I have been reloading for a while, but I am still not sure how much barrel heat affects accuracy. I read the Ladder Test thread and am going to try it with my .308. I shoot in FL where the temp is around 50 to 60 in the winter. I have been waiting for te barrel to cool to "warm" between shots, sometimes 5 to 7 minutes. I still don't like the idea of firing a warm barrel as compared to a cold one.

I am trying to determine how much variation is due to the temp as compared to the actual load.

Any suggestions would be appreciated.

Thanks, Dan

A lot f it depends on what's hanging on that barrel (if anything). Barrels expand when hot, and will expand faster than any other metal work hanging off them ...basicly expanding while being tided to other metal parts, so then tend ot bend.

Most bolt actions don't have anything hanging on the barrel (some old models did use a foreward barrel band in the fore end). BUT the barrel can still warp form (1) internal stress (2) non-uniform thickness. Not all barrels have bores that run dead stright down the middle of the barrel...can be dead on center at both ends, and still off dead center in the middle. Less common that it once was, but have seen shortende barrels that were off cener once shortened, but the orgianl muccle was on center...so the hole was "bowed".

Heat wille ventually get to the actiona s well...which is tightly bedded to the stock...and just won't allow much expansion. That doesn't happen until the barrel is "way hot".

Are places tha make their living by "de-stressing" barrels...as you'd expect, if the barrel had no stress the process doesn't do jack...and if the barrelw as way-stressed, it does some good. Reports of effectivness varies, but i'd say it proably would do the most good on the WORST shooting brrels, and few people are willing to spend the $ on a bad shooting barrel (becasue a 70% "better" group isn't so impressive if the group started out hat-sized?).

As for velocity...that isn't too major. Also takes some time for the heat to transfer to thecase...and from the case to the powder charge.

PRobalby aslo a differnce in frictionb etween a hot barrel and a cold one ...and a pile of things i haven't thought of right off the bat.

Best barrels just shoot slightly larger groups as they get hotter...and collect more fouling. MOST barrels will show a tendency to wander a bit as they get hotter.

Get a box of commercial match ammo — I don't care whose you buy or if you roll your own — and shoot four 5-shot groups at different paces and with 15 minutes between groups for cooling. You already have some idea what it does at a 5-7 minute pace, so use 2 minutes between shots for the first group, then 1 minute between shots for the second group, then 30 second pacing for the third goup, then about 15 seconds for the 4th.

If the groups walk off the center of the first shot in one direction, and this effect is exagerated as you fire faster, it is a good indication of axially assymetrical stress and or you have a barrel contour not coaxial with the bore. In the former cas, you need to get the barrel stress relieved by cryo treatment. In the latter case it needs to be sent to the maker for correction or recontoured on a lathe (see geometry, below).

On the other hand, if the group walks the same distance for the first three shots and just stays there regardless of how fast you fire, then you are looking at fouling shots making the difference or you are shifting in the bedding and need to pull the gun apart and look for oil to clean out or for worn bedding or bedding errors like the barrel touching the stock. You may need to get the bedding re-done. If it is a commercial barrel, firelapping the bore can reduce fouling shot effect, as can using a bore lubricant like MolyFusion.

If the groups are more or less centered, but just not good and the ladder test doesn't find you a sweet spot, have the barrel geometry checked:

Is it reasonably straight (they don't have to be dead perfect to shoot well)?
Are the rifling and throat in reasonable condition?
Is the rifling of even depth all around the bore?
Is the crown symmetriclal around the bore axis?
Is the chamber concentric with the bore axis?
Is the chamber within specs?
Is the barrel contour symetrical around the bore axis?

Most of these need to be checked on a lathe. One other cause to look for is uneven locking lug bearing; this can be checked by applying magic marker to the lugs, closing the bolt while pushing forward on it, then pulling back on it and rocking it back an forth a couple of degrees a few times, then pushing forward on it again while rotating it to the opening position, then pulling it out. The ink should rub off at least 2/3 of each lug. If it one lug has twice as much or more area rubbed clean than the other, you need to get the lugs lapped.

If the groups are good except one out of 5-10 inexplicably go out and you have 3000 or more rounds through the barrel, it is probably shot out and needs to be replaced.

Of course, you may find the ladder finds a sweet spot, and that's that.

