Group difference suppressed/un-suppressed

[razorsharptokill]

I have had great success with my PSA 20" grendel with my 7.62 AAC can on it and my 130 gr. TGK and TAC. Sub half MOA. I loaded some up using Match Rifle, shot them with A2 flash hider and no adjustment to gas. HORRIBLE groups! I couldn't find the right sized wrench to adjust. Any clues as to what size it is? POI shift was about 6" low and 2" left which is no problem. I'm making this my backup gun for Wy. Mule deer and want to save the 1.5lbs of weight. Do you think it was the gas? The harmonics/Gas? Very surprised this bullet shot shot so poorly. Rest was ROCK solid. I shot some 123 AMAX through it to confirm it wasn't just a bad load combo. Same results.

 

[archp625]

Tagging in because I am curious but Dang man, thank you for your service!!

 

[JoeDirt]

Theres a lot involved with point of aim shift with cans. I think most of it has to do with barrel harmonics. All my guns shoot better with a can on. A few I cannot shoot at all without my can. Other than "tuning" your gun, ie changing breaks, adding weight to the barrel and/or finding a more forgiving load you might be out of luck.

 

[BRTreedogs]

I just put my aac sdn762 on my 6.5 and it hated it as well. Groups opened way up.

 

[Rover31]

Putting a weight on the end of the barrel, you are changing the harmonics.

 

[chutinlead]

You might check alignment. If all your cans make it group worse, your muzzle threads might be slight out of alignment and bullets coming too close to the can.

 

[razorsharptokill]

To clarify, this was without the can. It has shot exceptionally well with it attached. Going to confirm with known load and shoot it suppressed just to verify.

 

[tx_shooter]

To clarify, this was without the can. It has shot exceptionally well with it attached. Going to confirm with known load and shoot it suppressed just to verify.

I was surprised to see such good results with 130gr loads in your Grendel. My JP 6.5 Grendel is a dime stacker with 123gr loads with and without my Energetic Arms Vox suppressor. The only difference is POI shift.

That said - what profile & length is your barrel? A lighter profile will be more sensitive to weight changes. Might be a good excuse to buy an ultra light can.


Just one Jarhead's thoughts to another. I'm a boot compared to your years though - 2002 - 2006 @ FAST Co and then Golf Co 2/4 .

 

[razorsharptokill]

20" medium profile I would say. 1/8 twist. All of the Hornady 120ish weight bullets shoot well. Oddly the 129 SST was not as impressively accurate. Going to back up and shoot the known load, with suppressor to eliminate any unknown variables. I was unable to adjust the gas due to no wrench for the set screw. Very difficult to extract brass. Basically a single shot rifle at that point.

 

[BRTreedogs]

I'm confused on what you are asking.
It shoots the 130 suppressed well?
It shoot the 123 non suppressed poorly?
Does it shoot the 123 suppressed well?

It won't extract the 123s? Suppressed or not?
If you have the gas turned down for the Suppressor it will not give it enough to cycle non Suppressed

You want to save weight by ditching the Suppressor? Why are you switching bullets?

 

[razorsharptokill]

Ok... previously.. the known 130 gr. TAC load shoots lights out accurate with and without suppressor with only a POI shift. Groups with and without suppressor, and other loads, are generally good. New but VERY similar load with same 130 gr bullet, unsuppressed and no adjustment to gas system, shot horribly. Understandably the gun malfunctions due to the gas difference.

Just curious if the gas AND the removal of the suppressor weight is causing the poor accuracy. Variables here are the new load combined with the removal of the suppressor. Going to go back to verify known load WITH suppressor, then shoot new load also with suppressor. Apples to apples.

 

[BRTreedogs]

My guess is your cycling issues are gas related.

123 issues are twist rate. If you have a fast twisted barrel you may be spinning the lighter bullets to hard.
Are the bullets similar style? Aka both boat tail etc? That all plays a part.
Some rifles just don't like certain bullets. It could be anything.
You need to narrow down the variables, switch one thing at a time like you are planning to do.

 

[Weldor]

Have you chronographed the 2 loads? I had similar issues with a 224 valk. barrel made by blank. The loads were close and only small velocity change , but that barrel did not like it suppressed or not.

 

[razorsharptokill]

Groups were better today shooting suppressed but not mind blowing, Upper end of each 130 gr TGK load are 2400-2500. The later being the Match Rifle. Groups were better but not as stellar as the previously pictured 5 shot group with TAC and 130 TGK. 120 gr bullets still shoot acceptably and several are MOA or less at 300 yards so cant ask much more than that. Going to shoot some 550 yard groups with a few handloads and some factory tomorrow. Best group today was a factory 123 gr AMAX.