Headspace difference affecting group sizes

[jsthntn247]

I've been trying to figure out why my load is horizontally stringing on my 300 yard targets. I worked the load up using a ladder and OCW test and knew it was in a large node but couldn't get rid of the horizontal. By accident I set my fl bushing die up and set the shouders back .004 on 11 cases instead of my normal .001. To my surprise when I shot a 15 shot group in pracitce (11 set back .004 followed by 4 at the normal .001) all 11 bumped .004 stayed in the X ring followed by the last 4 (.001) stringing as normal. I let the barrel cool for 30 minutes and shot an 11 shot group that was the exact same load as the first one except all of these had been bumped .001 and they strung just like the last 4 had. I let the barrel cool again and shot 7 rounds bumped .001 but at .015 off the lands instead of jammed like the first 2 groups, and all shots strung again. I loaded up 20 rounds bumped .004. when I got home, and shot them the next day without any horizontal stringing problems. Any ideas on what is happening? The 3 targets from the first day are below.

 

[Alex Wheeler]

What action?

 

[jsthntn247]

Stiller Predator

 

[Grimstod]

I have never heard of tuning your headspace. :-\ sure doesn't look like a coincidence. What sort of action are you using?

 

[searcher]

What was your initial bullet seating depth? If it was ajam by just a few thou or close to jam and reacted better when you increased the shoulder setback, it may indicate a preference for not being jammed or as much as it was. My own experiences have been that a few thousandths in shoulder setback variation will not affect a group at 300 yards the way yours has been as per your photos. More likely, your gun is showing a preference for light jamb or wanting to be off the lands a bit alltogether - and the extra shoulder setback allowed that to occur. When you moved the bullet out .015" off, that was a big move and your gun simply may not have liked it that position either. Perhaps a retry using your original load, only increasing the bullet seating by .004" or so will put the bullet where you had it, without the minor inconsistencies of the shoulder setback can cause.

 

[stool]

HEADSPACE IS A FIXED CHARACTERISTIC OF THE GUN, head clearance is what you are talking about. how many times did you fire your cases PRIOR to establishing your base sizing ??
MY GUESS is that you used once fired brass and it was not fully formed to max chamber length. more firing, longer case, needs more sizing.

 

[Raythemanroe]

I think most would say seating depth adjustment is needed

 

[jcampbellsmith]

I'm not sure I follow your process. I suggest you start your load development again using one size of case. You've too many variables in the mix at the minute to draw any useful conclusions in my opinion.

Regards

JCS

 

[fguffey]

Re: Headspace difference affecting group sizes

I will assume you are saying the case has head space.

SAAMI SAYS: " that is one of the most common misunderstandings....etc.." The case does not have head space, the chamber has head space, the case has length" The length of the chamber is not adjustable.

As to your question about the length of the case from the shoulder the case head: TIME, the answer is time.

F. Guffey

 

[Raythemanroe]

How are you measuring the "headspace"? I would leave or adjust the die to bump .001 and then trim your cases.. Then start over with seating depth.

Ray

 

[gaboon]

I think most would say seating depth adjustment is needed

I'm not sure I follow your process. I suggest you start your load development again using one size of case. You've too many variables in the mix at the minute to draw any useful conclusions in my opinion.

Regards

JCS

+1
Let the gun tell you what it likes.

 

[bigedp51]

When you pull the trigger the firing pin hits the primer and pushes the case forward until the shoulder of the cartridge case contacts the shoulder of the chamber and the cartridge goes bang.

The case with .004 shoulder bump pushed the bullet .003 further into the lands.

In 1969, Tommy Roe had a hit single called "Jam Up and Jelly Tight" :

 

[Erik Cortina]

Go back to the brass that's bumped .001" and seat bullet .003" deeper and shoot a group, then .006", .009", etc. do a test that covers about .021" (7 groups) and your groups will shrink.

 

[22BRGUY]

I agree with most here that say the headspace is the first item to be addressed and then to have between .001 and .002 shoulder bump/ headspace set as a proven beginning point of building precision accurate handloads. From there, we can begin to experiment with various powders and powder charges, bullets, seating depths, primers, etc etc etc. but headspace is not a primary tuning method outside of the .001-.002 area. Without a doubt, by changing your headspace, you would have different group size differences, but to start with .004 or other longer headspace dimensions would not be a place to start from to develop your most accurate loads. JMHO

 

[artbosco]

Easy solution. If headspace difference is effecting group sizes, eliminate the difference. Accuracy is all about consistency, consistency, and consistency.

 

[jsthntn247]

Easy solution. If headspace difference is effecting group sizes, eliminate the difference. Accuracy is all about consistency, consistency, and consistency.

I will, I always want to know "why" something happens in order to possible prevent something similar in the future from giving me problems.

 

[stool]

but then you are wasting time and effort on an error and not moving forward. get back to the accuracy challenge and skip the error enlightenment.

Easy solution. If headspace difference is effecting group sizes, eliminate the difference. Accuracy is all about consistency, consistency, and consistency.

I will, I always want to know "why" something happens in order to possible prevent something similar in the future from giving me problems.

 

[Raythemanroe]

You will save your self a headache and components following the advice given I notice your talking about shoulder bump like bumped or jammed like in seating depth.. I think Erik means to bump your brass back .001 with the die..


Ray

 

[LRPV]

When you pull the trigger the firing pin hits the primer and pushes the case forward until the shoulder of the cartridge case contacts the shoulder of the chamber and the cartridge goes bang.

The case with .004 shoulder bump pushed the bullet .003 further into the lands.

In 1969, Tommy Roe had a hit single called "Jam Up and Jelly Tight" :

If the difference was truly caused by the shoulder being set back more on those particular cases then I'm with Ed. Try some loads with the bullets seated farther out not deeper in the case.

 

[jsthntn247]

Go back to the brass that's bumped .001" and seat bullet .003" deeper and shoot a group, then .006", .009", etc. do a test that covers about .021" (7 groups) and your groups will shrink.

When initially working the load up I found the center of the node at 100 using the ocw method then I verified that with a ladder test at 300. I then took that load and started with a jam and worked out to. .039 off in .003 increments. It shot best jammed to .006 off with jammed having 7 fps e.s. for 10 shots.