6 Inch .30 cal Form 1: 6 baffles and subsonic .300 BO

Longshot85

Incognito
PX Member
Minuteman
Jan 19, 2011
413
199
36
I have performed the first initial test using some Black Hills 220 grain OTM.

New build with 10.5 inch barrel

This is a Ti tube/Ti end cap, stainless cone baffle build (6 baffles) bore of can is around 0.360 inches throughout.

Test session was extremely short and I did NOT have my magneetospeed to verify MV.

The cones only had the bore hole at time of testing.

I fired 2 NON suppressed rounds to check function and both fired but failed to eject.

Then fired 2 suppressed rounds with this form 1 build and it was MUCH louder than anticipated but rounds ejected fine. (Adjustable gas block installed just have played with it yet, Law Gen3 folder and JP SCS with standard weights)

I have since gone back and added some ports on the baffles ( 8 holes on blast baffle....then 6 holes for next 2 baffles, then 4 holes, 3 holes, then none on last baffle).

I have not had another chance to test.

Basically I am wanting feedback to see what your thoughts are on the possibility of subs actually being quiet with only having 6 inches of real estate and 6 baffles.......

Is it possible this Black Hills 220 grain OTM is actually supersonic out of a 10.5 inch barrel?

I have my magneetospeed and will verify but range time is super limited as well as the ammo (and EXPENSIVE) and I'm not set up to reload yet for .300 BO

After ports added, muzzle on right
20200815_190204.jpg

20200815_190430.jpg

Before ports added (muzzle left)
20200802_192402.jpg
 
Last edited:

Bevo

Sergeant of the Hide
PX Member
Minuteman
Dec 15, 2018
209
162
TEXAS
No, your 220 grain OTMs are not supersonic.

I’m very interested to know if the ports make a difference.

Clipped or DHC (double hybrid clip) baffles have worked very well in my form 1 cans, but anything to disrupt the flow of gas moving thru the bore should have a positive effect. A straight hole thru 50 or 60 degree cones isn’t gonna do much.

I’m in the middle of a shorty can build myself. It will be a 5” Ti tube with 5 baffles (2 SS, 3 Ti).
 

Longshot85

Incognito
PX Member
Minuteman
Jan 19, 2011
413
199
36
I agree that simple bore holes are prolly not going to be very effective. I hadn't finished up with adding the ports yet but a chance to test came up so I jumped.

I have another 9 inch form 1 can and it has simple cone baffles with ports pretty much identical to what I showed on this new 6 inch. That 9 inch can works GREAT on sound suppression and accuracy is fantastic.

I will update on change ports have when I have a chance to test again.
 

Longshot85

Incognito
PX Member
Minuteman
Jan 19, 2011
413
199
36
Well I tested today, gathered data and had a few revelations.

1. When fired, it goes bang appropriately and ejects brass......but will NOT strip the next round out of the magazine. The bolt does go into battery after ejecting the brass but does not strip next round.....and I tested a PMAG and old scholl metal mag.

A good friend with a lot of knowledge recommended getting a lighter buffer spring. For me that means reaching out to JP for their spring tuning kit since I have a SCS.

2. I am at 476 feet above sea level and temp was 80F. I brought the magneetospeed today to verify velocity.
I tested 5 shots: 1072,1073, 1041, 1089 and another that was right in the same area of speed.

Looking at facts about speed of sound I don't see how it could be .......but it sure sounded like I was still getting sonic crack......please chime in

I'll throw in some pics

The ports did help but it still sounds like I'm getting the crack 20200822_140356.jpg20200822_140528.jpg20200822_140441.jpg


I'm loving the Law Gen 3 folder and JP SCS law kit

20200822_134020.jpg
20200822_134017.jpg
 

db2000

Gunny Sergeant
PX Member
Minuteman
Mar 27, 2020
539
229
Seems like a no brainer but make sure you put the plunger back in the Law Tac. I accidentally left it out one time and had the same issue.
 

awpk03s

Private
PX Member
Minuteman
Jun 17, 2017
391
221
Ohio
Maybe try a DHC in addition to the ports? Can’t see how it would hurt anything?
 

Longshot85

Incognito
PX Member
Minuteman
Jan 19, 2011
413
199
36
Seems like a no brainer but make sure you put the plunger back in the Law Tac. I accidentally left it out one time and had the same issue.
You made me paranoid since I did fire it folded ....I went and checked safe and all law parts are there now so therefore present during testing. Thanks for suggestion though.

This is literally a brand new build with less than 20 rounds fired
 

awpk03s

Private
PX Member
Minuteman
Jun 17, 2017
391
221
Ohio
Can you please provide an example just to make sure I'm on the same page
Here’s some picture examples, not my actual pictures or cones though. Basically clip in a + pattern similar to as shown, one set of sides being deeper than the perpendicular sides.
I did both of mine this way, and got almost no POI shift.
IMG_6866.jpegIMG_6865.jpeg
 

Longshot85

Incognito
PX Member
Minuteman
Jan 19, 2011
413
199
36
Ah yes, exactly what I was thinking of

There's one main issue holding me back from doing that and it's the fact I used thinner walled stainless cups for baffles vs thicker stock like those in the pic. I could double clip my baffles with either a drill press or dremel but I don't know if the material would be strong enough not to become weakened and compromised/fail. What I mean by that is if I double clip them it would leave relatively small corner left of thinner material that would be much more prone to becoming damaged enough that they end up breaking off and getting blown down the bore themselves.

I'm not metallurgist or structural engineer so maybe someone smarter can tell me if there's any real risk of that or if they will hold.
 

Longshot85

Incognito
PX Member
Minuteman
Jan 19, 2011
413
199
36
Per the mfg website they are 304 stainless and 112 degree cones