In order for any moderator to perform at its best, you must get the fitment correct and establish a cleaning regime that suits your shooting frequency.
If not, you will have a badly fitted and sometimes dangerous moderator and suffer the consequences of moderator failure long before its sell-by date. It constantly amazes me that some people never clean their rifles, let alone any ancillary equipment – they are just stacking up trouble for the future.
Regarding correct fitment, do not be dissuaded from a proper threading job just because you cannot afford it. Most of the cheaper threading jobs can leave your moderator either unsecured or misaligned – and certainly can be detrimental to accuracy.
Threading and alignment
Problems occur when threading jobs are incorrectly carried out.
To achieve a proper thread on a barrel muzzle, you have to consider that you need to keep the moderator aligned with the bore axis and not the outside diameter of the barrel. Why?
Well, some rifle bores do not run exactly true through the barrel and so a thread cut square to the outside diameter will often have the moderator canted off in one direction, causing the potential problem of a bullet, on exiting the bore, having a higher probability of contacting one of the internal moderator’s baffles, with disastrous consequences.
This is particularly relevant with the new trend for tighter and tighter baffle dimensions – smaller apertures through which the bullet passes to maximise noise reduction. When you get a barrel threaded, make sure the gunsmith understands proper alignment.
Also, if the crown of the barrel has been machined (common in barrel-reduction cases), check it has been recrowned properly. Again, I have seen threads that are good but the crown still has rough saw marks. No rifle in this state will shoot, believe me. Check, too, the thread has no residual cutting swarf and that all the sharp edges are taken off.
Undercut and size
Another important feature is the thread is undercut at its base, allowing the moderator to sit square to the face of the barrel, with proper and equal contact.
If not, the moderator will have a tendency to want to lean or tension to one side, again very non-beneficial and dangerous. This next point may seem simple, but you should ensure the gunsmith cuts the correct thread size to match your own moderator.
There are many thread size options open to the potential moderator virgin, but I always choose the largest that can be cut on the barrel diameter while maintaining enough shoulder for the moderator to butt up to.
You can choose to go for a coarser thread pitch (ie, ½ UNF 20Tpi instead of ½ UNF 28Tpi), but a coarser pitch requires less turning of the moderator to take it off. Many moderators come with metric threads, like the M17x1, that suit a larger barrel diameter and many possess a mounting shoulder to align the moderator to the barrel face.
This is all fine as long as the area is kept clean and not allowed to corrode. Once cut, ask to have the newly threaded sections reblued, otherwise corrosion will start sooner than you think. At the same time, have a protective thread cap made so the threads are protected when the moderator is not fitted.
Snug, but not too snug
A thread should have a snug fit to the moderator, but not so tight you exert any real force. It should engage the first section and glide down the threads using a single hand. The contact with the muzzle shoulders, if cut square, is enough to keep it from unscrewing and ensures perfect alignment to the bore.
This factor is just as important for a muzzle-mounted moderator as it is for an over-the-barrel model. In fact, with moderators that sleeve down the barrel, the rear supporting bush can also be a contentious issue.
If you fit an over-the-barrel moderator to your rifle and look at the gap at the rear of the moderator with the bush removed, you should see a perfect concentric equal diameter between it and the outside diameter of the bore. If you do not, then the thread is on the skew, so when you fit the rear bush and tighten the moderator fully, the barrel will be tensioned between the muzzle and this point, as the moderator tries to straighten the misalignment.
This is not good for the rifle and certainly detrimental to accuracy. If there is proper alignment, then a tight rear bush is beneficial; if not, a couple of thou clearance would be better suited.
I know this may all sound a bit much, but you can ruin a good rifle very simply and quickly by having a bad threading job done.