More info. Here's one for the suppressor experts. Update!

[opps]

Squirt wire pulling gel in before you start. May change that first shot.

 

[Bear44]

A couple thoughts on this- you seem very certain that it's the ambient air in the can that's causing this so try to eliminate it as an issue by spraying some computer cleaner (compressed CO2) through the can. It'll also cool it down. riskier, but you could spray butane in it and hit it with a lighter to burn it off. It's not going to be explosive, just a small jet.

I've blown a deep breath down a 9mm can to eliminate air to minimize FRP and it seems to work.

A few cc's of water as an ablative might be worth trying with subs.

Since they're subs, a thought is that you don't really have a cold bore shot since a few minutes to "clear the gas" is also enough timre for the barrel to return to ambient temps.

In that case, you could try shooting the first round at a target, next few at a different target. Then after a cool down, the next first round goes on the same target as the first round so that all of your "cold bore" shots are in the same POA.

I recall that ARmaster shooter (forgetting his name) found that the first and last round from an AR mag always had a different POI due to the bolt closing and locking.

Since this is a bolt action hunting rifle, it's the cold bore shot with air in the can that I need consistent. I doubt I would ever take a shot at game beyond 100 with it and at that distance the difference in POI for follow up shots is negligible with the Hornady Sub-X load. It was radically different with two other loads I tried.

The shift at 200 yards with this load is more of a curiosity than anything else, but it does confirm gas in the can, as opposed to air in the can, is a legitimate concern when establishing a zero and overall accuracy of a suppressed weapon shooting subs. I wonder how many folks think they have a well zeroed weapon based on strings of fire with gas in the can, but are in for an unpleasant surprise on a cold bore shot.

 

[Bear44]

Another thing I discovered yesterday is that my POI with no can is way different than with the can. I took the can off to get a good MV before trying for 200 yards. I use a muzzle mounted magnetic Chrono and the bullet path is too far away to get a reading with the can on.

With the rifle zeroed at 100 yards with the can, I was completely over the top of the CMP 100 yard target without the can. I could actually see the difference when I checked the bore sighting. That's how I know it was high.

I adjusted the scope enough to get on paper, got my MV readings, then put the can back on, reset the scope to it's original reading and I was right back on with POI. The rifle is a Model Seven with a light barrel, but I did not expect the weight of the can to move the barrel anything close to that much.

I made the mistake of not recording the needed scope adjustment without the can. Ah well, another day.

 

[SOLGardener]

I've been shooting suppressed guns for the better part of 20 years and I've never seen these kinds of results on any combination fo gun and suppressor.

My Mk12 and M4-1000 groups were consistent and the CBS was inside of the group. And I fired many CBS shots at critters and it was always consistent from the first cold shot to the last hot shot.

If it were my rifle, I would mike the barrel all of the way around to see if it's threaded concentrically, I would check with a bore rod to make sure the can is on dead straight.

Perhaps it's off enough that you aren't getting baffle strikes per say, but the bullet is a hair away from one side of the baffles?

I seem to recall that a POI shift with and without the can is indicative of concentricity issues either in the straightness of the bore, concentricity of the threads to the bore center, or in the shape and/or center of the baffles.

Lots of tolerance stacking going on.

BTW, what's the twist rate? 1:8? 1:6.5"? Have you checked the twist rate vs trusting the reported numbers?

 

[Bear44]

I've been shooting suppressed guns for the better part of 20 years and I've never seen these kinds of results on any combination fo gun and suppressor.

My Mk12 and M4-1000 groups were consistent and the CBS was inside of the group. And I fired many CBS shots at critters and it was always consistent from the first cold shot to the last hot shot.

If it were my rifle, I would mike the barrel all of the way around to see if it's threaded concentrically, I would check with a bore rod to make sure the can is on dead straight.

Perhaps it's off enough that you aren't getting baffle strikes per say, but the bullet is a hair away from one side of the baffles?

I seem to recall that a POI shift with and without the can is indicative of concentricity issues either in the straightness of the bore, concentricity of the threads to the bore center, or in the shape and/or center of the baffles.

Lots of tolerance stacking going on.

BTW, what's the twist rate? 1:8? 1:6.5"? Have you checked the twist rate vs trusting the reported numbers?

Good info.

It's 1-7 twist and I have not checked it, but there is no sign of keyholing on this load. There might have been a tiny bit on one of the other loads.

I haven't measured for concentricity, but I have run a rod and it looks good.

 

[Burdy]

Once you finally get the POI figured out you will realize how underwhelming terminal performance is with subs anyway.

"The rifle is a Model Seven with a light barrel, but I did not expect the weight of the can to move the barrel anything close to that much."

I've seen barrel harmonics do crazy things, doesn't always have to do with weight.

 

[Bear44]

Once you finally get the POI figured out you will realize how underwhelming terminal performance is with subs anyway.

Sent from my Pixel 3 using Tapatalk

Agreed! They are neat, but there's no getting around the fact that a 200 grain bullet traveling at less than the speed of sound has similar terminal ballistics whether it's a 300 Blk or a 45 ACP. That's why accuracy is so important. You've really got to make a perfect shot.

This is also why I'm waiting for my stamp to arrive for the suppressor for my 458 Socom. Maker Bullets makes a 500 grain 458 bullet that expands to nearly 1.5 inches at subsonic velocity. Two and a half times the weight means two and a half times the energy. Combine that with a massive wound channel and you really do have a killer round.

 

[SOLGardener]

checkout this military arms channel video on the SIG rattler and some ballistics on subs. i was surpriaed at the energy figures. the bighest advantage that 300 blk has is pretty much BC. there isnt much more energy in a 220 grain 300blk over a 9mm 147gr. not saying its a useless roind, but i thougyt the numbers would be higher.

the rattler is badazz though.

 

[Burdy]

checkout this military arms channel video on the SIG rattler and some ballistics on subs. i was surpriaed at the energy figures. the bighest advantage that 300 blk has is pretty much BC. there isnt much more energy in a 220 grain 300blk over a 9mm 147gr. not saying its a useless roind, but i thougyt the numbers would be higher.

the rattler is badazz though.

Yeah, well, you get ridiculous false comparisons like that when you forget to change the grain weight on your labradar. A 300 BLK subsonic is roughly twice the weight of 9mm at the same velocity so saying they are similar is ridiculous. He screwed that up. There will be roughly 50% more energy from the .300 BLK which is significant.