Scope mount adjustment question

Scope mount adjustment question

Joined: February 9th, 2014, 3:56 am

July 27th, 2014, 9:43 pm #1

I was going to post this on the main page but since you guys have a vast knowledge of scopes and the scope rifle combo in question is being prepared for an FT match next weekend I figure it would be in my best interest to post my question here. Next weekend I will be shooting in a neighborhood FT fun match. One of the rules is that the rifle cost less than $300. Not a big deal for my neighbors as they all have crap that cost less than $300. I only have one rifle that fits the description. A HW30S I got from PA back in January for $283 out the door. I recently put a scope on it with some UTG quick disconnect mounts. I wanted the quick disconnect mounts as it has great open sights and I use this rifle to teach my 9 year old daughter how to shoot. I scoped it for kids that come to my FT matches in Granbury, TX in case they show up with an open site, plastic junk gun they can use my HW30 instead. Today I went out to see if my little rifle was sighted in. I found a great pellet for it today JSB Exact RS 7.33gr. Now the question starts. I shot a 10 round group at 20 yards with said pellet that was at the most a 1/4" hole outside to outside. It was right in the bullseye. So for fun and for research before my match next Saturday I shot at an FT target out at 35 yards. My intent was to see how much approx. hold over I would need. The pellet did drop as to be expected but it made a nice group around 3" left. I adjusted the scope accordingly and commenced to knocking the target down with every shot. Before I left the range I shot another group at 20 to see what effect I had from adjusting the scope to the right. Of course at 20yds it was shooting 1/4-1/2" to the right. I assume this is a scope mount issue that will require shimming or something. I figured I would get some advice from the experts. I am, buy the way, left handed if that make a difference. Thanks,
Craig
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Joined: January 1st, 2012, 11:50 pm

July 27th, 2014, 9:58 pm #2

Loosen the scope mount caps and rotate your scope a few degrees CW. The vertical line of the reticle should intersect the bore.

And/or, you might be canting the rifle when holding it. A bubble level mounted on the rifle can help with that.
Last edited by Scotchmo1957 on July 29th, 2014, 12:03 am, edited 1 time in total.
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Joined: September 7th, 2001, 3:52 am

July 27th, 2014, 10:24 pm #3

I was going to post this on the main page but since you guys have a vast knowledge of scopes and the scope rifle combo in question is being prepared for an FT match next weekend I figure it would be in my best interest to post my question here. Next weekend I will be shooting in a neighborhood FT fun match. One of the rules is that the rifle cost less than $300. Not a big deal for my neighbors as they all have crap that cost less than $300. I only have one rifle that fits the description. A HW30S I got from PA back in January for $283 out the door. I recently put a scope on it with some UTG quick disconnect mounts. I wanted the quick disconnect mounts as it has great open sights and I use this rifle to teach my 9 year old daughter how to shoot. I scoped it for kids that come to my FT matches in Granbury, TX in case they show up with an open site, plastic junk gun they can use my HW30 instead. Today I went out to see if my little rifle was sighted in. I found a great pellet for it today JSB Exact RS 7.33gr. Now the question starts. I shot a 10 round group at 20 yards with said pellet that was at the most a 1/4" hole outside to outside. It was right in the bullseye. So for fun and for research before my match next Saturday I shot at an FT target out at 35 yards. My intent was to see how much approx. hold over I would need. The pellet did drop as to be expected but it made a nice group around 3" left. I adjusted the scope accordingly and commenced to knocking the target down with every shot. Before I left the range I shot another group at 20 to see what effect I had from adjusting the scope to the right. Of course at 20yds it was shooting 1/4-1/2" to the right. I assume this is a scope mount issue that will require shimming or something. I figured I would get some advice from the experts. I am, buy the way, left handed if that make a difference. Thanks,
Craig
Your mounts may not be centering the scope over the receiver, a common problem with mismatched mounts and scope grooves (11mm mismatched to 3/8", for instance).
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Joined: February 9th, 2014, 3:56 am

