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Normal Topic Does your firearm fit correctly? Part eight. (Read 526 times)
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Does your firearm fit correctly? Part eight.
Dec 10th, 2018 at 2:33am
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I have had a few questions so will clarify the last part of my last post. The idea is that now you have worked out exactly where on the shoulder the butt should be positioned for maximum comfort and minimum slippage/movement. If you are having trouble with this, try getting an associate to assist.

Don a dark cotton top. Adopt the desired firing position with a firearm that you can shoot all day comfortably and accurately.  Have your associate use Taylors Chalk to mark out (trace) the butt onto the top.  This allows you to clearly visualise the angles involved once you dismount the firearm and help you understand where you need to get to. While the firearm is mounted in the firing position, take a measurement of the angle on the Y-axis of the rifle butt while is firmly mounted to the shoulder in the normal firing position to allow it to be plotted on graph paper.

At the same time use a tape measure to record at 10mm intervals from heel to toe how much gap there is between butt plate and body tissue. This will vary from 0mm to sometimes as much as 20mm or even more. Again this can be plotted onto graph paper (or into a CAD drawing) to “map” the natural body curve.

Now to the handgrip.

Start by adopting the desired firing position while holding an imaginary firearm. Observe the Y-Axis angle of the palm of your hand. I will guarantee it is anything but vertical! In most cases, the bottom (outside edge) of the palm will be angled significantly away from the handgrip (outwards) and in the opposite direction to the angle of the butt in the shoulder.

This typically creates an undesirable need for conscious action and effort by the firer to hold the handgrip perfectly vertical, thus breaking the cardinal rule: The sight picture should be achieved and maintained without any conscious effort by the firer”. To be fair the fact that the Butt and Handgrip angels tend to oppose each other there is a degree of mitigation. However, this does not change the fact that the fit is poor and in turn, control is reduced requiring an increase in conscious effort to avoid cant. Not good!

In the absence of an adjustable handgrip (perhaps 95%of examples), the matter is corrected by “trimming and packing” the grip to match and the hand shape and angle to align “centre” the grip axis within the naturally positioned hand axis.

I always try to avoid trimming if possible and instead pack the opposite side to the trim requirement is to shift the centre of the contact point as required. Usually, around 3 – 5mm packing is required. I use adhesive sheets of Sorbothane as they are impervious to anything in nature or any cleaning maintenance chemicals, offer a non-slip vibration reducing point of contact and are easily trimmed with scissors and can be layered/removed as required. They do not mark or damage expensive stocks.

At this time, consideration of the trigger finger to trigger shoe alignment must be given. In an ideal world, the centre of the ball of the trigger finger should naturally rest in the centre of the trigger shoe with an almost 90° bend in the finger. The contact area should be minimal.  The firer should be 100% relaxed and not needing to exercise any control to achieve this condition.

In most cases, there is no provision to adjust the trigger position or distance from handgrip to trigger shoe. There can be a temptation to address this by adjusting the trigger take up or pull weight settings. This is not ultimately useful as the problem is just being shifted to a different area and not corrected. Where there is an Anschutz style trigger bar, carefully consider the trade-off between trigger shoe location and take up travel/pull weight as these are not always properly synced and you can end up with very poor trigger feel or weighting.

My typical solution is to pack (use Sorbothane) the grip to bring the entire hand back or forward and align the finger with the trigger. This is more witchcraft like slow, meticulous fiddling (usually exasperating as well) and requires considerable trial and error to find the best result. However, once the correct result is achieved the vast majority of trigger operation sins will be eliminated as torquing, tugging, slapping etc. will be eliminated (mostly) by good fit and alignment. With a well-fitted firearm, cant is eliminated and so the resultant effort to correct cant does not exist to cause trigger finger action misalignment. A good fit also corrects any reaching, crimping or any other physical gymnastics required to simulate a good fit. In short, firer accuracy moves closer to matching firearm accuracy potential.

Be aware that the correct fit can feel quite uncomfortable for a start. This is because the body has adapted and learned that the firearm feels a certain way and when this changes the interpretation is that of discomfort. The critical thing is to have assistance during this time and you are able to have external confirmation that the fit is correct.

Please be aware that this process will take time. It will cause doubt and likely require responsible administration to both firer and associates bottled oral lubricant (I find Glen Fiddich Winter Phoenix or XO Hennessey with a Siglo Six cigar work well to foster relaxed contemplation) while on any one of many breaks away to allow heads to clear. In other words, take frequent overnight breaks from the task. Take your time, do this in little bites with much consideration at each step of the way (more so if you are actually trimming material off as it is hard to put back)

In my next post, I will start on Cast, Comb and sight position.
  

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