Gamo Shadow 1000 - Reverse choke

[expomatic]

I ran a pellet thru the barrel and found it was nice & tight for about 1/3 of the way to the muzzle...then the pellet almost fell out!

Has anyone noticed this awful 'reverse choke' on their Gamos? I'm trying to determine the lack of consistency with my groupings, and no, my hold isn't THAT bad!

Any thoughts would be appreciated, TIA.

[vinceb]

How does the gun shoot?

[Gene_SC]

What brand pellet are you running through the bore. Generally Gamo's have a decent bore with good rifling. It could be the pellet you are using. I own 13 Gamo air rifles and 4 of them have the S1K powerplant and barrel. Only two of the like a certain pellet and the others shoot with good consistancy with even different brands of pellets. Try pusing a good brand name pellet through the bore and let us know what you find. Gene

[expomatic]

Hey guys, thanks for ringing in.

I've tried all sorts of pellets, from all sorts of manufacturers with the same results.

Perhaps it's some kind of fouling resulting from its early days of mild detonation (right outta the box). Maybe I'll take a bronze brush to it this time, instead of the usual nylon. Maybe I got too much Moly60 slinging around?

Other than that, the rifle is fairly accurate some days (3/8" @ 25yds), and other days, not so much (1 1/2" - 2" @ 25yds). I've looked at all the usual suspects like scope mounting, stock screws, barrel lockup,  etc, and have pretty much
ruled them out. The rifle has about 4000 rounds through it now, and has already broken 2 mainsprings and destroyed a Leapers 5th gen scope. I am planning to strip it down again and put in a milder spring/tar & shave down that heavy top hat - It has always bucked like a mule. I was also thinking about adding mass to the stock via putty - anything to add weight to the thing.

Hey Charlie daTuna, any ideas?  Thanks guys!

[Gene_SC]

Mike, do not use anything other than a nylon brush. Air gun barrels are way softer than real powder burner barrels and you will screw up your rifling grooves with a bronze or brass brush. If your Gamo is less than a year old you can call Gamo and explain the problem and they will send you another one. But do not use a bronze or brass brush in your Air Gun bores... Yikessssssssssssssssssssssssss

Gene

I used a metal brush w/ JB paste on my 440's bore and absolutely destroyed the bore. At 15 yds, the first shot always hits the bullseye dead-nuts, then all the subsequent shots apparently completely miss the paper, as no additional holes appear!

(?!?!?!?)

Point: Judicious use of a soft-metal brush isn't likely to hurt anything. Brass is, after all, softer than even the mild steel in an airgun bore. This is one of those internet folklore cautionary tales you aren't likely to ever see empirical backing for.

[CharlieDaTuna]

Mike I suggest that you never use any kind of metal brush on the barrel of any pellet gun including brass. As Gene stated, use only a nylon brush and either GooGone or Simple Green.. Also keep in mind that there is no acid or powder residue burned into the barrel of a pellet gun like there is in a powder burner. Also, never use commercial cleaning chemicals like JB Paste that are used to clean barrels in powder burners. Just remember that every time that you strip clean the barrel (using a brush) on most pellet guns (and unlike powder burners), the barrel will need to be seasoned all over again to regain any velocity and accuracy that may have been lost.

Strip cleaning usually causes a change in velocity and accuracy until it has been shot awhile and re seasoned. This can take as many as a couple hundred shots or or more. Just pulling a few patches through the barrel once in awhile using GooGone, then dry ones  is usually more than sufficient.

Personally, on my own guns, I don't pull patches on them until they come out white. I would much rather stop when there is still a little grey on the patch. If it's white, it's too clean in my opinion.

The time to strip clean the barrel is when there is a drop in velocity and/or accuracy or every couple thousand shots if needed or if questionable. Keep in mind that the lead deposits in the barrel act as both a seal as well as a lubricant and actually benefits the gun.

[expomatic]

Thanks everyone for your input.