July 27th, 2014, 10:37 pm #4

Well I liked Scott's diagnosis better. You could be right though, I remember when I bought the mounts they were for 11mm - 3/8" reciever grooves. Kind of generic. I may need to see if I can adjust the screws to bring back in alignment or just ditch them and get some BKL self centering mounts. I will muddle through it next Saturday until I have time to figure out. At least I know what it is doing. I am a Kentucky windage shooter anyway. I just guess where I should aim shot to shot and hope for the best. No mill dots here. Typically it is just hold over/hold under. Now I get to add wind age into the mix. Should be fun.
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Joined: June 30th, 2011, 11:13 pm

July 28th, 2014, 5:25 pm #5

I was going to post this on the main page but since you guys have a vast knowledge of scopes and the scope rifle combo in question is being prepared for an FT match next weekend I figure it would be in my best interest to post my question here. Next weekend I will be shooting in a neighborhood FT fun match. One of the rules is that the rifle cost less than $300. Not a big deal for my neighbors as they all have crap that cost less than $300. I only have one rifle that fits the description. A HW30S I got from PA back in January for $283 out the door. I recently put a scope on it with some UTG quick disconnect mounts. I wanted the quick disconnect mounts as it has great open sights and I use this rifle to teach my 9 year old daughter how to shoot. I scoped it for kids that come to my FT matches in Granbury, TX in case they show up with an open site, plastic junk gun they can use my HW30 instead. Today I went out to see if my little rifle was sighted in. I found a great pellet for it today JSB Exact RS 7.33gr. Now the question starts. I shot a 10 round group at 20 yards with said pellet that was at the most a 1/4" hole outside to outside. It was right in the bullseye. So for fun and for research before my match next Saturday I shot at an FT target out at 35 yards. My intent was to see how much approx. hold over I would need. The pellet did drop as to be expected but it made a nice group around 3" left. I adjusted the scope accordingly and commenced to knocking the target down with every shot. Before I left the range I shot another group at 20 to see what effect I had from adjusting the scope to the right. Of course at 20yds it was shooting 1/4-1/2" to the right. I assume this is a scope mount issue that will require shimming or something. I figured I would get some advice from the experts. I am, buy the way, left handed if that make a difference. Thanks,
Craig
I am setting up a rifle for my first FT match. The POI is right on in the 20-30 yard range, but close shots hit a wee bit left and 40+ yard shots are near 3/4" off to the right. Since my rifle has the front mounting block separate from the breech mount (AA s200), I am guessing a slight skew of that front block might be causing the alignment issue.

The BTFA Scope Setup Manual indicate that this issue is not much of a problem http://www.fekete-moro.hu/bfta-setup-ma ... en.php#352). I guess you halve the difference and change your POA depending upon the distance. Being anal, I want to correct the alignment problem so I have one less factor to consider on each shot. I have considered shimming or adjustable mounts.

I look forward to input from forum members to your question as it may help me choose the best method to get my scope aligned more accurately.
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Joined: December 30th, 2008, 6:16 pm

July 28th, 2014, 5:32 pm #6

Take the scope and mounts off the rifle, and remove the action from the stock (if needed). Then loosen the set screw on the forward mounting block, but keeping some tension. Upturn the action, and place it on a perfectly flat surface, like a granite sink top. Push down slightly to level the block with the breech. Pick up the rifle and gradually tighten the set screw. If the forward block moves again, start over...

If this doesn't work, then repeat the above, but remove the forward mount from the barrel... and turn it around. Reinstall and relevel as above.
Last edited by MB-BOB on July 28th, 2014, 5:36 pm, edited 1 time in total.
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Joined: June 30th, 2011, 11:13 pm

July 28th, 2014, 6:22 pm #7

Going to try that this afternoon.
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Joined: January 1st, 2012, 11:50 pm

