Suppressors Overbore can confusion

[fireguyty]

So here it goes. I have a DTA rifle, and a QD Ti 338 SAS can. I have had this set up for about a year. I found that the SAS shrinks groups up with my 26" 338 Lapua barrel. With my 22" 308, it seems to leave the accuracy the same.

About 6 months ago, my Sin City bros turned a 6.5 Creedmoor barrel for my DTA. Its 26.5" and crazy accurate. My SAS spreads the accuracy in this barrel bad. So, when I shoot 6.5 I never run suppressed. I kind of figured that this was due to the bore diameter. After all 338 = better, 308 = same, and 6.5 = shit.

The other day, I felt like trying a new shorter tube and my boys turned me one at 22.25". Just like all their work, it shoots bug holes. As an after thought I tried it suppressed. It is just as accurate!

I had initially blamed the problem on the can being so overbore, now I have no idea. Both 6.5 Creedmoors are Benchmark 1-8" 3 groove.

Any ideas?

 

[The Mall Ninja]

Re: Overbore can confusion

Changing the barrel length will change the barrel harmonics, a shorter barrel will be stiffer and will not "whip" as much making your groups tighter.

 

[fireguyty]

Re: Overbore can confusion

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: The Mall Ninja</div><div class="ubbcode-body">Changing the barrel length will change the barrel harmonics, a shorter barrel will be stiffer and will not "whip" as much making your groups tighter.</div></div>

I fully understand shorter is stiffer. However both are medium palma contour which is pretty beefy. Both are equally accurate so far as my shooting and reloading goes unsuppressed. Are you saying that being 4ish inches shorter is enough to counteract the weight of the can?

Please don't interpret my skepticism as being doubtful or disrespectful, I'm just trying to wrap my head around this.

Appreciate the reply,
Ty

 

[JFComfort]

Re: Overbore can confusion

Dane has had a similar experience with his Elite Iron .308 can. Shoots like crap on his 6.5mm Creedmoor match gun (26")but does well on the 20" 6.5 Creedmoor and we need to do some testing with the 16.5" barrel.

I wonder if the weight of the can amplifies barrel whip so it shoot like crap but then again my 6.5mm Creedmoor match gun (26") did well with the Delta P. .308 Brevis so.... Could it have something to do with the gasses?

 

[David Hineline]

Re: Overbore can confusion

I am guessing the thread mount on end of barrel is crooked causing the bullets to skim the end cap deflecting.

 

[SSSamurai]

Re: Overbore can confusion

Did you try a different load? You may have changed the harmonics enough to make that load shoot terribly, but I would bet you could tailor a different load that would shoot well. Bump the charge up or down a bit and see if it tightens up. I do my load development with the can on.

 

[Guest]

Re: Overbore can confusion

C/L of the barrel, matching the C/L of the stack or core, is everything.

 

[Stone842]

Re: Overbore can confusion

What is C/L? Thanks

 

[RollingThunder51]

Re: Overbore can confusion

Center line or, in other words, keeping the center of both the barrel and the armature stack in absolute alignment.

 

[Miles2go]

Re: Overbore can confusion

Another vote for off center line. I bet a nickel your smith won't accept that answer.

 

[D Miller]

Re: Overbore can confusion

A little more back ground info on my 308 can and 65 barrels.



At first my thoughts were a bunk suppressor until we stuck it on a 308 and it produced a .5-.75 moa group with the suppressor and a random load. That abruptly put the bad suppressor theroy to rest.

the 308 can shooting 6.5s has never performed well on any long(24"+)tube.

All of these rifles and barrels are .75moa or less.

-28" 7mm Saum- 1moa, the suppressor opened it 7s groups up slightly but no where near as bad as the 6.5s

-24" Lothar walther heavy var contour- shot like ass suppressed at 2moa+

-26" Rock MTU- still 2moa+

-JFComfort's 6.5 creedmoor- 2+ moa

-26" Rock Rem var- again 2moa+ At this point i threw it in the safe and didnt shoot it again for over a year.

-20" rock varmint it shot just as well suppressed as it did un suppressed much to every ones surprise.

-16.5"- hope to test it this weekend and report back.




While talking with Ty about the suppressors we started scratching our heads as a pattern was emerging. At this point I cant rule anything out from slightly off center to barrel harmonics. However the only thing consistent is my suppressors past poor 6.5mm performance across different barrel manufactures, contours, rifles, work from different shops and finally to DIY work.

 

[MTETM]

Re: Overbore can confusion

I can't help your theory on the barrel length with the 6.5.
I run a SAS 308 can on my 6.5 SLR..it is a Benchmark 1:8 but it is at 27.5 inches and a standard palma. Better than 1/2 MOA elevation to 1000.
The load is off max by at least 2 grains of powder. May be your load is over pressure with the can affecting your accuracy.
I had a load that would shoot great without the can, but it was at top end of pressure, when I tried it with the can, THE group when to hell and all the primers dropped on the ground!
I backed things down and it went to shooting, just a bit slower.

My current load is 142's at 2820...
Hope you get it resolved.