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Posted: 1/31/2006 3:16:07 PM EDT
i have picked up a jpoint, and watched their CD that came with the product..

they stated something that I always thought was a 'myth'

Upper to lower "play" has no affect on accuracy, correct?

According to JP, it does...?
Link Posted: 1/31/2006 3:46:54 PM EDT
Two things come to mind:

1. To what extent does it? If you are down to your final 0.05 MOA of possible accuracy improvement not attributable to the shooter, the upper to lower play may contribute to that minute accuracy increase. Most here can't take advantage of that, anyway. It's similiar to top fuel drag racing. Every little thing that you can do to get another 10th of a horsepower out of that motor and make it stick to the pavement makes a difference. For the average racer, these things seem silly. For the average driver, they seem ludicrous.

2. JP has products to sell to fix this problem and will have a case for why you need them, whether it's true or not. Personally, I believe it's true in the minutest aspect of accuracy and not practical except for the most accomplished of shooters. For your average plinker/blaster/armchair commando, upper to lower play has no impact on accuracy.

As always, YMMV.
Link Posted: 1/31/2006 5:24:36 PM EDT

Originally Posted By mongo001:
Two things come to mind:

1. To what extent does it? If you are down to your final 0.05 MOA of possible accuracy improvement not attributable to the shooter, the upper to lower play may contribute to that minute accuracy increase. Most here can't take advantage of that, anyway. It's similiar to top fuel drag racing. Every little thing that you can do to get another 10th of a horsepower out of that motor and make it stick to the pavement makes a difference. For the average racer, these things seem silly. For the average driver, they seem ludicrous.

2. JP has products to sell to fix this problem and will have a case for why you need them, whether it's true or not. Personally, I believe it's true in the minutest aspect of accuracy and not practical except for the most accomplished of shooters. For your average plinker/blaster/armchair commando, upper to lower play has no impact on accuracy.

As always, YMMV.




that was i always had in the back of my mind...

i didn't realize J&P was such a 'match grade' oriented company until after the video..
Link Posted: 1/31/2006 8:56:38 PM EDT
As someone mentioned to me, the upper holds the sights//scope and barrel, so won't make a direct accuracy difference on upper/lower fit, but will make a difference for consistency in how you address those sights/scope.
Link Posted: 2/1/2006 5:15:12 AM EDT

Originally Posted By NightOwl:
As someone mentioned to me, the upper holds the sights//scope and barrel, so won't make a direct accuracy difference on upper/lower fit, but will make a difference for consistency in how you address those sights/scope.




very good point also...
Link Posted: 2/1/2006 8:14:34 AM EDT

Originally Posted By NightOwl:
As someone mentioned to me, the upper holds the sights//scope and barrel, so won't make a direct accuracy difference on upper/lower fit, but will make a difference for consistency in how you address those sights/scope.



+1

Link Posted: 2/1/2006 10:57:06 AM EDT

Originally Posted By mongo001:
Two things come to mind:

1. To what extent does it? If you are down to your final 0.05 MOA of possible accuracy improvement not attributable to the shooter, the upper to lower play may contribute to that minute accuracy increase. Most here can't take advantage of that, anyway. It's similiar to top fuel drag racing. Every little thing that you can do to get another 10th of a horsepower out of that motor and make it stick to the pavement makes a difference. For the average racer, these things seem silly. For the average driver, they seem ludicrous.

2. JP has products to sell to fix this problem and will have a case for why you need them, whether it's true or not. Personally, I believe it's true in the minutest aspect of accuracy and not practical except for the most accomplished of shooters. For your average plinker/blaster/armchair commando, upper to lower play has no impact on accuracy.

As always, YMMV.



What he said.
Link Posted: 2/1/2006 12:55:03 PM EDT
Could it be that the major concern is the shift that may occur between the upper and lower from when the shot is taken and when the bullet leaves the barrel?


You have the gun sighted on your target, you have it locked in via the stock and lower.
If the upper moves from its postion against the lower after you fire the shot, but before the bullet leaves the barrel, then the POI will change from your POA.

The amount of change between the POI and the POA will depend gretaly on the amount of movement between that upper and lower. Angular mathematics can tell us that a small change at the point of origin can result is a great change over a long distant. But in this case, the amount of change or play is likely to be insignifcant.

What if you were to take some of that rubberized tool paint and pull a small layer on the meeting surfaces between the upper and lower? That stuff would probably take up any up down slack.

If you have front to back play/slack, that rubberized paint may also do the trick at the rear of the receiver, but it may not last long with repeated opening and closing. Maybe try an accuwedge.
JP had screw/tighting pins, but I wonder with they would induce wear on the ting holes of the lower.

Maybe some plasti-gauge could tell you the amount of play present.

Link Posted: 2/1/2006 3:29:57 PM EDT

Originally Posted By NightOwl:
As someone mentioned to me, the upper holds the sights//scope and barrel, so won't make a direct accuracy difference on upper/lower fit, but will make a difference for consistency in how you address those sights/scope.



Repeatable accuracy is affected by the upper to lower fit. The way the hammer (attached to the lower) strikes the firing pin (in the upper), the way the bolt carrier (in the upper) transitions into and out of the buffer tube (attached to the lower), the way the next round is loaded from the magazine (attached to the lower) into the barrel (attached to the upper) after firing a shot. All these things theoretically affect accuracy because the play between the upper and lower shifts the movements from shot to shot, its not consistant in a sloppy fit. Consistancy breeds accuracy.

However as someone mentioned these changes are so minute that 99.9999999% of firearm shooters, even target shooters, wont be affected by it.

But in theory yes fit affects accuracy.
Link Posted: 2/4/2006 12:08:27 AM EDT
[Last Edit: 2/4/2006 12:09:44 AM EDT by AR15barrels]
Link Posted: 2/4/2006 5:14:36 AM EDT

Originally Posted By AR15barrels:
By the way, how many here know what plastigauge is?



Link Posted: 2/4/2006 9:27:30 AM EDT
Link Posted: 2/4/2006 11:59:29 PM EDT
Just reading a post and what do I see........platigauge??! There be motorsports folk here, or at least engine builders. Yep I know what it is we go through it by the case!
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