New 6br, help reading pressure and load development

[Broz]

I picked up my new build in 6br and now have the barrel broken in. So I started load development. Barrel is a Kreiger 1 in 8 stainless LT Varmint 28". O give touching the lands is 1.813". I started with 105 Bergers and 107 SMK.s and Varget using CCI 450's. Anything over 28 gr and I start to see cratoring of the primer. I took it to 30 gr and the cratoring was very evident. However, no other sign of pressure. No shiney spots on head, very smooth easy bolt lift. Should I stay with the 28? It shoots well but velocity is down. According to my exbal program with corrected dial ups, I am just under 2700 MV.

I have loaded for years but never for a 6br.

Thanks for any help.

Jeff

 

[NorCalMikie]

You might try that same load with the bullet jammed into the lands about .010. Might just eliminate the pressure problem. Won't cost you anything to see.

 

[halfmoanut]

I would try a different primer,450's are actually a magnum primer.headspace could also be an issue.All of my reading of a BR is 2850-2900fps is about tops in velocity.

 

[rocketron]

check the size of the fireing pin hole. that was/is the problem with my 223 and 6br (rem action) the primers had a crater but the edge of the primers were still round. the 223 bolt was sent out to get bushed because it was the worst of the two.

 

[fayettefatts]

I have loaded for the 6br for two seasons now. From what I have read, primer cratering can be a sign of high pressure. It can also be caused by a loose fit between the firing pin and bolt. My rifle craters primers as well. When I work up loads, I don't worry about cratering. Look closely for flattened primers or ejector marks on the case. Any marks and I consider the load to be too hot. I've also read that jamming the bullet in a 6br may actually reduce pressure. Magnum primers have thicker cups than standards, so I would guess that standard primers would crater worse. Good Luck!

 

[Laurie]

check the size of the fireing pin hole. that was/is the problem with my 223 and 6br (rem action) the primers had a crater but the edge of the primers were still round. the 223 bolt was sent out to get bushed because it was the worst of the two.
(posted by Rocketron)

+ 1 on that. The 6BR with a small primer, likewise other such cartridges including 6.5X47L, really need a small dia, firing pin with a close fit in the bolt-face hole to avoid primer cratering, which very quickly becomes primer piercing which you definitely want to avoid. My Remy 700 action / Border Barrels 6BR runs 105gn Berger VLDs above 29.7gn VarGet which is almost as high as I can go without problems, anmd that produces a relatively modest MV just under 2,800 fps from a well-worn barrel.

I also have a 6.5X47L built around an FN SPR tactical rifle action (Winchester 70) with an even fatter firing pin and it craters at very low loads, so I have to run 150-200 fps down on other people's rifles using BAT or Barnard actions.

You don't say what your action is and I can't tell from the photograph, but that's almost certainly where your primary problem lies. The only answer short of a gunsmith turning the pin down and bushing the bolt is to use BR / SRM primers which use thicker / stronger cups than standard models. CCI-BR4 and CCI-450 are very tough, Rem 7 1/2BR better than standard models, but will crater at lower loads than the CCI models. I can't speak about Fed 205Ms never having tried them in my rifles. The other answer is to keep the loads down of course, just find a 'sweet spot' that groups well under the charge weight that produces serious cratering. You can live with minor cratering, but really do want to stay below the really bad level that will likely see primers pierce if something changes that increases pressures on the day, such as it bein g very hot, even though VarGet is classed as a heat-insensitive 'Extreme' powder.

I hope this helps.

Laurie,
York, England

 

[Travelor]

The first place to check is firing pin vs bolt face firiong pin hole as stated above. Even if this is suspect, I would first change primers before doing anything else to see of that helps. Remington 7 1/2 primers are well thought of and are supposed to be harder. If this works it is a cheap fix.

Another thought - does your gun have a tight neck chamber? check a fired case and see how easily a bullet can be seated into it by hand. If it will not drop through the neck, you should consider turning the cases.

I have a Remington 6mmBR that will just not tolerate Varget loads due to high pressure signs (with 30 gr of Varget) that my other 6mmBR's take in stride. I found that changing to VV550 corrected the pressure problems and I can still get the same velocity and accracy with this powder. Why..... I do not have a clue... but it works.

Take care,
George

 

[sdneil]

Jeff-I went to RL 15 last year, Varget at 29-30 grains was way to hot in my 6BR, 8 tw, RL 15 at 30 is good to go in mine,you might try it with CCI 450.

 

[Broz]

Great replies everyone !!

Here is some more info from what I learned.

1: Bullets fit tightly in fired Lapua case necks. I can push them in but it is a snug fit. But I really dont want to turn necks if I can avoid it. This is a Prairie dog rifle and I want it easy to load for.

2: Forgot to say, the action is a Wby Vanguard / Howa. Also the last barrel was in 6mm/284 and I had this problem with it too using WLR primers. I just wrote it off then to the hot 6/284 round. So I suspect you are all correct on the firing pin to bore clearence, but I will investigate.

3: I will get some RL 15 and some other primers. But that takes time as I live in rural Montana and finding rare components is a challenge.

4: I have only seated to the lands and only with the 105 Bergers. It didn't shoot well so I started backing off. The 107 smk's shot good right off the bat so I worked with them. It is early in the load developing process. I will go back and put a few bullets .010" in the lands and see what it says.

