Do you think glass bedding might help my temp related verticals?

[GJgo]

Hey All,

I have a Sako 75 in 6PPC-USA that I love to shoot. It's 100% factory with the trigger at a crisp 1lb. The barrel is fully free-floated. Last year I did my first ever match with it, just to see how we'd do, and I shot a grand agg (25 @ 100 and 25 @ 200) of .5" using a bipod, a sandbag, and a metal folding chair. So, for my first time, I think I did pretty well and look forward to getting better with practice and experience.

So, here's the issue. When the barrel is cold, the gun shoots high for 3-4 rounds. As it warms up the POI tracks down, and after 4 rounds or so when the barrel is up to temp the POI stays rock solid and doesn't shift as the barrel heats up further, even with 10-15 shot strings.

So, when I did the competition, I ended up spending my low shots as warm-up rounds instead of using them as intended- to judge the wind, etc.. They were esentially useless in terms of gaining information before going upstairs and running the string.

So, is this a scenario that anyone has a known fix for? Ideas or suggestions such as glass bedding? I don't mind one fouling shot, but 3-4 seems excessive.

 

[Chawbaccer]

I would try something non permanent before commiting to it. Have you tried a pressure point at the forend? Just fold up some card until you have a good and tight fit. You can also try for more pressure towards the breech of the barrel.

 

[Strongbad]

If it were just a hunting rifle, I'd concur with the pressure point. On a competition rig though, I think your original thought is the way to go. That thing needs to be floated and properly bedded. You shouldn't have to heat the gun up. That would indicate a stress issue with the gun or it's touching/pushing on the stock somewhere.

 

[nicholst55]

Agree with Strongbad; something is in a bind, and it shifts as it warms up. Eliminate that stress point and your problem should disappear.

 

[BADUNAME27]

V. Strings vs. bedding

Hey All,

I have a Sako 75 in 6PPC-USA that I love to shoot. It's 100% factory with the trigger at a crisp 1lb. The barrel is fully free-floated. Last year I did my first ever match with it, just to see how we'd do, and I shot a grand agg (25 @ 100 and 25 @ 200) of .5" using a bipod, a sandbag, and a metal folding chair. So, for my first time, I think I did pretty well and look forward to getting better with practice and experience.

So, here's the issue. When the barrel is cold, the gun shoots high for 3-4 rounds. As it warms up the POI tracks down, and after 4 rounds or so when the barrel is up to temp the POI stays rock solid and doesn't shift as the barrel heats up further, even with 10-15 shot strings.

So, when I did the competition, I ended up spending my low shots as warm-up rounds instead of using them as intended- to judge the wind, etc.. They were esentially useless in terms of gaining information before going upstairs and running the string.

So, is this a scenario that anyone has a known fix for? Ideas or suggestions such as glass bedding? I don't mind one fouling shot, but 3-4 seems excessive.

Lets pick this apart.

Ok, you have a rifle that strings shots until the barrel reaches a certain temperature.

If the barrel is floated with the receiver being the only thing in contact with the stock, then there's another issue.

It's the barrel itself. Take 100 barrels and spin them in a lathe through the spindle bore of the machine and 99 of those barrels will look like a skip rope down the hole. (here's the really wierd part)

That 100th barrel that doesn't have runout won't shoot for crap. Seriously.

Now, here's the issue and it has to do with how barrels get made.

(this is going to end up being a little long but I promise its worth the read)

Take a round bar of steel and grab it by both ends in a machine (deep hole gun drill) Spin it up to an rpm of anywhere between 1000-2500 rpm (depending on material, type of machine, cutter geometry, etc) now your barrel is supported only on the ends. The center is left unsupported.

The rotational forces, harmonics, vibration, etc are causing some runout (skip roping) at the center of the barrel, however the theoretical spindle centerline does not change and this is what the drill runs on. (assuming the cutter geometry is done right of course) So, so long as that barrel stays spinning, the hole is straight. When you shut the machine off the barrel's outside goes back to being straight and now you have a crooked hole.