July 28th, 2014, 7:25 pm #8

I was going to post this on the main page but since you guys have a vast knowledge of scopes and the scope rifle combo in question is being prepared for an FT match next weekend I figure it would be in my best interest to post my question here. Next weekend I will be shooting in a neighborhood FT fun match. One of the rules is that the rifle cost less than $300. Not a big deal for my neighbors as they all have crap that cost less than $300. I only have one rifle that fits the description. A HW30S I got from PA back in January for $283 out the door. I recently put a scope on it with some UTG quick disconnect mounts. I wanted the quick disconnect mounts as it has great open sights and I use this rifle to teach my 9 year old daughter how to shoot. I scoped it for kids that come to my FT matches in Granbury, TX in case they show up with an open site, plastic junk gun they can use my HW30 instead. Today I went out to see if my little rifle was sighted in. I found a great pellet for it today JSB Exact RS 7.33gr. Now the question starts. I shot a 10 round group at 20 yards with said pellet that was at the most a 1/4" hole outside to outside. It was right in the bullseye. So for fun and for research before my match next Saturday I shot at an FT target out at 35 yards. My intent was to see how much approx. hold over I would need. The pellet did drop as to be expected but it made a nice group around 3" left. I adjusted the scope accordingly and commenced to knocking the target down with every shot. Before I left the range I shot another group at 20 to see what effect I had from adjusting the scope to the right. Of course at 20yds it was shooting 1/4-1/2" to the right. I assume this is a scope mount issue that will require shimming or something. I figured I would get some advice from the experts. I am, buy the way, left handed if that make a difference. Thanks,
Craig
Edit: I sometimes use a mirror to align the reticle and look back into the rifle bore. I made some corrections below with the following assumptions, all views are through the eyepiece end of the scope, not the objective. Any further reference to left, right, CW and CCW is as viewed through the eyepiece.

Ron suggested mismatched mounts might be the problem. It's really the same problem. The mismatched mounts can throw off the scope rotation in relation to the bore. In either case, it can be corrected by rotating the scope into alignment.

This issue has come up a number of times, so I drew up a diagram to illustrate the problem.

I show both a scope mounted level and a receiver mounted level. You only need one. Scope mounted levels are usually adjustable. Receiver mounted levels are usually not adjustable. The receiver level will work if you have well centered mounts. The scope level can work either way. I use one or the other depending on the rifle and mounts. But I prefer a scope level as it can correctly compensate for imperfect mounts.



Diagram 1A shows a rifle with scope cant. The mounts are centered, but the scope is improperly rotated. The scope mounted level is correctly aligned with the scope reticle but the scope/reticle assembly is rotated such that it does not intersect the bore. This is an easy problem to diagnose. If the rifle is sighted in at the apex, close shots and far shots that require holdover would be hitting to the right in line of the canted reticle.

Diagram 1B shows the same rifle with the scope rotated into correct alignment. Either type of bubble level can be used with this setup when in the field. The sight is aligned correctly for all distances.

Diagram 2A shows a rifle with rifle cant AND scope cant. The mounts are "mismatched". As shown, any shots requiring holdover will hit to the right and any shots on the downward part of the trajectory will fall to the left.

Diagram 2B shows the same rifle with the scope correctly rotated to eliminate the scope cant. The rifle is aligned with the rifle mounted level. That won't work with the offset mounts as it causes the intersect line to be canted (rifle cant). In this instance, shots all the way out to the apex will be seem OK, but the very far shots will be falling to the left.

Diagram 2C shows the same rifle leveled according to the correctly mounted scope. The receiver mounted level cannot be used. The rifle stock looks canted. But that does not matter as long as the scope/receiver assembly is vertical. The sight is aligned correctly for all distances.

The two important points:

1) The vertical line of the reticle should intersect the bore.

2) The reticle must be held level when shooting.

The scope mounts can be centered or mismatched, either is just as accurate if you follow those two points.
Last edited by Scotchmo1957 on July 29th, 2014, 12:03 am, edited 1 time in total.
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Joined: January 1st, 2012, 11:50 pm

July 28th, 2014, 7:44 pm #9

I am setting up a rifle for my first FT match. The POI is right on in the 20-30 yard range, but close shots hit a wee bit left and 40+ yard shots are near 3/4" off to the right. Since my rifle has the front mounting block separate from the breech mount (AA s200), I am guessing a slight skew of that front block might be causing the alignment issue.

