Installing a can made my ammo SD go to $#!+?

#1
So, I'm going to caveat this by saying that this is a VERY limited experience, with one load in one rifle, over a literal handful of rounds. That said, I had what I feel is a very odd thing occur; I ran 5 rounds through my (338 WM) rifle over a Magnetospeed V3, and with no can installed, my SD was low-ish; around 9 FPS. These were kinda-sorta sighters, as I had re-mounted the scope. The first two rounds were getting me to the bull, and the last three rounds went into the same hole.

I then installed the can (SAS Vengeance), and fired 7 rounds of that exact same load (285 A-Max over 70.0 gr H4831SC in Win brass, lit off by CCI 250 primers) and noticed that my SD had more than doubled to 20.x FPS. I'm not quite sure what to make of this.

Obviously, between the two strings, I had to re-mount the Magnetospeed bayonette, but I used the alignment rod each time to make sure that the bayo spacing was close but not too close. Additionally, that group was significantly larger than the final three rounds of my sighter group. Unfortunately, that represented the last rounds I had of that particular load, so the rest of my shooting that day doesn't have any basis for comparison to the initial non-suppressed group. I will say that none of the other loads I tried would group for shit... like, bad enough to make you wonder if the scope is moving around (it's that initial group that convinces me that the scope isn't moving around). Unfortunately, I re-tightened the can onto the mount once it was warm, so it was (temporarily) stuck in place so I was unable to re-shoot un-suppressed groups with different loads.

Anyhow, after reading LL's feedback regarding SAS cans, I figured that I ought to give my can a once-over. I did the ol' proctological bit with it once I got home and got it off the rifle, but I can't see anything that jumps out as obviously wrong. I thought that maybe I was getting some baffle strikes (the groups were that bad), but I can't see any evidence of that, either. Now, here's something else... this same can, on a 300 WM host, has put up consistent sub-MOA groups; if it wasn't for this, I'd think that something in the can is just wonky.

I think that the next step is to go back to the range, NOT over-tighten the can, and shoot back-to-back suppressed and un-suppressed groups with the same loads that put up such horrid groups before. The gun has a CF barrel, but I wouldn't expect such a massive change in accuracy (and SD) due to the harmonic impact of installing the can.

Has anyone had anything similar happen?
 
#2
I am new to the 338 game and have no suppressor for it but out of my saker I have seen several times that it actually improved my sds vs unsupressed. Accuracy was about the same suppressed vs unsupressed.
 

BOLTRIPPER

Not Carlos Danger
#3
me thinks it a chrono issue.......something hung at the end of a barrel is a tad different that's chrono 6 to 10 ft from the muzzle.....i do know that suppressed will get you several fps faster than without the can
 
#4
i would agree, i bet it has to do with the magneto sensor distance to the bore axis. may have been too low with the suppressor on and not detecting accurately.
 
#5
If your load was on the edge of pressure w/o the can adding a can will push it over the edge, numbers wise. Not necessarily to the point of bolt lift or other pressure factors.
 
#6
I'll have to double-check my setup; in regard to the possibility of the rounds being over-pressure, that is absolutely a possibility... I'm definitely on the, uh, warmer end of things in that regard.