WTK: Hornady 175 Sub-X load Data for 300 BO

I looked on Hodgdon's site. The lowest grn bullet they recommend with h100 subs is 190 grn. May need to go with a faster powder?

I'd check this forum out if I were you. I used it a few times when I was loading for .300 BlkOut.

I'll check my Hornady #11 manual

Will you be testing by chrono or by sound? You may run out of bullets if testing by sound. Pretty easy to get to that 1050 "sweet spot" with a chrono. Since 4227 is your slowest powder, I would start with it, around 9.0 grains, and see what it shoots.

Tony243 said:

Will you be testing by chrono or by sound? You may run out of bullets if testing by sound. Pretty easy to get to that 1050 "sweet spot" with a chrono. Since 4227 is your slowest powder, I would start with it, around 9.0 grains, and see what it shoots.

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I do not have a Chrono.

338 dude said:

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Which # is that

A few years ago AA1680 was considered the magic dust for 300BO heavy bullet subsonic loads.

My Hornady ap only lists a 190 gr Sub-x bullet for 30 cal.

Here are my subsonic loads for 300 BO, 7" barrel, suppressed with about 1050 fps

190 subx 13.0g AA1680, 2.081 COAL CCI 41
225 Hornady Match, 12.5g CFE BLK 2.203 COAL CC41

I found loading subsonic for the 300 BO to be very sensitive to seating depth, especially with CFE BLK. I get the best results with little to no free volume in the case. To tune in on the seating depth, I put the charge weight in a case that has been fired and not resized or decapped. I then find the seating depth based on where the bullet rests lightly on the charge. This method was suggested in some older thread on this forum. If you search around some you should be able to find some good information on loading subs on older threads on the forum.

I would recommend trying to borrow a chronograph for your efforts to insure you're getting consistent velocity with a reasonable SD/ES. In someways, shooting subsonic in kind of like shooting long range or with a .22 LR where you get a lot of drop fairly quickly over distance so variation in velocity results in vertical stringing.

The issue is those bullets are misleading with the name. You will want a heavier bullet to get to the Subsonic ranges. That bullet is made for supersonic loads but will expand at lower velocities that you will get out of a 300BO.
look at the 200 grain bullets for real subsonic loads with a 300BO.

Warning, do NOT go off sound or speeds!!!! you will need to test each load for key holing! otherwise you will have a baffle strike and you get to blow up a can, expensive mistake. Get a good Chrono, borrow one and then test at 100 yards or 50 or key holing. You will be surprised at how easy it is to not stabilize a bullet and get a baffle strike.

AA1680 is good for 16" barrels
I use a 200 Norma for my 8" barrel, but did a lot of testing to eliminate any key holing.
all using 220 gr bullets

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I used IMR 4198 and the Hornady 208gr BTHP with excellent accuracy and sound characteristics. I'd tend to agree with @waveslayer as far as using heavier bullets goes.

joelpend said:

A few years ago AA1680 was considered the magic dust for 300BO heavy bullet subsonic loads.

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I use that powder a lot in 300bo along in 45-70.

You'd probably need Trail Boss powder to accomplish a subsonic load with the 175 Subx. See attached screenshot from Hodgdon.

Like others have stated, use a heavier projectile for subsonic use. The 190 Subx seems to do ok, but for reliable expansion, Maker Rex bullets may be a better option.