What makes a rifle loose its tune?

N

nonliberal

Guest
If a rifle seems to be in "perfect" tune for a while and then just changes out of the blue, what causes that.

Some things I eliminated.
switched to a proven scope that I know works well.
action screws are torqued the same.
Same jug of powder.
same box of sorted bullets.
same Wilson seater die that is still set where I indexed it when I found my best setting.
Had the barrel bore scoped and it looked great along with the crown.
Kelbly rings are tight.
same pieces of Lapua brass, seperated but half anealed, the other half left alone.
.001 shoulder bump
rounds are loaded inside in the AC, and fired within 3 minutes of loading.
Temps are withing 5-10 degrees.
Almost no wind condition.
Rest and rear bag are the same with no problems and placed the same on the same bench that was marked for placement.
Tried diffrent cleaning intervals. After 10,15, 20 30, 50,shots shooting with WS2 and no change.

I had two loads with two different bullets that worked well and now neither of them are in tune. They dont shoot "bad" but its obvious something isnt right anymore. Seating depth changes does seem to help or hurt the groups but I still havent found the "sweet spot" that it use to enjoy.

It does'nt really have any flyers, just opened up groups.
30x47 HBR with approx 600-700 rounds on it.

Sorry for the long post but I wanted to give as much info as possible.

Thanks.
 
Almost no wind condition.

Be careful with that statement............ Better be using flags ... Regardless.

Pretty much the "30's" stay in a "aggable" tune better than .22's, 6mm's.....
Though bag stability from the recoil of the 30's requires extra attention.
As well as the shooters techniques at the bench.

Back to the load...... In the lands, out.... Work the charge a bit up, down lol...

My .02 worth...
cale
 
Non-Liberal

In the late 1950's, that would have been the $64,000 question. Now, I suppose it is the $1,000,000 question.........jackie
 
You didn't mention primers. Are they the same? Also, did your barrel cleaning technique change? Powder /carbon fowling? Neck tension change? Maybe try new brass. Let us know.
Greg
 
out of tune

cut barrell off and set back if nothin else works
 
Some of these

Personal Competitive desire, vision deterioration, trigger, bedding, rest set-up, missing a read of the wind flags.
 
I believe rifles do loose there tune, My rail gun says so and 5 other
6ppc's agree. There are times when my standard powders refuse to burn clean and begin to leave charcoal behind. Other times they can burn
clean and the patches are just nearly tan. When 133 shoots dirty, the tgts
are bad. Reading back thru Gene Beggs frustrations with 133, its clear
I'm not the only one. An interview in P.S. with a well known shooter
from Texas, says he once drilled flash-holes out and resorted to 4895
to retrieve his tune.
This past weekend I set my NJ measure at 52 1/2 with 133. fresh
from the jug. It weighed 28.2 grs. I left the lid off the measure(indoors)
but it rained all weekend. On monday, without changing a thing, I was
getting 28.6. What did my velocity do ???
My oehler was not set up, but I plan to test all this, if I have to steam the powder. A friend told me he is now getting 50fps more out of the same jug
Go figure, something changes
 
Sounds like you've been through all the basics to isolate any trouble spots. In this case, I would advise starting with a clean sheet of paper and go from there.

-Re-establish the 'just touching' figure for the seating depth. Don't use a barrel stub...seat a known .30 cal. accuracy bullet of the type you're using (BIB, etc) .025-.030 past the 'just touching' point. In other words, when the rifling marks just disappear as you seat the bullet progressively deeper, adjust the seating stem so it's .025-.030 shorter.

-Use a neck bushing that sizes the neck .003-.004 under what a loaded round measures over the pressure ring as a baseline.

-Double check the neck diameters on your loaded rounds to make sure they aren't too big. Neck bushings make a great go-no go guage if you don't have a micrometer that reads .0001's.

-Double check your case lengths.

I can't tell you how many times I've seen seating depths off, case necks too big and cases too long. Have you just recently started coating with tungsten disulfide? I wouldn't clean it until about 40-50 rounds during testing.

Just where I'd start....... -Al
 
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After the obvious is eliminated, the only thing left is changes in powder, due to suttle changes in mico-climatic conditions.
Bob
 
Thanks guys, those are some great responses.

I always use flags and the "almost no wind condition" was all vanes facing the same direction, no movement on the daisy, and just an ever so slight flutter on the tip of the tail.

The primers were all from the same case of Fed 205s, I tried every brand of small primer I could find and the Fed seemed to work best with this load.
I have 50 cases that have been fired 7 times but anealed, 50 cases that have been fired twice after fire forming, and 50 cases that have been fire formed only they are all kept and shot seperate. The die is a one piece with the neck honed for .0035 neck tension so it hasnt changed, and after being fire formed, runout is normally just under .001 .

The rifle seemed like it couldnt miss for a few hundred rounds and then it just went away. The guy with the bore scope said it looked great even in the throat area.

The WS2 was introduced to this barrel after about 50 naked bullets were used during break in then only WS2 coated.

I will try all the things mentioned one at a time even if if means starting all over.
I have an unopened jug of powder with the same lot #, I will try that also in case the other jug was able to draw moisture.

