Reloading for better accuracy with a suppressor

[HAZORD]

So my paperwork finally came through on Monday for a Gemtech 308 Quicksand suppressor. This model attaches by inserting the muzzle brake and giving the suppressor a 1/4 turn to lock it behind two large lugs on the muzzle brake.

I took it out to shoot on Tuesday and had mixed results. Put it on my EBR (Standard Model M1A), checked concentricity with the bore, and fired it, and the accuracy went from 1-1/2" groups to 5 or 6 inch groups that were 12 inches below nonsuppressed POA. I was shooting both LC ball ammo and reloads using 42.5gr 4895 in a new Winchester case behind a SMK 168). Needless to say I wasn't very happy with the decrease in accuracy by a factor of 4 and the massive zero shift.

I tried the suppressor on my Rem700 Varmint 223 and had 3 holes touching (very happy with that) with a 1 inch drop in zero shift. Also tried it on my AR-15 carbine with no decrease in accuracy.

So I called Gemtech on Wednesday. They wanted me to bring it in, since they are only 30 miles from my home. They looked at it, verified the concentricity and that there were no baffle strikes, and basically told me that they recommend factory gold medal match, and that I should try to find a handload that the rifle/suppressor combo like.

So, I'm wondering if anyone out there has experienced similar problems, and if anyone can suggest loads to work in an M1A with suppressor, that might have a better harmonic to repair my accuracy back to normal at least?

 

[mdmp5]

How are you mounting it on your m1a? No way your ammo is to blame

 

[neiltus]

Looking forward to follow ups on this.

I know, from my M14/M1As that doing anything to the front of the rifle can effect groups. One rifle of mine shifts seriously every time I clean the gas cylinder, even if I am careful about re-torque weight. I don't have experience with EBR types.

I would look at the mount, then consider if you did any cleanings or pulling from stock, after that I would consider weight on the front of the barrel-is it a standard weight barrel?

 

[mdmp5]

There are not many options for mounting a suppressor on an M1a, and I don't know if they all work well. Personally, I have a Vortex flash suppressor mounted on mine, and a Fisher suppressor that mounts on the Vortex. I honestly don't know much about the accuracy loss or gain, because I've only shot it a few times with the can on and I didn't take measurements or anything. I can tell you that the fit of the suppressor on the Vortex is loose. The can rotates back and forth a small bit. This is the way the can is supposed to fit, according to Fisher, and supposedly doesn't affect accuracy.

As far as the other methods, I honestly don't know how well the adapters work.

 

[scotharr]

The mounting system is the problem. You'll have to find a more secure way to mount it. This is a common problem with quick-attach mounting systems.

 

[pudge]

I have a yh QA 30 cal and i have found that in the 308 it helped to index the can to flash hider ,put a mark on each, so u put it on the same way every time
Then i found weighing brass tighten up group very much especially with autos i only use lapa now
My bolt gun with 18" shoots 1/2 or better with the fps of bullets staying within 12 pfs of each other
Auto was 1/2 gun with black hills before can and now with my loads with can between 1/2- 1". And the fps will vary 30fps or more with all the same loads.

 

[mtrmn]

I have the YHM QD 762 Ti. My largest POI shift on any of the several ARs I've used it on was about 1.5" at 100 yd. Some of the guns have no noticeable POI shift, but a couple of them I haven't shot enough with the can to really prove anything. But NONE of the POI's were 12" low unless I was using subs vs full house loads.

One of my AR's was a ban type that I had to get the barrel threaded on. When I installed the adapter/flash hider and torqued it down, it pulled the POI almost 2 feet off normal 100 yd zero. When I loosened the adapter the zero returned to normal. I did NOT try it with the suppressor. I sent the barrel to YHM and got them to cut/thread the barrel again and it came back right. Just a 19" bbl rather than a 20". Just my experience, not saying there's anything wrong with yours. I know nothing about Gemtech and their attachment methods.

 

[HAZORD]

The Gemtech quick attach mount uses a muzzle brake that has two large lugs that protrude from it. One lug is larger than the other, which indexes the suppressor to the same rotational location each time. The suppressor attaches just like the bolt in a rifle locks into position. You push the suppressor on over the lugs, and there is an internal spring that you push against, and when it is on far enough, you can rotate the suppressor to lock the lugs of the muzzle brake behind a flange on the suppressor. The spring internal to the suppressor puts pressure on the lugs to prevent rotation that would allow the suppressor to detach on its own. There is room for the suppressor to wobble around a little on the muzzle brake.