I haven't run a brass brush thru the barrel, yet. (!!!)
 
I bought some 1" delrin this weekend and turned down two new rear guides. Instead of the 1.4" preload that the factory guide provides, I inserted a 1/8" thick brass washer. This should reduce velocity and most importantly, twang. The factory guide gives about 0.065" clearance to the spring I.D., which is just awful. The new guide leaves about 0.005" clearance.

If it turns out that the rifle is too weak after the loss of the 1.4" factory preload, I'll just spin up some new THICK delrin washers (in increments of 0.5") and reinsert them and see what happens. I'll leave the tophat alone
until I've played around with the new guide/preload for a while. I'd be completely happy if the rifle was much easier to shoot at reduced velocity, if it didn't buck like a mule - say 800fps or so, instead of the typical 950fps.

Anyhoo, I have to wait until Monday to drill that 9.0mm locking pin hole in the base of the guide, as I just don't trust my drill press/vice combo to do an accurate enough job. Machine shops are much more reliable!

[expomatic]

Thanks Charlie.

I was wondering if you've ever lapped a Gamo barrel and found what I did, a 'reverse choke'. I wonder if I should lap the first 1/3 of the barrel  until the remaining 2/3 feels tight - or would that leave things too sloppy? Hey wait, i could try, very carefully, pushing a pellet from the muzzle end to about 1/2 the total length and then inspect the rifling marks on the pellet to determine if the 'loose' section of the barrel does in fact bite the pellet enough.

That way I could have some indication as to whether or not I should lap at all - is the 'loose' 2/3 of the barrel tight enough such that lapping the 'tight' 1/3 of the barrel, near the breech, would result in a properly choked barrel?

Your thoughts?

Charlie, you and I probably agree that it is inadvisable to do anything at all to an accurate barrel. This one isn't.  A Goo-gone/nylon brush wipe-down is highly unlikely to tighten the loose end of a  barrel.  Right?

You said 'never' use a metal brush and 'never' use commercial cleaning chemicals. Experience informs me that absolutes like those are typically --ummm -- wrong? Tom Gaylord, who I think we can agree is a pretty smart guy who has been highly involved with airgunning a looooong time - probably longer than you and I combined- advocates using - yes - a bronze brush loaded w/ - what?- JB paste for out of the box cleaning, or when problems come up.   He's not always right, but I do respect him, and by and large, he offers credible advice.

Mike - you are right, tight to loose is the complete wrong order. This barrel sounds like it is badly flawed. Given that, I wouldn't hesitate to use  measures well  beyond 'Goo Gone'  to try to find improvement. Here are actual idea to solve the problem:
1) Back to GAMO!  Best idea, IMO
2) New barrel
3) If the end of the 'tight' stretch of the barrel is at least 9" from the breech, you might just want to chop/re-crown it.
4) Use an abasive on a brush and scrub the tight spot till it 'matches' the loose section's I.D., then run snug-fitting pellets - last resort

Good luck.

[Gene_SC]

The only way that barrel will ever be right is to replace it. As I stated above number one is send it back to Gamo. Then you will be cooking. I would not even except the other options if I were going to use that air rifle.

Gene

[nyairman]

What Gene said...period.

Greg

[Rixtrix]

Why bother with "drastic measures" on a barrel you know is already not right? You're not going to do it any good, so why waste the time? If it's under warranty, send it to Gamo. If not, send it to a tuner who knowswhat works and what doesn't, unless you want to totally waste a gun.

Ric G

[CharlieDaTuna]

Well I’ll tell you Steve…. I have all the respect in the world for Tom and he does for me and he has his view just as a lot of other people do including you.

I do have contact with Tom and we have a good relationship. He is a very knowledgeable person and does provide a lot of good info to a lot of people. But…… and with all due admiration for Tom, throughout the years I have probably been through and tuned or worked on a couple thousand guns more than you or he has ever had in your hands on and probably ever will. Neither Tom nor I are someone that all of a sudden just popped out of the woodwork like some individuals and started providing advice. It takes many many years to acquire the good quality knowledge that can be passed on to others.

