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Discussion Starter #1
Hey all, thanks in advance for any advice you may give!

I'm brand new to both this forum, and the Ruger PC Carbine. Let me start by saying I LOVE this gun. I've got about 300 rounds through it at this point without a single issue other than the follwing, and the features are totally awesome.

I'm shooting Remington 115gr. HTP hollow points, and my groups have been unbelievably tight for a pistol caliber firearm. I have a Sight Mark Wolverine red dot, high mounted with a peep-through mount for the ghost ring sights as a backup. Kick *** setup.

Immediately after buying the rifle and red dot, I went to the range, sighted it in on a bipod at 25 and then 50 yards, was nailing tacks with both the optic and the irons. Feeling like a badass, I took it home, and went to about 15 yards from a standing position and was WAAAY off with the red dot - like 3 MOA low in elevation. Windage was good. Upon further investigation, the irons were true in both shooting configurations. Thinking the sight was loosened, I checked it, but it was tight as a drum (I wrenched it down at the range, it was going nowhere).

I didn't make any optic adjustments, but I then went out to 25 yards at home, set up a table, and with the bipod, I was on my mark like a champ - both irons and optic - without having adjusted anything. As soon as I stand up and fire without upward pressure on the forend from a bipod, I'm a good 3MOA low. As soon as I sit down and put pressure on the forend from the bipod, I'm on my mark. Again, iron sights remain consistently zeroed regardless of my shooting position.

I'm inclined to not blame the red dot, as the groupings themselves are super tight - averaging less than 3/4" at 25 yards. But consistently, they are the same amount off without pressure on the forend.

This is a truck gun for me, so I resighted at 15 (and then 25) yards from a standing position and left it. Now when standing, both the optic and the irons are putting me dead-nuts. When I sit and shoot from the bipod, I'm 3MOA high. Interesting and weird thing is, the iron sights (which on the PC Carbine are on the barrel side of the takedown) remained consistent regardless... very fishy.

I think I've been scientific enough about it at this point to make the following determination - the barrel side of the takedown is being pushed up to throw the impact point high when I'm stabilizing the rifle on a bipod. When simply standing, the pressure is less (just the pressure of my hand on the forend) and the impact point is lower.

Does anyone have any insight on this? Any flaws in my logic here? Not to sound full of myself but I'm a damn good shot and 3MOA is quite a severe discrepancy - Is it possible to tighten the forend to the receiver where they click together so this "travel" is eliminated? Is it even that or am I missing something?

Thanks SO MUCH everyone!
 

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Are you sure that your take-down adjustment ring is tight? I adjust it tight enough to be able to just reassemble the carbine after take-down.

Yes, a bipod can put enough upward pressure on the barrel to affect POI just as a sling can put enough downward pressure on the barrel to do the same in the opposite direction. But that does sound like a bit much.
 

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Just my opinion...if something were loose it wouldn't be that consistent. I'm inclined to think it has something to do with recoil. Much the same as a 300 gr. bullet impacting the target higher than a 200 gr. bullet.The gun resting on the bi pod has less downward force..
 

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Discussion Starter #5
Good thinking! I have a 10/22 takedown and have never had an issue, but I've never attempted to adjust the ring. You think finger tight or should I carefully wrench it down?

Thanks!
 

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Discussion Starter #6
Thank you for the reply bud. The recoil thought is a good one, perhaps its altering the POI moreso than the bipod. I was thinking about that after I wrote the post, the force of my hand supporting the forend can't be too much greater than the force of the bipod holding it... I'm not leaning on it or resting my beer on it hahaha
 

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Thank you for the reply bud. The recoil thought is a good one, perhaps its altering the POI moreso than the bipod. I was thinking about that after I wrote the post, the force of my hand supporting the forend can't be too much greater than the force of the bipod holding it... I'm not leaning on it or resting my beer on it hahaha
It would really depend on where you position your support hand when you shoot offhand. If you are like me and position your support hand back at or near the magazine well, which is the balance point of the rifle, there will be much less upward force on the fore-end of the stock. When I shoot the PCC offhand, half of my hand is under the receiver and only half under the barrel portion of the stock. If you mounted a bipod on the short Picatinny rail segment at the forward tip of the stock, the lever arm acting on the stock will be much longer. Since the barrel of the PCC is not free-floated in the stock, any upward pressure on the stock will be transmitted to the barrel.

The fact that the iron sights still shoot to POA whereas using the RDS, which is mounted on the receiver shoots 3 MOA lower than your POA when using the bipod, strongly suggests that the problem is due to a change in alignment between the receiver and the barrel. This would not affect the POI using the iron sights since they are both mounted on the barrel.

It doesn't take much misalignment to result in a 3 MOA change in POI. Three MOA is equivalent to a change in barrel alignment of only .05 degrees. Since the tangent of .05 degrees is .00087 if the distance between the receiver-mounted optic and the tip of the muzzle is 18" this is equivalent to only .00087 x 18" = .016" which is less than 4/10 of a millimeter up or down at the muzzle end of the barrel.

The barrel adjustment knob on the PCC clicks as you adjust it. What I do is take down the carbine and adjust (tighten) the adjustment knob one click at a time until I can no longer apply enough torque with my hands to reassemble the carbine. At that point I back it off one click.

I suppose the force applied to the barrel at the tip of the stock fore-end by a bipod mounted there could somehow change the barrel harmonics in such a way as to alter POI somewhat, but 3 MOA would seem to be way more than expected.
 

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It would really depend on where you position your support hand when you shoot offhand. If you are like me and position your support hand back at or near the magazine well, which is the balance point of the rifle, there will be much less upward force on the fore-end of the stock. When I shoot the PCC offhand, half of my hand is under the receiver and only half under the barrel portion of the stock. If you mounted a bipod on the short Picatinny rail segment at the forward tip of the stock, the lever arm acting on the stock will be much longer. Since the barrel of the PCC is not free-floated in the stock, any upward pressure on the stock will be transmitted to the barrel.

The fact that the iron sights still shoot to POA whereas using the RDS, which is mounted on the receiver shoots 3 MOA lower than your POA when using the bipod, strongly suggests that the problem is due to a change in alignment between the receiver and the barrel. This would not affect the POI using the iron sights since they are both mounted on the barrel.

It doesn't take much misalignment to result in a 3 MOA change in POI. Three MOA is equivalent to a change in barrel alignment of only .05 degrees. Since the tangent of .05 degrees is .00087 if the distance between the receiver-mounted optic and the tip of the muzzle is 18" this is equivalent to only .00087 x 18" = .016" which is less than 4/10 of a millimeter.

The barrel adjustment knob on the PCC clicks as you adjust it. What I do is take down the carbine and adjust (tighten) the adjustment knob one click at a time until I can no longer apply enough torque with my hands to reassemble the carbine. At that point I back it off one click.

I suppose the force applied to the barrel at the tip of the stock fore-end by a bipod mounted there could somehow change the barrel harmonics in such a way as to alter POI somewhat, but 3 MOA would seem to be way more than expected.
That's how I adjusted mine too. My gun, the ring was not even close new. Mater of fact I had a hard time getting the adjusting ring to move at all. i didn't want to mark it up, but I had to do a little prying on it to get the ring to move. I put a cheap red dot and change it out with a scope sometimes. Both are right on the money even when I change them around.
 
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