Need Help - Subsonic Rounds Tumbling

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Dolomite_Supafly
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Re: Need Help - Subsonic Rounds Tumbling

Post by Dolomite_Supafly »

markr6754 wrote:I had a response on another site stating that "boat tail bullets do not stabilize well out of short barrels". Has anyone else observed that, or heard that?
This 300 Blackout bolt gun easily stabilizes boat tail bullets at subsonic velocities. It stabilized 212 ELD-X as well at subsonic velocities as well as a bunch of others at lighter weights. Although not a boat tail it also stabilized a 265 grain bullet as well. That is an 8 twist barrel, not 7, at 3.5" long.

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markr6754
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Re: Need Help - Subsonic Rounds Tumbling

Post by markr6754 »

Okay...so I stopped by Cabela’s and bought a J Dewey 30 cal cleaning rod. Running this through the bore with a patch and it doesn’t complete a full rotation when the jag pops out of the barrel. This leads me to the conclusion that my barrel is not 1:7 twist, but something else.

I repeated the test. Multiple times with the same sad conclusion. Now, my selected bullet should still stabilize at this spin rate, but I cannot claim to have received the barrel I paid for. Worse is the $45 price I paid for a cleaning rod.
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dellet
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Re: Need Help - Subsonic Rounds Tumbling

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markr6754 wrote:Okay...so I stopped by Cabela’s and bought a J Dewey 30 cal cleaning rod. Running this through the bore with a patch and it doesn’t complete a full rotation when the jag pops out of the barrel. This leads me to the conclusion that my barrel is not 1:7 twist, but something else.

I repeated the test. Multiple times with the same sad conclusion. Now, my selected bullet should still stabilize at this spin rate, but I cannot claim to have received the barrel I paid for. Worse is the $45 price I paid for a cleaning rod.
An 8 1/2” barrel will only have a little more than 6 3/4” of rifling. So if you marked the rod at 7” and you had even as much as 1/2” of rod left when you ran out of rifling it’s real close to 1/7 and they are rarely exact. So the barrel should stabilize the bullet as long as the rest is good.
300 Blackout, not just for sub-sonics.
markr6754
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Re: Need Help - Subsonic Rounds Tumbling

Post by markr6754 »

dellet wrote:An 8 1/2” barrel will only have a little more than 6 3/4” of rifling. So if you marked the rod at 7” and you had even as much as 1/2” of rod left when you ran out of rifling it’s real close to 1/7 and they are rarely exact. So the barrel should stabilize the bullet as long as the rest is good.
Thanks dellet. So then, in all likelihood this is a 1:7 barrel. The bore is very clean now, thanks to many patches. I have an awesome.30 cal cleaning rod. And I have a mystery yet to solve. I’ll follow up with the bullet tests tomorrow. I unfortunately resized all of my brass yesterday, so I don’t have a fired case to use for the powder compression test.
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Re: Need Help - Subsonic Rounds Tumbling

Post by rebel »

markr6754 wrote:Okay...so I stopped by Cabela’s and bought a J Dewey 30 cal cleaning rod. Running this through the bore with a patch and it doesn’t complete a full rotation when the jag pops out of the barrel. This leads me to the conclusion that my barrel is not 1:7 twist, but something else.

I repeated the test. Multiple times with the same sad conclusion. Now, my selected bullet should still stabilize at this spin rate, but I cannot claim to have received the barrel I paid for. Worse is the $45 price I paid for a cleaning rod.
Holy Snikies Mark !!!!
I knew Cabelas was high, but crap. I sell those for less than 32 bucks. Oh well, that rod will serve you well for a long time.
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markr6754
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Re: Need Help - Subsonic Rounds Tumbling

Post by markr6754 »

rebel wrote:Holy Snikies Mark !!!!
I knew Cabelas was high, but crap. I sell those for less than 32 bucks. Oh well, that rod will serve you well for a long time.
I knew I was getting ripped off, but it's more important that I get to the bottom of this subsonic bullet instability. I had been thinking of getting a single piece cleaning rod, so shame on me for putting it off when I could have paid less.
On the subject of Cabela's pricing....they recently jacked the price of primers through the roof. I picked up some CCI Small Rifle for $32.99, knowing that it was a high price...but I need them to start loading my 300 AAC Blackout. Yesterday, the price was $40.99 on the shelf...higher than Federal which came in at $39.99. I didn't see that powder prices changed...but primers are over 24% higher than December. Good thing I loaded up on the Sellier & Bellot SRP when they put them on clearance for $28/brick.

