First time I have encountered this. Built an 18" upper and the rifle appears to only want to shoot when the suppressor is not mounted. I have used this AAC SPR-M4 on four different rifles/SBR’s and had no issues… comments please.
What do you mean by only wants to shoot when the suppressor is not mounted? Cycling issues, accuracy issues, something else?
Accuracy issues
Repeatable? Or are the shots going everywhere?
Check the torque on the muzzle device
What barrel profile you running?
How about providing some more details so we can help you out?
Sounds like you may need to develop a load for the barrel with the can mounted. If the barrel shoots without the can, then their is probably a load that will make it shoot with the can mounted.
Need more details on the parts. If the rifle shoots well without the can then it’s doubtful that the assembly can be too FUBAR. Based in the scant info Id say either the added weight on the barrel is messing with the harmonics and you’ll need to develop a load for that combo like Markm stated. Another thing might be your MD not being concentric with he bore. Not enough out of whack to make a difference when the projectiles are going through he MD, but add the extra few inches of the can and you could be getting too close to a baffle or endcap. Is this MD the same kind and manufacturer as with all other rifles?
Also… If the can locks up tight/isn’t rattling on the end of the barrel… I think a load can be made for it.
I’m not looking to trash the manufacturer so please don’t take the parts list as an effort to do anything other than for the purpose of this evaluation.
Mega billet set upper and lower.
Mega 18" barrel
AAC 51T miter mount and SPR-M4 suppressor
Giessele HiSpeed match trigger
MI Gen 2 SSI Ultra light
Noveske Switchblock
BCM FA bolt and carrier
Ammunition tried has been 50 grain, 55, 60, 69 & mostly 77 Sierra MK’s with XBR in 1/10 grain increments.
Well off to the range to try one last time before a phone call to Washington state. I’m going to try switching out the bolt carrier group on a wild goose chase.
How is the clearance inside the rail? (the gas block isn’t hitting the hand guard when the barrel flexes right?)
How far off are you on Accuracy??
Have you considered trying some factory ammo? Are you not grouping or is it grouping but you are having a POI shift?
2.5 MOA vs best today was .65 MOA without the can.
Iraqgunz, with all due respect Factory ammo is not of the quality I have proven to load nor does it give the control when attempting to find a barrels node.
More loading this evening…
I do not think you will find the problem with load development.
My experience testing different powders, bullets, and over all length can take a gun shooting 1 inch at 100 yards to maybe 1/2 inch groups.
I do not know what the problem is but its major?
Switchblock sits outside the hand guard… no problems there.
2.5 moa to 0.65 moa just by removing the suppressor… that points at the muzzle device and/or suppressor, right? Can barrel harmonics alone make such a big swing in accuracy?
I wonder if could be that particular mount? The military suppresses longer barrels and I have to wonder if there isn’t some kind of issue with the can/mount interface. I would also contact AAC for some feedback.
I have seen this happen with a thread mount can (Gemtech HVT) which I initially thought to be a handloading issue or an issue of the threads not being cut concentric to the bore. The barrel was cut by a local smith and sent off to adco to be corrected. Adco sent it back stating it was good to go, never did find the problem. The can shoots great with other guns. There has to be an explanation but I havent found it yet, it just works out that way sometimes. I use a KAC NT4 on a half dozen different guns and it shoots great with its loose attachment system on all of them.
Assuming that you’ve tried all the MITER combinations to see if that alleviates things. Not impact?? Does the can lock up tight in the mount or can it wiggle.
If the thing shoots .65moa loud then it should be related to the can. Any sign of bullet contact with the endcap or baffles??
Harmonics can really screw up accuracy, but you should be able to find one combo that works. Have any other powder around to see if that would help??