Inconsistent groups

[rogersdan]

I have noticed that after the first 20-30 shots the groups from my High Standard (Citation, Hamden) open from 2" to 5-6". I thought it might be fatigue or poor technique, but I've carefully checked it using a rest - same results. It doesn't matter if the barrel and chamber are clean or if it has 400-500 rounds through it, the gun shoots much tighter groups with the first 20- 30 shots of the day. Any ideas what the problem might be?

Thanks, Dan

[yana]

If its not due to anything dirty than the only thing I can thik of is (barrel) temperature.
Do you shoot fast?

[rogersdan]

I shoot 5 shots - usually takes a minute, maybe two - look through the scope, reload, shoot again. I have never noticed the barrel being "hot".

[-TT-]

If it happens every time, clean dirty or otherwise, I'd guess it's the chamber tightening up with a little heat. Seems like a much larger change than expected though. Does it happen with different brands of ammo, especially US vs European?

Maybe try pointing a hair dryer at the chamber before firing and see if it groups tightly from the get-go? If so, a good gunsmith might find a fix.

[rogersdan]

I've tried three different ammos; CCI Standard, Aquilla Target and Aquilla Pistol. Results are the same regardless, after 20-30 shots the groups open up. Thanks, Dan

[oldcaster]

If you are shooting iron sights, I would check the rear sight and make sure it isn't moving. If the spring is missing it will flop up and down. If you are shooting a red dot, I would suspect either the rings are moving or the scope is messed up. I doubt seriously if the gun is actually shooting that much different because a few shots have been run through it.

[ojh]

Just a sidenote: according to what I know about physics, when the chamber warms up it should expand, not tighten. Heat expansion is like enlarging a photograph, proportions stay the same.

rogersdan, when you tested it using a rest, was it a rigid clamp like Ransom Rest or did you hold the pistol in your hand and used sandbags etc? If the latter, then the human factor is still present. Also if you have to aim each shot, possible problems with sights have an effect.

[noproblem]

Ask someone else to shoot 0 - 50 shots and see you get the same results. Ask them without telling them what you are looking for to see what happens

[JD Mahan]

Just a thought, check to make sure your front sight isn't loosening. I had that problem on one of my barrels.

[aprilian]

To rule in (or out) the heat issue, take a heat gun to the range. Shoot 10 shots on the cold barrel and then heat it with the heat gun. If your accuracy falls off at that point it is something moving with the heat expansion. If not, you get to test what else can be different at the magic 25th shot.

Make sure you only use one magazine in your future tests. Multiple magazines (particularly with the HS) will add an unneeded variable.

[trboat]

At what range?
Are you sandbaging or a clamped rest?

I have the same gun which groups 5/8” or so rested at the short line and holds that.
I assume it would do better than that in a Ransom
I am with the poster above- have someone else work with gun and see if the result is the same.

[10M_Stan]

If this is indoors at ~50 feet, then the only critical factor I can think of is a worn or damaged crown on the barrel. That's fairly easy to check with a clean barrel and a magnifying glass. Good luck!

[CR10X]

(1) Check and make sure the barrel stud is not so tight as to create a bulge or high spot in the barrel. Generally you will see leading there if it is. A tight pull through with a patch will help you find choke spots.

(2) Even worse case is where I had a HS Victor barrel with one of the rib mount holes drilled all the way into the bore. The gun would shoot great when it was clean, but after a few shots it would get progressively worse. The lead would eventually plug the hole and then create a point where the lead would begin to streak down the barrel from that point.

(3) Check the chamber and see if it is to proper dimensions or rough in the throat area. Some HS can benefit from a little touch up with a finishing reamer, in particular right at the forward end of the chamber (where the carbon ring starts to form).

CR