looking for the Starline brass. I will be putting more rounds together once I receive these items. Thanks again. Being a newbie sucks! But with all of you out there to help out it shouldn't be long before I can get things figured out. I'm the type of person that is challenge motivated. So thanks again!
The bench rest boys will sort their bullets for length from base to ogive which is not needed for 300 blk but measuring will show you how much the length of a bullet can vary which will vary your OAL measurements. This is most likely what you are seeing with your OAL. Also I have not had much success with swageing out the military crimp in brass. Cutting the crimp out has worked much better for me, Sinclair has tools for this that will fit a electric screw driver. I also taper crimp most all of my AR loads for better ES this really helps on subsonic loads.