AL, When you say to check to make sure diameter of loaded rounds arent to big. How much expansion clearance do you look for?

Thanks for the help guys.
 
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The guy with the borescope

Ask him if there's a black build up just forward of the chamber neck area..prior to the lands...
 
nonliberal said:
AL, When you say to check to make sure diameter of loaded rounds arent to big. How much expansion clearance do you look for?
Thanks for the help guys.
Click to expand...

On these .30's, I like to see no less than .002 total neck clearance. I've run as tight as .0015 total with no problems but have also seen some inconsistent accuracy at .0015 with the .30's...especially after the cases have been fired a few times.

There's a few things to bear in mind when we're working in this area:
- The neck diameter of the reamer may not be exactly what the print says it is. Make sure and double check the chamber neck diameter.
- As brass is fired and sized, brass does flow foward. If you're set up with minimal neck clearance when the cases are new, you can get into trouble pretty quickly and not realize it. I've seen these .30's release the bullets with z-e-r-o (or less!) neck clearance and still not show show any pressure signs. Since the gun showed great accuracy at first, this may be a good place to look for issues.

I know this isn't a popular opinion, but I believe that the neck clearance a certain combo needs is directly related to the amount and what area of the cases are being resized.

It's pretty unusual for a .30 cal. barrel to just lay down and die with that low of rounds through it. But I'd never say "never", either. :eek: Whose barrel is it?

Wilbur makes a good point also...gettin' into barrel with some JB or Iosso is good preventative maintenance. And if you have a lot of gap between the end of the case and the end of the neck in the chamber, stuff can get built up in there and give you gas. :D I'm a minimal clearance guy when it comes to case lengths for that reason. :)

Hard to diagnose this stuff 'long distance'....but just recently Woody on this forum helped me figure out a trigger issue that had me scratching my head. :cool:

Just where I'd start looking...opinions being like body parts, 'ya know? Hope this helps..keep us updated, okay? -Al
 
Thanks Al, That could very well be an issue. I previously thought the chamber was .332 but i just noticed I get pressure on the bolt and scratch marks on the brass at .331. My loaded rounds are .330 at the pressure ring. Maybe I should turn another .001 off the brass. The barrel on it right now is a Broughton but I have a couple Rock creeks that shoot good also I could try.
I think your probably right about the barrel not dieing just yet because Im shooting moderate loads (not real hot) of 748 with WS2 coated 10X 130 and 150 bullets, with the Small primer pocket Lapua brass.

Wilbur your right, I should have asked him specificly about a carbon ring, but it was Ron Hoehn with the scope that was also shooting in the match and he was just being nice by looking at it for me. I did'nt want to bother him to much during a match.

Thanks again.
 
A couple of other thoughts:

With the 30X47L case/748/130-150's combo, things usually work best at higher pressures. Don't be afraid to lean on it as it's tough to put enough 748 in these cases to hurt stuff. From my experience, 748 can be a bit quirky at lower pressures and in changing humidity...Benchmark, N135 and N133 are killer powders in this combo. Last season, Randy Robinett and I were shooting the breeze on a Friday test session at Webster City, Iowa. There were a few guys practicing and the humidity was really up there and it was overcast..the powder clouds were pretty pronounced when someone fired. As the wind carried the smell of burnt power over us, Randy looked up and said: "Hey...who's shooting 748?" :D

With coated bullets in these .30's, gains are sometimes found in opening the small flash hole size to something in the .072-.075 range.
 
That makes since, here in St.Louis the temps may stay the same but humidity swings greatly, especially with all the flooding going on.

I have all the powders you mentioned and I might need to revisit them.
The 135 works good with the large primer pocket brass but it doesnt seem to do very well with this small primer Lapua brass. I used a K&M PPC uniformer that opened up the flash hole a very small amount but maybe I need to open them up some more to get the extruded powders to work better.

I get a bit of a powder cloud myself even when Im shooting 46 grains @ 2975 fps with the 130s.
 
Al Nyhus said:
A couple of other thoughts:

With the 30X47L case/748/130-150's combo, things usually work best at higher pressures. Don't be afraid to lean on it as it's tough to put enough 748 in these cases to hurt stuff. From my experience, 748 can be a bit quirky at lower pressures and in changing humidity...Benchmark, N135 and N133 are killer powders in this combo. Last season, Randy Robinett and I were shooting the breeze on a Friday test session at Webster City, Iowa. There were a few guys practicing and the humidity was really up there and it was overcast..the powder clouds were pretty pronounced when someone fired. As the wind carried the smell of burnt power over us, Randy looked up and said: "Hey...who's shooting 748?" :D

With coated bullets in these .30's, gains are sometimes found in opening the small flash hole size to something in the .072-.075 range.
Click to expand...

Al nailed it! The small primer flash holes needed to be reamed bigger to make the better extruded powders work. It made a huge difference in group and consistancy. The rifle is shooting good again.

Now even though its against popular opinion I cant wait to drag out the 6br and sacrifice some brass for testing on it. Its like discovering another vital part of load development that I didnt know existed.
 
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