Velocity issue with my new build 6XC

[mikecr]

I really think you're on the right trail now.

 

[2dogs]

My rifle is a standard 6X with a 24 inch Hart barrel. I get 3050 fps with 107 SMKs but Im using IMR4350 not H4350. I tried X4350 by AA but like you I didnt see anywhere near the speed I was expecting. Accuracy is in the .35" range at 100 yards in windy hot nasty S. Texas weather.

Hope this helps, I suggest you try the other 4350.

Thanks for the update.

 

[JohnMill]

40X
looks like you're on the right track. I'd keep going up 'til I got the vertical out of the groups ( and catalog those bugholes for revisitation). Then shoot 5shot groups. If you are shooting long range, go to it. Member the load has to hold together for 22 shots in 22 minutes (or some such). RCW3 says they won't all do it. If yours don't then you might go with the 8202 (SPClark) (proven load, proven shooter) and see how that works. Competition is different than dogs n chucks ncoyotes n things. Pick uur poison.
John

 

[WyleWD]

+1 on JohnMills' post. WD

 

[40X Guy]

Thanks to everyone for the suggestions and help. I will start again at around 40.2 grains and go up in increments to around 41.5 and see what happens. As to IMR 8208, I may have to try that as well as the H4350 may not get me the speed I would like. This rifle is pretty much for LR Groundhog matches not for serious comp. Heres a pic of the rifle, stock is Shehane Tracker 1000L. Will keep the updates coming.

Frank

 

[bozo699]

Nice rifle Frank, glad to see it all come together for you, just a side note 39.5 was about the limit in my rifle, above that and primer pockets went south in just a few rounds, I understand you want more speed and I guess I was lucky because I got just over 3000 with the 39.5 grains but unless it was essential to achieve above 3000 fps your 39.0 grain load looks great to me, I am tickled when mine soot in the two's that looks low single digit to me You have gained 107 fps with the addition of 1.5 grains of powder so you haven't reached your max ocw I guess, it is strange how two rifles of the same chambering can be so different I think mine would have had ejector marks on them at 40.5 grains good luck Frank and keep us informed I am very curious where you end up at.
Wayne.

 

[mikecr]

There have been a few articles on this site about different barrel speeds from various land/groove dimensions offered -vs- bullet diameters by brand/lot.
If I remember right, a tighter combination can produce ~+100fps, but could shoot worse if bullets are really pushed.
I get the impression that some have hit on preferred combinations(accuracy wise).

 

[JohnMill]

when I was just about to build an 6XC, I read everything I could come up with including some off beat search terms. I ended up selecting everything recommended by DTAC. I do not believe you could go wrong following his lead and if it doesn't work then your (Or my ) shooting is suspect.
I later changed to 6MMSuperLR as I believe it is a slightly less stressed round. I did not get it finished and so can not offer any real answers.
Still, with the 6XC, if you read everything that Tubb has written on that cartridge, I think the answers are there.

John

 

[markr]

How many rounds thru the tube? I know my last few 6mm bbl's sped up dramatically after 100rds, hitting peak around 150 or so, easy 100 FPS on some loads.

I only have 39 rounds thru the barrel, and that thought crossed my mind also. Am definately going back to H4350 and see what happens.

Frank

It has been my experience that an exceptionally fast or slow barrel will show itself immediatly and will continue to stabilize for maybe the first hundred rounds, then will be stabile till it's seen better days. One shouldn't even make a judgement about this until a suitable powder is used. Caution....exceptions to this could certainly occur.

 

[Rtheurer]

Two Perfect matches for the 6X47 Swiss Match which is very very close to the 6XC are Reloader 19 and Norma 204. I shoot 105 berger VLD's and reach up into the 3000fps real easy with those two powders. 3100 is reachable on the uper limit. I would try 40 grains and work up to around 43grains in both powders. I also use BR2 CCI primers. Something mild.

Worth a Look if you have some on hand.

Russ t

 

[40X Guy]

Two Perfect matches for the 6X47 Swiss Match which is very very close to the 6XC are Reloader 19 and Norma 204. I shoot 105 berger VLD's and reach up into the 3000fps real easy with those two powders. 3100 is reachable on the uper limit. I would try 40 grains and work up to around 43grains in both powders. I also use BR2 CCI primers. Something mild.

Worth a Look if you have some on hand.

Russ t

Russ, I can get my hands on some Norma 204 powder to try and I am going to try 8208 powder as well if the H4350 does not get me the speed I want. As far as primers I am kind of stuck on using the Fed match primers as they have served me well. Could a primer switch net 50fps more? Thanks everyone!

Frank

 

[spclark]

Could a primer switch net 50fps more?

Probably not unless you switch to a magnum charge type. Most common effect is a change in ignition consistency perhaps with improving deviation.

