Friday, February 22, 2008

Why does my rifle shift its aim point? - Part 1

by B.B. Pelletier

Before I start, Pyramyd Air is closing out the Walther RedStorm pistol and is offering them at a terrific savings. This will be your last time to get this pistol.

This will be a series that explores one of the most interesting and confusing conundrums of airgunning - the point of impact shift. I hear about it frequently and the complaint sounds like this. "I get my rifle sighted in, then come back to it in a day or so, only to find that the point of impact has shifted. If I sight-in again, when I come back to the gun, the POI has shifted once more. The gun is very accurate, but why can't I keep the groups in the same place?"

Here is a second variation of this same theme. "I'll shoot a group of several shots and then suddenly the gun throws two or three shots wide of the group. Sometimes if I continue the shots will go back to the first group but other times, the new POI is where all the pellets will land."

I actually did a report on the problems of scope shift that you might want to read, though this series will be detailed in far greater depth.

This series is prompted by a reader comment that came in while I was at the SHOT Show. Hegshen said "I own an AirForce Condor and have been experiencing POI shifts that I can't solve. I've tried everything and have sent my rifle back to AF for them to inspect.

Hegshen and I then had a lengthy discussion about his problem, which you can read in the comments section of the third installment of the Benjamin Discovery report. Normally I would play 20 questions with the person until something I said triggered the right neurons and he did something that corrected the situation. But this time was different.

I happened to be at the AirForce plant testing the final prototype of the new Diana scope base (it works well, by the way), and I asked if they had any guns in for repair. They had two, and one of them was from a guy with the same problem as Hegshen, so I knew I had found his gun. This time, I figured I would test the problem rifle myself, and see first-hand if the gun was shifting its POI. What's more, I would document the entire process so you could see what I go through when analyzing a problem like this one. POI shift is one of the most common problems airgunners have today, so what we do here should really help a lot of you.

Step one - clean the barrel!
I did all the repairs at AirForce when I worked there, and whenever guns came in with complaints of poor accuracy, I always cleaned the barrel first thing. Of all the guns I ever tested for accuracy, I only found one barrel that was bad. It had a poor choke and I couldn't get it to shoot no matter what I did. But dozens of other rifles shot perfectly. I didn't take the time to test a rifle before cleaning because no one cares what it was doing before it got fixed and time is money. So, cleaning the barrel is always the first step, unless the barrel cannot be cleaned due to gun construction.

I've already described how to clean a barrel, and there are several posts in which I list the materials and steps to do the job right, but this time I took pictures to show you what I'm talking about. Here we go.


The gun, letter describing the problem, Dewey cleaning rod tipped with a brand-new brass brush and a jar of JB Non-Embedding Bore Cleaning Compound.



This is how much JB paste I put on the brass brush.


The cleaning rod and brush meet with a lot of resistance when I first try to push them through the bore. Part of this - maybe most of it - is due to the friction of the brand new brush, and some is due to the crud in the barrel. I don't know until the session is over - after the brush has passed through the length of the barrel 20 times in both directions - how dirty the barrel really is. A lot of dirt and some lead flakes usually come out of the barrel.


When the brush first enters the barrel, a lot of JB Paste is scraped off at the breech. When I pull the rod back out, I'll apply this paste to the brush again.


Stroke after stroke, the brush is passed through the length of the barrel. Whenever possible, I try to hold the Dewey cleaning rod by the ball bearing handle to let the rod rotate and the brush to follow the rifling. However, for the first 14 strokes, there's too much resistance in this particular barrel to allow that. Either this was a very dirty barrel or this brush was very large.


After all the cleaning, the brush looks like this. This was not a dirty barrel, after all. This much crud is normal from an average barrel.


Following the cleaning, the rod is wiped clean and the brush is exchanged for a cleaning jag. Clean dry patches are then pushed through the bore in one direction, only (breech to muzzle). Continue pushing clean dry patches through until the come out clean. In this case, I was having difficulty getting the final residue out of the bore, so I wet a patch with Otis bore cleaner and pushed it through to soften the residue. The job was easier to finish after that.


Here are the cleaning patches I passed through the bore to remove all the residue from the JB Compound. They start in the upper left corner and proceed to the right. On the lower row of patches, the first (left) one had two drops of Otis Ultra Bore Solvent on it to soften the remaining residue. Otis is airgun-friendly and won't harm the seals. Note that there are still a few marks on the final patches. They'll never go away. This barrel is clean.