 

[mtrmn]

I DID have to modify my reloads a bit when I got my suppressor to get my groups back due (I assume) to a change in the harmonics caused by the extra weight of the suppressor. But never had such a drastic change in group size or POI as that reported by the OP on his M1A.

Since he has good results with other platforms I would have to lean towards a problem with the M1A platform/suppressor compatability, not ammo. In other words, it's entirely possible that the outside influence on barrel harmonics or bedding etc from the added weight of the suppressor is the root of the problem. With such extreme changes in POI and group size, I would think that the problem would be something basic or obvious (to an M1A expert)like a loose barrel or something.

My YHM attaches via acme/buttress type square threads on the flash hider and screws down against a spring loaded ratcheting lock plate. I have found that I can thread mine on tight and then back it off 1 "click" on the ratchet, which allows the suppressor to wobble a bit. This prevents the suppressor from seizing and the wobble has no measureable effect on target or sound suppression ("measured" by ears only). So MY suppressor wobbling or not wobbling doesn't affect MY accuracy results on paper. YMMV

Disclaimer: I am NOT an expert on any of this. I'm simply relaying my experiences in the hopes that the added info may ignite a spark of inspiration that could lead to a solution for the OP.

 

[scotharr]

The Gemtech quick attach mount uses a muzzle brake that has two large lugs that protrude from it. O... The spring internal to the suppressor puts pressure on the lugs to prevent rotation that would allow the suppressor to detach on its own. There is room for the suppressor to wobble around a little on the muzzle brake.

This is why you will never get a high degree of precision from a suppressor mount of this type. That ability to wobble greatly enlarges your group size. Get a properly threaded can if you want best accuracy. Then again, we are already talking about an M1a....not exactly the most accurate rifle anyway.

 

[leid]

OP,
It sounds like the Gemtech folks checked the alignment of the QD mount/can with your bore. It takes less than three thousands runout at the barrel crown of an M14 to cause a strike on an AAC 762SD can end cap. Carbon buildup must be completely removed from the barrel crown before installing the QD mount for proper indexing. After assembly, I check bore alignment with a polished steel dowel to verify alignment. I do get impact shift with the can installed but LC M80/M852/M118LR ammo groups fine suppressed or unsuppressed. All that said, an M14 barrel flexes quite a bit when fired. Barrel harmonics with the can installed will probably be different. Bullet shift is only a couple inches at 100yds. with my rifle but the AAC can screws on the QD mount very tight with no discernible movement at all. If you feel movement in yours, it sounds like an end cap/baffle strike waiting to happen IMO. Best talk to Gemtech some more. Good luck!

Watch the flexing at the flash suppressor:

M1A Match Rifle 7 62 - YouTube

This is what approx. 0.0028" runout on the M14 muzzle crown looks like at the suppressor end cap: a bullet would occasionally just barely scrub the end cap yielding "shotgun" group size. You might have a fine group going only to have the next round go wild. Sound familiar, OP? Make absolutely certain of your bore alignment.



The black marker leads to what the end cap looked like after several dozen bullet scrubs. Light scrubs like this can be hard to detect so look very closely:



Older model AAC 762SD works good, lasts long time:

 

[HAZORD]

Leid,

Thanks for the photos and info. When I watched Gemtech check the fit of my suppressor, the rod they used was well centered in the opening of the suppressor. The can does not fit tightly on the muzzle brake. It has some play, but we moved the can around, and there was still clearance between the rod in the barrel and the edge of the opening in the can. I was thinking that I was getting hits on the can, but we didn't see any marks. After seeing your photos, I will now look more closely.

To tell the truth, I'm not really very happy with this problem. As I said, it works great with 223, but why should someone have to pay 308 can prices for one to use on a 223? I didn't like the sloppiness of the can on the muzzle brake when I first tried it out. Of course the "seller" said it would be OK, and we called Gemtech and they said they needed the clearance for temperature expansion.

I'm seriously considering using a center punch to stipple the outside of the muzzle brake to increase its diameter and then turn it down, so I can get a tighter close sliding fit with the inside of the can, but before I do that, I'm going to post my problem on one of the suppressor forums and see what experience people are having with this. I can't be the first person with a Gemtech Quicksand that has had this problem.

 

[leid]

HAZORD,
Doc Phil Dater used to be the best suppressor guru I knew of. See if he is still around. My experience is that if a quality can does not increase accuracy with proper bore alignment, I start looking for issues with the barrel threads/mount. Also look at getting a ported or adjustable gas plug for your M14 & a BFA Breech Shield will keep gas out of your face. Good luck!

 

[HAZORD]

Leid,

I already have an adjustable gas plug on the EBR.