The Marquee barrel makers have all developed ways to mitigate this so its typically not a problem with high dollar custom barrels.

but here's where it can get you into trouble again. The barrel needs to be contoured and polished. If this step is poorly done a significant amount of material is left on one side of the hole and it is going to have more influence on the opposite side when it heats up. (expansion due to heat)

This is what I think is happening to your barrel by what you are describing.

NOW to screw this all up again.

If your barrel is a factory Sako chambered in PPC (pretty sure Sako is the only mainstream manufacturer to offer this cartridge btw) then that barrel is almost certain to be hammer forged. Hammer forged barrels can shoot surprisingly well but if you understand how they are made, its easy to see how things could get a little crooked during the manufacturing process. If I'm right then all the bedding in the world isn't really going to do much for you. You may just have to shoot a bunch of sighters at your next match before you go for record.

Make sure your barrel is fouled before you go for record too as this can also cause weird things in shot groups.

Vertical in shot groups caused by bedding issues typically happen regardless of barrel temperature. If your saying the gun settles down once it gets warmed up then you may never get rid of that until you hang a new barrel on the action.


Hope this helped and wasn't too confusing.

Chad

 

[Thomas Garrett]

GJgo, I had the same problem with a couple of my long guns, M1A, 700 Bdl, Gustav (Reinhardt Fajon) conversion., Had all three Glass bedded by a friend ( used to be a President's 100 gunsmith), Fixed all three. Now all shots are on the dot. 1st, 5th or 10th rounds no deviation anymore. Remember once it's done there is no going back unless your replace the stock. Good Luck!

 

[krs]

GJgo,

You didn't say it but it sounds like you participated in a benchrest rifle match?
If so, my compliments on your fine first results, and double those compliments because of the limitations of your equipment.

A Sako rifle in 6 ppc is a fine thing indeed and it is capable of better accuracy than 90% of all the rifle shooters in the country ever achieve, but for benchrest competition it is really not capable of competitive results.

Were there several rifles on the firing line that had stocks painted like custom cars? Actions you didn't recognize? Wide flat forends? Long 36x or more scopes. Thick barrels with little or no taper?

Before you spend a great deal of effort and money trying to improve the results you get with the Sako, start looking into the characteristics of those rifles that I'm assuming you saw.

My first benchrest gun, or rather the rifle that got me intriqued with the pursuit of ultimate accuracy in rifle shooting was a Sako "Benchrester", a single shot version of their Varminter that came with a 2 ounce trigger in the Sako "A" action. Despite all of my best efforts I could never achieve results better than .375" aggregate. I was doing everything right with the wrong equipment.

It wasn't long before I bought a used Hall actioned rifle that had originally been built by Fred Sinclair, the founder of Sinclair's (an outlet of rifle accuracy necessities then, though now they seem to concentrate more in mousegun accuracy things). With that rifle and a new barrel soon after I was on the road to the ultimate in rifle frustration . (My Sako was relegated to a role as a very good field shooter of little pesky rodents. I still have it but never take it out anymore).

There are a couple of useful books that I can recommend. One is glen Newick's "The Ultimate in Rifle Accuracy", and the other is "The Benchrest Primer", a compilation of topical articles written by many of the top dogs of the game at the time. Both are somewhat dated now but I'm not aware of anything better that's come later.

Do you have windflags and are you reloading? A fellow named Bill Gravatt and the above mentioned Fred Sinclair put together a book: "Precision Reloading and Shooting Handbook" which contains a good deal of information about the techniques of the sport in addition to being a fine tutorial in what's needed to produce reliably accurate ammunition at benchrest levels.

To all.....There are several competitive shooting games. Many of them are difficult to do well and those who achieve good performance in any of them have my high regards. I do not want anything above to be taken to mean that I think there is only one way to do accurate shooting. Benchrest rifle is about making very small five shot groups at 100 and 200 yards in all conditions.

