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Discussion Starter · #1 ·
I have a new CZ 17 HMR Varminter, that I have fired twice at 100 yards. Both times the groups were terrible at first, but after firing about 25 rounds they started to tighten up. The first day (off a folding table with bags) using a 12 power cheap Bushnell scope, Erik's trigger kit mods, and nothing else, my best group with Hornady ammo was 3 rounds in less than 1/8" and two vertical flyers that opened the group up to 7/8"! I got pretty excited and thought that if I could eliminate the flyers I'd have a 1/8" MOA rifle.

The next day, I decided to float the barrel, and sealed the raw wood in the barrel channel. I used a concrete shooting bench and a good bench rest instead of the bags. Again, my groups were all over the place, until I had shot about 25 rounds, when they stated closing up. My last group using CCI ammo was about 3/4".

Now I have heard of heated barrels decreasing accuracy, but never INCREASING accuracy. Does anybody have any suggestions? Is it possible that the heated barrel is expanding and putting pressure on the forearm of the stock? I guess I could check for floating clearance after the barrel is heated and see what I find.

Tomorrow I am mounting a 24 power Simmons Scope on Beeman Rings, and trying again.

Do you think the problem couldbe something totally unrelated to the heated barrel?
 

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I've seen this happen with my 17VS too. But I always attributed it to myself more than anything else. Last time it was after a pretty stressful day at work. I was seeing horrible groups with flyers all over the place when I first started. But I wasn't concentrating on what I was doing either. After about 50 rounds, I had calmed down, my pulse rate came down and I started breathing correctly and doing all of the things that I should do. The group sizes came back down then.....
 

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Assuming you started with a clean bore for the first session, and assuming you cleaned it again while doing the mods before the second session, perhaps it's simply that this rifle needs to be fouled a bit before the groups really tighten up? I've seen that with the .22LR, and would suspect it here, too. JMHO
 

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One of my .22s( Marlin 39a )does that. I swear it shoots much better warmed up. I also have a CZ .17 Varmint, except for an occasional flier it shoots the same cold or warm. Guns can be like women HARD TO FIGURE OUT !!!
 

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I've been watching guys shoot IR 50/50 and RBA matches and it seems that just about everyone at the beginning of the matches shoot 5-10 shots at the spotter target to warm things up.

I've tried it, not shooting matches and it seems to work.
 

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Discussion Starter · #6 ·
Well, in thinking about it, the one thing that was the same both times, (besides starting with a cold barrel) was that I had taken the action out of the stock and reset it both times before firing. The first time to do the original trigger job, and the second time to slightly change the trigger and then to float the barrel.

So one possibility is that the action takes about 25 rounds to seat properly. Once seated by firing , it starts getting more consistant. So once I get my new scope mounted, I'll try again, but this time without having removed the action from the stock, and see if I am better from the get go.

Also, I've seen some of you guys mention that you needed an initial break-in period for the gun of 200 to 500 rounds before it seemed to settle down.

Since these are jacketed as oppossed to plated bullets, copper fouling is a distinct possibility, although it doesn't relate to this specific problem. If I find copper fouling, I'll do the tedious old barrel break-in routine, like I am doing for my 30-06.
 

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Oh NO! the cold barrel goons will start swooning soon, you mean you actually shot enough shots to get the barrel warm? Of course my oppinion is that a barrel isn't warmed up till is burning the oil off it's surface.
 

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Match rimfire shooters, whether smallbore or benchrest, will NEVER start for record until they shoot at least 5 shots to warm the barrel. Usually its more like 10 to 20 "heaters." So what you've observed is not unusual at all.
 

