Inconsistent Neck Tension

[c18rch]

I have been having problems with the accuracy of my .243. It will shoot 1/2 moa 5 shot groups all day long with brand new brass and is still ok on the second reload. But by the 3rd and 4th reloads the groups open up to 3 inch!!

I pulled the bullets with an RCBS mechanical puller to see if the powder charges were consistent but found the bullet tension varied greatly from bullet to bullet.

I am using Sierra bullets and Lapua brass which i have since measured and weighed and they are consistent. The load is fairly mild 41g of Vit 160 and i clean the insides of the necks to remove fouling and resizing lube.

Anyone any ideas??

Thanks

 

[jb1000br]

Explain your sizing process.

 

[c18rch]

I lube the insides of the neck using a rcbs neck brush and rcbs case lube. Very little lube is applied to each case and only on the inside of the neck. I then size the case using either an rcbs FL sizer or hornady neck sizer set up as described in the instruction leaflet until the shell holder bumps the bottom of the die then backed off 1/4 turn. I then clean insides of the neck using a piece of disposable paper cloth.

 

[USAPatriot]

I lube the insides of the neck using a rcbs neck brush and rcbs case lube. Very little lube is applied to each case and only on the inside of the neck. I then size the case using either an rcbs FL sizer or hornady neck sizer set up as described in the instruction leaflet until the shell holder bumps the bottom of the die then backed off 1/4 turn. I then clean insides of the neck using a piece of disposable paper cloth.

Just out of curiosity why are you lubing the inside of the neck? I've never sat down with anyone while they loaded their ammo, but in 25 years or so I've never lubed the inside before and even the outside, any lube that gets on the neck is incidental to resizing the body, or if I'm just neck resizing I'll give the neck a wipe with a silicone cloth, resize and leave it at that.

My first guess as to the cause of your problem is that after 4-5 firings your case necks just need a proper resizing, all using the same sized bushing, so the bullets will have the same neck tension holding them in. I'm not familiar with Hornady equipment so can't say what those dies are doing for you. -Rod-

 

[bigbull]

I also lube the inside of the necks and have never had a problem. The only diff. is that I use a Q-Tip soaked in a degreaser to clean the lube after the case is sized. Perhaps there is lube left inside the neck and giving you inconsistent tension. If this fails to cure your tension problems I would try annealing the necks or changing brass lots. Also check for neck thickness between your cases just in case although Lapua is usually very consistent.
bigbull

 

[dgc940]

Out of curiosity do you anneal your brass?

 

[jb1000br]

I don't think neck tension is the issue here...

If you are setting the die to touch the shellholder, then backing off 1/4 turn, then you most likely are not moving the shoulder upon resizing.

This may be causing headpace issues that the rifle doesn't like.

You need to measure headspace.

https://www.hornady.com/shop/?ps_session=f99397a2e5139fb2bf44d0d4d6c73354&page=shop%2Fbrowse&category_id=4ffc0a8772783e83440ac87ed0c3ee5b

Shop around...

Also, RE: neck lube...I don't like the idea of burning more petroleum products in the bore than I have to. I lube my necks with dry moly powder from NECO www.neconos.com and it works great to make bullets seat consistently.

Hopefully you still have a batch of loaded brass that shoots well...measure the HS before firing, and compare that ## to the batch that doesn't shoot well.

JB

 

[c18rch]

I am definitely bumping the shoulder back. I place a small blob of grease on a case shoulder to check this. The grease was spread once re-sized and the case was dented where the grease was placed. This would also not explain why some of the bullets were more difficult to pull than others would it?

I'll check the head space anyway though.

Thanks

 

[jb1000br]

spreading grease doesn't mean you moved the shoulder.

The amount the neck tension may have been off due to neck hardening would not turn a 1/2" gun into a 3" gun. I bet if you had a 3-thou difference in neck tension it still wouldn't shoot 3"

Something else is wrong...

JB

 

[USAPatriot]

A 1/4 turn seems excessive though...but again, Hornady dies and I are strangers. With my Reddings, and formerly with RCBS, I put just enough space between the die and shellholder to see daylight between the two as viewed with a patch on the otherside to catch some light.

Um, how many rounds have you put through this rifle? Through the barrel? Are you the original owner? -Rod-

 

[memilanuk]

'Quarter turn' and 'blob of grease'... Do yourself a big favor and get the right tools to measure things. Get either a Hornady headspace comparator,used to be Stoney Point) or a RCBS Precision Mic, and measure this stuff right.

If you do the math, which is pretty simple, 7/8x14tpi dies move 14 complete turns per inch of travel, or one revolution of the die,360°) moves the die 1/14th of an inch. 1/14th of an inch is about 0.071". 1/4 of *that*, is a little under 18 thousandths. Thats how much you are backing that die off. Not 2-3 thousandths, like you would be if you were using the proper tools.

Did I mention get the proper tools?

Just tryin' to keep you safe, man.

I don't, at this point, have a good answer about your varying neck tension,you mentioned bullets took different amounts of force to pull). If you still have some cases that should shoot well, and pull the bullets from them, and compare that to the ones that are *not* shooting well... what kind of difference do you observe?

 

[c18rch]

Thanks

I'll let you know if I find anything. This is the same proceedure I use in all my rifles all use lap brass, vit powder and rcbds and hornady dies but this is the only one causing problems.

 

[ArtinNC]

I'd say if you anneal the necks it will probley take care of the Inconsistent neck tension . If you have over sized the necks a couple of times they work harden.

Art

 

[arthurj]

I don't know enough to say, but just throwing this out, could there be some donuts forming in his cases?

 

[Lane]

I have recently registered to this site. I know there are many variables specific to your specific problem. Methods, techniques, can be addressed by people that have more experience then myself. Obviously you are still working with your original batch of brass as one of your load components. I'm curious if you still working with your original supply of primers, powder, bullets. Another consideration that is basic but important is changing out components from lot to lot as a variable. I wish you luck in correcting your specific problem.

 

[jo191145]

I won't get into all the possible variables but.
Switch to graphite for your necksizing.
If your brass is the real culprit you should feel a difference when neck sizing.
If you can feel a difference in the force required to seat a bullet accuracy is sure to suffer.

Did somebody say Donuts? I'm hungry!!

 

[c18rch]

I have checked for donuts. There are none.

I loaded 50 rounds up yesterday using my usual load and shot 2 25 shot groups. Out of the 50 rounds 30 or so went into an inch group with the remaining 20 going out of the group. I reloaded the 30 or so cases that grouped again and have shot them today. They all group fine. 1/2 moa 5 shot groups.

I also managed to get hold of some sako brass and found that 41.5g of vit 160 shoot just as well. These are once fired. I have not had chance to reload them yet to see if the same problem occurs with these cases after multiple reloads.

 

[Lane]

A observation and a assumption on my part. You seem to be chasing minuscule groups. Perhaps it's time to review the case/chamber measurements. Sometimes the measurements taken new-unfired brass, measurements after firing, and then once more after sizing through what ever technique neck, full or partial will tell a lot about problems. Review the measurements taken with the datum length compared to the SAAMI minimum. The fix to your problem in my opinion will be found comparing all the measurements in your load notes. A idea that may help!