Question about vertical stringing shots?

[Jasper1573]

Today, I was shooting in a 500 yd F-Class match. My first sighter shot on a 10 inch metal plate was about 4 inches at 6 o'clock.

My scope was adjusted 7.5 MOA up to compensate for a 300 yard zero. About 7 or 8 shots into the string of 20, I dropped the elevation adjustment down 1 click to 7.25 MOA to compensate for barrel and chamber heating. Of the first string of 20, they were all in the 9 and 10 rings with a few inside the X ring.

While later talking with another shooter, he remarked that maybe I needed to have the rifle stock bedded and the barrel floated. I explained to him that the stock came with an aluminum block from the factory (HS Precision) and that the barrel of the rifle is free floated from the factory (Remington 700 5r in .308 Win).

He persisted in a very nice way that vertical stringing is usually a symptom of the barrel in some way having a binding tension on it. I replied that I believed the issue was an unfouled barrel that upon fouling and heating, caused the ammunition to shoot higher due to heating in the chamber after several rounds had been fired.

Do you think that there may be an issue with the floating of the barrel once it heats up and thereby putting some tension on it during firing?

 

[triggerman770]

vertical stringing

how much clearance do you have down the barrel channel? It needs to be about the thickness of a business card to give room when hot. it should also be consistant the length of the barrel.
Did the rifle come from the factory in the HS stock?
also get a torque wrench or driver and be sure your action screws are the same number.. with the aluminum block you can torque them to 65 inch/lbs.
try running a card the length of the barrel and see if it binds

 

[Jasper1573]

Yes, the rifle came from the factory with the hs precision stock. There is well more than a business card thickness on either side of the barrel between the barrel and the stock, probably a 1/16 of an inch or more. I did notice that the distance from the barrel to the stock is slightly different on each side, but the gap is large. I thought this was odd, but I have seen other rifles like mine, and they are not exactly centered in the fore end of the stock either. You would think they would be, but no necessarily so. I will check that the screws holding it all together are torqued to 65 inch pounds as well as the clearance under the barrel.

Thanks.

 

[triggerman770]

one more thing

check your bases on your scope, they shold be 30-35 inch/lbs. and of course the ring clamp can be 40 or so inch/lbs. if a base is loose it can cause verticle stringing

 

[rbernie]

Vertical stringing can also be caused by velocity fluctuations. It may not be the rifle but the ammo....

 

[GIJOEL]

As rbernie said velocity...
The ammo can be affected by the chamber of the rifle getting progressiley hotter. Pressure increases with heat, and more pressure means more velocity. If you load a round in a 200 degree F chamber and it sits there for 10-15 seconds the velocity would be affected compaired to a round loaded into a 75 degree chamber.

 

[gamestalker]

I encountered the exact same thing with my 700 and after searching for every possible cause, I found it was the scope rings. After the first couple rounds they would begin to change orientation. I discovered it when I was swapping VX-III's from another rifle thinking it might be the scope. I discovered the rings had actually been flexing and digging into the bases. I changed the rings out with a Leupold Dove tail set up, and now my groups are consistently together rather than stringing.

 

[Jasper1573]

I appreciate the info and advice. I tend to believe that GIJOEL's diagnosis might be the closest to the truth. My rings are Larue Tactical QD rings, and they return the rifle to the same zero each and every time. They are mounted on a Larue picatinny rail.

The ammo is handloaded by me, and I have found that it is pretty consistent, plus or minus 25 fps from a cold chamber, but when the chamber heats up, I pick up some velocity after it has reached a stable temp, say after 5 rounds or so.

I truly didn't believe that the rifle has any real issues, but I am asking to ensure I am not missing something. I will have my gunsmith take a look at it next time I have it up there.

 

[GIJOEL]

I have been reading Understanding Firearm Ballistics by Robert A Rinker. I can process about 20 pages a night if I'm lucky but the information is invaluble if your into reloading or accuracy or anything involving shooting stuff. I probably would have passed over your post a week ago without a second thought having not gotten through Ch. 4 and 5!

 

[twofifty]

Jasper, what do you use for a front rest?

 

[Jasper1573]

First, twofifty, I use a Harris bipod in 6-9 inch size. It is fastened securely to the front swivel button on the forestock.

Second, GIJOEL, can you enlighten me/us about what is in chapters 4-5 that specifically caught your attention?

 

[edchun]

I would have said ammo, but if your handloads have that small of an ES-- it's probably not that. Rings and rails have varying torque specs by manufacturer. I use seekins rings and badger rail. Rail to receiver is 15 in/lb. ring to rail is 55 in/lb and ring to ring is 15 in/lb. FWIW. Maybe it is your breathing. I find that if don't release the shot at the bottom of my natural respiratory cycle, I will string vertically. Good luck.

 

[Jasper1573]

Yep, breathing control is something that I work on with each shot, but also heartbeat. I can control my breathing, and let the round fly after 3 long breaths, but timing it between hearbeats is a true challenge.