Accurate subsonic 300 BLK load ( bolt action) ?

[5Baize]

Hi guys,

I've got a bolt action 300 BLK, Tikka T3 action 18" long barrel, 1:8" twist.

Overall, I'm really disappointed by the accuracy. I've tried different handloads, bullets ( 220 smk, 208 eldm, 190 subx, 200gr lapua special subsonic), powder ( N110, N120, RS30). And I can't get anything that would consistently stays within less than 1MOA.

Is it me, my rifle or just the round that is inherently not accurate?

Has anyone succeeded in producing a 0.5 MOA subsonic load for his bolt action blackout?

What is the best approach for subsonic laod development? Stay as close as possible just below sound velocity, well below ? Sitting depth role? Case fill? Neck tension? Magic bullet for flying slow.

 

[dantiff2]

Hi guys,

I've got a bolt action 300 BLK, Tikka T3 action 18" long barrel, 1:8" twist.

Overall, I'm really disappointed by the accuracy. I've tried different handloads, bullets ( 220 smk, 208 eldm, 190 subx, 200gr lapua special subsonic), powder ( N110, N120, RS30). And I can't get anything that would consistently stays within less than 1MOA.

Is it me, my rifle or just the round that is inherently in accurate

How deep down this rabbit hole are you prepared to go?? hahaha

Primers make a huge difference and powder needs to be very, very consistent when dealing with sub loads. It's not as forgiving as filling the case and shooting supersonic.

I have no input to offer with jacketed bullets at subsonic speed but the load workup and development sure was fun with cast bullets!
Dan

Edit to add: Your goals may be too ambitious... Out of all my subsonic adventures- across multiple different calibers, I have yet to find one that with go under MOA consistently. I can get MOA or just over, but not under.

 

[5Baize]

I'm used to precision reload. I've got the gear ( supertrickler / mandrel dies / neolube / etc....).

I'm used to sub-Moa reload or even 1/4 MOA, so I'm already all the way in the rabbit hole .

What primer made a difference ?

 

[Krogen]

Not that this is your trouble, but I had a heck of a bad time with bullet runout. So much that I could see it just by rolling the cartridge across my bench. No need for a runout gauge! It was something about the short case, long bullet, minimal neck contact, flaky dies, and who knows what else. When I fixed the runout issue, it fixed my accuracy troubles. To cure the runout issue, I started seating bullets about 25% in, then turning the cartridge 90 degrees and seating another 25% in. Continue this until fully seated. Nothing magic about 25%, just seat partially and turn. Rinse and repeat.

 

[dellet]

Sub MOA at what distance?

You want a bullet that is jump tolerant, the 220 SMK and 208 ELD are both very good candidates. Don’t be afraid of a .250” jump if that’s what it takes to get single digit ES numbers.

I Have better luck with velocities around 1000 fps and often as low as 950. If it’s for hunting bullet performance, expansion is more important than supreme accuracy, so be aware of the velocity threshold of a chosen bullet.

Of the powders you listed I would go with N120 and a magnum primer.

Tighten your tolerances. In your load ladder charge weight changes of 2% or less. When you only have 10 grains of powder, a 1/2 grain change is 5%. Same with a seating depth test, .005” movement will change the load density enough to effect velocity spreads.

If you want bench rest results, use bench rest standards. Good brass, consistent neck tension, accurate measurements. Just really tighten the quality control. The key is small changes and a good notebook.

It’s worthwhile to develop a good load at 50 or even 25 yards. Then move it to 100-200. What this does is drive home the point of how sensitive subsonic shooting is. A 1/2” group at 50 yards with an ES 15 fps, can easily be a 4” vertical string at 200 yards.

 

[dantiff2]

I'm used to precision reload. I've got the gear ( supertrickler / mandrel dies / neolube / etc....).

I'm used to sub-Moa reload or even 1/4 MOA, so I'm already all the way in the rabbit hole .

What primer made a difference ?

I saw huge swings with magnum primers. Standard small rifle was better, BUT I found the best ES in velo and accuracy with small pistol primers.

I have a theory that the more powerful primers were starting the bullet into the rifling and causing erratic case capacity issues. No proof but I tried a bunch and kept getting the same result. Just my personal observation.

 

[5Baize]

Thanks for the feedback.

I'll try small pistol primer to see if it gives me something interesting.

I'll also try lower speed speed.

Ideally I'd like 1 MOA at 200/yard so 2" group at that distance.

 

[long40shot]

I haven't hand loaded any yet, but to test your rifle, you might try a box of the 208grn Hornady Black ammo. My cheap savage AXIS II does very well with it.

 

[mic2377]

Use a faster powder and a lighter bullet. Red Dot or Bullseye and a 110-150 gr bullet is the way. This will provide superior ES/SD to the usual 200-220 gr loads that use a slower powder so they will cycle an AR.

 

[pupsdad]

I use 220 gr cast bullets for subsonic rounds and pistol primers.

 

[pupsdad]

My mistake Lyman 210gr #311284.

 

[Oso]

For what it is worth you have to forget about your expectations of shooting supersonic rifle. I have a custom CZ527 with 18” barrel that shoots 1 MOA with subs and .5 MOA with supers. Subsonics are closer to pistol performance, and wouldn’t you be happy with 1moa with a pistol. Depending on the bullet profile, reasonable expectation for shooting subsonic heavies from 300BO is 1-2 MOA.

Perhaps a better conceptual comparison is a .308Win shooting 220SMK is a sports car, call it a Ford Mustang, and a 300BO shooting the same bullet at only 40% of the velocity is a Cargo Van. They’ll both get you to the final destination, but the van will take longer and due to its size you may not be able to park in the front row.

