Subsonic Woes

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Festusxj
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Subsonic Woes

Post by Festusxj » Fri May 22, 2020 8:44 pm

Arright, First post, I've have been lurking for a while used a lot of the knowledge here to build my 1st .300blk.
SLR Upper/Lower/Handguard
Green Mountain 9" 1:7 twist barrel
Toolcraft DLC BCG
Geissele SSA-E trigger
JP adjustable gas

Build went great and the gun looks amazing! Had to re-attack the gas block alignment and it cycles supers just fine.

I bought some Seller & Belloit 200gr subs and... they were supersonic... Hmmm. So I reloaded some rounds
220gr Hornady ELD-X
11.5 down to 10.7gr of accurate 1680
Federal match Small rifle primers
2.20 COL

All Supersonic.... 2100-1900fps from my labradar

Ideas? Knowledge from the gurus? I'm stumped.

I'll post a picture if someone can tell me how to do it...

Thanks

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dellet
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Re: Subsonic Woes

Post by dellet » Fri May 22, 2020 9:45 pm

Quite simply, your Lab Radar is screwing with you. Check all the settings, and batteries.

Only other thing I can think of is is somehow picking up unburned powder. What is terminal velocity readings? If down range readings are 1000fps then powder won’t travel past the first reading. Unless you have you split yardages set really short as in about 2’.

Or I want the lot number on that powder, if 10 grains gets you 2000 fps with a 220 ELD, I’m sure I will get 4000 with a 125.
300 Blackout, not just for sub-sonics.

Festusxj
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Re: Subsonic Woes

Post by Festusxj » Fri May 22, 2020 11:15 pm

Ha! If it turns out to be the powder, you can have it!

Good call on Chrony being screwed up. I looked through the csv data for the shots recorded, and it's definitely in the street. I'll have to try again with the can on, but all of the rounds sounded supersonic to me and I haven't had problems with the crony before. I can't think of another reason why it would behave like that.... More digging...

Thanks again. I'll report back.

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dellet
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Re: Subsonic Woes

Post by dellet » Sat May 23, 2020 11:07 am

Part of the reason in know it’s a reading issue vs actual velocity is that you had more than one shot at it. The only way you get 2000 fps with a 220 grain bullet would leave a lasting impression.
300 Blackout, not just for sub-sonics.

RKB731
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Re: Subsonic Woes

Post by RKB731 » Mon May 25, 2020 11:54 am

Just one of many reasons to forgo the expensive Labradar and get a Magnetospeed 😁
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plant.one
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Re: Subsonic Woes

Post by plant.one » Fri May 29, 2020 12:13 pm

RKB731 wrote:
Mon May 25, 2020 11:54 am
Just one of many reasons to forgo the expensive Labradar and get a Magnetospeed 😁
two different tools for two different uses.


yes they both perform the same basic function... but the way you're comparing them is like saying a video recording is the same as a picture.

a magnetospeed samples two data points, and two only per shot. the labradar measures potentially dozens if not hundreds of them and gives you data throughout the whole barrel to target interval.
Reloading info shared is based on experiences w/ my guns. Be safe and work up your loads from published data. Web data may not be accurate/safe.
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bearcatrp
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Re: Subsonic Woes

Post by bearcatrp » Fri May 29, 2020 6:39 pm

You have to put the lab radar in pistol mode to register subs.

Festusxj
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Re: Subsonic Woes

Post by Festusxj » Thu Jun 04, 2020 10:26 am

AH ha! I’d forgotten the pistol mode! I’ll try it next time! Thanks!

Festusxj
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Re: Subsonic Woes

Post by Festusxj » Mon Jun 08, 2020 6:26 pm

Bearcatrp,

Spot on! Finally got back out and total success! The 9" barrel still makes some noise even with the can, but reliably in the 950 range.

Thank you

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