Now that the barrel is clean, I'll mount the scope and start testing next time.

48 Comments:

At February 22, 2008 8:48 AM, Anonymous Anonymous said...

Can you clean the Benjamin pump rifles using that method? I know that their barrels are brass and not as tough as steel barrels.

Al in CT

 
At February 22, 2008 8:50 AM, Blogger B.B. Pelletier said...

Al in CT,

No, you don't want to clean a brass barrel with this method. However, brass is less likely to get dirty and the velocity of guns with brass barrels is so low that they don't lead up.

So just shoot the gun and don't worry about cleaning it.

B.B.

 
At February 22, 2008 9:33 AM, Anonymous Anonymous said...

BB
I could have written those first paragraphs myself last night. Looking foreward to this series.
MCA

 
At February 22, 2008 9:52 AM, Blogger b cyrus said...

i am looking for info on scoping a disy 753 to silhouette shoot with using a 6 power adjustiable objective any opinions?

 
At February 22, 2008 9:54 AM, Anonymous Anonymous said...

BB,Hope your feeling better.You"ve been asked this before,but it was awhile back.Was wondering if you have anymore feedback on the custom Charliedatuna trigger mods for the Gamo CFX,and how hard are they to install for the average person.Thanks.

 
At February 22, 2008 9:58 AM, Blogger B.B. Pelletier said...

B Cyrus,

Consider the Bug Buster 2.

B.B.

 
At February 22, 2008 10:02 AM, Anonymous JP said...

Here's a question: can you use a firearm kit in air (.22), or would you be better to get an airgun-specific kit for your air rifle. With .177, I guess you would HAVE to get an airgun kit, but would a matching caliber firearm kit be oversize or too harsh? Also, how do you clean bolt actions that have no breach access, such as a Daisy 880: do you recommend disassembly, or would muzzle access be good enough? JP

 
At February 22, 2008 10:09 AM, Anonymous JP said...

BB, off topic. Just how long have you been in the [business? hobby?] of air rifles? What piqued your interest in this over firearms? I know what got me started (and I must say, your blog nurtured it very much), but why would others get into "...racing go-karts instead of racing cars...." I had a bb gun as a kid, but never been this far in until recently. JP

 
At February 22, 2008 10:16 AM, Blogger B.B. Pelletier said...

CF-X,

You must have missed my posts on that, or you think the CF-X has a different trigger than other Gamos?

http://www.pyramydair.com/blog/2007/12/testing-gamo-whisper-part-6-trigger-job.html

Although it may have an anti-beartrap lever, the trigger on the CF-X should be the same. So the installation should be the same.

B.B.

 
At February 22, 2008 10:18 AM, Anonymous Anonymous said...

About CharlieDaTuna's trigger. It is very easy to install, takes about 15 mins. I have two of his triggers and they are a MUST with any Gamo. Charlie includes thorough instruction sheet with every trigger he ships, you can also view the instructions on his website. It's the best $32 you can invest in an air rifle.

Chris

 
At February 22, 2008 10:21 AM, Blogger B.B. Pelletier said...

JP,

I don't buy cleaning kits, as a rule, though I do own some. I buy separate rods and brushes.

The .177 brushes are looser in .177 airgun barrels, and the .22 brushes are slightly tighter. You won't notice the difference in either case.

I would never clean a Daisy 880 because it goes too slow to get dirty. In an HW77, that does shoot fast enough to lead up, I use lubricated pure-lead pellets.

B.B.

 
At February 22, 2008 11:04 AM, Blogger B.B. Pelletier said...

JP,

Like most folks, I was a hobby airgunner since the early 1950s. When Air Rifle Headquarters was active they educated me and Dr. Beeman gave me the graduate course.

But why do I WRITE about airguns? Because very few others do. When my airgun subscription was cancelled I became angry and my wife suggested that I start a newsletter. I never claimed to know everything about airguns (still don't) but I have picked up a few things along the way.

You have gone as far as you have partly because there are places that support your interest. 20 years ago that couldn't be said.

B.B.

B.B.

 
At February 22, 2008 11:08 AM, Anonymous scott298 said...