The BTFA Scope Setup Manual indicate that this issue is not much of a problem http://www.fekete-moro.hu/bfta-setup-ma ... en.php#352). I guess you halve the difference and change your POA depending upon the distance. Being anal, I want to correct the alignment problem so I have one less factor to consider on each shot. I have considered shimming or adjustable mounts.

I look forward to input from forum members to your question as it may help me choose the best method to get my scope aligned more accurately.
Original diagram:


Corrected diagram:


Edit: It's tricky. I think that I misdiagnosed the scope cant direction. As a standard, lets assume all views are through the eyepiece, not from the objective. The original TOP diagram would cause the close shots to be right and the far shots to be even farther right. When viewed through the eyepiece, the second diagram is probably how yours is currently set:

Assuming no wind. Assuming no pellet spiraling. Assuming, you have a scope level or are attempting to hold level:

1) Your scope is rotated CCW in relation to the bore. That causes any hold over (close) shots to hit left. It would also cause any long holdover shots to hit left, except when:

2) Your gun is also canted CW and that causes the long shots to fall to farther to the right, which can override the left adjustment caused by the scope cant.

It gets tricky when trying to diagnose combined cant errors.
Last edited by Scotchmo1957 on July 28th, 2014, 11:43 pm, edited 1 time in total.
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Joined: September 14th, 2011, 12:50 am

July 28th, 2014, 8:11 pm #10

Edit: I sometimes use a mirror to align the reticle and look back into the rifle bore. I made some corrections below with the following assumptions, all views are through the eyepiece end of the scope, not the objective. Any further reference to left, right, CW and CCW is as viewed through the eyepiece.

Ron suggested mismatched mounts might be the problem. It's really the same problem. The mismatched mounts can throw off the scope rotation in relation to the bore. In either case, it can be corrected by rotating the scope into alignment.

This issue has come up a number of times, so I drew up a diagram to illustrate the problem.

I show both a scope mounted level and a receiver mounted level. You only need one. Scope mounted levels are usually adjustable. Receiver mounted levels are usually not adjustable. The receiver level will work if you have well centered mounts. The scope level can work either way. I use one or the other depending on the rifle and mounts. But I prefer a scope level as it can correctly compensate for imperfect mounts.



Diagram 1A shows a rifle with scope cant. The mounts are centered, but the scope is improperly rotated. The scope mounted level is correctly aligned with the scope reticle but the scope/reticle assembly is rotated such that it does not intersect the bore. This is an easy problem to diagnose. If the rifle is sighted in at the apex, close shots and far shots that require holdover would be hitting to the right in line of the canted reticle.

Diagram 1B shows the same rifle with the scope rotated into correct alignment. Either type of bubble level can be used with this setup when in the field. The sight is aligned correctly for all distances.

Diagram 2A shows a rifle with rifle cant AND scope cant. The mounts are "mismatched". As shown, any shots requiring holdover will hit to the right and any shots on the downward part of the trajectory will fall to the left.

Diagram 2B shows the same rifle with the scope correctly rotated to eliminate the scope cant. The rifle is aligned with the rifle mounted level. That won't work with the offset mounts as it causes the intersect line to be canted (rifle cant). In this instance, shots all the way out to the apex will be seem OK, but the very far shots will be falling to the left.

Diagram 2C shows the same rifle leveled according to the correctly mounted scope. The receiver mounted level cannot be used. The rifle stock looks canted. But that does not matter as long as the scope/receiver assembly is vertical. The sight is aligned correctly for all distances.

The two important points:

1) The vertical line of the reticle should intersect the bore.

2) The reticle must be held level when shooting.

The scope mounts can be centered or mismatched, either is just as accurate if you follow those two points.
Great post !!! Should be added as a sticky to the FT forum :). NFT
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