"HOT" bore groups opening up

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AaronKrebs

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Sep 5, 2021
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Utah, United States
Alright, I'm turning to the pros here. I have been shooting slugs out of an RTI Priest 2 in .177. This has the standard LW barrell. Not polygonal.

My standard practice is to burn a shot to get the reg leveled out. My first 5 shots will easily be .5" at 50 yds. If I go for 10 shots in that group, they will open up to as much as 1.25". If I wait for a minute and start a new group, it's back to all holes practically touching. Again, for about 5 shots. Then they open up significantly. It is very repeatable. It strikes me as similar to what one could see with a powder burner as the barrel heats up. What would cause it on an air rifle? I wonder if the regulator still hasn't fully settled in or if it is just a harmonics issue??
I would say that maybe it just isn't grouping but the first few shots are ALWAYS tight. The attached picture may not be perfectly convincing but I could shoot a sheet of tight groups if I only did 5 shot groups with a rest in between them. Maybe I'm just dense. Any ideas?

20240623_225429.jpg
 
PasadenaMike said:
Chronograph and it’ll tell you
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I am usually shooting over a chronograph. I have a pile of different slugs in different weights and diameters. I have settled on the JSB KO in 13.xx as the most consistent. They work well at about 960fps. I'm not getting major deviation when the groups start to move around. I suppose I could be rushing larger shot count groups, but not enough to start seeing them open up as much as they do. The part that's really getting me is that if I wait 30-60 seconds, the groups are tight again. And I highly doubt it is shooter fatigue.
 
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AaronKrebs said:
I am usually shooting over a chronograph. I have a pile of different slugs in different weights and diameters. I have settled on the JSB KO in 13.xx as the most consistent. They work well at about 960fps. I'm not getting major deviation when the groups start to move around. I suppose I could be rushing larger shot count groups, but not enough to start seeing them open up as much as they do. The part that's really getting me is that if I wait 30-60 seconds, the groups are tight again. And I highly doubt it is shooter fatigue.
Click to expand...
🤔so many variables.
 
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I believe I am seeing the same thing with my Marauder. I have Gen 2 synrod .22 cal. with original equipment. ( no reg, factory valve,etc., LW barrel) I have been agonizing over 5/8" groups at 25 yds. I am shooting thru a Crony and have good consistent velosities with these groups. I finally get to the point that I think I need a new barrel and I turn around and put 3 thru the same hole. So I checked my zero because I need to kill some tree squirrels that are eating my almonds. It only needed slight adjustment. Since I haven't got the shot yet I roll a target out and shoot one time each day and it is shooting very well right on target. Next day one shot, good to go, etc.
I actually prefer that to the FX low velosity first several shots issue everyone else is talking about. Now I'm afraid to but the balanced valve and all that in my gun where I may be dealing with "sticktion" and so on. It's perplexing
 
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I found this, hope it helps.


[IMG alt="jdanvers"]https://www.airgunnation.com/data/avatars/s/19/19763.jpg?1654695133[/IMG]

jdanvers​

Member​




I'm a relatively happy camper with this thing as a .177 slugger. :)

I originally purchased it brand new as a .25 but found that I really don't shoot it all that much in that caliber. I generally don't need anything bigger than .22. Cutting to the chase - I grabbed a couple of barrel kits from AOA and immediately fell in love with it as a .177 slugger slinging NSA 12.5's - the thing is awesome with those and extremely efficient to boot (ie; high shot count )

Then I saw that the jsb ko's had finally made it over to this side of the pond in .177 so I jumped on it and grabbed a few tins of them - I got 'em from Utah Airguns.

I've been shooting it with the .22 barrel this past week, also with jsb ko's ( .216's ) and . . . 'eh. It shoots them . . . good. Not spectacular, and certainly not bad but no where near as good as my Taipan Long w/.217 23g H&N's. That gun is, for me and the few guns I have, my .22 slug standard bearer. The RTI (so far) hasn't blown me away in .22 with slugs - it's not in the same league as the Taipan. It did blow me away with those 12.5 NSA's though in .177 so . . .

. . . I put the .177 barrel back in it and w/out changing my tune at all I just started shooting these .177 ko's. I had to adjust the scope after I figured out where on my little test target it was hitting but boy oh boy - once I did - holy mackerel! The attached photo is the 10 shots from the imported chrony string. Granted only 28 yards but as I've learned from some of you - get it nice & tight close first - then take it out longer at 70, 80, 90, 100 yds . . . that's going to happen tomorrow.

