It took me many years of owning AR style rifles before I decided to purchase a bayonet. Finally, a year or so ago, I made the investment and purchased an Ontario M9 Bayonet because one of my review rifles (Ruger AR-556) included bayonet lugs integral with the front sight and I wanted to check out this feature with a bayonet. Once I installed the bayonet on this rifle and prior to getting an adapter, it didn't take long for me to understand there was an issue. The 16" barrel on the Ruger rifle was longer than the 14.5" barrel length that was really intended for use with a carbine length gas system. This meant that the barrel ring on the bayonet would ride sloppily on the barrel instead of the larger diameter of the flash suppressor. In my mind, this made the use of a bayonet on this rifle not practical because I couldn't live with it rattling around. This next photo gives you a good idea on the fit issue.
Fortunately, the folks over at Tacticool22 read my review and suggested one of their products to remedy this issue. Tacticool22 offers an AR-15 Pattern Rifle Bayonet Barrel Adapter for $18.95 that should solve this issue. This adapter is basically an aluminum cup that fits over the threads of your muzzle device and rests on the shoulder at the end of the barrel. The adapter is held securely in place with the muzzle device. The features of this adapter (according to Tacticool22) are as follows.
Since this adapter functions primarily as a bushing, the actual aluminum alloy type is not critical. The part I received seemed simple, yet was well made and I was pleased with the anodized finish.
The adapter measured 1.58" in length with a 1.53" depth on the inside. The outside diameter measured 0.86" and the inside diameter measured 0.76", The hole measured 0.51". A key point here is that your barrel outside diameter should be 0.75" or less for this device to work. Also, if you are thinking about using this device on a .30 caliber barrel, then the adapter will not work because it will not fit over the 5/8" threads.
The adapter weighed in at 0.4 ounces which I consider to be negligible and has no perceived effect on the feel or function of the rifle.
To install the adapter, you first remove your existing muzzle device. Next, you place the device over the barrel and then install a new crush washer if your muzzle device requires clocking or just tighten your muzzle device as required. It might be a good idea to install a crush washer anyway when you install your muzzle device because these washers will also work like a torque limiter preventing you from over-torqueing the muzzle device. Tacticool22 also sells AR 1/2" Style Crush Washers in packs of five for $12. Also, I like to always use a little high temperature grease on the threads to help ensure I can remove the muzzle device if needed in the future. If for some reason your barrel diameter is less that 0.75", you can use some paper to wrap around the barrel to help you keep the adapter centered when tightening your muzzle device. Wrap the paper in layers to create the required diameter for the temporary paper bushing used during installation and then slide the paper out of the adapter when installed.
Once I got the adapter installed on my Rugger AR-556 and mounted my bayonet, I realized quickly that something was not right. The adapter did not extend back far enough to function as a bushing around the barrel in this area for the bayonet barrel ring.
I grabbed one of my other AR rifles, pulled the flash suppressor and started studying differences. The distance between the shoulder of the barrel (not including the threads) and the front of the bayonet lug on my Ruger AR-556 measured about 6.22" while that same distance on another rifle measured 5.88". This 0.34" difference was just enough to prevent this adapter from working on my Ruger rifle. You can see this difference in length between these two rifles below. I have to assume that the combination of Ruger's custom front sight and 16.1" barrel length (not 16.0") might have been the culprit, but honestly I'm not 100% sure.
This was a great data point for those wanting to purchase this adapter for their rifle. If you are interested in this adapter, you should take a measurement to ensure the distance between the edge of the bayonet lug and shoulder of the barrel (not including the threaded portion) measures 6.00" or less. This 6.00" or less dimension assumes your bayonet has a distance greater than 4.92" measured from the back of the bayonet to the back edge of the barrel ring which happened to be the dimension for my Ontario M9 Bayonet. Next measure your bayonet to confirm the length.
When you have a rifle that has a standard bayonet lug to barrel shoulder dimension, the Tacticool22 bayonet adapter works great. In the photo below, you can see how the adapter extends rearward beyond the bayonet barrel ring.
Depending on the finish of your barrel and muzzle device, the bayonet adapter's black anodized finish may or may not match the finish on these other components. Personally, I don't see this as an issue, but it is worth pointing out.
The Tacticool22 AR-15 Bayonet Barrel Adapter seems to work well as long as you verify some basic dimensions first to ensure that your rifle doesn't have an odd length of barrel forward of the bayonet lug. After mounting this adapter on one of my rifles and being very pleased with the results, this adapter will become a standard accessory for me in the future if the rifle has a bayonet lug and the dimensions work out properly.
After communicating with Tacticool22, they let me know that they will have a second generation bayonet adapter out that is 0.35" longer which will address the issue I had in this review with one of my rifles. Make sure you select the correct adapter when ordering one for your rifle.