Vertical stringing

[trb0]

Ive noticed all my groups have vertical stringing. Im wondering the cause as i know there are many. My concern is on a few cases i experince a little blowby on the seal. Im discardind these as i come across them. Do you think the blow by could allow enough drop in pressure to cause the stringing? Im shooting 61 grains of 4198 behind a 195 Barnes in about 87 degree heat. The gun is glass bedded and i try to maintain the same shoulder pressure on each shot. I know in a 6 PPC vertical stringing can be reduced by upping the powder but i am near the max in this heat. All sabots have looked good. Thanks for the input. Tim

[Richard]

Tim.........If you are loosing pressure, that relates directly to velocity and that relates to vertical! If you are using a chronograph, (and testing without a chronograph is like taking a bath without water ;D) this should be evident in your readings?
Minor velocity variations are often not seen at 100 yards.....particularly if velocities are relatively high to start with. (a 200 gr. bullet going 27 to 2800 fps might absorb 50 to 75 fps with no noticeable shift in POI at 100 yards) However, at 2 and 300 yards it start to rear its ugly head ;D
Richard

[trb0]

Richard, all groups have been at 100 yards. My only problem is Pacnor had to set my barrel back because the fluting was out of time. This caused me to have to trim more of the nipple than normal and it is almost recessed below the breechplug tool slots. The nipple is now wide enough that the seal is out near the wall of the cace and the cases are not all uniform in this area. Remington .243 brass so now it looks as if i may have to go inside the case and true them up to the same dimensions which is very time consuming but i will do it for accuracy. Tim

[onecardchuck]

trb0,

I don't know if I would be to concerned with your blow by causing enough pressure loss to cause vertical stringing especially at 100 yards. I can verify as many others using 209 primers blow by is just a fact of life, Richard is right the only for sure way to know is to shoot over a chrony.

I also know that when I have a group that has vertical stringing I always end up with an inconsistent cheek weld to the stock, and I mean every time I start to get a little lax that is usually what it is. Also make sure you have a good fit with the gun to you. I do not know what kind of a shooter you are but just offering my two cents when I know the gun has no issues. If you are suspect of the gun then take someone else to the range with you and have them shoot the gun if the same thing happens then it maybe time to start breaking things down.

Hope this helps,

[trb0]

Thanks Chuck. Its a brand new build and ive only shot 3 groups in horrible shooting conditions. 90 plus degree heat and horrible humidity. Something else im concerned with is the barrel sweating on the inside when using a cooling rod. Theres plenty of condensation on the outside. Do i need to run a dry patch thru before dumping the powder? I will get it all worked out im just bored waiting on better shooting conditions. Tim

[onecardchuck]

Tim,

I always run a dry patch through after the cooling rod because if you get the powder wet that will affect velocity and also could cause vertical stringing.

Best of luck and keep us posted.

[edge]

IMO, there is a HUGE difference between blowby with a 209 and that using a case with a rifle primer!

The 209 primer fits inside the nipple and while you get some blowby the majority of the flame is forced to follow the hole through the BP and it prevents most pressure from coming back through the BP.

With a case and rifle primer if you have more than a few thousandths of clearance then much of the flame can go around the nipple causing inconsistent ignition and does little to stop pressure loss through the BP.


IMO

edge.

[nic58]

Maybe something in this article can help?

www.6mmbr.com/verticaltips.html

[Richard]

trbo.............Herman and I shoot in very hot and humid conditions just about every week in the summer. I NEVER feel any condensation on the exterior of my barrel. When I remove the rod it is always dry. Prior to putting it in the barrel, I dry it with a cotton terry bath towel. I then wipe with a paper towel. The rod is inserted for 30 to 45 sec. and withdrawn dry. I use two patches to condition the bore. Herman uses NO patches after removing the rod and he has no problem with condensation? I am not making my barrel "Cold?", just removing the heat leaving it close to ambient temperature...........No sweating!
Richard

[trb0]

Thanks Richard this may be part of my problem. Ive been using 2 cooling rods and the barrel is very cold to the touch with plenty of sweating.How long after the shot do you put it in , leave it, then load it after removing it. This in 85 to 90 degree heat. Thanks Tim

[moto357]

just to verify what edge said, when i first put my remington together earlier this year i tried mill out the inside of the cases for uniformity. i had a hunch my drill press being older than dirt might not be 100% square, but had to trust in the process. long story short it wasnt quite square and was getting exactly what was said, miss fires, hang fires and various fps.

[trb0]

My situation is a little unique because of them setting the barrel back to retime the flutes. I chucked my breech plug up in a lathe to make sure the nipple was perfectly square and checked it with a concentricity gauge. It now comes really close to the case wall and if you look inside the case in this area it is rounded at the shoulder. I have minimized the blowby except for a very light smoky haze on the inside of some cases. I just got some xtp's so i can practice without spending a fortune. I will set up a chronograph and check my velocities. Thats about all I know to do.