B.B.--Scott298 reporting in. Upon getting my gun back from Umarex-by the way every stock screw was never tightened-I cleaned my gun just as you have described above. I put a brush thru the rifle using the brush and the non-embedding bore cleaning compound doing 20 strokes in both directions and re=applying the compound as it piled up at the breech. Next I soaked a patch with a cleaner-degreasser and It only took 2 patches for them to come out clean. I held the bore up to a light -looked thru the breech an all seemed fine-did I miss a step or do something wrong. This was the 1st time I used a wire brush and the compound on the gun. The rod and brush are the rws brand. Also I met little resistance when the brush 1st entered the breech and I had on a heck more of compound that what you are showing.Thanks-Scott298

 
At February 22, 2008 12:56 PM, Blogger Ozark said...

BB -
Thanks for the detailed pictures - it's great for us who haven't tried this cleaning paste yet.

Ozark

PS - this is your reminder for a how-to on bench shooting.

 
At February 22, 2008 1:17 PM, Anonymous Anonymous said...

B.B.&Chris,Thanks for the info. on the Gamo trigger mod.Went back to your post BB and installing it seems pretty simple.

 
At February 22, 2008 2:29 PM, Anonymous nate in mass said...

Hi BB,
The talk yeaterday of oiling pellets got me thinking, should I be oiling mine? I dont know if youve written about this before, but I would be interested in learning about why you oil, and in what applications you should do it. Also any bennifits or drawbacks it may have. Again i dont know if youve already done this, if you have please direct me to the page. Thanks

Nate in Mass

 
At February 22, 2008 2:32 PM, Anonymous .22 multi-shot said...

BB,

Thanks for the pictures and filling in a few details with the cleaning procedure!

.22 multi-shot

 
At February 22, 2008 3:04 PM, Anonymous nate in mass said...

Sorry
I just read the rest of yesterdays comments. Probly should have read that first.

Nate in Mass

 
At February 22, 2008 3:07 PM, Anonymous Anonymous said...

B.B.
How do you recommend cleaning rifles and pistols when you cannot run a rod through the breech, such as under lever/side levers. CO2 guns, many pcp and ssp guns? If cleaned from the muzzle, then the paste will end up in the breech; is that a problem? With larger caliber firearms it is often not possible to reverse a brush or patch once in the bore, so if the breech is not longer than the brush I foresee a serious problem but don’t know the solution. Not cleaning is an option, but surely the guns may have rough bores or lead buildup. What do you suggest?

Thanks,
Farmer

.

 
At February 22, 2008 4:02 PM, Blogger B.B. Pelletier said...

Scott298,

I can't say why you felt so little resistence, except to say it's not normal. Could you have used the wrong caliber brush? But if it's a .177, that would be impossible.

Maybe RWS brushes are undersized.

You can't look through the bore to tell if it's dirty. You have to run a pact through. A shiny bore can give you a dirty patch.

B.B.

 
At February 22, 2008 4:09 PM, Blogger B.B. Pelletier said...

Farmer,

Guns that have to be cleaned from the muzzle are a problem. That's why I keep all my used brushes after cleaning breakbarrels. I search for one that doesn't stick when reversed. Or I can sometimes find a short bruch that can be reversed in the loading port - but that's rare.

A pull-through brush will be very short and the next-to-last resort.

The final resort is to clean from the breech when the rifle is disassembled. I never take one apart just to clean it, but when it's apart is a great opportunity that shouldn't be passed up.

Of course I sometimes don't clean them at all!

B.B.

 
At February 22, 2008 6:00 PM, Blogger waynew said...

BB,
You mentioned in an earlier blog regarding scope shift that a temperature change can affect POI. Like Hegshen, sometimes I will get a shift of POI of about an 3/4" at 30 yards. My gun will consistently hit the new POI.

Like heghen, I am confused about the whole thing. Is it possible that a temperature change of 15 degrees F is the cause? How much will temperature variation affect POI?

Thankyou,
Wayne

 
At February 22, 2008 6:09 PM, Blogger ajvenom said...

Thanks for the wilson / Taurus comparison. I sold my S&W .357/.38 revolver many years ago. If I were to get another handgun, a good 1911 .45 acp model is all I'd ever get. I've drooled over the Wilson CQB (close quarter battle) at the shop everytime I've walked by it. My question is do you have any knowledge on the Wilson KZ-45(tactical safety) handguns and how they would compare?

 
At February 22, 2008 6:11 PM, Blogger waynew said...

Oh yeah,
It is an rws 350 shooting JSB Exacts.

wayne

 
At February 22, 2008 6:14 PM, Blogger B.B. Pelletier said...

Wayne,

I can'
t give you amounts of shift, but yes, a temperture change does affect poi.

