Does virgin brass spring back more than multi fired?

[deadlyswift]

Guy's, I'm not sure as to why my necks are not expandeding like I thought they would? Upon fire forming and in the very first stages of working up a load for my 6br Broughton 5c barrel here is what I'm getting.

Once fire Lapua Brass

28.5 gr working up to 31.5gr of varget

95gr Berger hunting Vld

CCI BR4 primer

Broughton 5c barrel

Chambered with my Dave Kiff Reamer .272 neck

Now I was expecting my necks to come out around .271, .270 at the least. Well they are coming out .268 That would be .004 spring back? I loaded my brass striaght out of the box. About 50 ramdom pe. of my first choice of weight sorted brass chambered just fine. So.... I figrued I'm neck sizeing and I would just load straight out of the box and shoot. Fire form, break barrel in, and see what direction to go in when preping for my ladder test. So... is my caliper lieing to me? I'm using a $40 Lyman caplier that I have had since 1997. Are they getting worn and not accurate? I have shot up to 31.5gr. (all powder charges where loaded to touch lands) with no pressure signs. So... am I not pushing enough pressure's to expand the brass fully? .004 spring back seems to be a bit much, (way much IMO), but my Virgin brass loaded dia. is .266. Is Virgin brass just that stiff? My Unfired brass is messuring .264. I do need to figure out what is going on, so I can choose the right bushing to use, or order the right bushing to use in my die? Neck tension is a big deal to me, and has serverd me well so far when working up a load in the past. I don't like to brag a lot, but I'll post a pic of a 5 shot group just for you guys to see. The barrel is shooting well and very early! Only 45 rnds down the tube and this is where I'm at so far. 95gr berger 31.3gr varget seating to touch. Target was shot at 150yrds.

I feel this gourp is a great group. I do love my Broughton Barrrel so far! It's just the messurements on my once fire brass (necks) have got me stumped, as to what to try next? What bushing to go with? Do I trust my caliper's? I can slide the 95gr berger in and out of the neck with just a slite push when the bearing surface enters the mouth of the neck, and I mean a slight push by hand! This is with once fired brass in a .272 chamber, but the neck is messuring .268 on the Capliers? I figured on a .267 bushing, but not with a .268 fired neck? If anyone can tell me, or explain to me what I'm doing wrong, or what might be wrong with my equipment (capilers) It would be greatly appreciated!!
Thanks
Mark

 

[RonAKA]

In another caliber and brand of brass I have seen fired brass neck OD's much smaller than I had expected. This was with a light to modest load. After I had the issue I annealed the brass and increased the load. Now the necks fire form larger and as expected.

I did not see that with Lapua brass in 6BR. In theory softer brass should spring back less, and as it work hardens it will spring back more.

This said, the fired size is somewhat irrelevant to choosing a bushing for sizing. The important factor is the diameter of your bullet or even more specifically the diameter of the pressure ring, and the thickness of the brass in the neck. Combined this can be measured by the OD of a loaded round (measure in the pressure ring area of the neck). Subtract 0.002" from this number and you are very close to your ideal bushing size. On my older cardboard box Lapua this works out for me to be 0.267". However, it seems the newer blue box brass is 0.001" thinner, and on the diameter the bushing may need to be 0.002" smaller, or say a 0.265".

Hope that helps some,

 

[fdshuster]

Mark: My loaded round neck dia. with the older Lapua 6BR in the brown cardboard box has a loaded round neck dia. of .269", with an occassional .2685". Fired case neck dia. as they come out of my .272" chamber necks (2) are .271" with an occassional .2705". Are you using the new Lapua in the blue reusable plastic box? I know you have the chambering reamer so I'm assuming it is stamped .272 NK? Most all my ctgs. do have a spring-back of .001" total regardless of number of firings on the case. Let me know what you find, I have a blue box of Lapua 6BR, but have not loaded any yet. Can you take the measurement with a micrometer?

 

[bozo699]

Mark,
I am sorry to report I can't help you with your spring back problem, but if shot a group like that out of a new barrel with breakin loads @ 150 yds.
I WOULD BRAG That is a awesome group.
Wayne.

 

[jo191145]

Failure to obturate?? Its possible.
Since I had my first issue with hardened brass I keep a close eye on such things.
I would'nt expect it from new brass but stranger things have happened.

Simple test: Try to seat a bullet in a fired case. Does it fit? With a .272 chamber and assuming "blue box" brass it should be a little loose.
How much carbon on the necks?

First thing I would do is load up one rd in .3gn increments and shoot off an Audette ladder. I would start at 31.3 and go higher yet. See if theres a point where your brass comes out at .271-.270.
If it does you know the problem.
Mandatory warning.... You know your over "book data" already. Use your own discretion.

 

[deadlyswift]

Frank,
Yes my reamer is stamped .272. It has the NK and the FB stamp on the end. I am shooting cardborad box brass. Bought the brass back in Feb of this year. Neck wall thinkness is .013 messured with a ball micro meter. I think out of 300 pe I found 1 pe that was .014. The once fired brass messures at .268 on my calpliers, and the bullet will slide in to the case by hand. I'm still leaning toward my capliers not messureing accurate? Maybe try my uncles capliers and see what they give me. Might even take the brass to work and messure with some of the machinst's capliers on the other end of the plant.