I will keep at it and may even try some lighter bullets. Has anyone shot the 87 gr V-max out past 600 yards? Dont suppose they would make a good antelope bullet either.

Thank you all!
Jeff

 

[RJinTexas]

Jeff, if your planning on using this load for p-dogs your going to be disappointed with the performance of target bullets. You seriously might want to try 105 Amax if your wanting to shot heavy bullets. Better yet for dogs inside of 500yds you should try 29.5/H322 & 75gr Vmax. Little or no cratering signs in either my 14 & 8tw barreled unbushed 700's and I've never pierced a primer after firing close to a couple thousands rounds of this load in temps sometimes as high as 100 degrees. Buy the way nice looking build.

Regards
RJ

 

[Steve Blair]

There should be .002-.003" bullet clearance after firing. If the bullet is not cleanly released it will affect both pressure and accuracy. You may need to take a light neck cut which, if done properly, will certainly not hurt accuracy and consistency.

 

[Broz]

There should be .002-.003" bullet clearance after firing. If the bullet is not cleanly released it will affect both pressure and accuracy. You may need to take a light neck cut which, if done properly, will certainly not hurt accuracy and consistency.

Well, I just checked and the fired cases are measuring .2425" to .2435" most are .243"

I have noticed the rifle will send one out of group a 1/2 to 3/4" once in a while. Could this be the problem with the flier and the cratored primers?

If so, I have the stuff but have seldome used it. Please define "done properly"

Thanks!
Jeff

 

[Steve Blair]

I meant that the neck wall is a uniform, appropriate thickness and smoothly cut to the shoulder. A sizing die with bushings helps a lot to size only as much as needed after turning. For naked bullets, .002-.003" tension is usually enough. Coated bullets may require another .001-.002" tension. A good rule is to cut and size no more than necessary to do the job.

The link below is a good article by German Salazar about neck turning.

http://www.6mmbr.com/neckturningbasics.html

 

[Broz]

Steve, I am going to try this. I have a Forester trimmer with all the attachments for neck trimming. I will shoot for taking off .001 all around, and if I am correct, this will give me a fired case id of .245".

I have been using Redding bushing dies and did a full size for the first go using a .003" bushing under loaded neck size. I am now going to neck size with a .002" under bushing.

All sound correct?


Thanks!

Jeff

 

[Steve Blair]

Your plan is sound. Make sure that the new bushing diameter is .002-.003" under the loaded diameter after neck turning.

You will probably find that most cases will remove brass only on a portion of the neck taking a .001 cut. It will not cause a problem to leave a small amount of untouched neck on one side. It is still better than it was.

 

[Broz]

I did it and I believe it helped the rifle shoot more consistant. I turned 10 case necks. Loaded 5 with 30 gr of varget and 5 with 28 gr. 28 shows very little if any crater and was shot the tightest yesterday. The 30 gr is definatly not as accurate but out of both groups no fliers. The high one on the 28 gr group was pilot error. I knew it the minute it went off.

After firing all 10 cases I measured the neck ID and all are .245" to .2455" so I pulled that off. I think this might even have helped the crater problem a little bit. But I noticed one had a bit of resistance on bolt lift. So, I feel the load is border line too hot. It is less accurate anyway so it is not worth pursuing. Wind is a gusty 10 to 15 today so the groups were shot at 120 yards. Not a good day to shoot but I feel I made progress.

Thanks for all the help. I will turn all the necks and look at different powder or bullets for more velocity.

Thanks a ton!
Jeff

 

[rocketron]

I will keep at it and may even try some lighter bullets. Has anyone shot the 87 gr V-max out past 600 yards? Dont suppose they would make a good antelope bullet either.

i can tell you the 87 gn v-max hold together at 200 yds out of a 30" 7.5 tw w/30.3 to 31.0 gn of varget and .010 jump. not bad groups just need to work on getting out some vertical string. 30.7 seemed to be the best. i plan on using them for pa ground hogs his summer.

 

[smokin99]

Broz,

If you want a PDog rifle go with 87gr VMax and 30.5gr of Varget with the 1:8 barrel, with my 1:10 I shoot 75gr VMax...... Ive taken the 75gr VMax out to 1000yards before on steel many times, call TRGRMAN he was there with me... Theres a caculation based on RPM for the best SPLAT Factor from FPS versus Twist of barrel,,,, and if I remember correctly I said to go with a 1:10 barrel for the best performance on a PDog....oh well Also the 75gr bullet is allot more consistant that the 87gr bullet,,,,,ask RJ we've had this conversation many time and he was right.

VLDs suck and are Totally worthless for spat factor of PDogs which is what a Varmint Hunter wants,,,,,at least I do! Time for your next 6mmbr build....LOL

 

[Broz]

Smokin, I went to order some "87 gr V-maxes" yesterday. I could only find Hordaday 87 gr BTHP is this right? I looked at Hornadays website and they don't show a 6mm 87 gr V-max So you must be talking about the BTHP?

Thanks!
Jeff

 

[Steve Blair]

Jeff,

Those are two different offerings from Hornady. Powder Valley has the 87 V-Max in stock. Hornady does list it, but not from the initial selection page. ???

http://www.hornady.com/store/6mm-.243-87-gr-V-MAX/