As Dellet stated, you will need tight tolerances on you reloading process to have chance to reach .5 MOA. Forget about any of the extreme expansion bullets with blunt noses and deep hollow points, such as the Hornady SubX. Think of these types of bullet profiles as a UHaul Moving Van… not going to be very accurate. For what they lack in pinpoint accuracy they make up for with additional expansion/lethality.

Welcome to the “Science Club”… you now get to do a bunch of experimenting to find out what works best in your gun. You’re using a bolt rifle so you can use any size/type of bullet from 110gr - 230gr to load at subsonic velocities. Also, your Tikka will allow you to play with load lengths greater than 2.26” (PMag restriction) for the super heavy / long bullets. You’ll get to learn hands on load density and its effect on performance especially if you try lighter bullets (shorter).

 

[dellet]

For what it is worth you have to forget about your expectations of shooting supersonic rifle. I have a custom CZ527 with 18” barrel that shoots 1 MOA with subs and .5 MOA with supers. Subsonics are closer to pistol performance, and wouldn’t you be happy with 1moa with a pistol. Depending on the bullet profile, reasonable expectation for shooting subsonic heavies from 300BO is 1-2 MOA.

Perhaps a better conceptual comparison is a .308Win shooting 220SMK is a sports car, call it a Ford Mustang, and a 300BO shooting the same bullet at only 40% of the velocity is a cargo van. They’ll both get you to the final destination, but the van will take longer and due to its size you may not be able to park in the front row.

As Dellet stated, you will need tight tolerances on you reloading process to have chance to reach .5 MOA. Forget about any of the extreme expansion bullets with blunt noses and deep hollow points, such as the Hornady SubX. Think of these types of bullet profiles as a UHaul Moving Van… not going to be very accurate. For what they lack in pinpoint accuracy they make up for with additional expansion/lethality.

Welcome to the “Science Club”… you now get to do a bunch of experimenting to find out what works best in your gun. You’re using a bolt rifle so you can use any size/type of bullet from 110gr - 230gr to load at subsonic velocities. Also, your Tikka will allow you to play with load lengths greater than 2.26” (PMag restriction) for the super heavy / long bullets. You’ll get to learn hands on load density and its effect on performance especially if you try lighter bullets (shorter).

The thing I’ll add and or disagree with is that sub MOA at 200 is possible. Takes two things besides hard work. First is a bullet known to be stable flying completely through the trans sonic range. 950-1350 fps. The next is meticulous brass prep.

Reading wind wont hurt the effort, consider flight time. 200 yard benchrest with 3000fps MV verse 1000 fps MV doesn’t take rocket science to figure the difference in flight time.

If you want all the headaches for sub MOA with supers at 1000 yards, try subs at 2-300.

 

[linebaugh]

First off 2" at 200 is not realistic. Your ES numbers would need to always be single digit for starters and I have not seen that consistently in the subs I have worked with.
If your goal is 2" at 200 I would advise you to give up now. Just money and time wasted or how much frustration you can handle. 3 inch at 200 is probably realistic if you are a diligent reloader and find a good combo.

The first thing I would do is try different powders. 3 powders is not enough. I went through 7 or 8 on my last sub build before finding something that I could live with. BTW what I could live with was an aveage of around an inch or a bit more over multiple 3-5 shot groups at 100.

Neck tension is critical as is all of the other norms. I personally did not see any real difference in 3 primers tried but mine is not a 300 whisper and is LRP. I did not try pistol primers as it never occured to me... i would have!

If you have not done it yet take your chrony and watch every shot for speed vs impact position. I was never able to get single digits personally and my ES is about 18 on average. That was trying a lot of different ideas such as seating depth, primer change, and neck tension not to mention a lot of different powder and 3 bullets. The ES alone causes a lot of vertical. Many times I would have groups well under 1" wide but they would be up to 2" tall.

Ironically in my round H110/296 ended up being the best which was surprising since it has the lowest fill rate. I used this powder out if frustration BTW so dont be afraid to try things.

If you get it figured out post your findings as I am working on another subsonic build now and the more info the better.

 

[5Baize]

Thanks.

Neck tension wise, what is better low or high?

 

[padom]

LC converted brass, CCI 450, CFE BLK, 220smk subs ate stupid accurate and stupid quiet in my 10" Rainier Ultramatch 300blk..

https://imgur.com/a/LYRxUm0

 

[dellet]

Pretty typical shooting from my wife. 200 yards, 208 AMax, 3X red dot, Handi Rifle off a Caldwell front bag, unsupported in the rear. Paper is 4”x6” with a 2” and 3” dot.
More often than not, she keeps it under 3”.
Not exactly sub MOA, but not exactly the rifle for it either. By the vertical it looks like a munitions department failure.

 

[linebaugh]

Thanks.

Neck tension wise, what is better low or high?

My ES numbers came down with a tighter neck.

 

[Oso]

LC converted brass, CCI 450, CFE BLK, 220smk subs ate stupid accurate and stupid quiet in my 10" Rainier Ultramatch 300blk..

https://imgur.com/a/LYRxUm0

Curiosity- did you convert virgin LC brass or range brass?

 

[padom]

Curiosity- did you convert virgin LC brass or range brass?

Ive converted 10s of thousands of matching headstamp LC once fired..

I have a dedicated 300blk conversion toolhead for my 650 that decaps and forms/sizes the brass 90% of the way in first station, then i have a carbide 300blk dillon FL size trim die with Dillon RT1500 automatic trimmer on it. This stations finishs the sizing to 100% and trims the neck to 300blk trim length. Lastly I have a 21st Century mandrel die with 308 turning mandrel in last station that makes the neck ID perfectly straight and sets final neck tension...

I then SS tumbled them. I chamfer and debur when im ready to load them and anneal after first firing

https://imgur.com/a/fWrGNsk

https://imgur.com/a/fUH75DE