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Barrel Heat Increasing Accuracy

nevadaccw,

So one possibility is that the action takes about 25 rounds to seat properly. Once seated by firing , it starts getting more consistant. So once I get my new scope mounted, I'll try again, but this time without having removed the action from the stock, and see if I am better from the get go.
Approximately 75% of the 'improvement' in accuracy you noticed was, in fact, the barreled action reseating itself in the stock after your disassembly...! ! ;)

New experience: depending upon the quality level of your scope, you will notice that it may take a few rounds for a W or E change to 'settle in'; this is due to the stiffness of the internals of the scope adjusting to a new position; less in expensive scopes, more in inexpensive scopes...! ! ;)

For any copper fouling you may see, just use a good copper solvent like Hoppe's Benchrest, Shooters' Choice, or Sweet's 7.62; follow the directions...! ! :eek:

Good Luck...! ! :)
 

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i've also been told not to leave a live round in a hot chamber and expect it to group with the others, it cooks the powder, just fire it at a sighter and start over......
 

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Discussion Starter · #11 ·
You guys have come up with some good responses. Thanks, it all helps, what a mystery this is at times.

Yesterday, I got the 24 power mounted, but by time I got out on the BLM land, the wind had picked up to gusts as much as 50 mph. Got some great experience in veritcal stringing with a headwind.

Regarding hot actions and hot ammo, I had the heck scared out of me the other day. I had been chronographing loads for my Beretta which is rebarreled in 357 Sig. I had some nice accurate loads worked up, and took a box of 50 out to shoot. My gun had been sitting in the sun, and was almost too hot to touch. When I fired, it was like shooting a 44 magnum. The velocity had jumped to 1,767 fps! The SAAMI spec for the calibre is 1375 fps. I am lucky I didn't blow up the gun it was so overpressured.

On the same day, my Remington 597 in 22 Magnum almost blew the back out of a case. The flat at the back of the head was rounded like a balloon!

Today I am heading back out before the wind picks up to try again.
 

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I think your gun could just use being shot some more. My cz just needed to be broke in. I wouldn't wonder or be concerned until you get 500 rounds or so through it and clean it 5-6 times to get all the gunk out of it. Shooting and using just to settle the barrel in seems to work. Also it takes a bit to get use to a different trigger. Mine is a .22 lr though, and not the .17, but it takes a bit to get the brown gunk out of the barrel, and shooting and using it seems to be the best way.
 

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Discussion Starter · #13 ·
Thanks Sharkman. I was wondering about that gunk you mentioned. I had just it out of the box, didn't even clean it first before firing the first two times. It took me 130 patches to get the barrel clean. I couldn't believe how dirty it was. I have had a lot of guns, and this barrel had more gunk inside than any I have cleaned. I am using a dewey coated rod, which does go through the 17 HMR, unlike the 22 which hangs up inside.
 

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Forester said:
Match rimfire shooters, whether smallbore or benchrest, will NEVER start for record until they shoot at least 5 shots to warm the barrel. Usually its more like 10 to 20 "heaters." So what you've observed is not unusual at all.
That is correct. Myself and every smallbore competiter I know fire at least 5 rounds into the berm before putting rounds on paper.
 

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I wouldn't have believed it either, as a long time centerfire shooter. But, at least, the 22 rimfires do take a number of shots to "come in." In my first ever match, two weeks ago, I peppered shots down range until they started landing in the X of the RBA sighter......about 5 shots and they were centered on the X solidly. Some guys used quite a few more but my Lapua ammo supply was limited and I had to use it wisely.
 

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I have one rifle with a fluted barrel that shoots it's best when the barrel is warm or hot to the touch--the more the sun shines on it, the better it shoots. It takes 12-15 shots to warm it up to the point it shoots it's best. This is a bad situation for a hunting rifle--but great for a target rifle--the warmer it is the better it shoots-I like it:D
 

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My NEF Hummer does the Hot barrel trick too. It takes about 10 to heat it up and then it'll settle down. It also hates a clean barrel. After cleaning it (I mean, one pass with a bore snake) you might as well berm shoot the first 10 rounds before trying to find paper, after that you're in business.
It'll shoot a 3/8 group after it's warmed up. I even did a little experiment last week. I didn't clean it from Tue. to Thurs. and left it in the sun in the dakota Thur. for 2 hours. Got it out and she went straight for the x ring. :confused: NOW, what was it? the not cleaning or the heating up.. OR both...:eek:
 
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