In field target I have been in a fall match when the temp dropped by 30 degrees in an hour and everyone's scope had to be recalibrated. It was fun to watch all the high-tech guys scramble to determine which tempo scale to believe (most had three temp-based range scales on their scopes).

It didn't affect me because I'm such a mediocre shot that I only have a single temp scale on my scope.

B.B.

 
At February 22, 2008 6:16 PM, Blogger B.B. Pelletier said...

ajvenom,

I almost bought the KZ-45. It out-shoots the CQB! But I'm such a conservative fuddy-duddy that I want an all-metal pistol.

B.B.

 
At February 22, 2008 7:06 PM, Anonymous Dr. G. said...

B.B.,
Can a Leapers scope be used on a 54 without breaking? A knowledgable buddy of mine suggested the Bushnell Elite 4200 Series for this rifle, but since I have had very good results using 3 different [much less expensive] Leapers scopes on other air rifles, I was hoping to use one on this kickin' rifle. Thanx. - Dr. G.

 
At February 22, 2008 10:13 PM, Blogger ajvenom said...

Son of a biscuit, I forgot to ask about springfield's 1911 acp or XDs.

Oh well, I think I'll have to check out a wilson kz-45 someday. I'm was never a big fan of the Taurus, but I figured they'd be better than that for the money.

 
At February 22, 2008 10:51 PM, Anonymous Marc said...

Speaking about the Diana scope mount, any idea of when it will be available for sale since it is final testing?

 
At February 23, 2008 12:39 AM, Blogger Revwarnut said...

B.B.
Somewhere in your blog both you and a blog member had suggestions for setting a scope back to optical center. I can't find it now or I'd have posted this there, but I have run accross another method that appears to be the simplest of them all.
"Try using a small mirror, and a piece of small clear glass, e.g. picture frame glass. Place the glass on top of the mirror, then place Objective end of scope on top of the stack. Adjust the two sets of crosshairs that show up......until they are one. Worked for me!!!!"

Anyone else ever try this?

JBA

 
At February 23, 2008 12:58 AM, Blogger Revwarnut said...

By the way I found this at the Talonairgun.com bulletin board site. Which by the way, I just noticed that it refered to the very blog I was looking for!!! Now I know I am past bedtime, and I had better hit the sack!! LOL!
For those who would like to see the articles mentioned. The Talonairgun link for Optically Centering the Scope is http://talonairgun.com/forum/viewtopic.php?t=1142

Your original blog on the subject is http://www.pyramydair.com/blog/2005/07/how-to-optically-center-scope.html

Thanks B.B. Pelletier/Tom Gaylord!

p.s.
Is it true that A. Those 2 are never seen in the same room together? B. Are you also a "mild mannered blogger for the Daily Pelleter" able to fly faster than a Gamo Raptor from a 3000psi PCP? Do pellets really just bounce off your chest?? The world wants to know....(grin)

 
At February 23, 2008 9:08 AM, Blogger B.B. Pelletier said...

Dr. G,

Leapers scopes are very tough. I imagine they are at least as tough as a Bushnell 4200, and their TS platform models are probably tougher.

B.B.

 
At February 23, 2008 9:09 AM, Blogger B.B. Pelletier said...

Marc,

I expect you should be able to buy the new Diana base by mid-year at the latest.

B.B.

 
At February 23, 2008 9:12 AM, Blogger B.B. Pelletier said...

JBA,

I've never heard of this method of optical-centering, but if it works and saves time, I'm for it.

Once you have centered the reticle, then you must use adjustable scope mounts to zero your rifle.

B.B.

 
At February 23, 2008 12:37 PM, Blogger Revwarnut said...

B.B.
I just tested that mirror technique on my 2 spare scopes, a Bushnell Banner 3x9 and an Optronics 4x. It took me less than 3 minutes from removing the caps on the adjustment knobs to centering BOTH scopes! And the Banner took a good 2 full turns to center on one axis and the other I needed a penny to turn the knobs with!!
I used a 4" mirrored candle coaster that had fairly thick glass to do this.
I found by experimenting that up to a point, the thicker the glass is, the better, you not only get more light in to see what you are doing, but the farther out you are from the mirror surface, the more it amplifies the deviation.
I also found that you need to hold firmly to the end of the scope on the glass because any little movement causes the image to shake.
With that said, you will need to also remove any rubber pads that might be on the bottom of the coaster. Best thing is, you can get these things at any Target, Walmart, Goodwill, Hallmark, or candle store.... etc., and you will not have to cut any glass or worry about sharp edges! I also found that clear plastic gives a false image, so use glass.