 

[GJgo]

Gentlemen,

Thank you all for your detailed posts. I have some thoughts that I'd like to turn into more questions.

Longrifles, Inc.- Assuming your presumption at the end is in fact the case, and I do go ahead and have it glass bedded, is there any chance that it could make it shoot worse?

Also, if I do decide to hang a custom barrel on it in the future, would I not be able to do that if it was bedded?

krs- Thank you as well. I know well that this will never be a competative rig for the BR game, but since I'm not at a point where I can invest in a "real" BR rifle (getting married!) my goal is to learn as much as I can about the game and my ability with this one before I take that next step. In the (registered BR) match I did, I was in fact literally the only person that had a factory rifle- all other 20 or so guys and gals there had a high dollar custom BR rig and those rediculously expensive front rests. I was also the only newcomer. Be that as it were, I still managed to out shoot a couple people. So, I'm very happy with the Sako, and knowing that it will never be a .2 agg gun I am very happy with it being a .4 or .5 agg gun- I'd really just like to see if there's anything I can do for this one little issue of the cold vertical rise!

I do not have windflags yet, nor do I have a good front rest or a decent stool even. Working on it. I do handload and am happy (for now) with my load- I've shot many .2 and .3 groups wth it, just no aggs that small yet! I think the gun can do it- not so sure about the shooter yet..

 

[Horsemany]

At our matches we have a "Varmint class" for guns like that with factory barrels. The full blown customs are "Open class". There is a place in the Benchrest world for that gun to be sure. I'd bed it and see what happens. You've got nothing to lose really at this point.

 

[koginam]

I have found two ways to solve the problem you have. Remove the barrel and heat the barrel in an oven at 300 degrees for 15 hours, or have it cryoed both will remove any stress in the barrel. While it may be hard to find a oven big enough to hold the barrel until I had one made by a potter friend of mine I used a metal garbage can and a heat lamp with an oven thermostat. I wrapped it with a hot water tank insulating blanket, it worked fine. But now I prefer to have my barrels cryoed. After the stress is out of the barrel stringing is gone. I have several varmint rifles that get rather hot while hitting PD's, none have a problem with stringing.

 

[shinz]

Koginam, whilst this is a bit of a thread hijack, hopefully the info will be useful to others in various disciplines. I'm fascinated by your comment re cryo treatment. I have a lightweight barreled hunter in 7mm which I can't get to group for sh*t. Its a very slim contour & while this won't help, it comes from a maker who stress relieved all his barrels before turning. The comments above about off centre holes pricked my mental ears up but your comment re cryo & stress relieving got my attention big time.
Question after a too lengthy preamble Can this cryo bizz be useful on light as well as target contour barrels?
Steve

 

[koginam]

I believe it can help, I have a Oly arms Ar-15 upper 20 inch barrel made in the 80's its not a heavy barrel, it has gotten so hot that oil smoke comes out of the handguard, yet the groups open up only 1/2 inch after fast sustained fireing, but there is no stringing, the barrel was shooting 2 inch groups before I had it cryoed with stringing after 10 shots, (high and to the right) after cryoing the groups remained the same but no stringing. I cryo the barrels before chambering and countering because of the ease of machining and again after they are completed. I don't think cryo will improve accuracy on a bad barrel, if it didn't shot good before it was cryoed it wont shoot any better after, it just won't string the shots after heating up. I have sent many customer barrels in for cryo treatment because of stringing and it has helped them all. Having said that you have to have the barrels cryoed by someone that knows how to do it, it isn't a easy process it has to be done correctly.

 

[GJgo]

That said, who do you use?

 

[koginam]

These guys are very good. Send only your barrel.

http://www.300below.com/cryo-processing/firearms-cryo-barrel.html

 

[shinz]

Koginam, thanks for that response, sorry that I "lost" the thread for a bit. I appreciated the response. We've got an outfit in NZ that does cryo treatment, I'll give them a bell & see what they've got to say.
Steve.