My time is very limited at this writing, however, I will post our Engineering and Design Considerations of the M14.CA Tension Adjustable Op Rod Guide for your review. Any further questions or tweaks, feel free to call me direct. Thank-you. Frank
The theory behind “free floating” a rifle barrel to improve accuracy seems simple … “If nothing
touches the barrel when it oscillates through the vibration cycle immediately after a shot has been fired [
aka barrel harmonics ] a free floated barrel should be more consistent in returning to the same orientation
for the next shot.” And, as demonstrated on the firing range, with improved consistency in barrel harmonics,
improved accuracy often does occur. A rifle with the receiver properly bedded and held solidly to the stock,
with the barrel “free floated” will often shoot better than it did with some contact between the barrel and the
fore end. This simple theory is well proven in single shot and bolt action rifles.
However, free floating an M14 barrel is not quite as simple. The gas and spring operated semiautomatic
M14 rifle has a very heavy reciprocating mass consisting of the op rod, bolt, spring, and cartridge
all frantically thrashing around under the barrel and inside the receiver. This heavy reciprocating mass can
and usually does have a significant impact on M14 barrel harmonics. And because this heavy reciprocating
mass is working on the barrel to receiver joint, true full length free floating of an M14 barrel could cause
extra flexing, inaccuracy, and potentially even early failures of the receiver. So, the M14 design is better off
if the barrel is only partially “free floated,” and at some point supported rigidly in line with the receiver .
In a conventional wood or fiberglass M14 stock, the point chosen to connect the barrel to the forearm
is at the stock ferrule/barrel band, right behind the gas assembly, at the very tip of the forearm. Bedding the
receiver with precise vertical tension of the tip of the stock forearm to the gas assembly and barrel band, is
the well proven classic method of getting the M14 barrel to vibrate more consistently. Creating more
consistent barrel harmonics through unitizing [ minimizing play ] the gas assembly, and achieving precise
upwards forearm to barrel tension, works ... and it works well … but this is more of an art form, done by
experienced M14 craftsmen on an individual basis on each individual rifle. This method is not suitable for
modern mass production methods.
In theory, solidly connecting the M14 barrel to the forearm closer to the receiver by using a larger,
reinforced, rigidly held, heavy duty op rod guide [ aka “partially free floating the M14 barrel” ] should be a
viable way to minimize M14 barrel oscillations, and/or possibly make the barrel harmonics more consistent
and repeatable. The KISS principle is applied here by eliminating all the many variables and built in play
inherent to using the complicated gas assembly/ barrel band/stock ferrule interface.
Where the new M14.ca op rod guide design differs from other “free floated” M14 op rod guide
designs is that the M14.ca guide is adjustable, to allow for perfect fit with civilian M14 clones. It has the
largest surface bearing area of any ORG. It offers a self-lubricating feature found in no other ORG with
special relief cuts at the front and rear for packing grease. The ORG is quad-locked and is buttressed inside
the Blackfeather “RS” stock like no other and it uses 5 set screws. 3 of these 5 set screws allow you to
maintain the vertical alignment of the ORG prior to installation and the other 2 set screws lock the large,
vertical adjustment screw used for barrel tensioning and accurizing the M14. Our ORG is also pinned using
a tensioned, coiled, stainless spring pin for extra strength. The ORG is seated on a large steel bedding
surface embedded inside the Blackfeather “RS” stock to account for wear in this location.
Note that US GI M14 receivers are held to incredibly tight external dimensions, and will usually fit
the also incredibly precise CNC machined alloy bedding surfaces consistently and properly. But many of the
civilian M14 clones may have receivers that are slightly off from true GI M14 dimensions. With the M14.ca
adjustable tension design, there is no longer any need to shim at the front or the back of the receiver to stock
bedding surfaces to achieve perfect vertical alignment and proper barrel to forearm tension. Vertical/tension
adjustment is now built right in to the new op rod guide.
When adjusted with the standard tension settings recommended, the M14.ca op rod guide has
demonstrated a noticeable improvement in AVERAGE accuracy shot by the same rifle in M14 conventional
type stocks … with average calculated over groups fired with several different brands and weights of .308
WIN and 7.62 NATO spec ammunition. This standard setting uses the adjustability built in to the op rod
guide to adjust vertical alignment of barrel to forearm precisely, even with slightly out of spec receivers, and
then to add some slight DOWNwards tension to preload and stabilize the barrel/forearm connection. This
slight vertical pre-tension is precisely adjustable, and adjustments are repeatable, to achieve the best average
accuracy with most loads.
Once adjusted properly, the pre-tension can be locked in, and if necessary the barreled action can
quickly be removed and replaced in the stock. This quick removal and replacement feature is unique to the
M14.ca design, and allows multiple “upper” barreled receiver assemblies to be swapped into the same stock,
with minimal disruption to zero.
For those who want to experiment further, barrel to forearm vertical tension is now adjustable, so that
the system can be fine tuned for best accuracy with an individual load. Like the Browning Boss muzzle
weight device, the M14.ca adjustable op rod guide can be fine tuned to create more consistent barrel
oscillation and return to zero for a specific load. But unlike the boss, which is attached at the muzzle, the
M14.ca op rod guide works further back on the M14 barrel. With either system barrel harmonics can be
made more consistent for that one specific load, and accuracy with that specific load can improve
significantly.
The M14.ca Blackfeather “RS” alloy stock was designed to tremendously improve the balance, fast
handling and ergonomics of the M14 rifle. Because we have no control over the all too many variables in
INDIVIDUAL M14 rifles, we can make no accuracy guarantees for the Blackfeather stock. However, in
high round count range testing, we demonstrated that a near standard M14 clone [ tested in five different
conventional stocks ] went from a best group of 1 3/8”, to a best group of 7/8” after fitting and tuning in the
BF stock.
And these were FIVE shot 100 yd groups.
The new Blackfeather “RS” op rod guide (ORG) is thicker, wider, and protrudes down further than a
standard M14 ORG. Both sides of the ORG and the insides of the alloy locating bosses inside the forearm
are precision fit and finely finished. They are designed to minimize rotation … but to still allow for easy
removal and replacement of the barreled M14 action into the Blackfeather stock, and also still allow smooth,
precisely adjustable vertical travel for tension tuning.
The thickness has been increased to provide maximum linear bearing length against the
approximately 5/8” long barrel boss on a standard weight M14 barrel. This increased linear bearing,
combined with the precisely sized .802” ID hole in the ORG [ which is fits snugly around the .800” OD of an
in spec barrel boss ] minimizes any potential wobble brought about by the back and forth motion of the op
rod inside the guide.
The ORG width has also been increased significantly, and has been precisely matched to the two
massive alloy locating bosses inside the fore arm of the Blackfeather stock. The interface between these
oversized parts is loose enough to allow smooth and precise vertical adjustment and the quick removal and
replacement of the barreled receiver into the Blackfeather stock, while still large enough and tight enough to
minimise rotation of the ORG around the barrel…which is an all too common accuracy robbing condition
with many M14 type rifles.
End
. Also I think that we tend to shoot surplus ammo which tends to produce larger group sizes that would tend to hide the influence of the ORG with smaller round counts.