JBA

 
At February 23, 2008 5:25 PM, Blogger B.B. Pelletier said...

JBA,

Thank you for the feedback on this procedure. It appears we now have a quick way to center scopes.

I'll see what we can do with it.

B.B.

 
At February 24, 2008 9:38 AM, Blogger Dylan said...

What is the value of a pre 1965 "Hahn 45 BB" single action revolver with 90% finish? I am unsure if the gun will hold air as it seals the 12 gram on the neck and only daisy cartridges have a long skinny enough neck to seal. The frame is bent from somebody using pliers to try and make a crossman co2 seal but the barrel insert and all the other internals are not bent and function well.

 
At February 24, 2008 10:21 AM, Blogger B.B. Pelletier said...

Dylan,

If the gun were new in the box it would be worth $90-100, but with a bent frame it's now a parts gun. Worth maybe $20.

B.B.

 
At February 24, 2008 2:57 PM, Blogger ajvenom said...

BB,

Do find it hard to leave airgun forums alone, even for one day?

I thought I was the only one who had such a strong addicted to airguns and airgun forums.

Then again, it is your forum and part of pyramydair. Maybe you're just a dedicated employee?

Well I feel your forum is a good one, mainly because I think people are looking for honesty and experience. Plus all the detailed hints and pictures really rock!!!!

 
At February 24, 2008 4:01 PM, Blogger B.B. Pelletier said...

ajvenom,

I'm glad you enjoy this blog.

B.B.

 
At February 26, 2008 1:55 AM, Blogger Bob from Oz said...

G'day BB

In times gone past I used to get a piece of 4x2 wrap it round the patch holder tightly and push through. Is this jag method like putting a bent piece of 4x2 through like a pull through?

Any chance of a quick dissertation with a few pixs on how to use patches and with what attachment? Or is it alreadt in a blog?

Is it easier to buy precut patches or is there an alternative/s?

Bob

 
At February 26, 2008 6:24 AM, Blogger B.B. Pelletier said...

Bob,

If I understand your question, a jag is a pointed brass tip that pushes a cleaning patch in one direction, only. I don't have a jag pictured anywhere, so in the final segment of the report I will picture it for you, along with how it works.

I buy oversized patches and cut them to size as I need them. They are much cheaper that way, plus I get the exact size I need, which is more important.

B.B.

 
At March 03, 2008 5:23 PM, Anonymous Anonymous said...

Does Kano Kroil work well for cleaning airguns? I'm a hunter and i have alot of cleaning supplies for guns but not specifically for air rifles.I just ordered the IZH Baikal 513M and i was wondering if i could use my gun cleaning supplies for it?

 
At March 03, 2008 5:44 PM, Blogger B.B. Pelletier said...

Kroil is penetrating oil that falls into the solvent category, so I'd have to say no for airguns. Solvents can attack the seals.

B.B.

 
At March 03, 2008 5:47 PM, Anonymous Anonymous said...

does anyone know how long a 1377 with the stock attached is

 
At March 04, 2008 5:29 PM, Anonymous Anonymous said...

B.B.

i was wondering if i should disassemble and clean the inner parts of the TX200 i am soon to get. would it be good to know how to disassemble it and to know how it works than just simply oiling the outside of the barrel and cleaning the bore of the rifle? and if so, what things should i get? oil (no petroleum right?), grease, bore solvent, chamber lube. so is disassembling and getting to know the parts a good thing or a bad thing? and should you only have to do this once? (say when you first purchase the rifle) i know the chamber lubing and bore cleaning is done every 1000 shots or so. just wondering

Ben

 
At March 04, 2008 5:58 PM, Blogger B.B. Pelletier said...

Ben,

I am sorry to break this to you, but your new TX 200 won't need anything like that for at least 10,000 shots. I have one with more than that and I've never been inside.

The TX 200 is so well-built that all you have to do is shoot it. In fact, if you lay off the Crosman pellets, you'll never have to clean the barrel, either. Just shoot it and enjoy.

Now, if you are just curious about what's inside, read this 13-part blog about tuning a spring gun:

http://www.pyramydair.com/blog/2006/08/spring-gun-tune-part-13-range-testing.html

B.B.

 
At March 10, 2008 6:25 PM, Anonymous DB said...

1377 guy,
It is 26-1/8 inches measured from barrel tip to butt plate.

DB

 

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