Not looking to hijack my own thread, so please read and ignore. I'll be continuing with my bullet checks today. I'm trying to open up a case neck enough that I can do the powder tests requested by dellet.
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Re: Need Help - Subsonic Rounds Tumbling

Post by markr6754 »

dellet wrote:I was going to hold off on this until you knew the twist was correct, but here's what I would do if it is. Or anything faster than 1/10.

More thoughts on this that concerns the bullet.

Look closely at any you have loaded and look for a ring on it that is not there on ones that you have not seated. It's possible at that charge weight you are compressing the powder and deforming the bullet.

What you can do is to take a fired case that the bullet will sip in and out of, then put in your powder charge and lightly seat the bullet on the powder. Then measure the length. If it's more than 2.250" bullet deformation is possible.

Next thing is to make sure you're not loading it too long for the chamber.

With a round made up, (live is ok, but without primer and powder is best) pull the upper and then the carrier group out. you should be able to insert the round into the chamber with finger pressure and have it fall out with gravity. If not, then the bullet may be hitting the lands and becoming off center when fired.

Last, if either of these two things happen, I would drop the charge to 10.5 grains and seat the bullet as above and load some rounds at that length and check the holes again.
dellet, I've completed all of the checks. First, I opened the neck of a resized case using a 3/16" socket. Worked beautifully. A bullet could just drop in, similar to my Hornady Modified Case. I seated a used primer, then added 11.6gr A1680, my initial load. I placed a 220gr Lapua Scenar L bullet gently on top and measure the OAL. It was 2.1442". I found that I could lightly compress the charge using just the thumbwheel of the caliper and get it down to 2.140". As there was just the slightest pressure I knew that I was neither distorting the bullet, nor was I compressing the powder. As I am seating this bullet to 2.250" I believe that I have a bit more wiggle room before this becomes a compressed load.

I further discovered that I could put 11.8gr of A1680 and the case is full with this bullet at 2.250". I did this just to see how much tolerance I have in my powder drop without turning these into compressed loads.

Finally, I chambered a static round (case, bullet) in the barrel with finger pressure, and it falls out with gravity. I then loaded it into a magazine, chambered the round by releasing the bolt, the extracted it to see whether the round hit the rifling. It did not. The round is unmarked, except a little scuff below the ogive, most likely from riding feed ramp into the chamber.

So all tests passed with flying colors. There doesn't appear to be a reason these rounds don't stabilize, they just don't.

I guess I'm back to the beginning.
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Re: Need Help - Subsonic Rounds Tumbling

Post by Dolomite_Supafly »

Shoot at something other than the paper you are using. Cardboard, a piece of wood, anything other than that paper.

Can you post pictures of the unstable holes?

Like I said before I have shot printer paper and with slower bullets it will tear odd looking holes. Even 22's do this with certain types of paper.
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Re: Need Help - Subsonic Rounds Tumbling

Post by markr6754 »

Dolomite_Supafly wrote:Shoot at something other than the paper you are using. Cardboard, a piece of wood, anything other than that paper.

Can you post pictures of the unstable holes?

Like I said before I have shot printer paper and with slower bullets it will tear odd looking holes. Even 22's do this with certain types of paper.
Haven’t learned how to post pics here. I took a couple to send to Palmetto State Armory...wanted them to see what’s happening with their upper. I’ll go read the how to for this site to see if I can figure it out.

As to shooting...I shot thick NRA targets...like construction paper, and I’ve shot flimsy paper targets...both do the same. I need to load more ammo before attempting to shoot again, and I have some heavy card stock I can print a target on. Everything I do is indoors so I have to shoot what I can hang from their target holders.

I setup an account at Flickr. Not sure if these images will work, but it’s a start!
https://flic.kr/p/23SV2sg
https://flic.kr/p/23SV2x6
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dellet
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Re: Need Help - Subsonic Rounds Tumbling

Post by dellet »

A couple things.

You know the barrel at least should work.

You know the load is put together right mechanically.


Dolomite might be correct. The target pic looks bad and that's the next thing to make sure of..

Were these targets in a frame or basically just hung from the top?
300 Blackout, not just for sub-sonics.
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