DLT 1,646 Posted November 10, 2013 Report Share Posted November 10, 2013 Finally had a chance to test my S 5.45 both with and without the ak74 style muzzle brake I had threaded the barrel for. Well to my surprise, the point of aim changes almost 20 inches over 100 yards. I was stunned. There is no evidence of the bullet striking the brake at any point. I can only figure that this copy of the 74 brake is creating a high pressure zone on the right side of the rifle, causing my rounds to go consistently left. I've noticed that the brakes on my SGL and SLR both have vent holes on the right side, while this cheaper brake does not. I wonder, are those holes there because the Russians saw similar results? Would drilling my cheaper brake in the same general areas correct the issue? Or should I just say screw it and replace it with something like a Tabuk, or AR style brake instead which pretty much just vents everything out into the atmosphere. Opinions and experiences are welcomed. Quote Link to post Share on other sites
Mullet Man 2,114 Posted November 10, 2013 Report Share Posted November 10, 2013 Put real '74 brake on it. 1 Quote Link to post Share on other sites
Matthew Hopkins 1,065 Posted November 10, 2013 Report Share Posted November 10, 2013 (edited) those small staggered holes on real 74 brakes are there for gas to vent out of those holes, to keep the rifle from rising to the right and up in full auto firing. whether it has anything to do with POI, I really, really doubt it. it's the 4 holes that are drilled at slight angles up and down in the front of the brake that vents the gases evenly Edited November 10, 2013 by Matthew Hopkins Quote Link to post Share on other sites
Sim_Player 1,939 Posted November 10, 2013 Report Share Posted November 10, 2013 (edited) Drill holes in the cheap copy. You have nothing to lose. If it doesn't work, replace it. I put a Bulgy 74 FSB and a nice 74 brake in my 5.45 Saiga. Edited November 10, 2013 by Sim_Player Quote Link to post Share on other sites
mancat 2,368 Posted November 10, 2013 Report Share Posted November 10, 2013 Well this is not very common result with other users of the Tapco AK74 style brakes. Maybe something about yours is defective? They are definitely cheezy and less effective than the real thing, but offer some benefit - how much is the question. Also keep in mind that the 14mm threaded copies of the AK-74 brake are really freaking heavy by comparison. They might be heavy enough to change the barrel harmonics in a serious way in some cases. Quote Link to post Share on other sites
Spartacus 1,619 Posted November 10, 2013 Report Share Posted November 10, 2013 I've noticed a significant POI change with/without a typical slant brake too. Quote Link to post Share on other sites
dashowdy 141 Posted November 10, 2013 Report Share Posted November 10, 2013 (edited) 1. is the brake loose and not concentric to the bore. 2. The only way the bullet could be affected would be a strike, the bullet has left the barrel by the time the gas is coming out so it should not be off because of that. 3. Get the real 74 brake even if you just use an adapter to do it, they are 1010% worth it and I did not see the light until I put one on, now I cant live without it,jmho. Edited November 10, 2013 by dashowdy 1 Quote Link to post Share on other sites
sobrenegade 795 Posted November 10, 2013 Report Share Posted November 10, 2013 This may sound stupid, but did you install a crush washer? It's a proven fact that even that will change POI. Probably not, but I thought it could be the culprit. Quote Link to post Share on other sites
Remek 771 Posted November 10, 2013 Report Share Posted November 10, 2013 Interesting discussion. I put a brake on my saiga x39, a '74 type brake with a crush washer. I am noticing the same movement to the left. At the same time, I noticed my front sight seemed to have moved and figured I did it in clamping down to thread the muzzle. I started moving the front sight and trying to get a centered aim, but havent used a rest yet. I need to get this figured out. So, what I gather is that brakes change direction significantly. Correct? Also, crush washers are known to change direction slightly. Correct? Anything else I should be looking at? Quote Link to post Share on other sites
dashowdy 141 Posted November 10, 2013 Report Share Posted November 10, 2013 The consensus seems to be that a little loose is ok but wobbly is not, I always file the back to fit and leave just enough so the brake has some breathing room and have never had issues. I never could get the crush washers to keep it indexed properly the brake would always come loose so I just drilled my sight tower and did a homemade detent pin, got the idea from cobra. Quote Link to post Share on other sites
