Faxon 7.5" 1:8 vs BA 8" 1:7 Twist for subs and supers

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gmfonda82
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Faxon 7.5" 1:8 vs BA 8" 1:7 Twist for subs and supers

Post by gmfonda82 » Mon Jul 26, 2021 4:12 pm

I decided to finally build a 300BLK pistol after seeing the SB-Tactical Q brace. So I purchased a Faxon 7.5" 300BLK Gunner 1:8 barrel and a Daniel Defense MFR XL 9" handguard to cover a small amount of my suppressor or Linear Compensator. Upon doing more research I saw a lot of folks say subs will keyhole with a 1:8 twist. The Faxon barrel is a tad smaller than the 8" BA barrel I bought to cover my butt in case 1:8 keyholes, and I like the Faxon profile. My suppressor is rated to down to 7"(SilencerCo Omega 45k) so I wanted to go as small as I could for supers but occasionally do some subs, maybe up to 220 grain. I know bullet length matters more than weight but will subs really keyhole in 1:8 twist? I have seen many different answers to this question. So I bought a BA 8" 1:7 twist barrel just in case and was going to return the Faxon but is there any point? I might keep both if 1:8 works fine and give the BA 8" 1:7 to a friend.

I have tried searching but there is not a definitive answer just lots of conjecture.
Last edited by gmfonda82 on Mon Jul 26, 2021 6:34 pm, edited 3 times in total.

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dellet
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Re: Faxon 7.5" 1:8 vs BA 8" 1:7 Twist for subs and supers

Post by dellet » Mon Jul 26, 2021 5:24 pm

Until you get to bullets over 1.5" long, you won't notice the difference because of twist. Weight comes into play with longer bullets. How the weight is distributed can and will make a difference. A bullet 1.750" long and 250 grains will be much more stable than the same length and 180 grains.

Until you get into some of the long custom solids, it won't matter. Th Lehigh 195 ME, is an example. it can get a bit edgy in a 1/8 at super low muzzle velocity like below 900 fps., but other factors also come into play. Same goes for a Hornady 225 ELD that's something like 1.650".

Just test without the suppressor on to be sure.

I shoot lot of bullets up to 220 grains in a 1/10.
300 Blackout, not just for sub-sonics.

gmfonda82
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Re: Faxon 7.5" 1:8 vs BA 8" 1:7 Twist for subs and supers

Post by gmfonda82 » Mon Jul 26, 2021 6:08 pm

So it sounds like I should not be worried all Subs will keyhole but to make sure the bullet length is shorter for the weight like in 200 grain subs?

I do reload, is it better to just reload my own to make sure I can keep the length down and the weight up?

Will a 1:7 twist make that big of a difference?

I just picked up a box of these besides pulling the bullet how or where can I find the length if Magtech does not have it listed?
https://magtechammunition.com/products/ ... -subsonic/

75% of the time I'm going to be using supers, I have a variety of sub guns like the MPX, MP5, GHM45, Banshee 10MM, and Stribog that are what I would use primarily for HD with a sub, and honestly, it would be the MPX out of all of them I would pick up first. But I want to be able to use subs in case I am hog hunting or something that makes sense to use supers. Like the use of quiet heavy bullets with my suppressor if I ever found myself in a situation where I went from outdoors to indoors and need to "operate" quietly and switch from supers to subs. In almost all home defense situations I would use my 10.3" LMT that's suppressed but I like options.

My last quest is in regards to how to use super and subs on a truck gun, backup HD, 300blk pistol. I am going to use a Holosun 510c or 503G or the new Primary Arms Micro Prism with 300blk ACSS for supers and was thinking of putting on Magpul offset pro's to use for sub use. Zero one for each, but is it possible to zero 25 yards with offset irons?

gmfonda82
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Re: Faxon 7.5" 1:8 vs BA 8" 1:7 Twist for subs and supers

Post by gmfonda82 » Tue Jul 27, 2021 12:19 am

So should I just keep the Faxon 7.5” 1:8 twist? The reviews on the Faxon are really good with sub MOA accuracy, versus returning it and keeping the BA 8” 1:7 twist barrel.

Also will Magpul Offsets pros work for subs in close range? If it does work I’m trying to figure out a way to mount a surefire or Olight with Arisaka in-line mount or offset mount so I can wrap my hand around the handguard.

I was also adding a adjustable gas block but should I even do it or just add a Hanson gas block from another build attached with set screws not pinned which should work.

I appreciate all the advice. I would just like a couple more opinions on 1:7 and 1:8 twist? I will be hand loading my own Ammo after the initial zero and testing. Any recommendations for sub and super bullets? I have the powder and a thousand cases of unloaded 300 brass, I have shot this before (years ago out of a much longer barrel) and also I bought new brass. The new 7.5” or 8” barrel pistol is new to me to build versus a longer 16” 300blk rifle.

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dellet
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Re: Faxon 7.5" 1:8 vs BA 8" 1:7 Twist for subs and supers

Post by dellet » Tue Jul 27, 2021 3:49 pm

If you can narrow down the questions to a few that really matter to you, it would be helpful. For every question you asked, there are probably 3-5 options.

Decide if you want primarily sub or super, what bullets you want to use and what powder, set the gun up accordingly.

1/8 is SAAMI twist rate, it's what all the testing was done on. Nothing wrong with that. In a short barrel where velocity is limited, nothing wrong with a 1/5 either, but a lot of bullets start coming apart above 2200 fps or 300,000 rpms. So not the best for light supers.

Hanging a bunch of crap all over everything so you can have 14 different sights and scopes is not something that interests me so can't help you there. A quality 1-6 that illuminates seems to work just fine. I'm not tacticool enough to know which hole to look through under life and death pressure, I just prefer to be able to shoot something in the face within 20 yards without having to take time to aim.

bullet lengths
https://www.jbmballistics.com/ballistic ... gths.shtml

stability calculator
https://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi
300 Blackout, not just for sub-sonics.

gmfonda82
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Re: Faxon 7.5" 1:8 vs BA 8" 1:7 Twist for subs and supers

Post by gmfonda82 » Wed Jul 28, 2021 9:50 am

Thank you for the replies and the useful info.

I guess my only question relates to how to manage supers and subs on the same platform? I have a Leupold VX-3i 1.5-5x that would work nicely for supers and I could either attach a canted RMR or use a set of offset Magpul Pro’s for subs. Besides a light and backups or an RMR, I am not hanging anything else off the gun. I don’t think an optic and a light is a ton of stuff, and adding some backups wouldn’t be terrible if they served a purpose for subs or as backups if the optic broke. It’s going to be a light gun anyways for the Wrangler or a hog gun to go with my 12.5” 6.5 Grendel pistol build.

Again back to my question I asked before, are offsets fine for close quarters to 100 yard engagement?

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Re: Faxon 7.5" 1:8 vs BA 8" 1:7 Twist for subs and supers

Post by dpete » Sat Aug 28, 2021 7:57 pm

As long as your eyes are young enough to be able to focus on the rear apperture, the front pin, and the target at the same time offsets are fine.

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