FAQ

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TL;DR: If your barrel is less than 12″ (14.5″ if using a conversion kit) get the lightweight kit (or pistol bundle). If your barrel is 12″ (14.5″ with conversion kit) or longer, get the stainless adjustable (or rifle bundle), unless you are planning to use primarily SV and subsonic, then get the lightweight.  

Generally we recommend the following as a starting point, broken down by barrel length and ammo type:

12-16″ barrel:

High velocity ammo: Stainless adjustable using steel internal weights

Standard velocity ammo: Stainless adjustable using aluminum or steel internal weights, or lightweight adjustable using steel internal weights.

Subsonic ammo: Stainless adjustable using aluminum internal weights or lightweight adjustable using steel internal weights.

8-11.5″ barrel:

High velocity ammo: Stainless adjustable using aluminum internal weights or lightweight adjustable using steel internal weights

Standard velocity ammo: Lightweight adjustable using steel or aluminum internal weights

Subsonic ammo: Lightweight adjustable using steel or aluminum internal weights

4-7″ barrel:

High velocity ammo: Lightweight adjustable using steel or aluminum internal weights

Standard velocity ammo: Lightweight adjustable using aluminum internal weights*

Subsonic ammo: Lightweight adjustable using aluminum internal weights*

*Cycling problems may occur when using subsonic or SV ammo with a very short barrel. Remove the weight if consistent trigger resetting issues are experienced. Short barrels result in HV ammo being subsonic and subsonic ammo being very subsonic.

The weight decreases bolt bounce and reduces bolt velocity, all other things held constant.  This results in reduced or eliminated port pop when shooting suppressed and less fouling in the action both suppressed and unsuppressed.  Eliminating bolt bounce is critical for full auto function.  

Optimized bolt velocity means the powder burns more fully before the case is extracted, reducing fouling, noise and gas blowback to the shooter. It makes the rifle feel smoother, and reduces battering of the bolt carrier and lower receiver (especially when combined with a buffer), and also increases consistency shot to shot with the cartridge in battery longer.

Testing bolt weight function and/or tuning (requires true last round bolt hold open): Choose the lightest configuration (aluminum body, aluminum internal weights), load a single round into the rifle with a magazine and fire (in a safe and legal manner). If the bolt locks back, increase weight in your adjustable bolt weight one step.  Repeat until bolt hold open fails and then reduce one step.  At that reduced weigth, fire at least 10 shots to verify consistency of bolt hold open.

If your rifle is not equipped with a last round bolt hold open that works with the bolt release lever (no, the CMMG/Black Dog mag follower hold open does not count), check for the trigger reset.  Increase weight one step at a time until the trigger fails to reset, then lighten by 2-3 steps. 

If you reach maximum bolt weight and all 10 rounds result in bolt hold open and trigger reset, leave the weight at heaviest configuration.  

TLDR: Deluxe Weight

If using an FRT or a mix of ammo types in semi-auto or barrels less than 12″, the deluxe weight is recommended.

For high velocity ammo only in barrels 12″ or longer, the deluxe weight kit or standard adjustable weight kit.

For standard velocity or subsonic ammo or barrels less than 12″, the deluxe weight kit

There are many variables involved in a blowback system, and for the sake of the majority of this discussion, we’ll assume that bolt mass is held constant (more on this later). Listed roughly in order of significance:

Ammunition: This one’s pretty obvious, the more powerful the ammo, (generally) the more impulse that pushes back on the bolt.

Without getting too far into the weeds on the physics, when a force summed up over time, you get a quantity known as “impulse” (in the weeds: impulse is the integration of the force with respect to time, or the area under the force-time curve). Simplified, if the force is constant, the impulse is force multiplied by time. This why, for example, you can floor your car and get to 60mph in 10 seconds (high force), or you can gently accelerate and get to 60mph in 30 seconds (low force). Either way the impulse is the same, and it resulted in you getting to 60mph, but the forces were different as was the time that that force acted over. A small force acting over a long period of time can result in the same velocity as a large force acting over a short time. Remember about impulse for later.

In the AR22 as in other blowback semi-autos, the impulse is caused by the pressure generated during firing pushing back against the case, and thus pushing on the bolt, causing it to move and cycle. Something like a CCI Velocitor (40gr, 1435fps) has a much higher total impulse than, say, a CCI Quiet-22 (40gr, 710fps). With the same bolt mass, the Velocitor will cause a much higher bolt velocity.

What does this mean for me? It means that at some point, if you use ammo low enough on the power spectrum, your gun will cease to cycle fully or at all. Conversely, if you use high powered ammo, you may get an undesirably high bolt velocity (which is then corrected by adding mass to the bolt…more on this later)

Barrel length: Again, we’re oversimplifying here, but remember impulse and how it gets larger if the force has more time to work? This is why longer barrels lengths result in higher velocities — the force has more time to push on the bullet. Likewise, the bolt will gain more velocity with longer barrels.

What does this mean for me? It means that the longer the barrel, the lower power ammo you can cycle given the same bolt mass. For example a 4.5″ upper may be able to barely cycle federal bulk pack (36gr 1260fps) while a 16″ upper may not only cycle but have an undesirably high bolt velocity (which is then corrected by adding mass to the bolt…more on this later)

Springs: Springs have a smaller effect than you may initially think — at the instant the cartridge is ignited, there are several forces in play. There is the force from the recoil spring and hammer springs that are holding the bolt back, and then there is the force generated when the cartridge ignites. Imagine a minivan stalled on a railroad track with a train quickly approaching. Now imagine that an elephant is standing outside the van pushing on the van in order to try to hold it still when the train hits. That elephant standing there is like the spring — it is are imparting a force on the van that seems pretty large if you don’t consider the train, but compared to the train, the force doesn’t amount to much at all. If you increase the spring power (say by putting a big dodge ram diesel pushing against the minivan, you can counteract some of the force of firing, but it’s still pretty minimal in the scheme of things.

Once the bullet leaves the barrel, however, and the force from the firing goes to zero, and the springs begin slowing the bolt down gradually over the travel of the bolt. Swapping to heavier springs can influence how hard the bolt hits at the rear of travel, but they don’t slow the bolt much initially.

What does this mean for me? It means that unless you’re shooting very low powered ammo that is barely able to cycle the action, you’re not going to see much change with reasonable changed in spring strengths. You’ll probably read on the forums at some point about reduced power hammer springs being needed to cycle with subsonics and/or short barrels, which falls into the “barely cycling” or “almost cycling” category.

Bolt Mass: Finally, we can discuss bolt mass. If all things are held constant, and you add mass, the bolt velocity drops. So adding a BoreBuddy weight results in lower bolt velocity with a given ammo, barrel, and spring combo. Optimizing bolt velocity smooths out the operation of the system and helps with reliability.

What does this mean for me? Added weight and thus optimized bolt velocity means the powder burns more fully before the case is extracted, reducing fouling, noise and gas blowback to the shooter. It makes the rifle feel smoother, and reduces battering of the bolt carrier and lower receiver (especially when combined with a buffer), and also increases consistency shot to shot with the cartridge in battery longer.