jdtravers 637 Posted November 10, 2013 Report Share Posted November 10, 2013 If the muzzle brake caused a "Point of Aim" shift, then it must be poking you in the eye somehow. Obviously you mean a "Point of Impact" shift. How does it group at 100 yards? Is it tight or shotgunned? Just wondering if you altered your original front sight during the installation process of the brake. If the sights have not changed and you are using the same ammunition, the ONLY reason for that much of an impact shift is the bullet is skipping off the brake somewhere. Use a flashlight and see if there is a very fine line of copper trace inside the comp/brake. It will just be a bit of discoloration about .020 wide. Crush washers DO NOT cause an impact shift. Don't know who came up with that one, but it is pure BS. Crush washers only help index the brake while maintaining the proper tightness/torque value. Muzzle brakes will not cause a significant point of impact shift if they are installed correctly. Put a bore rod/gauge into the barrel and see if there is enough clearance or if the rod is contacting the brake. This is the same check you would do when installing a suppressor on a rifle or a pistol. You really need to check to ensure there is not a strike on the inside which will destroy a suppressor but only deflect the round in the brake. Jack Checking the clearance of the muzzle brake on a 7mm Sako, using a precision bore rod which is machined for a 7mm bore only. Seperate rod for each caliper. 1 Quote Link to post Share on other sites
Remek 771 Posted November 12, 2013 Report Share Posted November 12, 2013 Thanks JT. Your advice is very much appreciated. For me, the first I found of the point of impact change was after install, and I thought the same about the front sight. I looked at it, and sure enough, it was way off. So I took it home, and realigned it with caliper measuring to be sure it was centered, with the intent to then see what happens and adjust it again at the range. I got to the range (25 yards only, as I was beginning new adjustments). It was shooting way left. I moved it to center, but have to see how it groups, as i was running out of time (also did some skeet and plinking beforehand as I had to get the energy out). I will also be looking into it tonight after work to see about interference inside the rifle. Quote Link to post Share on other sites
DLT 1,646 Posted November 12, 2013 Author Report Share Posted November 12, 2013 I've come to the conclusion that the added weight of the muzzle brake is causing the barrel to whip in an.augmented fashion. There is no evidence of impact on the brake itself. When compared to the standard muzzle brake used in the modern era russian-made rifles this American made break is heavier and attached at the very tip of the barrel. Quote Link to post Share on other sites
mancat 2,368 Posted November 13, 2013 Report Share Posted November 13, 2013 (edited) DLT, if you're going to use the AK-74 brake on a 14mm thread, the best thing to do is use a 14-24mm adapter and use a real 24mm 74 brake, or the 24mm CNC Warrior clone, which is a very close copy. The 14mm copies have no expansion chamber and improperly staggered gas ports.. The expansion chamber is really important for the brake to operate as intended. As I stated before, the 14mm clones are basically muzzle weights, not all that useful. Getting the 24mm device properly indexed without a detend pin is a PITA though.. If I had a 14mm threaded Saiga without a detent, I would just install a birdcage FH myself. Edited November 13, 2013 by mancat Quote Link to post Share on other sites
MLM0358 107 Posted November 13, 2013 Report Share Posted November 13, 2013 Assuming it's not a comp strike, then as JT said, it's most likely a concentricity issue. There are two several permutations The threads on the comp are not concentric with the bore of the comp or the threads on the barrel are not concentric with the bore of the barrel. 1) Shoot the gun and note the POI 2) Rotate the comp 180 degrees and shoot again. If the POI changes, then there is a concentricity issue. Quote Link to post Share on other sites
dashowdy 141 Posted November 13, 2013 Report Share Posted November 13, 2013 Mancat speaks the truth, you have to try it to believe for some folks myself included. make your own detent pin, really not hard. Quote Link to post Share on other sites
DLT 1,646 Posted November 13, 2013 Author Report Share Posted November 13, 2013 Thanks, I think I will try the flash hider option first until I get some extra change and then do a complete swap of the fsb and brake with a Bulgarian one. Quote Link to post Share on other sites
LuPiN8oR 333 Posted November 13, 2013 Report Share Posted November 13, 2013 Assuming it's not a comp strike, then as JT said, it's most likely a concentricity issue. There are two several permutations The threads on the comp are not concentric with the bore of the comp or the threads on the barrel are not concentric with the bore of the barrel. 1) Shoot the gun and note the POI 2) Rotate the comp 180 degrees and shoot again. If the POI changes, then there is a concentricity issue. Thank you so much!!! I am going to try this first on my pap m92 before i try to cant the fsb/gb as i have the same issue when i installed the cnc clone 4pc flash hider! Quote Link to post Share on other sites
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.