Conceptual problem with 300 blackout

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Desentis
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Re: Conceptual problem with 300 blackout

Post by Desentis »

Your guess is spot on for the sub loads.

It was the opposite for the supers. About 4”

I’ll try to post some pics
Desentis
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Re: Conceptual problem with 300 blackout

Post by Desentis »

S&B 147

Image

Sig ht 120

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Mbc 245 sub

Image
Desentis
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Re: Conceptual problem with 300 blackout

Post by Desentis »

Looking at those spreads I feel compelled to add that my 308 ranch rifle shoots under moa all day long off a bipod.
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dellet
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Re: Conceptual problem with 300 blackout

Post by dellet »

Here's two groups of 208 Amax using CFE Black and Hodgdons data. One from an 8" barrel the other 18". The unmarked holes were from the 18" 1/10 twist. That is why the look a bit oblong, not really stable, you can see that in some of you bullet holes. There was also a velocity spread of over 200 fps.

Tye reason for a Chronograph is that load was by the book and in the 8" barrel was barely 800 fps and about 900 in the 18"

Image

Here's what happens when you compress CFE Black. Left hand target. The right hand target is a gain a loose fill, that was a 150 FMJ, note the velocity and 300+ fps velocity spread.

Image

After a little more tuning of the load and more compression. 11 shots at 50 yards, flyer was self induced so I shot another round.
Image

I wrote all that up when that powder first came out below. If you are going to use that powder, compress it. 98% of your problems will go away.
viewtopic.php?f=141&t=100097&hilit=cfe+ ... s&start=10

If it was me......

I would verify twist rate, then slug the bore by lubing it well and pushing a lead bullet though it, I would be looking for a loose spot. Slugging it may not be that big of deal right off.

Then I would do what every one else in the world says is wrong and shoot it off a soft front bag, resting the barrel, not the stock on the rest. A towel rolled on on your Caldwell will do If you don't have a big front bag. If your groups improve, you know without a doubt the problem is in the stock. Soft front bag and a soft rear or squeeze bag. I have been known to rest my off hand on the barrel in front of the scope.
300 Blackout, not just for sub-sonics.
Desentis
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Re: Conceptual problem with 300 blackout

Post by Desentis »

Great info. I was setting the bullets further and further out to get closer to the rifling!

Will compressing it help that instability?

Thank you very much.
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dellet
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Re: Conceptual problem with 300 blackout

Post by dellet »

Desentis wrote: Thu Dec 17, 2020 6:52 pm Great info. I was setting the bullets further and further out to get closer to the rifling!

Will compressing it help that instability?

Thank you very much.
With that powder, most likely.

It is such a low pressure, high gas volume powder, that it can't expand the bullet enough to fill the bore. So the gas blows by the bullet and cuts or deforms it. Same thing with the supers where you are not limited by an upper velocity. Seems like the more powder you stuff under the bullet, the tighter the groups get.

Since you're limited by velocity with subs, all you can do is increase internal case and start pressures by seating deeper. A bullet that likes a long jump is your friend. Fine tuning with seating depth for accuracy by worrying about jump is pointless, if you have a triple digit ES that guarantees an inch or two of vertical at 100 yards.

That does not explain the factory ammo, but honestly accurate sub loads are more difficult to produce than people think.
300 Blackout, not just for sub-sonics.
Desentis
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Joined: Thu Dec 17, 2020 2:48 am

Re: Conceptual problem with 300 blackout

Post by Desentis »

It was a while ago... I might have popped off most of those factory subs while I was sighting in the new rifle. i don't have many notes on the velocity or pictures of targets with those. I know I tried some factory loads towards the end but it might not have been many.

My goal was to develop my own subs, so I switched over to handloads pretty early in the process.

I'll report back on my results.
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