Jo191145,
yes this is what my next step will be once I get at least 100 pe. fire formed. The 95gr bullet isn't the bullet that I'm going to shoot in this rifle the most. I will be shooting the 105gr berger vld in comp at 600yrd, and sometimes at 1000yrd. I'm taking my 2 other Broughton barrels to my smith next week to chamber them in 6brx with my Dave Kiff reamer. The BRX I will most likely end up shooting at 600, and 1000. Pushing back the 6br barrel as a varmint barrel. I'm aware I'm well over book data. I always start loading with a mild load from book data, and 9 out of 10 times with every load I have worked up, I'm well over book max, before pressures show up. Even in my factory 308 barrel I don't get pressure signs with the 175gr berger long range BT bullet until 45.8gr of varget, and thats in 96* 60% humidity. Even then I'm only getting a small ejetor mark on the head of the case. Not until 46.2gr do I get flat primers and stiff bolt lift, but 44.2gr with a .010 jam, and a .336 bushing is where peak performance is at. That load preforms even at 1000yrds F class at Camp Butner.

Wayne,
I try not to brag much! Usally when I do it bites me in the butt, and I end up making a fool of myself, so I try to keep a low profile. Thanks for the compliment on the group. Even tho It may-be a great group for 150yrds my ???s are will it do it consently. So this is the reason for me trying to work out witch bushing to start with upon loading for my ladder test. I will say I'm very Impressed with Broughton Barrels!! This barrel broke in literally under 5 rounds. I kept cleaning with different numbers of shots down the tube, because I just couldn't believe what my patches where telling me. Broke out the Hawkeye at about 15rnds total, and the Hawkeye spoke the truth, and backed up what the patches were telling me. Shot 5 more and cleaned just for the hell of it because I have never had a barrel break in so quick. Shot 25 rnds after that without cleaning. (5 rnd sessions) After the last 5rnds I ran two wet patches of Butch's down the tube while it was still warm, packed up and came home. Barrel soaked for about 2hr with those 2 wet patches. Ran a bronze brush down the barrel 10 times. (wet) Lliterally...I ran 4 wet patches, and the barrel was clean! I confrimed it with my Hawkeye bore scope. The barrel was as clean as the day it came home from my smith. All tho I have until this barrel only worked with factory barrels. I'm wanting custom hand lapped barrels on everything I own now! I knew things would be better with custom barrels compared to a factory barrel, but I wasn't expecting what this barrel has done! It's kinda like I'm in a whole knew world now! I'm still a little dumb founded as to what I have seen out of this barrel with only 45rnds down the tube! The day this group was shot. I shot in a condition that I always have tried to avoid. (shooting in a boil) Conditions where some what good that day. Light winds 3 to 4mph from left to right. Before I shot this group I was really studying what the wind was doing. The boil would hold for 10sec or better and then a slight 3 to 4 mph wind would come for about 4 or 5sec. I chose to shoot in the boil because it held longer and was more consitent. I got off 3 rnds in the same conditions then had a slight wait and got the other 2 off in what appeared to be the same conditions as the first 3.

Back to my topic I guess I'm trying to figure out if my tools are messuring right? I was expecting .271 or .270 fired necks. If my capliers are messureing .268 with fired brass on the neck? Some ppl even size with a .268 bushing.....So if they are sizing with a .268 bushing, and I'm getting a .268 unsized neck would the bullet even slide into the case by hand? This is what has me stumped. I'm wanting to try and have .003 clearance with my loaded round. My reason for going with a .272 no turn neck. expecting my necks to come out .271 sizing down only .004 with a .267 bushing, then having a loaded round of .269 in a .272 neck. Not that this would be the right bushing or what would produce the least runout, or best groups, but it was what I kinda had in mind where my starting point would be, and minimze barrel life on load development?
Thanks
Mark

 

[jo191145]

Mark

Quite possible its your caliper then. They do go bad.
I had the same cheap pair of Frankford Arsenal since I started loading. Worked great for years.
Buddy dropped them on the deck. Threw em off .020" and even after recalibrating they just aren't accurate.
Buddy got me another cheap set and they aren't worth didlly either.
To be honest I don't have a pair at the moment I trust. Good thing Christmas is coming.

 

[gilream]

I'm not a competitive shooter but i have found that a good micrometer is the only way to get an accurate measurement on your case necks. The caliper is just not the tool for the job IMO. You need to measure accurately down to the thousanths of an inch. I've used a mitutoyo mechanical micrometer and a digital mitutoyo caliper for 15 years and love 'em. Congratulations on some great shooting and i share your enthusiasm for the custom barrels. I rebarreled a 7MM Rem. Mag this year with a Douglas premium barrel and was amazed as well with the easy break in and easy clean up. Virtually no copper fouling at all.