Nick

Thanks for the responses. I bed the action and am waiting for it to cure to shoot again. It is a Remington 700 BDL DM stainless synthtic (sporter model). I don't like the factory stock due to the flex and the fact that the action does not sit firmly in the stock unless you tighten up the screws. I bed it with accraglass and opened up the barrel channel, removing the pressure point.

I've always know that a hot barrel could string shots, but according to what I've been reading, most matches allow only a minute or so between shots. Obviously, they are shooting heavy barrelled rifles, but I never thought that I could shoot that fast and stay on the paper. I have not shot the ladder test yet, but will first. I like the suggestion by Unclenick regarding the 4 groups and will try it also.

Hopefully the barrel is not out of whack, but if I have to, I'll have a gunsmith look at it. Just to make sure I understand, how long should I wait between shots in a group when testing new loads for accuracy?

Thanks agian for the help.
Dan

...the fact that the action does not sit firmly in the stock unless you tighten up the screws...


Something's not right here. It sounds like you had a bedding problem. Also, if the action wasn't tightened down uniformly to the stock, this could explain your problem by itself.

Something's not right here. It sounds like you had a bedding problem. Also, if the action wasn't tightened down uniformly to the stock, this could explain your problem by itself.


That doesn't sound good. Would expect a barreled action just laid into a stock to want to tip to the heavy/barrel end, but in a well bedded stock if the action is pushed down hard by hand just hand pressure, it should tend to want to stay there.

Try this:
Remove barreled action from stock, then replace it.. just snug up the screws barely snug.

Flip rifle over so stck is "Up" and clamp it in a padded vice (done't need a real vice for this, a cleaning vice will work nicely).

Tighten the action screws with your finger tip feeling at the tip of the forend/barrel (If you had a dial indicator, would be a good place to use it...but a sensitive finger can detect some mighty small motions).

Alternate the screw tightening. Loosen one, tighten the other, etc.

IF you can feel movement as you snug the scews up to normal tightness (not Godzilla tightness) you probably have a bedding problem.

I have a Savage 10FP that came with a worthlessly flimsy thermoplastic stock. Resting on a bipod pushed the fore end up against the barrel underneath. The rub marks were my first clue. Funky thing to put on an otherwise accurate rifle, and kept it from grouping sighters off the bipod at the Gunsite PR class I bought it for. I put a Choate varmint stock on it and took it to the Long Range Firing School at Camp Perry the following year and my first 800 yard target posted a 99. Good gun. A ridiculous factory stock that is probably causing needless damage to Savage’s reputation.

Nick

It's hard to explain how the stock fit before the bedding job, but I will try to do so. I have had the same problem with a Rem 700 ADL synthetic in 7mmMag. Before any bedding or sanding, if you squeezed the receiver/barrel into the stock applying pressure right above the barrel lug, the barrel would press on the forend and the rear tang would be about 3/32th of an inch above the stock at the rear screw. If you squeezed the tang down, the barrel would pivot upwards at the forend and leave a space of about 1/8th of an inch between the end of the stock and the bottom of the barrel.

It was so similar of a problem with both guns that I assumed it was simply the design of the guns. Both of these guns shot decently with most loads I shot (about 1.5 inch groups), but I am not OK with that. I know these are not target grade guns, but working with a gunsmith for 3 years taught me that most any modern bolt action can shoot .75 MOA or better.

I bed both these guns with Acraglass and the bedding problem is gone. Both are rock solid and the barrels are free floated well. I have been working up some new loads from scratch for these two rifles and have actually never shot a factory round through them. Not having ever loaded for these calibers, I just did not know how much I could blame heat for the "flyers". There could be a problem with my loads, trigger pull, barrel, chamber, crown, etc., but I could not help but wonder if the hot barrel was to blame.

I think the Acraglass is cured, so tomorrow I will shoot it a few times. I will let you all know the verdict.

Thanks again for the help.
Dan

I have found just in my shooting style that I get too excited when I am shooting and tend to shoot 5 shot groups pretty quickly. I am talking 30 seconds between shots. Just last weekend I was shooting and put my hand on the barrel and could just barely leave my hand on it after the 10th shot. Both groups I had shot before that were not one holers but were honest 1" pentagons.