So I’ll say it again….I suggest that one never use any kind of metal brush on the barrel of a pellet gun including a brass brush. There isn’t any reason to use one to begin with. The only exception might be the high end guns that use a high grade steel in their barrels instead of the lower grade metal used in most pellet guns manufactured today. It doesn’t take a rocket scientist to know that there is no acid or powder residue introduced and burned into the barrel of a pellet gun like there is in a powder burner. And do they not require acids and abrasives to break them down so they can be removed. So again, do not use commercial cleaning chemicals like JB Paste that are used to clean barrels in powder burners. Some can and will pit softer metals and can completely ruin a gun. I have seen what can happen, I’ve had a number of them on my bench and have seen the results, it’s happened many times before and will many times again, especially if they follow the advice of a few.

If nothing else, doing it as I suggest, I can guarantee with 100% accuracy that absolutely nothing can happen that can possibly cause harm to their barrel and at the same time provide all the maintenence needed. All of the old pro turners that have been around for years and some longer than me….lol have been saying this for many years and is what they have taught me many years ago. … And it’s even more significant today than it was back then.

By the way, where did all the other old pro tuners disappear to???…. I guess I know why people call me an “old timer” now. The years have sure flown by and I guess I’ve earned it.

Next item: I don’t think I or anybody else said that GooGone was going to resolve his problem and was never the objective. The intention was to point out that your point about how and/or what to use for servicing the barrel was in my opinion and also many other knowledgeable people to be poor advice. Everything in my post was referring to the use of metal (including brass) brushes and cleaning chemicals or compounds.

For those that look for advice, think about what some people say put forth and evaluate just what it is that they are saying and please don’t do or use something just because someone “says” so. Keep in mind that most of the information that the members provide is with good intentionsfrom their own personal experience and pass on what they have done and what worked for them in a given situation. And that’s good and what our forum is all about. But it’s also amazing to me just how much misinformation is passed on out there but unless I can see that it is dangerous, or can cause damage, I don’t usually say much.

For those of you that write and read some of the posts, suggestions and solutions. That’s what our forum is all about and the foundation the Gene and I built this forum on. Sharing!!! We welcome that and look forward to it. If you have doubt or a question and to you it’s important to have a best answer possible and the answers presented are questionable, go to a reliable source that can give you well established, well informed and acknowledged information or solutions…. There are a few very knowledgeable people out there that will share that with you and I certainly don’t mean myself in particular. I get 40-50 e-mails a day including some asking me about things or statements because “they read” or “someone suggested this” or that or “is this true”. Believe me, I get enough e-mail and phone calls as it is and as anybody can tell you, I answer each and every one of them and if I don’t have an answer, I direct them as best I can where to go to hopefully find it or I’ll find it and get back to them. I’ve been doing it for a lot of years and it’s made part of who I am today.

But please… before you personally contact someone … do a little research on your own. That’s part of the fun of it and most answers are out there. …. perhaps in the library, oron my website or other pro-tuner’s websites.

I'm gonna have to second Bob's advice.  I am a gunsmith, have been since 1950 and I've been building NRA Bullseye match 1911's for all those years...plus a ton of other work, of course.  I have used JB paste on rare occasions but never, ever on a match pistol.  JB can dull those sharp edges on the lands and that's the last thing you want to do to an accurate barrel.  These little .177 bores have small lands as it is and I surely would not want to diminish their effetiveness any further by rounding off those land corners.
I use a nylon brush to clean out a NEW bore and then soak a mop with FP 10 (Gasp!) and run that mop through the bore until it's black.  Then I spend lots of time just running patches through it 'till I'm satisfied all the FP10 is gone and the bore is clean.
As for routine cleaning of a bore...I'm not an airgun 'smith and I'll defer to Bob on that.  But still, no metal brushes or JB Paste!

Bob