In my hardware the two best performing primers historically have been BR-2's (pricey) and the Wolf KVB-7 'Russian' items. Fed 210M come next, good enough if that's all I have on hand.

 

[Rtheurer]

I think its worth a try. Like Mr Clark pointed out I have better SD and ES's with the CCI primers in this case. Maybe a small purchase of 100 primers at your local gun shop to test would be simple cheap way to go about it?
I have seen velocity increases and decreases in other cases like the 223 but not this one ( Rem vs CCI450). I have only used two. 210 M and CCI BR2's.

I think you will be suprised by the Norma 204. It most likely will group best at around 42.5 to 43gr. Maybe a little more since your case capacity is a tad more than my 6X47 Swiss Match. Please start lower just in case though. This is a Highly underated powder for these medium cases.

RT

 

[40X Guy]

I have some CCI Br primers on hand and will try them with some 8208 tomm. Also have a container of 204 powder coming monday thru a shooting friend. Will keep everyone posted.

Frank

 

[40X Guy]

Update with IMR 8208 XBR- Loaded up 3 each at .012 off lands with Sierra 107's at 36.1, 36.4, 36.7 and 37.0. Group with 36.1 was not good, group with 36.4 was acceptable but sticky bolt lift, shot the 36.7 and pressure was there and group opened back up. Velocity was 3072 fps with the 36.7 load. I will pull the bullets out of the 37.0 loads. For this weekends match I will use the 40.2 grain load of H4350 at 2980 fps as I am running out of time this week. Anybody have any suggestions on where to start with Norma 204 powder? I am also considering Quickload pretty seriously after browsing the Neco site.

Frank

 

[Rtheurer]

Frank

Start at 42 and work up to 43 or a little more since the XC has a tad more volume than the 6X47 Swiss Match case.
I was thinking 8208 was too fast for this big of case. Its more like N135 than anything. Might be fine for a 60gr Varmint bullet but a 107 class bullet might be too much. And yes Quick Load says its a poor match. 204 Norma shows its a great match.... which is what I have found in my case. Low Pressure and great accuracy.

Best of Luck
RussT

 

[jlmurphy]

+1 for the Quickload. I have it and it predicted the exact velocity I chronographed while working up loads for my 6X47, it saves a lot of time and money.

 

[spclark]

Update with IMR 8208 XBR- Loaded up 3 each at .012 off lands with Sierra 107's at 36.1, 36.4, 36.7 and 37.0. Group with 36.1 was not good, group with 36.4 was acceptable but sticky bolt lift, shot the 36.7 and pressure was there and group opened back up. Velocity was 3072 fps with the 36.7 load. I will pull the bullets out of the 37.0 loads.

Bearing length on the 107SMK is 0.392", Lapua 105 Scenar 0.424", the Berger 105VLD 0.379". I started out with 8208 @ 37.0 grains in Norma 6XC cases last year, got great group @ 600 yards with the 105VLD (home-coated hBN), 3,140 fps SD 4. Add another grain I got more vertical dispersion, 3,215 fps SD 9 but flatter primers. Never fired the 39.0 grain rounds I'd brought along. Used the 37.0 grain load last year & this with good results out to 1,200 yards until I ran out of Bergers.

Recent tests with the Scenars (also hBN-coated): 34.6 gn 2950 fps SD 18, 34.8 gn 2953 fps SD 13, 35.1 gn 2974 fps SD 6, 35.3 gn 3017 SD 7 with a good vertical node at both ends.

Curiously, brass tests using Tubb's GenII 6XC and some cases I'd made up from Lapua's small-primered Palma brass showed almost identical speed, deviation and vertical at the 35.3 grain load level. Hopefully the small primer Lapua cases will prove worth the effort for extending primer pocket life? I'll be backing off the 37.0 grain load now that I have a new supply of 105VLD's; large primer brass seems to suffer after three or four firings while accuracy is dependable.

 

[Rtheurer]

Frank

I just went through my stash of load data and I see I had good luck with 40gr of R19 and a 105VLD as well. running in the 3000fps+ range. 36 to 37.5gr of N550 showed promise as well.

Remember this is with a 6X47 Swiss Match with a tad less volume so These loads may or may not need to go up in your XC Case.

 

[spclark]

I just went through my stash of load data and I see I had good luck with 40gr of R19 and a 105VLD as well. running in the 3000fps+ range. 36 to 37.5gr of N550 showed promise as well.

My tests last year included N550 (and H4350, H4831sc, RL-17; taking 8208XBR along was an afterthought) also: 35.5 gn 2820 fps SD 39, 36.5 gn 2905 fps SD 16, 37.5 gn 2990 fps SD 5. Vertical in the latter group - 3" @ 600 yd - was half that of the first two. This was to be my "back-up" load if the 8208 turned out not as promising in match conditions as test lead me to believe.