This is just off of a kind of rickety table on the deck at my house and shooting off of a bipod - no sand bags or anything like that at the rear. I'll sand bag it and get real super steady at the range tomorrow - but for down & dirty, 10 shots and not even having changed my tune at all. I'm kind of a happy camper. :)

Below is text summary of imported string from my chrony and again - these 10 shots are the 10 in the included photo.

Name: First Shot String RTI w/.177 JSB KO's
Notes: Imported from Chronograph, String 1, on 9/4/21 6:08 PM
Shots: 10
Average: 987 ft/s
SD: 3 ft/s
Min: 984 ft/s
Max: 993 ft/s
Spread: 9 ft/s
Power Factor Average: 13
Power Factor Low: 13
Power Factor High: 13
Weight: 13.4 gr.
 
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Were that my rifle, the magazine would get a good examination to see if there was an alignment problem with parts of it. Shooting groups by loading it singly with a loading tray would be next.

Going over it to find if anything is loose is another thing to do.

I'd also consider setting up a jig and bolting it to the bench to see if the problem wasn't the rifle.

Cheers,

J~
 
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There is a variable involved that you haven't yet found. I don't know what it is, but I would shoot without the magazine if you're not already. With any accuracy issue, it's always worth giving the barrel a thorough cleaning. Honestly, I don't think either would cause the problem as you describe it. It is a conundrum for sure. Good luck.
 
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I second what Headshots said about barrel cleaning. Your “first 5” group looks like what my slug guns do when they need cleaned. Then its back to cutting holes at 50 after the barrel is seasoned again. After a good cleaning be patient for the first 10 shots or so as your slugs walk around a little before they settle into shooting in the same spot. If they never settle into a tiny cluster, its back to work.

The problem with not being demanding enough to have all your slugs basically touching at 50 is this. If you are happy with a 1” group at 50, many guns can shoot that a decent percentage of the time and not even be close to using the right components or settings. When you are on the edge of a horrible tune/setup, nothing is ever consistent. Or the only thing that’s consistent is fliers. Good luck.

Another thing that could be going on is your barrel might need a polish. If you are indeed close with your settings and slug choice, you could have streaks of lead causing fliers. I would be surprised if the bore on your RTI wasn’t already very nicely finished. But you never know.
 
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I think what Aaron says is real and it seems like no one is on board with that. I am trying to confirm my findings. I shot yesterday morning and shot was right on. I shot this am and shot was right on. I shot this afternoon to see if it is temp related due it is 60's in am and 90 F now and shot is right on. So I have a 3 shot group that is under 1/4 inch at 25 yds. and I agree this is so far but I think I am seeing what Aaron is observing.
 
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It sounds like there aren’t many things you haven’t ruled out. If the air is regulated to consistent pressure through out each shot string that’s not the problem. If you’re using several different magazines and it’s still happening then move on. You seem to have found a pellet the gun likes. It sounds to me like it’s a temperature thing. Either the barrel is heating up or there is a stress issue in the barrel that shows as things warm up. Try shooting one round per minute for ten minutes see what the grouping does.

Rick H.
 
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Vetmx said:
Looking at the target you posted. I don’t see a gun/slug combo accurate enough to judge anything. I’m not being a wise guy but you haven’t found the right combo/settings. You’re not shooting groups, you’re just putting random holes in paper.
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That's why I excused my target in the original post. I have much better examples with multiple 10 shot groups. Just not handy. The knockouts end up making a clean 1" circle, worst case. .178 Nielsen's were hole in hole for multiple shots but would throw a nasty flier randomly. It seems like it does better with fatter slugs but maybe debris or some irregularity, maybe at the choke, sends them out of whack. Smaller diameter slugs like H&Ns, usually mic at .176, are a complete no go. The KO are spot on at .177 and have been most consistent. Along with the 13gr Zans. I'm starting to suspect either fouling at the choke or possibly the barrel not fitting snuggly within the shroud. The gun responded very well to a thorough cleaning. I keep hearing that the LW foul up quickly but I thought that was with the polygonal. I got maybe 75 shots before it was back to throwing fliers. I never clean my FX liners, and they do phenomenally with the proper slug.
 
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